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Particles

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Documentation Team

Judy Bayne, Grahame Fuller, Amy Green, Edna Kruger, and Naomi Yamamoto.

Softimage Portal • 3

ParticlesThis section covers features about creating particle simulations using the particle operators that have been in Softimage since the first version: the Particles operator, the Fluid operator, and the Explosion operator.

• Basics for Particle-based Simulations on page 4General concepts and tools used for particles.

• Particles on page 25Working with the Particle operator which is the main operator for creating particles in Softimage.

• Fluid on page 113Working with the Fluid operator.

• Explosions, Fire, and Smoke on page 121Working with the Explosion operator.

• Rendering Particles and Fluid on page 133Rendering particles from the Particle and Fluid operator.

4 • Autodesk Softimage

Chapter 1 Basics for Particle-based Simulations

You can use all the simulation powers in Softimage to create your own compelling scenes—all the tools are there. You can use the particle, fluid, and explosion simulators to create any number of particle simulations. Natural forces, such as wind, gravity, and turbulence, let you add realism to all simulations. You can create collisions using any type and number of obstacles.

The Three Particle-Based Simulators

There are three separate particle-based simulators in Softimage that are special in the effects they create and the tasks you can perform with them.

• The Particle simulator is the standard “all-purpose” tool that you can use to create the widest variety of particles. All particle shaders work with this simulator, and many of the tools available for particles apply only to it.

For information on this simulator, see Particles on page 25.

• The Fluid simulator specializes in, you guessed it, fluid-type effects such as water, oil, or mud. The Blob shader is applied to it by default to achieve a liquid appearance.

For information on this simulator, see Fluid on page 113.

• The Explosion simulator specializes in smoke, flame, and spark effects associated with explosions and fires. The Explosion simulator creates its effects using three different phases for smoke, flames, and sparks. You can choose to use any combination of these phases to achieve the effects you want. As well, this simulator uses only the Explode shader, as it is designed especially for the three phases.

For information on this simulator, see Explosions, Fire, and Smoke on page 121.


This section describes some of the basic tools and tasks used for all particle-based simulations, including where to get commands and ways of viewing and playing back simulations.


Viewing Particle-based Simulations

Creating particle simulations is a visual process that requires many ways of viewing. There are a number of display modes (and the render region) in which you can visualize particles.

You can also hide particles completely and display or hide the particles’ attributes (such as their ID numbers and trails). As well, you can display particles as points only, which makes displaying them very fast.

Selecting a Display Type

You can view particle-based simulations using any of these display types in a viewport. You can also use a render region when you’re previewing the effects of the shader you’ve applied to the particles (see Previewing Shaders in the Render Region on page 139).

The type of basic shader attached to the particle type determines the look:

• Billboard is the default shader for the Particle simulator.

• Blob is the default shader for the Fluid simulator.

• Sphere is another basic shader you can add to determine the particle shape.

For more information, see The Basic Particle Render Type Shaders on page 141.

Wireframe

In Wireframe display, the particles are shown as camera-oriented hexagonal outlines the size of the particle’s radius, and colored with the particle’s color at the appropriate frame. The particles are shaped this way to show you the orientation of the particle, which matters when you’re using rotation (see Rotating Particles on page 59).

Wireframe display - Blob shader


By default, the particles are aligned with the camera’s X and Y axes, but if you have sprite or billboard tangency activated or you’re using rotation, they will use these settings so that they’re oriented correctly to the camera (see Billboard Shader (2D) on page 143).

Shaded

In Shaded display, they particles are shown as flat (constant) colored hexagons, the size of the particle’s radius, and colored with the particle’s color at the appropriate frame. The camera orientation for the particles is the same as for Wireframe display.

Textured

In Textured display, you can preview many particle options so that you don’t always need to draw a render region. The particles are displayed as alpha-blended bitmaps that use the color and alpha information defined for the particles. The particles are also properly integrated with scene objects in depth.

Shaded display - Sphere shader Shaded display - Billboard shader


You can also use textured mode to see the defined particle shapes and other values, including:

• Sprites (not animated ones) and their angles.

• Tangency to particle velocity when using sprites or billboards

• Particle rotation

• Particle transparency settings

• RGB color from sprites, instead of particle color

• Alpha source modes (RGB intensity, alpha channel, particle alpha)

• An approximate form of Color Burn (in the Billboard, Sphere, and Blob shaders), which is turned on or off depending on whether the Burn value is greater than 0.5 or not. At a value of about 0.5, the textured particles should match the look of the rendered particles fairly closely.

• The Image node if connected to the shader’s render tree. If a sprite is also connected, it overrides the image.

• Texturing is not supported for the Sphere and Blob (3D) shaders.

Textured display - Billboard shader


Displaying and Hiding Particles and their Attributes

You can display or hide all particles in the viewports. As well, you can display or hide certain particle attributes, such as the particle ID or trail, on selected and/or unselected particles.

When you hide particles, the simulation is muted which makes it faster to play the scene. This is useful if you want to keep the particles in the scene, but you’re not working on them at the moment.

To view or hide particles in a viewport

• Click the eye icon in a viewport and toggle the Particles option in the view menu.

or

1. From the same view menu, choose Visibility Options.

2. In the Camera Visibility property editor, toggle the Particles option on the Objects page.

To view or hide particles in all viewports

• Choose Display > Visibility Options (All Cameras) from the main menu bar and toggle the Particles option on the Objects page in the Visibility Options for All Cameras property editor.

To view or hide particle attributes in a viewport

• In the Camera Visibility property editor, click the Attributes tab and toggle the Particle ID, Particle Points Only, and/or Particle Trail options for selected and/or unselected objects.

Particle ID displayed below each particle.

Particles displayed as Points Only. Particles displayed with Trail shows their velocity. These particles have a Speed of 25.


- Particle IDs are displayed under each particle, regardless of the display mode. See About Particle IDs on page 17 for more information.

- Particle points allow you to override the default particle display modes. When Particle Points Only is selected, points are shown regardless of the display mode. You may want to use this for faster performance or for a less cluttered display when you’re not tweaking the particles.

- Particle trails are lines giving a visual cue to the particle’s velocity (with the appropriate color variation). The amount of trail left by a particle depends on its velocity (see Setting Up the Particle Emission on page 35 for more information).

To view or hide particle attributes in all viewports

• Choose Display > Visibility Options (All Cameras) from the main menu bar and toggle the options on the Attributes page in the Visibility Options for All Cameras property editor.

Previewing Particles with Ghosting

Animation ghosting, also known as onion-skinning, lets you display a series of snapshots of animated objects at frames behind and/or ahead of the current frame. This lets you easily visualize the motion of an object, which can help you improve its timing and flow. Any type of animation can be ghosted, including objects that are simulated.

You can use ghosting to show the motion of particles (cached), but this may not be practical if there are many particles in the scene.

You can use different display modes for ghosting, such as the object’s geometry, motion trails, or simple points.


Finding Particle-based System Elements

There are many pieces to a particle-based system, so to help you find them and see their relationships, you can use the explorer or the schematic view. As well, there are special commands to make it easy to open the property editors relating to each particle system element.

Using the Explorer In the explorer, you can see the relationship of all the pieces in a particle system. This example shows the Particle simulator’s setup, but the same relationship concepts apply to the Fluid and Explosion simulators as well.

• The cloud is the root for all the particle pieces: the particles operator, clusters of particles, and references to the emitter and particle types used in the particle cloud’s simulation. The cloud node represents the cloud’s geometry (point cloud). The particles are points saved per particle type in the cloud’s Cluster folder. If you create more clusters of particles, they are saved here.

• ParticlesOp is the particle simulator operator (FluidOp is the fluid operator and ExplosionOp is the explosion operator). Click its icon to open the ParticlesOp property editor that also contains the associated Emission and Particle Type property editors.

• PEmitter is the particle emitter object (FluidEmitter is the fluid emitter and ExplosionEmitter is the explosion emitter). The Emission node and a referenced to the particle types it uses are found here.

Click its icon to open the Emission property editor, as well as the associated Particle Type property editor. The emission node is also connected under the ParticlesOp node.


• PType is the particle type, which defines the look of the particles. Click its icon to open the Particle Type property editor. The original particle types are saved in the scene in the Particle Type folder, but are referenced under the ParticlesOp and PEmitter’s nodes. They can be easily found under the ParticlesOp node in the Particle type list folder.

Events are also created per particle type, so you’ll find them wherever a particle type is listed.

• The Particle_Renderer shader is a child of the cloud’s Material nodes. This shader controls the output of all shaders used to render particles.

As well, you can define different shaders for each particle type to define their individual look. For example, the Billboard and Shape shaders are attached to the particle types for the Particle simulator by default. You can find these shaders under each Particle Type’s Renderer node.

Select the Scene > Particle Types scope to see all particle types available in the scene.


Opening Particle-based Property Editors

There are many different ways to open property editors for particle elements.

• By clicking on specific element icons in the explorer.

• By double-clicking specific nodes in the schematic view.

• By selecting a particle element in the viewport and pressing Enter.

• By selecting a particle element and choosing Explore > Particles in the main command panel.

• To open only the ParticlesOp property editor, select the particle cloud and choose Modify > Particles > Edit Simulation.

• By selecting a particle cloud and choosing one of the Inspect menu buttons on the Simulate toolbar, as shown below.

This is one of the easiest and most direct ways to open just the right property editor. Clicking a button displays all the elements of that type available for the cloud, such as all particle types that are associated with the cloud’s emitters. When you select an element, its property editor is displayed.


Using the Schematic View

The schematic view gives you an overlook of how all the particle system elements are related. As with the explorer, you can also open individual property editors by double-clicking each of their nodes.

You can view links between

• Clouds and their particle types

• Clouds and their emitting objects

• Particle types and their events

• Particle events and their obstacle objects (if collision is the event type).

To toggle the display of the particle type and event nodes

• Choose Show > Simulation.

To toggle the display of links with emitter and obstacle objects

• Choose Show > Simulation Links.

To refresh the schematic view

• Select the nodes you want to refresh and press F5.

• To refresh the Scene Root, select nothing and press F5.


Selecting Objects with Dynamics

If you have many objects in a scene, it can be difficult to select only the objects in the simulation. With any of the Select filter options active, you can make sure that only simulation elements can be selected. This includes any object that has dynamics: particles, hair, rigid bodies, soft bodies, and cloth.

To use the selection filters

• In the Select panel of the main command panel, click the little arrow button and select Obj w Dynamics from the filter list.

• To select only rigid body constraint objects, select Dynamic Constraint from the filter list.

Spreadsheet Queries for Particles

You can get particle information for a selected object (or the scene) by running queries in the spreadsheet. This makes it easy to see, for example, which force or obstacle objects are attached to which particle cloud, and then select those objects or change their values.

To get information using a spreadsheet query

1. Select any particle, particle cloud, particle emitter, force, or obstacle object.

With nothing selected, you can run a query to find all force and obstacle objects in the scene.

2. In the spreadsheet, choose any of these queries from the Query menu for the selected object: Hair, ParTypes, Emissions, Events, Forces, and Obstacles.

For example, a particle cloud is selected and the Particle Types query is run to get the following information:

- To select an element, right-click its name and choose Select Object.

- You can also enter information or toggle options in each cell.

Click arrow to display filter list.


Mappable Parameters and Particles

Mappable parameters are parameters that can be connected to weight maps, texture maps, and UV properties. The purpose of mapping is to modulate the effect that a parameter has using the values of the map. For example, you can change the rate of emission of particles according to the saturation or luminance values on a texture map, effectively reducing the rate of emission.

All mappable parameters are identified in their property editors with a connection icon.

Weight Maps

You can apply a weight map to any mappable particle parameter.

Texture Maps

A texture map is the combination of a texture projection and an image. It has most of the attributes of a texture (including the projection parameters) but it cannot be rendered. To create a texture map, you select the texture projection method, then link an image file to it. The combination creates the specific texture map.

Instead of one value being applied over the surface as with a weight map, a texture map applies a color. A texture map works by averaging the RGB values in the image file to come up with a value between 0 and 1. Any value over 0 has an effect on the connected parameter. The greater the contrast in the image, the more pronounced the effect on the connected parameter.

You can apply a texture map to mappable parameters for the Particle operator. For an example of how to use texture maps on particles, see Example: Mapping Colors to Particles on page 149.

Texture map created for particle emitting object (grid).

Texture map connected to the Map Color parameter. As particles are emitted, they take on the color of the applied texture map.


Getting Information about Particle-based Simulations

To help you use particles in scripting or expressions, you can get information on the particles in a scene. This applies to particle, fluid, and explosion simulations.

About Particle IDs When a particle is born, it has its own unique identification number (ID) that stays unique throughout the simulation. This number can be used for identifying particles for scripting.

The particle ID is distinct from the particle index in the array of particles. The particle index is the position of the particles within the collection of particles. As particles die, indices are reused.

The particle’s ID is guaranteed to be unique throughout the lifetime of the cloud whereas the particle indices are reused many times.

When a particle dies, so does its ID number so that they are never recycled, even when they have a duration of forever for their life span (see Setting the Particle’s Lifetime on page 48).

However, if the particle is tagged when it dies, a new particle keeps the tagged state. Those new particles are generated in the index left unoccupied by a tagged particle that died.

To view the particle ID number in a viewport, see Displaying and Hiding Particles and their Attributes on page 9.


Getting Particle Information

You can get information on the selected particle cloud or find out the number of particles in a scene. This information may be useful to use in scripting or expressions.

To get information on a particle cloud

• Select the particle cloud and choose Edit > Info Selection (or press Shift+Enter). The Info Selection dialog box displays the following information.

To get information on particles in the scene

• Choose Edit > Info Scene (or press Ctrl+Enter) and click the Components tab to see the number of particles in the scene, as shown here.

You can change the Name of the particle cloud here, but the other information is only for viewing


Playing Particle-based Simulations

Although playing back a particle-based simulation is very simple, there are a number of issues related to it. Each of the particle-based simulators has special modes of playback, you can cache the simulation in PTP files to make playback go faster (after the files are cached), and you can also use a special player to play these PTP files.

Playing the Simulation At the first frame of a simulation, no particles are emitted. One frame later, particles are emitted but not updated. One frame after that, the previously emitted particles are updated and new ones are emitted, and so on for the rest of the simulation.

This is done so that an animated particle emitter object is at the same frame as the particles it’s emitting. If particles were updated at the same frame they were emitted, the particles would be one frame ahead of the emitter.

To play and cancel a simulation

• Click the Play icon in the playback panel below the timeline or move the playback cursor in the timeline. You can see the simulation’s calculation on the progress bar that appears.

What you see depends on which Execution State Mode you’ve chosen for playback (see Choosing the Way Particle Simulations Are Played Back on page 31 for particles and Choosing How the Explosion is Played on page 125 for explosions—fluid doesn’t have a choice of execution modes).

• Click the Cancel button on the progress bar or press Esc to stop the simulation at any time.

Caching the Simulation in PTP Files

When you play a fluid simulation for the first time, the explosion simulation with Interactive mode, or a particle simulation in Standard Caching mode, the result is cached in files with the extension .ptp. These PTP files record the position and physical properties of each particle in the stream. The file sequence is written back each time you modify any parameter affecting the simulation. Caching the simulation to file means you can move to any frame and get an update, as well as play the simulation backward.

One PTP file is created for each frame of the simulation. By default particle simulations use the name Particles plus a number counter (such as Particles1.ptp); fluid simulations use the name Fluid followed by a number; and explosions use the name Explosion followed by a number.

To increase the speed of the playback, mute any viewport that you’re not using by middle-clicking its letter identifier (A, B, C, or D). You can also hide the default grid in any viewport (press G).


Changing the Default PTP Storage Folder

The first time you cache files for a particle-based simulation, the PTP files are saved in your temp folder, usually on C:\, depending on your system’s environment variable. The best solution is to choose an output folder and file name for each particle simulation you create, such as your current project’s Simulation folder.

Once you’ve done this, the PTP files for all subsequent particle simulations you create will be saved to this folder because the path is saved with your Softimage user profile.

To specify the storage folder for PTP files

1. Open the ParticlesOp, FluidOp, or ExplosionOp property editors.

2. On the Output page in any of these editors, specify an Output Sequence folder and file name for the simulation.

- If Usr is on, the path is displayed as you entered it.

- If Res is on, the resolved path is displayed.

If you reuse the same file name, that simulation updates the existing PTP sequence.

To prevent overwriting the default-named simulations, give each simulation a unique and descriptive name for its PTP files.

Keeping or Deleting PTP Files

Every time you delete a particle-based simulation, close a scene, or exit Softimage, you can automatically delete its PTP files. To do this, select the Clean Cached Files option on the Output page of the simulator’s property editor, as shown above.

If you keep the PTP files, Softimage doesn’t have to recalculate the entire sequence, so the next time you view a frame, it plays back much more quickly. As well, having PTP files allows you to play a simulation backwards and scrub back and forth on the timeline.

If there is not enough free space on your disk to calculate the PTP files, the particles won’t be shown and an error is triggered.

If you decide to keep the PTP files, make sure to check the storage folder you have defined for them and delete any unused files. These can build up quickly and take up lots of space if you don’t occasionally do some housecleaning!


Playing PTP Files in the Particle Player

If you have cached PTP files, you can play them back in the particle player. You specify the PTP files you want to play back, and the particle player creates a particle cloud with a simulation operator that reads the PTP files and simulates them. The PTP files are played back in real time, which is an optimum way of previewing them.

The simulation operator uses the basic simulation and emission properties and plays that information. To use the correct particle type information (color, sprite, etc.) for playing back for the simulation, you need to have the particle types that are used by that simulation in your current scene/project (particle types are saved at the project level).

Because you don’t need the whole particle system to be on your machine to view the PTP files, the player is very useful for sharing a particle effect library between multiple users.

To play back PTP files in the particle player

1. Choose Create > Particles > From File from the Simulate toolbar.

2. In the Load Cache File dialog box that opens, select any PTP file from a sequence that you want to play.

3. In the Particle Player property editor, set the Start Frame and number of frames (Duration) over which you want the sequence to be played.

4. For the Input Sequence, specify the first PTP file in the simulation sequence that you want to play back. The subsequent PTP files in that sequence are then played.

5. If you want to save the input sequence PTP files under a new name, select Write Output Sequence and specify a location and name for the Output Sequence PTP files.


Working with Individual Particles

Particles are actually points associated with a particle cloud. As a result, you can tag (in Point mode), delete (as you do points), or create clusters of them. Tagging allows you to manipulate the particles as points, which is especially useful if you want to deform a particle cloud.

If you create particle clusters, you can constrain objects to them (see Attaching Objects to Particles on page 105) and you can use cluster-based deformations to modify them, such as envelopes or shape animation (see Deforming Particle Simulations on page 101). Or to animate them individually, constrain them to an animated object, such as a null.

Although particles are points, there are some issues about using them for modelling. This is because with a simulation, particles vary in time. Particles are assigned into clusters based on their index in the particle cloud. An index (not its ID) is usually only recycled when a particle dies and new particles are only appended at the end.

The best way to use clusters for modelling is to make an initial state of them (see Creating an Initial State for Particles on page 86). This way, the number of particles in the cloud is constant from their birth.

For example, you can set an initial state on your cloud, remove the particle emitter, and make the particles live forever so that they don’t disappear. For such clouds, clusters stay coherent throughout the simulation.


Duplicating and Sharing Particle Simulations between Scenes

Particles effects are dependent on many things, including animation, the object that emits the particles, the particle cloud, and particle types. Because there are many elements involved, the best way to create a library is to keep all these elements contained within a model. This way you can duplicate, import, and export complete particle systems, allowing you to share them between scenes.

To create a particle model

1. Select the particle emitter object, the particle cloud, the natural forces used on the cloud, and the obstacle objects associated with the cloud.

2. Choose Create > Model > New Model from the Model toolbar.

3. In the Model dialog box, give the model a descriptive name.

When you bring the simulation into another scene, be careful not to scale the force objects because that changes their strength (Amplitude value)!


Chapter 2 Particles

The Particle simulator makes it easy to animate all types of phenomena that can be based on particles, such as dry ice flowing out of a flask in an alchemist’s laboratory, fireworks bursting in the night sky, or snowflakes falling gently on a gray winter’s day.

Particles are affected by elements of the scene’s environment, such as lighting and objects. As a result, you can create shadows for them, create accurate obstacle collisions using the actual objects, and even deform particle streams the same way you deform geometry. When it comes to previewing the effects, you can simply create a render region to immediately see the results.

Particles themselves are actually points, meaning that you can tag them like points, delete them like points, create clusters of them, deform them like clusters, and constrain objects to clusters of them.


What Makes Up a Particle System?

A particle system is an assembly of different parts that work together: the particle simulator, the cloud, the emitter, the particle type, and the shader. Natural forces and obstacle objects also affect the particle simulation, but are not directly part of the particle system’s structure.

The particle cloud represents the simulator that generates the particles. You can have multiple particle clouds in a scene.

The emitter is any object from which the particles are emitted, as well as the properties that determine how the particles are emitted. You can have multiple emitters per particle cloud.

Particle types are the “recipes” that describe what each group of particles looks like and how they behave. You can have any number of particle types in a scene and apply them to any emitter object, but only one at a time.

Particle shaders define the rendered look of the particles. There are several special particle shaders, but you can also connect standard shaders in the particle’s render tree. You apply particle shaders to the particle types.

Forces define how particles react to environmental phenomena such as gravity, vortex effects, wind, fans, turbulence, and drag.

Collisions with obstacles: The ground has been defined as an obstacle so that the lava from the volcano lands on it.

Upon impact with an obstacle, the particles can react in different ways, like bouncing, sticking, or emitting a different particle type. Collisions are one type of particle event that you can define for each particle type.

For information on where particle elements are in the explorer and other ways of finding particle elements in a scene, see Finding Particle-based System Elements on page 11.


• The particle simulator is the operator that generates the particles, represented by the particle cloud, as well as controls how the particles evolve and are affected by forces, obstacles, and events. The particle cloud is like the “root” for all the particle system pieces. It is actually a geometry (a “cloud” of points) that results from the particle simulator doing its thing. You can have multiple particle clouds in a scene.

• The emitter is associated to a particle cloud, and is a combination of two things:

- The object from which the particles are emitted.

and

- The set of properties defining how the particles are emitted, such as their rate (density), speed, and spread angle. You can have multiple emitters per cloud.

• One or more particle types is associated with each emitter but are actually associated with each particle cloud. Particles types are like the “recipes” or templates that describe what each group of particles looks like (mass, size, shape, color, etc.). You can have an unlimited number of particle types in a scene and apply them to any emitter object, one at a time.

When you create a particle simulation, the particle simulator generates clusters to identify which particles belong of which particle type.

• The particle shaders define the rendered look of the particles, letting you define the basic shape of the particles and set color, shadows, color burn etc. There are several special shaders created for particle systems, but you can also connect standard shaders in the particle’s render tree. You can apply particle shaders to a either cloud or to individual particle types of a cloud.

Scripting for Particles Particle event scripts (scripted events) replace and expand upon pre-collision scripts that were available in previous versions of Softimage. Whatever modifications you create in a scripted event are evaluated and “reinjected” into the simulation at every frame so that the next simulation step takes them into consideration. If you have a pre-collision script from a previous version, you can replace it with a particle event that is triggered at every frame with a scripted action.

For more information on particle events in general, see Creating a Particle Event on page 74; for scripted events, see Scripting a Particle Event on page 83.

You can use scripted operators with particles, but there is a limitation with them. Scripted operators modify the particles for the evaluated frame but the results are not used for the next evaluation of the simulation feedback loop. However, you can use scripted operators to create your own custom simulation or mimic flocking.


Basically, if you want to modify the velocity, position, or mass of the particles to affect the simulation, you should use a scripted event. If you’re just modifying non-dynamic attributes like the particle’s size or color, you can use scripted operators.

Using the SDK for Particles

When you’re scripting particles, you can use the information found in the SDK documentation. To access this documentation, you can open the script editor and press F1 or choose Help > SDK Guide from the main menu in Softimage.

The particle objects used can all be found under the Object link (the Object Model) in the Scripting Reference. These are the objects for particles: Particle, ParticleAttribute, Particle AttributeCollection, ParticleCloud, ParticleCloudPrimitive, ParticleCollection, ParticleType, and ParticleTypeCollection.

As well, see the SDK Customization Guide and the Working with Softimage for Developers sections for more information about particles. These guides are also available in the Scripting Reference contents.


Creating a Particle Simulation

To create a particle simulation, you start out by creating a particle cloud that is associated with the object you have selected to be the particle emitter. This can be either a default emitter shape or any object in your scene.

A particle cloud is a container object for all the information about the particle system. The cloud is a “cloud of points” that results from the particles operator (simulator), but it has no inherent topology of its own (that is, its points are not connected together to form a surface). A cloud also has no properties of its own, which matters if you want to use scripting with particles.

When you create a particle cloud, you define the global characteristics of the particle simulation, which are generated by the particles operator. It generates and updates the particles for the cloud, considering the emitting object and its properties, natural forces, and obstacles.

Multiple Particle Clouds and Emitters

You can have any number of particle clouds in a scene. Each particle cloud has its own volume shader with its own personal space, but you can overlap them in position.

To keep your scene simpler, however, you can attach multiple emitters to a single particle cloud (see Adding Multiple Particle Emitters to the Same Cloud on page 43). You can then define a different particle type for each of the emitters (one particle type per emitter) to create totally different particle streams from one cloud.

Particles being emitted from disk around burner.


Creating a Particle Cloud

To create a particle cloud

1. Do one of the following:

- From the Simulate toolbar, choose Create > Particles > From Primitive > From Cube, Disc, Sphere, or Grid to create a polygon mesh primitive object from which particles are emitted.

You can transform and deform this object as you would any other polygon mesh object in Softimage.

or

- Select an object that will be the particle emitter and choose Create > Particles > From Selection. You can use any type of object to be an emitter except a cluster.

If you want to change the emitter object later, see Setting Up the Particle Emission on page 35.

A particle cloud appears in the viewports, close to the global origin.

2. In the ParticlesOp property editor that is displayed, set up the following options to define the particle simulation.

To open only the ParticlesOp property editor later on, select the particle cloud and choose Modify > Particles > Edit Simulation.

3. Set the particle emitter’s properties on the Particle Emitter pages, as described in Setting Up the Particle Emission on page 35. You can also do this later.

4. Set up each particle type to be associated to the particle cloud and emitter on the Particle Type pages, as described in Creating Particle Types on page 44. You can do this later as well.

• You can move the emitter object away from the particle cloud, but it is not recommended to move the particle cloud away from the global origin.

• You can display or hide just the cloud icon in a viewport by toggling the Control Objects option in the visibility menu (click the eye icon). The particles themselves are still visible even if their cloud icon isn’t.

Particle cloud icon


Choosing the Way Particle Simulations Are Played Back

The way the particle simulation is updated depends on what you have chosen as the execution state when you create a particle cloud. You can play back the particle simulation and have all changes you make to the particles updated continuously (Live), you can calculate the changes only when you want (Standard No Caching), or you can cache the PTP files to play back as you like (Standard Caching).

For information on playing a simulation and caching PTP files, see Playing Particle-based Simulations on page 19.

Selecting a Playback Mode

You can set these Execution State > Mode options on the Simulation page in the ParticlesOp property editor:

• Standard No Caching (default) calculates the particle animation only when you click the Simulate button or go to a different frame, either by clicking the Play button below the timeline or moving the playback cursor.

This is useful for setting keys for the animatable particle properties or obstacle animations because you can move forward on the timeline without having to wait for the particle simulation to update. This mode doesn’t cache any PTP files, so you can’t play the simulation backwards.

• Standard Caching writes (caches) one PTP files for each frame in the simulation sequence, according to the Output Sequence name you have specified on the Output page in the ParticlesOp property editor (for information on PTP files, see Caching the Simulation in PTP Files on page 19).

When you first play the simulation, the PTP files are written so it takes a bit of time. However, once the PTP files are written, playback is faster than when no files are cached. As well, caching PTP files allows you to scrub the simulation and get the correct state, play the simulation forward or backwards, and play PTP files in the particle player for previewing (see Playing PTP Files in the Particle Player on page 21).


• Live mode allows you to play a simulation continuously for quick editing and tweaking. You can then view the effect of any modifications in real time.

Live mode is best when you play the simulation with looping on—this way you can tune parameters and immediately see what happens. Any change you make to a particle’s properties affects the particles from that point on: the simulation is not recalculated from the start. As soon as you skip forward, the simulation is computed from the current frame for all of the intermediate frames. The simulation is calculated using all the particles born at the current frame: all the particles are regenerated only when the simulation is started again from the first frame.

When you drag the playback cursor forward in the timeline, the particle cloud is frozen and won’t update until you click the Play button in the playback controls, which restarts the simulation from the first frame.

Muting the Particle Cloud

To mute the simulation

• Select the Mute Cloud option on the Simulation page in the ParticlesOp property editor.

This option mutes the simulation and temporarily freezes the particle cloud in its current shape. It stops generating or reading through the PTP files, but since the last PTP file is still there, the particle cloud acts like a static object when you play back your scene. The particle simulator is fully disconnected so any changes you make to the particle’s parameters are ignored.

Recalculating the Simulation

To recalculate the simulation from the current frame

• Click the Simulate button on the Simulation page in the ParticlesOp property editor.

This forces a re-evaluation of the simulation at the current frame, updating the particles to that point. The simulation is recalculated from the start frame to the current frame as soon as you modify a particle in a property editor or you move an obstacle or a force (if you’re not using Live mode).

Live mode is only used to view the changes you do on particles in real time when playing back, including viewing in the render region. However, when doing a final render or see the effects of motion blur on the particles, you need to use either the Standard No Caching or Standard Caching mode.


Managing Time for a Particle Simulation

You can decide exactly when the particles are simulated using the parameters in the Time Management group in the ParticlesOp property editor. These parameters deal with creating a simulation source, which includes the simulator, the particle types, the emission properties, the events, and the obstacle properties.

To set the source time

• Set the Source Time to Local to determine the simulation’s time relative to the source. The animation for the emission properties, particle type, obstacle properties, and events are all taken starting at the scene’s time 1 and onward.

This means that you can create a simulation with animation on any of these properties that start at frame 1 and lasts n number of frames. Then you can offset the simulation in time and still keep the same result. This mode is useful for building simulation models and then retiming them as you like.

• Set the Source Time to Global (default) to determine the simulation’s time relative to the scene. The animation on any parameters is read from the scene’s start of the simulation up to the scene’s end.

This is useful when you know what the timing of the simulation is, such as if you need to add simulation effects between frames a and b in a scene by animating the source parameters between frames a and b (every element is properly placed in time).


To set the simulation’s length

• Set the number of frames for the Duration.

The Source > Start and End frames are calculated depending on what you set for the Duration. These frames are where the source animation is read from in the scene’s global time. These values are for display only and cannot be changed.

- When the Source Time is local, Start = 1 and End = 1 + Duration value.

- When the Source Time is global, Start = Global Result Start (which is the Offset value) and End = Start + Duration.

• Global Result > Start and End displays at which frames in the scene the simulation will be played. These values are for display only and cannot be changed.

To offset the simulation in time

• Enter a value for Offset. This is the number of frames by which you want to offset the start of the simulation.

With Local time, an Offset affects the place where the simulation is being played, but does not affect the source itself. This means that whatever the offset, the animation on the source is always read between frame 1 and 1+ Duration in the scene’s global time.

To match the scene’s and simulation’s frames

• Click Copy From Scene to copy the scene’s first and last frame defined for the timeline to the simulation. This changes the Offset and Duration so that the simulation is played throughout the scene’s timespan.

• Click Copy To Scene to copy the Global Result > Start and End frames to the scene’s timeline.

Deleting a Particle Simulation

Deleting a particle simulation removes the simulation and the particle cloud icon, but you must remove the particle emitter separately.

To delete a particle simulation

• Select the particle cloud icon and press Delete.


Setting Up the Particle Emission

Once you create and set up a particle cloud to define the general behavior of your particle simulation (see Creating a Particle Simulation on page 29), you can set up how the particles are emitted. As well, you can change the emitter object or add emitter other ones to the cloud.

A particle emission is composed of two things:

• The object from which the particles are emitted.

• The set of properties that define how the particles are emitted, such as their rate (amount), speed, and spread angle.

You can specify more than one emitter for a particle cloud. Generally, you can attach as many emitters you want to a particle cloud, and then create multiple particle types per emitter for different effects. To have multiple emitters for one cloud, see Adding Multiple Particle Emitters to the Same Cloud on page 43.

By default, particles are emitted from the emitter object which you can move to another location in the scene. However, if you move the particle cloud (which is not recommended), the emitted particles are offset with respect to their natural emission point.

In addition to emitting particles from objects, you can also have emissions that are related to particle events (see Creating a Particle Event on page 74). In this case, the particles are emitted from other particles, depending on the type of event you’re creating.

If you have multiple particle clouds in a scene but don’t know which one is related to which emitter, select the particles coming from an emitter and the associated particle cloud is highlighted.

Disk is particle emitter object on the burner.

This emission is defined by a Rate of 300 particles per second at a Speed of 5 units per second.


Selecting an Emitter and Setting Up Its Particle Emission

To change an emitter object

1. Select a particle cloud.

2. Choose Modify > Particles > Set Emission from the Simulate toolbar.

3. Pick one or more objects in the scene that will act as the emitter of the particles, then right-click to end the picking session.

You can use any type of object to be an emitter except a cluster.

To set up the emission properties

4. In the Emission property editor that opens, define the properties of the particle emission.

The emission properties are automatically named based on the emitter object’s name. You can enter a new name for them in the Name text box. If you modify the name of the emitter object afterwards, the emission properties are not renamed.

Emission parameters are summarized in the following illustration. For a description of each parameter, see Particle Emission Property Editor on page 187.

You can constrain the emitter to an animated object to animate the particle flow emitted from it.

• Many of these parameters have Var (variation) parameters which let you add variation to the parameter’s value. For information on this, see Adding Variation to Particles on page 64.

• Any parameter with a connection icon is a mappable parameter. This means that you can modify their values using weight or texture maps (using images or sequences).

• Emissions that are created for particle events have their own Emission property page that is similar to this, but has some different options. See Emitting New Particles on page 80 for more information.


Particle Point of Origin and Direction

You can determine how the particles are emitted from the emitter object in terms of their origin of emission and their direction.

• Generation sets the point of origin from where the particles are emitted according to the geometry of the emitter object.

- Point: Particles originate from the points of the emitter object.

- Line: Particles originate from the edges (for polygons) or U/V isolines and boundaries (for NURBS) of the emitter object.

- Surface: Particles originate from the entire surface of the emitter object.

- Volume: Particles originate from within the volumetric boundaries of the emitter object.

- Fluid: Particles are emitted from the implicit fluid emitter object. This is applicable only for the Fluid operator (see Fluid on page 113).

• Direction sets the direction of particles emitted from the emitter object. Emission direction can be relative to the emitter object’s Local or Global reference or relative to the direction of the emitter object’s Normals.

These control the density (rate), spread angle, speed, and the amount of velocity inherited from the emitting object at emission time.

These control the origin and direction of the emitted particles.

ParType controls let you select and edit particle type attributes.

Connection icons indicate mappable parameters.

Orientation parameters control the orientation of the particle at emission.

Map Color lets you map an initial color for the particles.

Name displays and lets you change the emitter’s name.

Mute temporarily disables the emission.


Particle Amount (Rate) and Spread

Rate is the amount (density) of particles being emitted per second. The higher the value, the greater the number of particles being emitted.

You can choose to display only a percentage of this rate by setting the Particle % value on the Simulation page in the ParticlesOp property editor.

Point: Particles originate from points on the emitter object.

Line: Particles originate from the edges of the emitter object.

Surface: Particles originate from the surface (flat areas) of the emitter object.

Volume: Particles originate from within the volumetric boundaries of the emitter object.

Set the Particle % to a low value for faster playback while editing, then to the full amount you want when you’re ready to view the final state. You can overshoot the values for Particle % by entering in a higher value, such as 200%, to double the number of particles emitted.


Spread is the angle over which the particles are spread. The angle value you use is calculated from the point of emission and includes only “one side” of the emission.

If you’re using the Fluid operator (see Fluid on page 113), the number of particles is determined by the Mean Distance parameter in the Fluid property editor, not the Rate parameter on the Emission page. The Mean Distance is not animatable, so to animate the emission rate, you can key the Size of the particles and/or the emission Speed (key them both at zero when you want to have no particles).

Rate at5 units/second

Rate at 100 units/second

Particle Rate


However, the result is double the angle value to include both sides of the emission. For example, if you specify a value of 30 degrees, the particles are actually spread over an angle area of 60 degrees.

Particle Velocity The Speed defines the speed of the particle emission in Softimage units per second.

The Speed value is limited by the Allowed Linear Velocity Range that you set on the General page in the Particle Type property editor (see Defining a Particle Type on page 46). The minimum and maximum values set the absolute range of speed that a particle is allowed to go. Setting the velocity range is a handy way to avoid extremely high or low speeds when particles are affected by natural forces.

Particle Spread

Spread set to 15°.The result is a total spread of 30°.

15o


Inherit is the percentage of velocity that the particles inherit from an animated emitter object at emission time.

Emitting Particles on Subframes (Oversampling)

Sometimes you may need to add particles between frames when, for example, you are emitting particles from a fast-moving emitter. In this case, empty spaces can occur between particle emissions, creating puffs of particles. Emitting more frequently than once every frame (oversampling) helps to create a continuous emission of particles. When you oversample the particle emission, you can specify how many times per frame you want to emit particles.

To oversample the particles

1. Open the particle cloud’s Emission property editor and click the Distribution tab.

2. In the Subframe Emission group, set these options:

- Randomize position does a random spreading of the particles between two successive positions of emission. For a given particle, the emission position is computed in 3D space at the current frame (or subframe) and the frame (or subframe) before. The particle is randomly positioned on the line joining these two points.

This lets you do oversampling without much cost to the calculation time, but you don’t have much control over how the oversampling is done.

- Steps defines how many emissions occur per frame (1 is the default). For each subframe, a certain number of particles are emitted at the locations specified by the position of the emitter at this subframe. This lets you spread the particles in a controlled manner and still have some puffs, if you like.

Particle Speed

Speed set to 1 SI unit per second

Speed set to 10 SI units per second


Emitting Particles in Layers

The Stratified emission on the Distribution page of the Emission property editor allows you to emit particles in distinct strata (layers). If you emit particles with identical speed from a grid, you’ll see distinct planes of particles; if you emit from a sphere, you’ll see concentric spheres of particles; and so on for each geometry. Because this option takes into consideration the geometry of the emitter, you need to use Surface as the Generation type (see Particle Point of Origin and Direction on page 37).

What happens normally with particle emission is that each particle is initialized with a velocity and a position. The position is derived from the emission position as specified by the emitter and the particle velocity: a random portion of the velocity is added to the position. Thus two particles that should be emitted with the same velocity from the same plane end up at two different distances from the plane because the random portion varies with each particle.

When Stratified emission is active, the random part is removed so all particles are at the same distance from the emitter.

Editing Emissions Once you have created a particle cloud and set up the emission properties, you can easily open the Emission property editor by selecting the emitter object and choosing Modify > Particles > Edit Emission. The emitter’s associated Particle Type pages are also shown so you can edit them as well.

See Opening Particle-based Property Editors on page 13 for other ways of opening specific property editors.

Muting the Particle Emitter

You can mute a particle emitter which lets you isolate and fine-tune the effects of other emitters in a scene.

The Mute option in the Emission property editor allows you to temporarily disable the emission, meaning that you can easily test a simulation or play back a scene without this emission being calculated as part of it. This is useful if you have several particle emissions in the scene, and you don’t want to have them all simulate while you’re testing one.

As well, you can animate the muting to do such things as having particle bursts being intermittently emitted.

Disconnecting Emitters from the Particle Cloud

You can easily disconnect particle emitter objects from the particle clouds to which they’re associated.

To disconnect an emitter object

1. Selected the particle, fluid, or explosion cloud to which one or more emitter objects is connected.

2. Choose Modify > Environment > Disconnect Obstacle/Force/Emitter from the Simulate toolbar. Pick the emitter objects you want to connect, then right-click to end the picking session.


Adding Multiple Particle Emitters to the Same Cloud

While you can’t emit multiple particle types from the same emitter, you can specify more than one emitter for a particle cloud, each of which can have one particle type. You can attach as many emitters as you want to a particle cloud. You can use any particle type with any emitter, one at a time.

To add emitters to a particle cloud

1. Select the particle cloud to which you want to add one or more emitters.

2. Choose Modify > Particles > Add Emission.

3. Select all the emitter objects to add to the cloud and right-click when you are finished.

In the explorer, you’ll see an emission node for each new emitter under the emitting object.

4. All emitter objects emit the same particle type until you set up a new particle type for it as described in Creating a New Particle Type on page 45.

Each of these three particle types are emitted from a different object, but all emitter objects are associated to the same particle cloud.


Creating Particle Types

After you define the particle emitter object and the emission properties in the Emission property editor (see previous section), you can edit the characteristics of particles. The characteristics of these particles are collectively referred to as a particle type.

Particle types are like the recipes or templates that describe what each group of particles looks like. They define the particles’ physical characteristics such as their mass, size, and life span, as well as their color and interaction with natural forces and obstacles.

The particle points defined for a particle type belong to a cluster, which makes it easy to identify a particle’s owner. You can find the particle types in the Clusters list under the cloud’s node in the explorer. Because the particles associated to a particle type belong to a cluster, you can, for example, use a different shader on each particle type in a cloud (see Using the Particle Shaders on page 135) or deform the particles for each particle type using cluster-based deforms (see Creating Goals for Particles on page 89).

You can have an unlimited number of particle types and apply them to any emitter object in any scene, one at a time. As well, you can have multiple emitters using the same particle type. This lets you create a “library” of particle types presets (see Saving and Loading Particle Type Presets on page 49) that you can apply to any emitter in any particle system in any scene.

Particle type used for green fireworks is defined by the settings in its property editor. This shows some of its defining characteristics, such as color.


Creating a New Particle Type

To create a new particle type


- Open the Emission property editor. To access this editor, select the particle cloud and choose Inspect > Emissions and select the appropriate emission property.

or

- If you have the ParticlesOp property editor open, click the Emission tab.

2. Select an existing particle type to use from the ParType list, or click the New button beside the ParType list to create the new particle type.

This automatically associates the new particle type to this emitter

3. Click the Edit button to modify or assign properties to the particle type, as described in the next section.

To create a new particle type with no emitter

• Choose Create > Particles > New Particle Type > Billboard, Blob, or Sphere.

This creates a new particle type with a specific shader attached to the particles to give them the appropriate surface (see The Basic Particle Render Type Shaders on page 141).

After you create a particle type this way, you must associate it to an emitter and particle cloud as described in Adding Multiple Particle Emitters to the Same Cloud on page 43.

Displays a list of particle types.

Creates a new particle type, which you can then edit.

Opens a property page in which you can edit the selected particle type in the list.

You can find all particle types in a scene by selecting the Particle Types filter in the explorer.


Defining a Particle Type

The fundamental characteristics of each particle type are set in their property editors. The default particle type used in particle emission is called PType, and it appears at the top of the Emission property editor in the ParType list. You can modify the default particle type and save it under a new name.

To define a particle type

1. In the Emission property editor, click the Edit button beside the ParType list to display the Particle Type property editor for the current particle type, or click the PType tab below the Emission property page.

2. The Overview page in the Particle Type (PType) property editor contains the most commonly used parameters for particle types. Setting parameters here is the same as setting them on their respective pages in this property editor.

Click the General tab and modify the particle type properties as summarized in the following illustration.

Name displays and lets you change the particle type’s name.

Mass and Size specify how the particles physical characteristics make them react to forces and obstacles.

Allowed Linear Velocity Range sets the absolute range of allowable particle speed.

Life parameters control the length of time in seconds that a particle exists.

Rotation parameters control the velocity of the particles’ rotation, as well as their display.


Animating and Varying the Particle Type Parameters

Many of the particle type parameters have animation controls that let you vary the way in which their values are animated. Once you set keys for their values, you can choose to have the animation “defined” in a number of ways such as from Birth, Age, and Absolute (for Color and Size, you can also use Age %).

For example, to animate the particle speed, select Age for the Allowed Linear Velocity Range - Max parameter to slow down a particle over its lifetime, or use Abs(olute) to slow down all particles at the same time. See Animating Particle Type Parameters on page 52 for information on all of these.

Many of the particle type parameters also have Var (variation) and Seed parameters which let you add variation to the parameter’s value. For information on this, see Adding Variation to Particles on page 64.

Other Pages in the Particle Type Property Editor

For information on the other pages of the Particle Type property editor:

• Events—see Creating a Particle Event on page 74. This is available only for the Particles simulator, but you can create collision events with obstacles with any of the particle-based simulators by using the standard method of setting obstacles.

• Envir(onment)—see Setting Up Forces for Each Particle Type on page 109.

• Noise—see Adding Noise to Particles on page 62. This is available only for the Particles simulator.

• Interpart(icle Collisions)—see Making Particles Collide with or Avoid Each Other on page 71. This is available only for the Particles simulator.

• Fluid—see Defining the Fluid Particle Type on page 118. This is available only for the Fluid simulator.

• Explosion—see Setting Up the Structures on page 127. This is available only for the Explosion simulator.

• Color—see Setting a Particle’s Color on page 147.

• Sprite—see Rendering Sprites on page 166. This is available only for the Particles simulator.

• Instancing—see Creating Instances of Objects to Attach to Particles on page 106. This is available only for the Particles and Fluid simulators.


Setting the Particle’s Lifetime

You alone have the power to decide how long a particle lives by using the options in the Life section of the Particle Type > General page:

• Max Life controls the maximum length of time (in seconds) that the particle exists once it is emitted.

• Live Forever makes the particles live for such a long time that it seems like forever (69,999 frames, to be exact). This option is useful for effects such as creating static clouds in conjunction with an initial state (see Creating an Initial State for Particles on page 86). As well, you may want to select this option to have the particles always available as you’re tweaking their parameters.

However, if you need an effect to work based on the Max Life value that determines the particles’ life span (particles animated with Age%), selecting the Live Forever option eliminates that possibility. This includes using the Particle Gradient shader.

Setting the Particle’s Mass and Size

Size controls the size of the particle when it is born, in Softimage units. The farther away a particle appears in the viewing area, the smaller it appears when it is rendered. To have a particle change size over its lifetime, you can use the animation controls beside this parameter. For an example, see Creating a Size Shift with Age % on page 53.

Mass specifies the mass of particles, which determines how swiftly they react to the forces applied to them (except gravity) and how they react in a collision with an obstacle. The more massive a particle, the more difficult it is to change its motion. Therefore, to make a change in a particle’s motion, you need to apply stronger forces to a particle with more mass than to particle with less mass.

Particle Lifetime

A particle’s life is measured in seconds from the moment it is emitted (born) to the moment it dies. Sniff.

You can also keep particles alive for the entire duration of a simulation with the Live Forever option, sort of like life support. This is useful for creating static clouds, such as when you’re deforming clusters of particles, or you have objects attached to clusters of particles.

Death

Birth


Gravity, however, is a little different from the other forces. Gravity is a force directly proportional to the particle mass. The more massive the particle, the stronger the gravity force applied to it. As a result, several particles of different masses will all have the same motion if the only force acting upon them is gravity.

Saving and Loading Particle Type Presets

Each time you edit properties in a property editor, you can save your settings as a preset. Presets are simply data files with a .preset file extension that contain property information. Animation information, however, is not saved as part of the preset.

Presets let you work more efficiently because you can save the modified properties and reuse them as needed. As well, presets lets you transport information between scenes. With particle types, all the particle type information set in its property editor is saved, as well as its render tree (see Connecting Shaders in a Particle Render Tree on page 140).

To save a preset

1. Open the Particle Type property editor and click the Preset icon and choose Save Preset from the menu.

Mass determines how quickly particles react to forces, and how they react in a collision with an obstacle or with each other. More mass requires greater force to change their motion.

Gravity is a little different because it is a force directly proportional against the particle mass.

Size is measured in Softimage units. You can also animate a size shift using the percentage of a particle’s lifetime.

Particle Size Particle Mass

Preset icon


You can also save presets with the Particle Type page inside the Emission and ParticlesOp property editors. Just make sure that the Particle Type page is active (click its tab at the top of the current property editor).

2. In the Save Preset browser, select the folder in which you wish to save the preset. It is recommended that you do not save your presets in the DSPresets folder.

3. In the File Name text box, enter the name you wish to give the preset, then click OK.

To load a preset

1. Open a Particle Type property editor and click the Preset icon and choose Load Preset from the menu.

2. Make sure that you have the correct property editor open for the preset that you saved.

3. In the Load Preset browser, select the preset you wish to load and click OK.

The selected preset parameter values appears, replacing those of the currently displayed property set.

Deleting Particle Types After you’ve worked with particles for awhile, you may have a number of particle types defined that you no longer want to keep. To delete them, you need to use the explorer.

However, before you delete them, make sure that they’re not currently in use in a scene: if they are, you won’t be able to delete them.

To delete a particle type

1. In the explorer, select the Scene > Particle Types scope.

2. From the ParTypes > List, select the particle types you want to delete.


- Press Delete.

Preset icon

Select the Particle Types scope, then select a particle type from the List to delete it.


or

- Right-click the particle type and choose Delete.


Animating Particle Type Parameters

You can add realism to your particle simulation by animating certain particle values such as speed, color, and the influence of environmental forces. Particle values can change as a function of their own lifetime or as a function of the lifetime of the particle simulation itself. This lets you create effects such as making particles change color as they age or having all particles suddenly accelerate at a given point in time.

Particle parameters that are animatable have a list of control modes that lets you specify how they can be animated: Birth, Age, Age %, or Absolute.

Birth In Birth mode, the value of the parameter’s function curve at birth time is kept constant over its lifetime (Max Life value).

For example, particles retain whatever color is defined at time of their birth and stay that color until they die. Using this method, you could layer different colors by setting different lifetimes for each colored particle.

Absolute Abs(olute) is the same as Birth mode, but instead of keeping the value parameter constant, it evolves according to its function curve over the particle’s lifetime (Max Life value). This means that all particles get the same value over time independently from their age.

All of the particles change at the same time, no matter where they are in their lifetime. Think of filming some smoke with a regular lens on your camera, then adding a blue lens filter: all the smoke particles change color at the same time.

Age When the particle is born, the value of the parameter that corresponds to the function curve at the start frame of the simulation is used. Then the associated value evolves according to its function curve over the particle’s lifetime (Max Life value).

Transitions that you key happen at the frame you key them and continue to change throughout the lifetime of the particle. It happens based on the particles’ individual ages and occurs separately for all of them.

Also, Age lets you have transitions that do not happen if the frame they are keyed at does not fall within the particle’s lifetime. For example, if you key a transition at frame 50 but the particle dies at frame 35, you would have to increase the lifetime or move the key to be within the lifetime to see that transition.

For any of the animation controls to have effect, you must first animate the parameter (that is, you must first key its values to create a function curve). The different control modes only define how to interpret that function curve.


Age Percentage (Age%)

Age % uses function curve values defined by the particle type Size or the Color’s RGB and/or Alpha controls to map a shift range between 0 and 100% (a percentage of the particle’s lifetime). This creates a size or color shift effect over a particle’s lifetime (Max Life) that corresponds to the values defined by the keys. It refers to the percentage of the particle’s age as opposed to a particular keyframe, as Age does.

When you use Age %, keying the size or color over 100 frames gives you more predictable results because each frame represents a percentage point (one percentage point for every 10 frames). Then, for example, if you want the particle to change color or size halfway through its lifetime, you would key it at frame 50.

Creating a Size Shift with Age %

This example shows you how to create a shift by keying the particle type’s Size and then using the Age % mode to compress the animation into the particle’s lifetime.

1. Select a particle type and open the Particle Type property editor.

2. On the General page, set the Size to 0.2.

3. Go to frame 1 and click the Size’s animation icon to set a key for this value.

4. Go to frame 90, change the size to 2 and set a key for this value.

5. Select Age % as the method of animation for Size.

Now the size shifts within the lifetime of the particle (Max Life), not over the whole simulation of 100 frames (meaning that you can change the particle’s lifetime and the shift will retain the same proportions).

Always key the parameter’s values in another animation mode and then switch to Age % when you’re done.


6. Right-click the Size parameter’s animation icon and choose Animation Editor to see the age percentage function curves for the Size parameter.

Note: The fcurves are expressed in seconds, not in frames. 100 frames corresponds to 3.333 seconds if you are at 30 fps, or 4.17 if you are at 24 fps.

Size shift


Sketching Particles

In addition to creating particles that are emitted from an object, you can sketch particles. Basically, you draw a free-form curve and the particles are created based on the gesture of the stroke you made.

Sketched particles do not simulate and react to forces and obstacles like regular particles because they do not create a simulation operator. You usually add them to an existing particle cloud. However, you can animate the sketched particles’ properties to create changes, like increasing their numbers or the radius over which they’re spread.

Sketching works with snapping, which is particularly useful when painting particles on surfaces (snap to the surface). As well, you can sketch in symmetry mode (click the Sym button in the Transform panel and draw!).

Setting Up for Sketching

Before you start sketching, you can set up how the resulting particles are created, including which particle type to be used.

To set up for sketching particles

1. Choose Create > Particles > Sketch Particle Setup from the Simulate toolbar.

This opens the default Add Particle operator’s property editor. Changes you make here affect all subsequent particles that you sketch.

2. Set these parameters as you like, as described in Editing the Sketched Particles on page 57. Speed is an important parameter to set before drawing because the direction and speed at which you drag the Sketch Particles drawing tool determines the speed of the particles.

To select a particle type to use for sketching

• Right-click any particle type’s icon in the explorer (at the Scene or Project level) and choose Set as Current Particle Type. This particle type will then be used when painting.

This is especially important if you’re sketching new particles that are not associated to an existing cloud. If you’re adding particles to an existing cloud, its current particle type is used unless you specify another one to be current.


Sketching the Particles To sketch particles

1. Select an existing particle cloud to add particles to it or have nothing selected to create a new particle cloud for the sketched particles.

2. Choose Create > Particles > Sketch Particles from the Simulate toolbar. This activates a sketch tool similar to the Sketch Curve tool.

3. Draw a stroke in a viewport. When you release the mouse button, the particles are “painted” along the path that you drew.

The particles are drawn using the current particle type you set and the options you set in the default Add Particle property editor.

An Add Particle operator is added under the particle cloud’s for each stroke that you draw.

4. Press Esc to end the sketching mode.

If you want to modify the results of the sketching, remember that you can select, delete, and transform the particles in Point mode as you would any object points.

Particles sketched over a long curve, as well as on many dots.

Each stroke you draw creates an operator for those particles.


Editing the Sketched Particles

In the Add Particles property editor, you can edit the sketched particles. An Add Particles operator along with its property editor are created for each stroke that you draw, allowing you to edit each stroke.

To edit the sketched particles

1. Select the sketched particles you want to edit.

2. Open the Add Particles property editor by doing one of the following:

- Click the appropriate Add Particles operator icon in the explorer.

or

- Select any of the sketched particles and press Enter. If you have several strokes associated with one particle cloud, the property editor for each stroke is opened.

3. Set the following parameters in the property editor:

- Multiplicity multiplies the number of added particles. A value of 1 means that one particle is added for every sampling point on the curve you sketched.

- Radius sets how the particles are uniformly distributed within spheres centered at each sampling point on the curve. This parameter controls the radius of those spheres: the larger the radius, the more the particles are spread out.

- Speed is the speed of the particles as determined by the direction and speed at which you drag the Sketch Particles drawing tool.

To see the effect of speed after you’ve sketched the particles, select the sketched particles and choose Create > Particles > From Initial State (see the next section, Simulating the Sketched Particles).

- Spread controls the direction of the velocity. If the spread is set to zero, particles flow exactly along the velocity vector defined by the stroke you make with the Sketch Particles drawing tool. With a value higher than zero, the angle of a cone (in degrees) whose axis is in line with the stroke at that point. The particles’ velocity vector lies within that cone. This is very similar to the Spread on the Emission property page. The spread can be between 0 and 180 degrees.

The Advanced page offers Seed values for the Radius, Seed, and Spread parameters. This allows you to add variation to the value you enter for each of these parameters. See Adding Variation to Particles on page 64 for more information.


Simulating the Sketched Particles

Sketched particles do not simulate as regular particles, meaning that they do not have velocity or react to forces, obstacles, or events. This is because they do not have a simulation operator. However, you can simulate the animation of a sketched particle cloud.

To simulate sketched particles

• Select the sketched particles and choose Create > Particles > From Initial State.

This creates a new particle cloud (which has a simulation operator as any cloud does) that uses the sketched particle cloud as its initial state. Then the sketched particles have velocity and you can apply forces and obstacles to the new cloud.

For more information, see Creating an Initial State for Particles on page 86.

You may want to hide the sketched particle cloud after you generate the simulated cloud so that you don’t have duplicate clouds.

If you added the sketched particles to an existing particle cloud, you won’t see the particles evolve because the particles are added after the simulation has executed at each frame.

To make the new sketched particles a part of the cloud’s simulation

• Select the sketched particles and choose Modify > Particle > Set Initial State.

This bakes the cloud into an initial state so that the sketched particles are included in the simulation.


Rotating Particles

You can rotate individual particles to create many different effects, such as billowy smoke, flying debris, and swirling snowflakes. You can set a particle’s initial rotation (orientation) when it’s emitted and also set its rotation speed (velocity) per particle type to be used for the duration of the simulation.

Rotations don’t really consider collisions. That is, if a rotated particle collides with an object, it doesn’t change its rotation as might happen in real life (such as with faster rotation or changed rotational direction upon impact). You could animate the particle’s roll, pitch, or yaw; or emit another particle type without yaw upon collision.

3D or Billboard Rotations

You can rotate particles in either 3D (XYZ) or 2D (billboard style). 3D rotations can face any direction, allowing the particles to rotate in all three dimensions (roll, pitch, and yaw). Billboard-rotated particles always face the camera, allowing you to spin the particles.

To see the particle rotation, you must set the appropriate Face Direction of Particle Rotation value in the attached shader (see The Basic Particle Render Type Shaders on page 141).

Particles rotating in all directions (3D).


Roll, Pitch, and Yaw

When you rotate particles in 3D style, you can choose which of its axes (any any combination of them) around which the particle rotate. Like the classic airplane example:

• Roll makes the particle rotate around its Z axis.

• Pitch makes the particle rotate around its X axis (the airplane’s tail and nose move up or down).

• Yaw makes the particle rotate around its Y axis (the airplane’s tail and nose move laterally).

Setting the Particle’s Initial Orientation

You can set the initial orientation of the particles at emission time with the Orientation parameters in the Emission property editor. These determine the angle at which the particle is emitted, with 0 degrees being the default position with the particle upright and facing the camera.

• For Billboard, the value is simply set in degrees.

Roll rotates a particle around its Z axis.

Pitch rotates a particle around its X axis.

Yaw rotates a particle around its Y axis.

Particle in default orientation position.

Particle oriented to 45 degrees at emission.


• For 3D rotations, the value is expressed with three angles in degrees: Roll (Z), Pitch (X), and Yaw (Y).

Variance (the Var parameter) is also available for these parameters (see Adding Variation to Particles on page 64).

Setting the Particle’s Rotation Over Time

You can also set the rotation used by a particle type during the length of the simulation. The rotation is updated at every frame using the Rotation Velocity values defined in the Particle Type property editor’s General page.

Rotation is expressed in degrees per second. For example, setting the Roll to 180 would be rotate the particle 180 degrees in one second. The higher the angle, the faster the particle rotates. For example, set Billboard to 180 to make nice rolling particles.

The rotation takes into account the particle’s orientation angle at emission time, as set on the Emission page (see previous page).

The rotation is also interpreted from the cloud’s reference frame (the cloud’s XYZ coordinates), as opposed to the global coordinates.

However, with Align On Velocity active, the rotation is expressed in a reference frame as defined by the particle’s velocity vector (direction). This is very useful to control local rotations on particles.


Adding Noise to Particles

You can apply noise to each particle type to make random variations in the particles’ spacing and movements. Noise is simply randomness that is calculated mathematically. There are two patterns of noise that you can apply to particles: Brownian and Perlin.

Brownian noise is a “random walk,” like a jitter. It’s not completely random, but its movements are more general than Perlin. This random walk basically consists of steps in a random direction, with each step length having some characteristic value. Instead of having a totally random value at each frame, you offset the previous value by a random step amount. In the case of particles, this is a random 3D vector direction and scale. This offset is applied to whichever Intensity parameter you’ve specified for the noise: Position, Velocity, or Acceleration (see the next page for information).

Perlin noise has spatial coherence, meaning that several different particles in roughly the same location in space tend to have similar noise added to them (with Brownian, each particle is independent of the others). It interpolates between the random values. This creates a more controlled look, such as a “streaming” effect that can be achieved with noise. With Perlin, there is more structure to the noise while still appearing fairly random.

Particle simulation with Brownian noise: values of 1 for Position, Velocity, and Acceleration.

Particle simulation with Perlin noise: values of 1 for Position, Velocity, and Acceleration; values of 1 for Iteration, 0.1 for Scale, and 0.25 for Power.


To add noise to particles

1. Open the particle type’s Particle Type property editor.

2. On the Noise page, set the following parameters:

3. Select the noise pattern Type: Brownian or Perlin (see previous description).

4. Set the Intensity:

- Position: amount of noise to be added to particles’ position (in Softimage spatial units).

- Velocity: amount of noise to be added to particles’ velocity (in [Softimage spatial units]/[Softimage time units])

- Acceleration: amount of noise to be added to particles’ acceleration (in [Softimage spatial units]/[Softimage time units]^2)

5. If you selected Perlin as the pattern type, you can also set these parameters:

- Iteration: number of iterations of the turbulence algorithm (1 is a simple Perlin function).

- Scale: spatial correlation of the particles.

- Power: amplitude of the turbulence.

You can animate the Intensity parameters using the standard particle type animation controls: Birth, Absolute, and Age. See Animating Particle Type Parameters on page 52.

To create the effects of little trails, set the Scale value to 0.1 or lower.


Adding Variation to Particles

You can control the variation of particles per particle type parameter. By adding variation to a single parameter’s value, you have ultimate control over its specific effect.

To help out with using variance, you can set seed values for many of the variance parameters, as well as setting an overall seed value for all variance parameters in a particle cloud. This allows you to keep all parameter and variance values unchanged so that an effect remains intact, and then change the seed value to modify that effect. This can be very useful if you’re sharing a library of particle effects: they can stay untouched while you simply change the seed value for the cloud.

Setting the Variance (Var) Per Particle Type

Many parameters in the Particle Emitter, Particle Type, and ExplosionOp property editors have Var (Variance) parameters which allow you to add variance to their associated parameter’s value. The Var parameters define the range in which the random numbers are generated.

Variance can be animated, allowing you to have different animations for the parameter’s variance and its value. Variance is animated using two different distribution methods: Uniform and Gaussian.

• With Uniform distribution, random numbers are distributed uniformly around the parameter’s value using the Variance value. The parameter will always be in the range [ Value - Variance; Value + Variance ], never outside of it.

• With Gaussian distribution, random numbers are distributed as a bell curve around the parameter’s value using the Variance value. Most numbers will be in the range [ Value - Variance; Value + Variance ], but they may be outside of that range with [Value - Variance], and they will be outside of that range with [Value + Variance].

If you have the same value for both the parameter itself and the Variance parameter, different numbers result depending on the type of distribution you select. Numbers using Gaussian distribution will have greater variations than the ones using a Uniform distribution.

Var parameter associated to the Max. Life parameter.


Sowing Seeds for Particle Types and Clouds

To add a random value to the variance, there are Seed parameters for some particle type Var parameters, as well as a Seed parameter for the particle cloud that affects all Var parameters for the whole simulation. The seed defines which numbers will be generated in the range that the Var parameter specifies. Using a seed, you can change the effect as you like without having to change the parameter’s value or its Var value.

All Seed parameters work only if you have a value other than zero for the Variance parameter to which it is associated.

To set the seed for individual Var parameters

• Set the seed value for the parameters in the Particle Type property pages that have a Var parameter.

• Set the seed value for the emission parameters on the Distribution page in the Emission property editor.

To add a seed to the whole simulation

• Set the Simulation Seed value in the ParticlesOp property editor.

This adds an overall variance factor to all the parameters of the simulation that have a Var parameter. Using this you can, for example, create identical particle clouds and test different results achieved by changing only the simulator seed value.

Seed parameter associated to a Var parameter.


Setting Up Particle Collisions

When you set obstacles for particle clouds, a collision event is created for each particle type associated with that cloud. You can then determine how each particle type associated with the particle emission reacts to the obstacle. For example, the particles bounce by default, but they can also have other behaviors.

Collisions are just one of many different types of particle events that you can set up for a particle type. For more information on particle events, see Creating a Particle Event on page 74.

In addition to refining the collision event, you can further define how each particle type of the cloud reacts to the obstacle (see below), and you can set the accuracy of the particles’ collisions with the obstacle (see Setting the Accuracy of the Collision on page 69).

To create a collision with particles

1. Do either of the following:

- To set up an obstacle for a particle cloud, select the particle cloud and choose Modify > Environment > Set Obstacle from the Simulate toolbar.

or

- To set up an obstacle for a specific particle type, select the particle type in the explorer and choose Modify > Environment > Set Obstacle or create a Collision event as described in Upon Obstacle Collision on page 78.

When the first particle type (sphere) collides with the obstacle, a new particle type (smoke) is emitted and the first particle type bounces.


2. Pick one or more objects in the scene that will act as obstacles for the emitted particles, hair, cloth object, or soft body object. Right-click to end the picking session.

3. The Obstacle property editor appears in which you can set the obstacle’s properties.

4. When you play the simulation, the particles collide with the obstacle.

Determining How Each Particle Type Reacts to the Obstacle

After you’ve created an obstacle for particles, you need to set up how each particle type defined for the cloud reacts to the obstacle.

1. Open the Particle Type property editor for each of the particle types that the obstacle affects (each particle type associated with the cloud).

Selected particles will collide with the cone when it is set as an obstacle object.

Selected particles now collide with the cone because it is an obstacle for them.


2. Click the Envir. tab and modify the Obstacles properties on this page.

To set the elasticity and friction

• Set the values for Elasticity and Friction. The values set here are multiplied with the values that you have set for the Physical Parameters in the Obstacle property editor. The particle type values are a “scaling factor” for the obstacle’s values.

If you set the Collision action for the particle event to Bounce or Bounce & Emit (see Creating a Particle Event on page 74), the values set here have an impact.

To keep this relationship simple, it’s usually best to set the values for the obstacle first, then tweak the parameters here. This way you can maintain the obstacle’s parameters as a constant.

• Elasticity controls the amount of influence that gravity has on the particles as they bounce off obstacles. A low value makes the particles fall quickly without much bounce while a high value makes the particles bounce more.

• Friction is the amount of influence that surface friction has on the particles as they collide with the obstacle. A high value makes them stick to the obstacle while a low value makes them slide off.

These parameters can be animated using standard animation controls (Birth/Abs/Age) and jittered with Variance values. For more information, see Animating Particle Type Parameters on page 52 and Adding Variation to Particles on page 64.


To consider the size of the particles for collisions

• Select Use Size for Collision to consider the size of the particle when it collides with the obstacle. This creates more of an offset between the particles and the obstacle, depending on the size of the particle.

Setting the Accuracy of the Collision

On the Collisions page in the ParticlesOp, FluidOp, and ExplosionOp property editors, you can set the number of Iterations and Interframes, which specify the number of times that the particle’s position is calculated per interval or per frame, respectively.

Depending on the collision, you can set the values higher for situations in which particles collide with multiple obstacles in the same step and there is undesirable behavior. Basically, the higher the parameter values here, the more accurate the results, but the longer the calculation times.

If you’re using the Explosion simulator, you can also select Check Particles, which detects collisions between particles and obstacles and calculates how the particles will respond. If this option is off, only collisions with structures are detected.

Disconnecting Obstacles

You can easily disconnect obstacles from the particles to which they’re associated. When you disconnect an obstacle from particle clouds, the collision event on the particle type is removed.

Particle collision without considering particle size.

Particle collision with Use Size for Collision selected.


To disconnect an obstacle

1. Select the particle cloud to which one or more obstacles is connected.

2. Choose Modify > Environment > Disconnect Obstacle/Force/Emitter from the Simulate toolbar.

3. Pick the obstacles you want to disconnect, then right-click to end the picking session.


Making Particles Collide with or Avoid Each Other

Besides particles colliding with obstacle objects, you can make particles collide with or avoid each other. Interparticle collision or avoidance is supported between particle types defined for a single particle cloud (you cannot use multiple clouds).

You can make a particle type collide with itself or with another particle type. To collide with another particle type, you need to have multiple emitters on the same cloud (see Adding Multiple Particle Emitters to the Same Cloud on page 43 for more information).

You cannot create interparticle collisions and avoidance with the Fluid or Explosion particle simulators.

Two particle types colliding with each other with a Collision Radius of 0.5.

Two particle types avoiding each other with an Avoidance Radius of 1.5.


Making Particles Avoid Each Other

To make particles avoid each other

1. Open the particle type’s Particle Type property editor and set these parameters on the Interparticle Properties page.

2. In the Interparticle Avoidance group, click Enable to activate the avoidance parameters.

3. If you want particles of the same particle type to avoid each other, select Enable Avoidance with same Ptype.

If you don’t select this option, you must also set and activate the Avoidance parameters for the other particle types to be avoided.

4. Set the Intensity of the avoidance force, rather like an inverse magnetic force field. If you’re making the particles avoid other particle types, the total avoidance force among the particle types depends on the product of each of their Intensity values.

5. Set the Radius which is the maximum distance in SOFTIMAGE units from the particles at which the Intensity vanishes.

The Interparticle Collision and Avoidance parameters can be animated using standard animation controls (Birth/Abs/Age) and jittered with variance (Var) values.

For more information on animating, see Animating Particle Type Parameters on page 52; for information on the Var parameter, see Adding Variation to Particles on page 64.

Select Enable to set the Interparticle Avoidance parameters.

Select Enable to set the Interparticle Collision parameters.


Making Particles Collide with Each Other

To make particles collide with each other

1. Open the particle type’s Particle Type property editor and set these parameters on the Interparticle Properties page.

2. In the Interparticle Collision group, click Enable to activate the collision parameters.

3. If you want particles of the same particle type to collide with each other, select Enable collision with same PType.

If you don’t select this option, you must also set and activate the Collision parameters for the other particle types involved in the collision.

4. Set the Probability of the collision on a scale of 0 to 100, with 0 being no chance of collision and 100 being a guaranteed collision.

If you’re making the particles collide with other particle types, the total probability among the particle types depends on the product of each of their Probability values.

5. Set the Radius which is the minimum distance in Softimage units at which the particles collide.

6. Set the Elasticity to determine how much the particles bounce off each other when they collide.

- If you set this to 0, there is no elasticity; 1 is full elasticity.

- If you’re making the particles collide with other particle types, the total elasticity among the particle types depends on the product of each of their Elasticity values.

Tips for Creating Successful Interparticle Collisions

• Keep the Radius size as small as possible.

• Don’t let the particles go so fast that they bounce off each other too easily. To harness the speed, set the Allowed Linear Velocity Range - Max value for the particle type (see Particle Velocity on page 40). You can really control rambunctious particles this way.

• If the particles are bouncing around too much when they collide, lower the collision Elasticity value. Also check that the obstacle’s Elasticity parameter in the Obstacle property editor is set at an appropriate level.


Creating a Particle Event

Particle events are a combination of two things: a trigger and an action. The trigger determines what causes the event to occur and the action determines what will happen when the trigger is executed. Using these two elements, you can have different actions occur that are triggered according to certain conditions you set.

A common trigger/action combination is a collision/bounce, but there are many more options from which you can choose. For example, an event could be used to create fireworks: the particle trail is seen going up into the sky, then suddenly bursts into another type of particle at the end of its lifetime. Or you could create something simple with an event such as the smoky trail left by a hurtling fireball by emitting particles at every frame. Of course, one of the most common types of particle event is a collision. You can make different actions happen when a particle collides with an obstacle, such as having the original particle bounce off the obstacle, have it emit another particle as it disappears, or have it simply disappear upon impact.

Particle events are set per particle type, allowing you to have very specific control over an effect.

Liquid in flask ripples when a drop hits its surface. This is done

by activating a wave operator with a scripted action (scripted

particle event).


Overview of Setting Up a Particle Event

This is the basic workflow for setting up a particle event:


- Select a particle cloud and choose Modify > Particles > Add Particle Event from the Simulate toolbar.

or

- On the Event page in the Particle Type property editor, click the New Event button.

2. In the PEvent property editor that opens, select the event Trigger and set its Value (see Selecting the Event Trigger on page 77).

Select a particle cloud and choose Modify > Particles > Add Particle Event from the Simulate toolbar.

Select a Trigger and set its value. The trigger is the thing that makes the event happen. Here, the trigger is “at 30% of the particle’s age”.

Select an Action, which is the thing that happens when the trigger’s value is reached. Here, the action is that a new smoke particle type is emitted.

1

2

3

A typical event to set up is a collision. You can create collisions by using the Modify > Environment > Set Obstacle command and then picking the obstacle object for the particles.

This automatically creates a collision/bounce event for the selected particle type. Or you can create a collision event with the Add Particle Event command as described above.


3. Select an accompanying Action (see Selecting the Particle Action for the Event on page 79) that you want the particles to do when the trigger’s Value is reached.

You can also open the PEvent property editor in either of these ways:

• Select the event name from the Inspect > Events menu button on the Simulate toolbar, as shown below.

or

• On the Event page in the Particle Type property editor, right-click the event’s name in the grid and choose Inspect.

Muting a Particle Event

Select the Mute option in the PEvent property editor to temporarily disable the event. This means that you can easily test a simulation without this event being calculated as part of it.

If you set an obstacle for a particle cloud using the standard method with the Set Obstacle command, an event with Collision as the Trigger is automatically created for the particle type. However, you can still select the type of Action to occur at the moment of impact.


Selecting the Event Trigger

Particle events can be triggered at: a particle’s Age or Age %, every nth particle, every nth frame, a particle’s position (in XYZ), a particle’s speed or X/Y/Z speed, a collision with an obstacle, or when particles collide with or avoid each other.

An event will only do something if the value of the parameter used as the trigger reaches the trigger Value of the event. This trigger value can be randomized using the usual animatable variance and seed as any animatable parameter of the simulation (see Adding Variation to Particles on page 64). If a single variance is used, the seed is added to that of the particle to get a per-particle trigger value.

Using a Particle’s Age or Age %

• If you select Particle Age as the trigger, the event is triggered at the frame you specify in the Value text box. For example, if you specify 60 as the Value, the event is triggered when the particle has been alive for 60 frames.

• If you select Particle Age % as the trigger, the event is triggered when it reaches the percentage of the particle type’s Max Lifetime value (see Setting the Particle’s Lifetime on page 48), which is the number of seconds that the particle lives.

For example, if you specify 60 as the Value, the event is triggered when the particle has reached 60% of its Max Lifetime value.

At Every nth Particle or Frame

You can set an event to happen at a specific number of particles or frames. For example, you could have another particle type be emitted at every 10th particle that is born or have particles disappear at every 20 frames. You could also create a particle trail by having a particle type emitted at every frame or use a Value of 1 with the Every nth Particle option.


At a Particular Position or Speed

You can set an event to happen at a specific position or speed of the particles. For example, you could have a particle disappear when it reaches a certain percentage of its Y position or emit another particle type when a particle reaches a certain percentage of its Speed value (see Particle Velocity on page 40).

Interparticle Collision or Avoidance

You can set an event to happen when particles collide with or avoid each other. This trigger depends on the settings you have for the particle type on its Inter. page (see Making Particles Collide with or Avoid Each Other on page 71). For example, you could emit another particle type when the particles interact (collide) with each other.

Upon Obstacle Collision

A collision event is when particles collide with an object that you have selected as the obstacle.

• If you’ve already selected an object as an obstacle for particles (see Setting Up Particle Collisions on page 66), a collision event for each particle type associated with the cloud is automatically created, with the action set to Bounce by default. You can change the action type as you like.

• If you add an obstacle to an existing event, the trigger automatically switches to Collision.

• If you select Collision as an event’s trigger, but no obstacle exists, you must select an obstacle or else nothing will happen.

To select an obstacle for an event

1. In the PEvent property editor, click the Pick button in the Obstacle group.

2. In the viewport, pick the object that you want to use as the obstacle for this event.

An obstacle property is added to the object and is also nested under the particle type’s event property. If you pick an object that already is an obstacle (has an obstacle property), this property is nested under the event.


Selecting the Particle Action for the Event

After you have selected an event trigger, you must select the type of action to occur for the event. In the PEvent property editor, choose the behavior of the particle type from the Action list, as shown below.

If you have already set an obstacle for a particle cloud, a collision event is automatically created for you with Bounce as the default action. You can then open the PEvent property editor for it and select the action you want.

If you select Script as the action, you can created a scripted event, which allows for a great deal of control over specialized effects (see Scripting a Particle Event on page 83).

Bounce

Bounce causes the particles to bounce off an obstacle that you have specified. This is possible only when you have Collision selected as the event trigger. The dynamics of the particle bounce is set by the Physical Parameters in the Obstacle property editor, as well as the settings for Elasticity and Friction on the Environment property page for the particle type (see Setting Up Particle Collisions on page 66).

Stick

Stick causes particles to stick to an obstacle that you specify and remain there for the duration of their lifetimes. This is possible only when you have Collision selected as the event trigger.

1 Setting bounce elasticityIf the action is set to Bounce, values specified for the Elasticity of the obstacle and the particle type have the effect shown to the left.

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.1

.1

.5

Setting friction valuesTo simulate particle friction, the action must be set to Bounce, and a value of 0 (no bounce) entered in the Elasticity controls for the obstacle.

Values set for the Friction of the obstacle and particle type have the effect shown to the left.

The lower the surface friction value, the farther the particles slide.

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Disappear

Disappear makes particles disappear at the time of the event. For example, with a Particle Age trigger, the particles disappear when they reach a certain percentage of their Max Lifetime value.

Emitting New Particles Emitting particles is a little more complex than the other actions because you must specify the particle type that is to be emitted from the initial particle type. However, emitting particles in an event also allows for much more interesting effects.

Emit causes new particles to be emitted at event time (such as upon impact with the obstacle in a collision) while preserving the original particles for as long as their lifetime allows.

Second particle type (smoke) emitted when first particle type (sphere) reaches the Age of 40 (frames).


Emit & Disappear causes new particles to be emitted at event time while the original particles disappear.

Bounce & Emit causes new particles to be emitted when particles bounce off an obstacle (you must have Collision selected as the trigger). The original particles do not disappear. For example, you can make bullets skip across a rock and emit dust particles upon impact.

Creating the Particle Type to Be Emitted

When you select either any of these three Emit actions, you must select the particle type (the source) that will be emitted at event time.

To create a source particle type to be emitted

1. On the Particle Type > Events page or the PEvent property editor, click the Create button in the Source group.

When the first particle type (sphere) collides with the obstacle, a new particle type (smoke) is emitted and the first particle type disappears.

When the first particle type (sphere) collides with the obstacle, a new particle type (smoke) is emitted and the first particle type bounces.


This creates an emission property similar to the one used by emitters, but only with a set of parameters relevant to the particle’s emission. The emission is named according to the event’s name with an “_Emission” suffix added.

2. Open the Event Emission’s property page, select the particle type to be used as the emitted particle and set its properties.

By default, the particle type used for this emission is the first particle type listed in Particle Type List folder under the Particle cloud.

3. Set up the emission properties.

For information on general Emission properties, see Selecting an Emitter and Setting Up Its Particle Emission on page 36. The following are the parameters that are exclusive to event emissions:

- Rate: With regular emissions, Rate is the number of particles emitted per second. However, with an event emission, this value is simply the number of particles emitted at event time.

- Azimuth is the azimuth vector along which the emitted particle type is generated. This is basically the angle from the point of view of the particle emitter.

- Declination is the degree of declination of the vector along which the emitted particle is propelled.

- Birth Offset > Radius offsets each emitted particle (depends on the Rate value you specify here) in a sphere around the original particle type with the radius value you specify (in Softimage units).

While emitting a new particle type allows you to create more complex effects, you must take care in how you do this. Here are two things to watch out for when emitting new particle types:

• It’s possible to create a recursive loop when emitting new particle types for event. For example, if three particles are emitted every time a particle hits an object, these three particles in turn generate three particles when they hit an object, and so on. The number of particles grows exponentially and can cause a system meltdown!

• Creating new particle types with every new event leads to housecleaning issues. Unless you are very careful about editing each new particle type by name and content, you could quickly end up with a vast collection of anonymous particle types in your scene.


Deleting a Particle Event

To delete a particle event

• Do either of the following:

- On the Events page in the Particle Type property editor, right-click the event you want to delete, choose Select Item, then press Delete.

or

- In the explorer, select the Event under the Particle Type’s Events folder and press Delete.

Scripting a Particle Event

Selecting Script as the Action (see Selecting the Particle Action for the Event on page 79) lets you select and run a script that you have created to modify the behavior or appearance of particles. For example, you could write a script so that the particles change color when they collide with an obstacle.

When you select Script, the parameters on the Script page in the PEvent property editor are activated. You can either select a script file that has already been created or you can write the script directly in the edit (white) box at the bottom of this page.

Select an event from the particle type’s Events folder and press Delete.


Using a Script File

To use a script file

1. Select Use Script File on the Script page.

2. Provide the name of the File containing the script.

3. Enter the Proc. (subroutine) name to call.

4. Select the language it uses: either VBScript or JScript.

The subroutine must have three parameters in this order:

• Parameter 1- the particle cloud primitive that triggered the event.

• Parameter 2- An array containing the indices of the particles that triggered the event.

• Parameter 3- The current simulation frame.

For more information about writing particle events, see the SDK Customization Guide and the Working with Softimage for Developers guide. To access this documentation, you can open the script editor and press F1 or choose Help > Scripting Reference in it, or choose Help > SDK Guide from the main menu in Softimage.

Entering a Script

To use a script on the page

• Enter the script in the edit box on the Script page.

The context defines how the script is called:

• Per trigger particle: the script is called once for each particle that triggers the event. In this context, you can use these variables:

- inParticle: One particle that triggered the event.


- inTriggerParticleCnt: The index of the particle within the array of particles that triggered the event.

• Per particle: The script is called once for every particle in the cloud, whether it triggered the event or not. In this context, you can use these variables:

- inParticle: One particle in the cloud

- inParticleCnt: The index of the particle within the cloud

• Per cloud: This script is called once for the cloud. No extra variables are accessible here.

In all three contexts, the following variables are available:

• inParticleCloud: the cloud primitive

• inTriggerParticleIndices: the array of indices of the particles that triggered the event (whatever the context)

• inSimFrame: The current simulation frame when the event occurred

• inParticleCollection: The particle collection object


Creating an Initial State for Particles

When you’re working with particle simulations, you often need to have a certain state of the simulation be the first frame of the simulation. Instead of computing a pre-roll simulation to arrive at the correct state for the beginning, you can select any frame in an existing simulation and use that as the initial state. The initial state includes the number of particles that are already emitted at the start of simulation along with their properties.

To create an initial state, you must first create a particle cloud and set up the simulation to your liking. Then you can capture any frame of the resulting simulation to be the initial state.

When you set an initial state, a particle cloud and initial state property is created as a child of the existing simulation’s particle cloud, but without a simulation operator. As well, the particle types associated with the existing particle cloud are copied to the initial state. Then at the first frame of simulation, the simulation operator copies this initial state data to the simulated cloud and continues the simulation from that state onward.

Once you set the initial state, you can modify it to your liking, such as using deform operators to manipulate the particles.

Setting the Initial State

To set an initial state for a particle cloud

1. Create a particle cloud and set up the simulation as you like.

2. Run the simulation in Standard Caching mode (see Choosing the Way Particle Simulations Are Played Back on page 31) so that you can move back and forth among the generated PTP files.


3. Go to the frame that you want to set as the initial state. This will be the first frame of the simulation that is played.

4. Select the particle cloud and choose Modify > Particles > Set Initial State from the Simulate toolbar.

An initial state property is created and connected to the particle cloud’s simulation operator (the initial state has no simulation operator of its own). It is a child of the selected particle cloud. The cloud is hidden and has render visibility off by default.

You can repeat these steps to replace the initial state using different frames.

5. Play the simulation and see that the first frame of the simulation is the initial state that you set and the rest of the simulation continues as it did from that point onward.

6. If you like, you can delete the original particle cloud’s emitter to keep only the initial state of the particles.

Frame 27 of this flame simulation is saved as the initial state. Everything affecting the cloud, such as natural forces and obstacle collisions, is baked into the initial state.


To edit the initial state’s properties

1. Open the Initial State property editor by doing one of the following:

- Select the original or initial state cloud and choose Modify > Particles > Edit Initial State Prop.

or

- Click the Initial State Property icon in the explorer.

2. Select these options as you like:

- Select Mute to temporarily deactivate the initial state.

- Select Transfer Velocity to transfer the velocity of particles from the selected particle cloud to the initial state cloud. Deselect this to have static particles.

- Select Live Forever to make the particles in the initial state stay in the scene for many, many seconds. This option is useful for creating static clouds, especially when used in deformations (see Deforming Particle Clusters on page 103).

Disconnecting and Reconnecting Initial States

To disconnect initial states

• Select a particle cloud with an initial state and choose Modify > Particles > Disconnect Initial State. This does not delete the initial state.

To connect or reconnect initial states

• Select a particle cloud and choose Modify > Particles > Connect Initial State. This connects an unconnected initial state to its parent particle cloud’s simulation operator.

Creating a New Particle Cloud Based on the Initial State

You can create a new particle cloud based on the original particle cloud that has the initial state. This lets you keep the original particle cloud’s simulation and disconnect its initial state. This is useful, for example, to create a simulation from sketched particles (see Sketching Particles on page 55).

To create a new particle cloud based on the initial state

• Select the original particle cloud with the initial state and choose Create > Particles > From Initial State.

This creates a new particle cloud and adds a simulation operator. The emitter and particle type are used from the original particle cloud, but is not copied to the new cloud so you cannot change these properties.


Creating Goals for Particles

When you create a goal for particles, the particles are attracted to or repelled from it, similar to the way in which a magnet attracts or repels pieces of metal. With goals, you can create a number of particle effects, such as drops of water forming into a puddle, paint being sprayed over a surface, or a swarm of bees chasing after an unfortunate bear.

Basically, to make particles reach a goal you select the particles, then choose one or more objects that will be the goals. The particles then try to reach the position and/or shape of the goal objects. When the particles reach the surface of the goal, their velocity decreases and they “stop.” If the goal moves or its surface is deformed, the particles keep on trying to reach the goal’s surface.

Particle goals are part of the overall particle simulation, which means that any particles that are progressing toward a goal can also react to obstacles and forces that are applied to them. In fact, goals act as a force on particles, similar to how the Attract force works. For example, if gravity is pulling particles downwards but their goal is above them, the particles will remain in a static position if both these forces are of the same strength.

You can use almost any type of object as a particle goal (including multiple goal objects), including polygons, NURBS surfaces, curves, nulls, lattices, implicit objects, cameras, lights, and even other particle clouds.

As well, you can choose to where on the goal object the particles will go (the object’s surface, its center, or a point on its surface, etc.) and how the particles react to the goal (chase it, flee from it, stick to it, etc.).

Chase makes particles follow this animated goal.


Setting Goals You can set goals for particle clouds, which affect all particle types that are attached to it, or you can set goals for specific particle types on a cloud. You can also use more than one goal object to affect the particles.

When a particle is born, it is randomly assigned to a point on the goal object and it evolves towards this point throughout its life. If there is more than one goal, each particle is assigned at birth to one point on each goal object: the first particle born is assigned and attracted to the first vertex of each goal, the next particle to the second vertex of each goal, and so on. Each goal has a weight parameter that lets you blend (and animate) the influence of the different goals on the particles (see Setting the Goal’s Weight on page 97).

Setting a Goal for a Particle Cloud

To set a goal for a particle cloud

1. Select the particle cloud to which you want to set a goal.

2. Choose Modify > Particles > Add Goal from the Simulate toolbar.

3. Pick one or more objects that you want to use as goals (middle-click to branch-select a goal object), then right-click to end.

You can use almost any type of object as a particle goal, including polygons, NURBS surfaces, curves, nulls, lattices, implicit objects, cameras, lights, and other particle clouds.

4. In the Goal property editor, set the parameters as described here:

Determines how the particles react to the goal.

Mutes the effect of the goal.

Name of the goal object.

Determines where on the goal the particles move toward.

Sets the weight (influence) of the goal.

Determines the goal’s range of influence.

Offsets the target’s position.


After you’ve set the goal:

• A goal property is created under each object that you picked to be a goal.

• A goal property is created under each particle cloud’s particle type.

Setting a Goal for a Particle Type

In addition to setting goals for particle clouds, you can set a goal for each particle type on a cloud. As well, if the particle cloud already has a goal set for it, you can edit or mute it for this particle type on the Goals page.

To set a goal for a particle type

1. Open the PType property editor for the particle type you want to.

2. Click the Goals tab and click the New Goal button.

3. Pick one or more objects you want as goals for this particle type and right-click to end the picking session.

After you’ve set the goal:

• A goal property is created under that particle type.

• A goal property is created under each object that you picked to be a goal.

The parameters on the Advanced page let you set more advanced variation for the Local Radius, Weight, and Offset parameters on the Goal page. You can select the Distribution method for each one (Uniform or Gaussian), as well as set a Seed value—see Adding Variation to Particles on page 64.

Click in the cell to mute the effect of the goal.

Click in the cell and enter a new value for the goal’s weight for the ptype. You can also click the animation icon to set keys on the weight’s value.

Click to set a new goal for the particle type.

Right-click in the cell to open a menu from which you can select or inspect the goal object.

Click in the cell and enter a new name for the goal.


Choosing the Particles’ Behavior

Using the Behavior options in the Goal property editor, you can decide how the particles react to the goal.

Particle goals are part of the overall particle simulation, which means that any particles that are progressing toward a goal can also react to forces that are applied to them. In fact, goals act as a force on particles, similar to how the Attract force works, depending on the behavior you choose.

For example, if gravity is pulling particles downwards but their goal is above them and you have Spring as the behavior, the particles will remain in a static position if the gravity and the behavior are of equal strength.

To determine the particles’ behavior

• Select an option from the Goal Behavior list: Chase, Flee, Stick, Arrive, or Spring.

- Chase: the particles follow the goal object as if it was a magnet.

- Flee: the particles are repelled from the goal and move in the opposite direction of it, as if repulsed by its hideousness.

- Stick: the particles immediately stick on the goal object as they are born; that is, the particles do not move from the emitter toward the goal and then stick on it.

Chase makes particles follow this animated goal.

Stick makes particles appear on the goal object as they are born.


- Arrive: the particles move slowly toward the goal.

You then set the Landing Distance in Softimage units and Deceleration of the particles. This allows you to prevent the particles from overshooting the goal.

- Spring: the particles are linked to the goal by springs and dampers (viscosity) according to Hooke’s law.

The Spring Constant determines how stiff the spring is. If you set this to positive values, the particles are attracted to the goal; negative values repel the particles. The farther the value is from 0 (either positive or negative), the more “elastic” the particles become.

Viscosity (or damping) is the amount of resistance applied to the particles as they move through space, as if they were moving through fluid. This is similar to the effect of a drag force. The higher the value, the more the particles are slowed down.

Arrive makes particles slowly approach the goal in a circuitous manner.

Spring links the particles to the goals by springs and dampers.


Selecting the Target on the Goal

Using the Target options in the Goal property editor, you can choose to which geometry component on the goal object the particles will move towards.

To determine where the particles move toward

• Select an option from the Target list in the Goal property editor:

- Surface: each particle is attracted to a randomly selected position (a random U and V value) on a polygon mesh or NURBS surface.

- Point: each particle is attracted to a randomly selected point (control vertex) on the goal’s geometry.

- Line: each particle is attracted to a randomly selected position on edges, isolines, or curves of the goal geometry. If the goal object is a curve, make sure to select this option.

- Center: each particle is attracted to the center of the goal object.

If the goal object is a particle cloud, you can use only the Center as the target. As well, if the Target option you select isn’t supported by the type of object the goal is, the target object’s Center is used.

- Volume: each particle is attracted to a randomly selected position inside the target geometry.

If you deform the goal object, then hide it or make it unrenderable, the particles will take on that shape and make it look as if you’re deforming the particles. This is especially noticeable with the Target set to Volume. See Deforming Particle Simulations on page 101 for more information on other ways of deforming particles.

Particles cover Surface of goal object.

Particles at Points of goal object.

Particles along Lines (edges) of goal object.

Particles filling the Volume of goal object.

Particles at Center of goal object.


Offsetting the Target from the Goal

You can offset the goal object’s target so that the particles don’t aim exactly for the target as they move toward the goal. This is particularly useful when you set a variance for the Offset X/Y/Z values to make the particles move more randomly toward the target on the goal object.

To offset the target position on the goal object

1. In the Goal property editor, select an option from the Offset Reference list. This determines the reference point from which the target is offset from the goal object:

- World: the target is offset relative to the global center: the reference stays constant regardless of changes to the goal object’s position, orientation, or scale.

- Goal object: the target is offset relative to the goal object’s local position, orientation, scale, and shape.

- Goal point: the target is offset relative to the local reference frame of the points on the goal object; that is, the offset follows the state of the goal object’s normals and tangents.


2. Set the Offset X/Y/Z values. These are target offset coordinates in relation to the Offset Reference you’ve selected. The offset directs the particles to the goal’s target plus the offset.

- For World, the Offset X/Y/Z values are expressed along the X/Y/Z axes of the world (global).

- For Goal object, the Offset X/Y/Z values are expressed along the X/Y/Z axes of the object (local).

- For Goal point, the Offset Y value is the direction along the normals, while the Offset X and Z values are directions along the tangents.

Each Offset parameter also has a variance parameter (Var) so that you can produce a more random effect on the particles. For more information, see Adding Variation to Particles on page 64.

Target offset from goal by 4 units in Y with World as the reference.

Target offset from goal by 4 units on Y with Goal object as the reference.

Notice how the particles respect the local rotation of the goal object.

Target offset from goal by 2 units on Y (along normals) with Goal point as the reference.

Particles reaching Surface target on goal object.


Setting the Goal’s Range of Influence

You can set the goal’s range of influence so that the particles are affected only if they are within a specified distance (local radius) of the goal object.

To set the goal’s range of influence

1. In the Goal property editor, set the Influence to Local.

If you select Global, the particles are influenced by the goal wherever they are in space.

2. Set the Local Radius value to the number of Softimage units within which you want the particles to be influenced by the goal.

For example, if you set 5 as the value, the particles are not influenced by the goal until they are within 5 units of the goal.

The Local Radius parameter also has a variance parameter (Var) so that you can produce a more random effect on the particles. For information on the Var parameter, see Adding Variation to Particles on page 64.

Setting the Goal’s Weight

You can set the weight of a particle goal, meaning how much of an influence it has on the particles that are attracted to it. While you can set the weight for a single goal, weighting is most useful when particles have multiple goals to which they’re attracted. Each goal acts like a competing force on the particles, which is controlled by its weight. Setting each goal’s weight allows you to blend (and animate) the amount of influence the different goals have on the particles.

To set each goal’s weight

• Set a value for the goal’s Weight parameter between 0 and 1.

A value of 0 means that the goal has no effect on the particles, and a value of 1 means that the goal has full effect (100%) on the particles.

If there is more than one goal, the Weight values are multiplied together. For example, if there are two goals and they each have a weight of 1 (fully weighted), the particles are pulled equally between these goals so the combined weight effect is 50% for each goal. If the Weight is 0.5 for each goal, the combined effect on the particles would be 25%, and so on.


When each goal’s Weight is the same, the particles move between the goal objects, usually oscillating back and forth and then becoming static. If each goal’s Weight differs, the particles obviously move more toward the goals with the higher Weight value.

The Weight parameter also has a variance parameter (Var) so that you can can produce a more random effect on the particles. This is multiplied with the weight too. For information on the Var parameter, see Adding Variation to Particles on page 64.

Editing the Goal’s Properties

To edit the goal’s properties

• Do any of the following to open a goal’s property editor:

- Select the goal object and choose Modify > Particles > Edit Goal from the Simulate toolbar.

or

- Select the particle cloud that has a goal and choose Inspect > Goals > name of goal from the Simulate toolbar.

or

- In the explorer, click the Goal icon below the goal object or the particle type.

or

- On the Goals page in the PType property editor, right-click the Ptype.goal name and choose Inspect Item (see Setting a Goal for a Particle Type on page 91).

Particles move more toward the goal with a higher weight.


Muting Goals You can mute a particle goal which lets you isolate and fine-tune the effects of other goals in a scene, or of particles without being affected by the goal. This is useful if you have several particle goals in the scene, and you don’t want to have them all simulate while you’re testing one.

As well, you can animate the muting to do such things as having the particles being intermittently attracted to a goal.

To mute a goal

• Select the Mute option in the Goal property editor.

or

• On the Goals page in the PType property editor, click in the Mute cell for the appropriate goal (see Setting a Goal for a Particle Type on page 91).

Disconnecting Goals You can disconnect a goal from its particles by deleting the goal object’s goal property. This disconnects the goal from all the particle types on the particle cloud.

You can also disconnect a goal from an individual particle type. All other particle types on the same cloud remain connected to the goal.

To disconnect a goal from a particle cloud

• Open an explorer and delete the goal object’s goal property.

To disconnect a goal from a particle type

• On the Goal page in the PType property editor, right-click the goal name from which you want to disconnect the particle type and choose Select Item, then press Delete.


Scripting Particle Goals You can control particle goals through scripted particle events. With scripting particle goal values, you can create many effects. For example you can simulate particles flowing along a surface or a curve.

To script particle goals

• Enter the script in the edit box or select an existing script on the Script page of the particle type’s PEvent property editor.

See Scripting a Particle Event on page 83 for more information.

Particle Goal Script Attributes

Each particle has a set of particle attributes that are allocated to it when connecting a goal to the cloud. All attribute names start with “Goal_N_” where N is the 0-based index of the goals connected to the particle simulation. For example, if you have three goals for a particle cloud, you would have Goal_0_UVWI , Goal_1_UVWI, and Goal_2_UVWI.

• Goal_N_UVWI

This is the target position of the particle on the goal object (see Selecting the Target on the Goal on page 94). This is a vector of four floats. The first three values (UVW) of the vector correspond to the surface parametric values, and the last one (I) is an index.

- If the target type is Surface on a NURBS surface goal object, U and V are the parametric values of the surface. W represents the depth when the goal target type is Volume. I is the index of the subsurface.

- For a polygon mesh goal with the Surface target type, I is the index of the target triangle and U and V are the barycentric coordinates of the target on that triangle. W is the depth along the triangle normal.

- For Point type targets, I is the index of the point.

- For Line type targets, I is the index of the edge or subcurve or curve and U is the parametric value along this element.

• Goal_N_Offset

This is a vector that offsets the target point (see Offsetting the Target from the Goal on page 95).

• Goal_N_Weight

This allows you to set a different goal weight for each particle (see Setting the Goal’s Weight on page 97).


Deforming Particle Simulations

You can apply almost any of the standard deformation tools (such as lattices, cages, Push, Twist, or Taper) to particle, fluid, or explosion simulations. This is a powerful way of making complex particle systems, especially when combined with natural forces. For example, you could make a whirling tornado by containing a particle system within a twisted and tapered lattice and then applying a vortex force; or have a school of fish deform along a curve.

You apply deformations to particle clouds or clusters. Particle clouds are just like any other geometry meaning that you can apply standard object-based deformations to them. You also create clusters of particles in the same way as you do for standard points and then use any cluster-based deformations on them, such as shape animation or envelopes.

Deforming a Particle Cloud

You can apply all object-based deformations to a particle cloud. All particle types associated to the cloud are affected by the deformer.

To deform a particle cloud

1. Select the particle cloud you want to deform.

2. Choose any of the deformations from the Deform menu (in the Model, Animate, or Simulate toolbar).

In this example, Deform > by Curve is used.

If you’re using natural forces on the particle cloud you want to deform, you should apply the forces first and then do the deformations. This is so that the deform operator sits “on top” of the cloud and uses all the simulation information that it contains.

When particle streams are deformed by a curve, the direction of the particles themselves is not tangent to the curve. This is because a deformer is unaware of what particles represent: it only moves the particles as if they were points in a geometry. As well, the deformer acts after the simulator, so the simulator doesn’t know about it.

Particle system before deformation

Particle system deformed by curve


To deform a particle cloud using a lattice

1. Select the particle cloud.

2. Create a lattice by choosing Get > Primitive > Lattice. Set up the lattice to have the subdivisions and size you want.

When you choose this command, the lattice is automatically applied to the particle cloud because the cloud was selected.

3. Deform the lattice in any way, such as simply transforming its points or by using any of the standard Deform operators on it.

Create a lattice and deform it in any way, such as by transforming its points or by using any of the standard Deform operators on it, such as Twist or Bulge, as has been done on this lattice.


Example: Deforming Particles by Surface

You can create a cool effect of having particles “crawl” over the surface of an object by deforming the particle cloud on a sphere’s surface.

1. Choose Create > Particles > From Primitive > From Grid to create a basic particle system.

2. On the Emission page, set the Spread to 90 and the Speed to 0.5.

3. Create a default surface sphere on which you will deform the particles.

4. Select the particle cloud and choose Modify > Deform > by Surface. In the Surface Deform property editor, set the Scaling to X:1; Y:0; Z:1.

This spreads the particles over the surface of the sphere and makes them crawl instead of flying away.

Deforming Particle Clusters

To have finer control over deformations, you can deform particle clusters. This allows you to deform particles based on their particle type, not just the whole cloud, because particle clusters are defined per particle type.

You can do any of the following deformations on a particle cluster:

• Scale, rotate, and translate them, especially using proportional modeling.

• Create shape keys from them for shape animation.

• Use them as envelopes.

• Apply standard deform operators, such as Twist, Bend, and Surface.

• Use particles as cage deformers for other objects.

To deform particle clusters

1. In Point mode, select the particles you want to use for a cluster and click the Cluster button on the Edit panel.

Do this step for each cluster of particles you want to create.

2. Select the cluster you want to deform and use any deformation on it, as listed above.


Deforming Clusters in a Static Cloud

Although particles are points, there are some issues that make particle points different than standard points. The main issue to consider is that with a simulation, particles are born and die over the length of the simulation. This means that the same particles don’t necessarily stay for the duration. Particles are assigned into clusters based on their index in the particle cloud. An index is only recycled when a particle dies, and new particles are only appended at the end.

Because of these restrictions, the best way to use particle clusters for deformations is use them on a static cloud. To do this, you make an initial state of the simulation and have the particles live forever (see Creating an Initial State for Particles on page 86). This way, all the particles needed for the deformation are available by frame 1 and the number of particle clusters in the cloud are constant throughout the simulation.

If the cloud is not static (meaning that new particles are being generated during simulation and other ones are dying), the particle clusters do not stay coherent during the simulation, which means that the deformations on them do not stay coherent either.

For example, when you set shape keys, you set them on a cluster of a defined number of points. If this number changes, the shape keys don’t produce the same results.


Attaching Objects to Particles

Attaching objects to particles allows you to use objects as part of a particle simulation. You can attach any geometric object, a light, or a camera to particles to create many different effects.

For example, you could attach a blood cell object to some particles flowing through an artery and lights to others. Then attach a camera to one particle and its interest to another, and take a wild ride through the blood stream!

Depending on what type of simulation you’re creating, there are two ways in which you can attach objects to particles:

• Create instances of objects that are attached to the particles at render time, such as the bats attached to the particles in the image below.

or

• Create particle clusters and then constrain an object to the clusters. This is useful if you have particles that don’t constantly get born and die, such as with a static cloud whose particles live forever. The cluster can be an individual particle or a group of particles.


Creating Instances of Objects to Attach to Particles

You can automatically create instances of objects for each particle at render time. You can select a group of objects and instantiate them on particles. Each object in the group is assigned randomly onto a particle and stays with that particle for its lifetime. This is because the instance is based on the unique ID of the particle and not its index (see About Particle IDs on page 17).

The local transformation of the object’s tree is ignored when instancing so that you can scale the source objects to 0 or translate them out of view. The instances’ translation is always inherited from the particle’s position and the particle’s rotation and scaling can be inherited as well.

Instancing takes the objects at the current time, so if you need multiple objects to be all the same at different times (for example a flock of birds), you have to clone that object multiple times and shift it along its cycle.

To create instances

1. Select the objects you want to instance and create a group that includes them (press Ctrl+g).

2. Select the particle type to which you want to attach the instances and open its Particle Type property editor.

3. On the Instancing page, select Enable to activate instancing.

4. Click the Pick button beside the Instance Group text box. In the explorer, pick the group you want to instance.

Create a group of one or more objects, then pick them as the instances on the particle type’s Instancing property page.

Then when the particles are rendered, the instances of objects that are attached to the particles are rendered instead of the particles.

The instances can inherit the rotation of the particles, as well as their size.


5. If you want the instances to inherit rotation from the particle, select Rotation > From Particle; otherwise, select None.

6. For Scaling, there are four different options for how the instanced object inherits the particle’s size:

- By particle size scales the object uniformly by using the size of the particle as the scale factor.

- Non-uniform to particle scales the object to fit the particle’s bounding box using non-uniform scaling. This makes the object completely fill in the bounding box.

- Uniform to particle scales the object to fit the particle’s bounding box using uniform scaling. This makes the object fit in the bounding box, but without changing its shape.

- None: the instanced object stays its current size and is not influenced by the particle size.

7. The instanced objects are displayed as nulls and/or bounding boxes in the viewport. Draw a render region to see the object geometry on the particles.

Inheriting the Particles’ Orientation

When you constrain or attach objects to particles, the objects inherit only the position of the particle. However, if the particles are rotated, there are two things you can do to have the objects also inherit the particles’ orientation:

• Select the Align on Velocity option on the Particle Type > General property page to align the particle type’s orientation to the velocity of the particle (see Rotating Particles on page 59).

• Activate the Tangency and Normal options for the Object to Cluster constraint.

An attached cannot object inherit the particles’ size and color, but you could do this via a scripted particle event. You create a particle event that uses a script that sets the size and color of the attached object based on certain particle attributes. See Scripting a Particle Event on page 83 for more information.


Constraining Objects to Particle Clusters

Because particles are points, you can create clusters of them and then constrain objects to those clusters. This method is useful if you don’t have too many objects to constrain and you’re using a static cloud.

To constrain objects to particle clusters

1. Create a particle cloud and select Live Forever for the particle type’s Life span (see Setting the Particle’s Lifetime on page 48). This prevents the particle from dying, so its ID stays active throughout the length of the simulation.

2. Create an initial state for the particle cloud at a frame in the simulation that you’d like to be frame 1. See Creating an Initial State for Particles on page 86 for information on how to do this.

Initial states allow you to forego creating a pre-roll to get to the frame you want for frame 1. Initial states also help to deal with objects constrained to particles that haven’t been emitted yet. If you don’t set the initial state, these objects hang around until their particle appears.

3. In Point mode, select the particles you want to use for a cluster and click the Cluster button on the Edit panel. You can also select a single particle to which you want to constrain an object.

Do this step for each cluster of particles you want to create.

4. Create the object you want to attach, including the correct number of instances for the number of clusters to which you want to attach it.

5. Select the object you want to attach to a cluster or particle and choose Constrain > Object to Cluster. Pick the particle cluster from the explorer.

Do this for each object that you want to attach to each particle cluster.

6. Play the simulation and see the objects attached to the particle clusters.

If you have many objects to attach to many clusters, you may want to write a script to do this.


Setting Up Forces for Each Particle Type

After you’ve created a force, you need to set up the sensitivity to the force for each particle type that is defined for the particle, fluid, or explosion cloud. (For information on particle types, see Creating Particle Types on page 44.)

The values you set for the parameters here specify the degree to which the natural force acts upon that particular particle type. This means that you can have each particle type react differently to a force, including not being affected by a force at all.

This also means that you can leave a force’s values the same (useful if the force is affecting multiple objects in a scene) while changing only the particle type’s reaction to it.

To set up forces per particle type

1. Apply forces to a particle cloud by selecting it and choosing a force from the Get > Forces menu on the Simulate toolbar.

2. Open the particle type’s Particle Type property editor.

3. Click the Envir. tab and modify the values for each parameter that correspond to the forces acting on the particle type (that is, if you have gravity affecting the particle cloud, set the Gravity parameter’s value).

Attractorcontrol object


The settings you use here represent a percentage of the “global” effect that the force has. The value for any parameter here must be greater than 0 (zero) for its corresponding force to have an effect.

By default, each parameter’s value is set to 1 so that the effect works immediately at 100% of its strength, but you can change it to any value.

As with other particle type parameters, you can animate these parameters in different ways such as age, birth, and constant. For more information, see Animating Particle Type Parameters on page 52.

You can also set the Var (variance) value for each parameter, as well as the type of variance (Uniform or Gaussian). See Adding Variation to Particles on page 64 for more information.


Creating Custom Parameters for Particles

You can create your own custom parameters per particle type on a cloud, providing more flexibility when building custom particle behaviors through scripting.

Per-particle attributes are exposed to the Object Model and C++ API. See the SDK Object Model documentation for ParticleAttribute, ParticleType, and ParticleTypeCollection objects.

To access this documentation, you can open the script editor and press F1 or choose Help > SDK Guide from the main menu in Softimage. The particle objects used can all be found under the Object link (the Object Model) in the Scripting Reference.

As well, see the SDK Customization Guide and the Working with Softimage for Developers guide for more information about particles. These guides are also available in the Scripting Reference contents.

To create a custom parameter for a particle type

1. Open a particle type property editor and click the User Parameters tab.

2. Enter a Name for the custom parameter.

3. Select a parameter Type from the list: Integer, Float, Boolean, etc.

4. Click the New Parameter button.

The new parameter is added to the bottom of this property page and becomes a property of the particle type. In the explorer, you can find all custom parameters in the Parameters folder under the PType node. Make sure to use the All Nodes filter to see them.


Chapter 3 Fluid

The Fluid simulator applies hydrodynamic properties to particles, so you can create liquid-based effects such as water flowing out of a bottle or honey dripping from a spoon.

Fluid simulation uses its own particle operator (FluidOp operator) and emitters: only the implicit squares, disks, and cubes emitter object can be used with it—not any other object in Softimage.

However, many tools that are available for the particle operator are also available for Fluid. See Basics for Particle-based Simulations on page 4 for general information that applies to all particle-based simulators.

By default, the Blob shader is attached to the fluid’s particle type, which renders the particles as a liquid that exhibits hydrodynamic qualities. For more information on rendering, see Rendering Particles and Fluid on page 133.


Like other particle simulations, you can have the fluid particles collide with obstacles or be influenced by natural forces. You can use only the following natural forces with fluid simulations: eddy, fan, gravity, and wind.

Creating a Fluid Simulation

Creating a fluid simulation is similar to regular particles except that you can only emit particles from specific implicit objects. After you’ve created the emitter and simulation, a fluid particle cloud is created and you can set up the emission and fluid particle type in a similar way to particles.

To create a fluid simulation

1. Choose Create > Fluid > From Cube, Disc, or Square from the Simulate toolbar to create the emitter object and the simulation, represented by the fluid particle cloud (as shown below).

If you need the flexibility of the regular particle system but want fluid-looking particles, use the Blob shader with the Particle simulator.

You cannot have multiple emitters on a fluid cloud.


2. In the FluidOp property editor, specify the dynamic attributes of the fluid simulation.

The following are the most basic options to set, but for a detailed description of each parameter, see Fluid Property Editor on page 184.

- For information about options on the Output page, see Caching the Simulation in PTP Files on page 19 and Restarting Fluid Simulations on page 120.

- For information about options on the Collisions page, see Setting Up Particle Collisions on page 66.

3. Set the Start Frame at which the fluid simulation is applied and the Duration, which is the number of frames over which the fluid simulation is applied.

4. If you want to use the start and end frames set for the scene’s timeline, click Copy from Scene. Likewise, you can copy the values that you set for the Start Frame and Duration here to the scene’s timeline by clicking Copy to Scene.

5. Set up the emission as described in Setting Up the Particle Emission on page 35.

6. Set up the particle type as described in the next section, Defining the Fluid Particle Type.

7. Render the fluid simulation with the Blob shader attached to the particle type (default). See Blob Shader (3D) on page 144 for more information.


Number of Particles

To set the number of particles in the simulation

• Mean distance sets the distance in Softimage units from one master particle to another. This determines the number of master particles and is strictly related to particle density. The lower this value (the smaller the space between particles), the greater the density of particles.

• Slave ratio is the percentage of slave particles in relation to master particles that are set with Mean distance. A value of 1 means that there are as many slave particles as there are masters. The slave particles are randomly distributed on the surface/volume of the emission.

Frothiness

To add frothiness to the fluid

• Set the Foam %. This determines what percentage of the particle density will be used as foam. Particles with a density lower than the value here and with a value higher than the Foam speed min. are rendered as foam.

• Foam speed min. determines which particles may be rendered as foam. Particles whose speed is higher than this value could be rendered as foam. The Foam % is also taken into account: particles with a density lower than that value will probably be rendered as foam. Basically, if a particle is not very “quiet,” it will probably be rendered as foam.

Mean distance value of 0.5. Mean distance value of 1. Mean distance value of 5.

Because the number of particles is determined by the Mean Distance value, the Rate on the Emission page is ignored (see xxx). The Mean Distance is not animatable, so to animate the emission rate, you can key the Size of the particles and/or the emission Speed (key them both at zero when you want to have no particles).


Muting a Fluid Simulation

Muting allows you to temporarily disable the fluid simulation, meaning that you can easily play back a scene without the simulation being calculated as part of it.

To mute the fluid simulation

• Select the Execution State > Mute option in the FluidOp property editor.

Deleting a Fluid Simulation

To delete a fluid simulation

• Select the fluid’s cloud icon and press Delete. This removes the simulation and the cloud icon.

You must remove the emitter separately by selecting it and pressing Delete.


Defining the Fluid Particle Type

Once you have created the fluid simulation, you can set up the particle type. The main properties for fluid are on the Fluid page in the Particle Type’s property editor. However, you can also set other properties you wish to assign the particle type (such as color, size, and mass) on the General, Color, and Envir. pages. See Defining a Particle Type on page 46 for more information.

To set up the fluid particle type

1. From the Emission page’s Par Type controls, select the particle type whose particles you wish to use in the fluid simulation and click the Edit button. You can also create a new particle type by clicking the New button.

2. Click the Particle Type tab to modify the particle type’s parameters. Then click the Fluid tab to display controls for setting the particle type’s fluid attributes, as follows:

Viscosity

Viscosity sets the level of resistance to flow in a fluid. Lower values, such as 0.07, simulate the flow of a watery liquid. For a more syrupy fluid, increase this value to 1 (maximum).

Heavier fluids also depend on gravity to define their behavior. By decreasing the gravity, you slow down the fluid dynamic (the result is similar to increasing the Viscosity), and vice-versa.

The particle type’s Mass also makes a difference in the viscosity of the fluid—make sure to set this to an appropriate level for the right effect. A larger Mass value makes for more viscose results. Click the General tab to set this—see Setting the Particle’s Mass and Size on page 48.


Surface Tension

Surface Tension sets the degree of liquid tension on the particles’ surface. Due to surface tension, particles that simulate liquid in the shape of a cube, for example, tend to transform into a spherical shape as they fall to the ground. A low level of surface tension makes the particles hold their original cube shape longer.

Coriolis Force

Coriolis sets the angular speed of a Coriolis force, which is the rotational motion of fluid, such as that of water emptying down a drain. The higher the value, the stronger the Coriolis force acts on the liquid simulation.

Compressibility

Compressibility sets the degree to which the simulated fluid can be compressed. Setting a low value reduces the amount of bounce behavior in the fluid.


Restarting Fluid Simulations

You can reuse and display an existing simulation to restart the simulation computation from the first non-computed frame.

Any time a scene is reloaded, each of these simulation operators verifies if its old PTP file sequence still exists. To do that, the file sequence “magic number” is compared with the magic number saved with the operator. If the PTP sequence still exists, an automatic restart on the last valid frame is performed.

From that frame on, further recomputation (due to any change in parameter, obstacle, emitter, particle type, etc.) starts from the Restart Frame+1, while all frames between the Start Frame and Restart Frame are preserved.

To restart a simulation

1. From the Output page of the FluidOp property editor, specify the Output Sequence file name in which to save the simulation in .ptp files (one file per frame). These files record all the simulation data for each frame of the simulation (see Caching the Simulation in PTP Files on page 19 for more information).

2. Play the simulation to record the frames to file.

3. On the timeline, go to the frame at which you want to restart the simulation and select Restart from file on the Output page.

4. Click the browser button (...) beside the Output Sequence file name and select the .ptp file with the frame number that corresponds to the current frame you’re at.

All the frames of simulation before this frame are read from the file which means that they don’t have to be recalculated. Computation then starts from the current frame onward. When you restart, the simulation properties’ values can be different from those used to generate the .ptp file.

5. Each time you exit Softimage, delete a simulation operator, or close the scene, you can automatically erase all .ptp files that were recorded and cached. To do this, select Clean cached files. If you don’t select this option, the .ptp files are saved in the folder with the Restart file name you specified.


Chapter 4 Explosions, Fire, and Smoke

You can use the Explosion simulator to effectively reproduce various kinds of explosions and a whole range of related particle phenomena such as smoke, dust, gases, flames, and sparks.

Explosion simulation uses its own particle operator (ExplosionOp operator) and emitters: only the default sphere or cylinder emitter objects can be used with it—not any other object in Softimage.

As with real explosions, there are different elements or “structures” found in simulated explosions. It is from the interaction and dynamics of these structures that an explosion takes shape.

Blast coming from the bottom of a rocket.


Like other particle simulations, you can have the explosion particles collide with obstacles or be influenced by natural forces. There are two different approaches to managing obstacle collisions: collisions with structures only, or collisions with structures and particles. The computation time is directly proportional to the collision precision settings.

As well, see Basics for Particle-based Simulations on page 4 for general information that applies to all the particle-based simulators (Particle, Fluid, and Explosion).

Explosion Shapes

You can have two kinds of emitter shapes: spherical and cylindrical. The shapes are generated from the explosion’s object icon, associated to the explosion cloud:

• The spherical shape (as shown below on the left) is for explosions that are fairly spherical in shape with a well-defined center.

• The cylindrical shape (as shown below on the right) is useful for explosions where there is an emission area and a directional particle vector, like a mushroom cloud or the blast from a rocket as it takes off.

You can use only the following natural forces with explosion simulations: eddy, fan, gravity, and wind.

Explodes in a spherical shape.Explodes in a specific direction.


You can translate, rotate, scale, and deform the emitter object to animate the shape of the explosion. The more the emitter is deformed along a direction (or set of directions), the more the emission and speed of structures is enhanced accordingly.

Explosion Structures

There are different components or structures found in simulated explosions. It is from the interaction and dynamics of these structures that an explosion takes shape. Each of these structures are emitted from the same emitter object, and you can set each structure up on its own property page in the ExplosionOp property editor (see next section).

The structures are actually particles themselves working as a little system and each of these particles, in turn, emit their own particle types, so you can think of a structure as a type of “master particle.” Particles created from the structures inherit the structure’s speed at the moment of their birth.

Each structure has its own dynamic behavior that you can define by its path and speed. In addition, the particles associated with the structures have their own parameters for defining their paths and speeds during their lives. You can also apply external forces (such as gravity and wind) to influence the movement and behavior of each structure.

Each structure is associated to one of three phases: Flame, Smoke, and Sparks. You can have any or all of these phases present in a particle simulation. For example, if you wanted to create fire, you might use only the Flame and Smoke phases.

If you select the Flame phase, a light is generated. You can constrain the light to the position of the explosion icon; its color, defined frame by frame, is equal to the average RGB of all of the flame’s particles. The light emission is proportional to the particle density.


Creating an Explosion

Creating an explosion simulation is similar to regular particles except that you can only emit particles from the specific default objects.

After you’ve created the emitter and simulation, an explosion particle cloud is created.

Then you must select and set up any or all of the three phase structures: Flame, Smoke, and Sparks—see Setting Up the Structures on page 127. After you set up each phase, you must then set up its corresponding emission properties (see Setting Up the Phase Emissions on page 129) and particle type (see Setting Up the Phase’s Particle Type on page 130).

To create an explosion

1. Set the start and end frame for your animation on the timeline.

2. From the Simulate toolbar, choose Create > Explosion > From Sphere or Cylinder to create the emitter and the simulation, represented by the particle cloud, as shown below.

You cannot have multiple emitters on an explosion cloud.


3. In the ExplosionOp property editor, set the parameters for the simulation.

Choosing How the Explosion is Played

1. Select the Execution State > Mode to determine how the explosion is played back:

- Not interactive doesn’t calculate the particle animation until you move to a different frame, either by clicking the Play button below the timeline or moving the playback cursor.

- Interactive updates the particle animation each time you modify a particle parameter. The simulation is recalculated from the start frame to the current frame as soon as you modify a particle in a property editor or you move an obstacle or a force.

Interactive is especially useful for tuning rendering properties like the color and size of particles: these properties do not involve dynamics so they are recomputed very quickly.

- Disconnected doesn’t calculate the particle animation at all. This is useful for setting keyframes for the animatable particle properties or obstacle animations by and moving back and forth on the timeline without having to wait for the particle simulation to update.

Disconnected basically mutes the particle operator and detaches the particle system. The particle system can be reattached by selecting any of the other options.

2. Set the Start frame at which you want the explosion simulation to begin and number of frames for the Duration.

Defines collisions with obstacles.

Sets frame range of explosion simulation within the scene.

Scales the whole simulation in Time and Space.

Sets an overall variation to the explosion simulation.

Determines which explosion phases (structures) are created.

Sets the output files.

Determines the way simulation is played back.

Sets the percentage of particles to generate. Low values are useful for quicker previewing.

Structure properties for each phase.

Emission properties for each structure and its particles.


3. Click Copy from Scene to match the Start Frame and Duration settings to those set in the scene’s timeline or set the frames here and click Copy to Scene to set the scene’s timeline’s range.

Scaling the Explosion Simulation

To change the speed of the explosion simulation

• Set the value for the Time Scale. If, for example, you divide this value in half, the whole simulation evolves at twice the speed.

To change the size of the explosion simulation

• Set the value for the Space Scale. Modifying this parameter makes the overall size of the explosion larger or smaller without changing its shape.

Deleting the Explosion To delete the explosion

• Select the Explosion cloud icon and press Delete. The cached animation is deleted too.

If you want to delete the emitter object and emitter light, you must do this separately (it may be easiest to use the explorer for this).


Setting Up the Structures

You can have any or all of the Flame, Smoke, and Sparks structures (see Explosion Structures on page 123) active as phases of the explosion. For example, if you only want to create a candle flame, you can select only the Flame and Smoke phases, or select only the Smoke phase for a cloud or smoke trail.

After you select a phase, you must then set up its corresponding structure properties (see below), emission properties (see Setting Up the Phase Emissions on page 129), and particle type (see Setting Up the Phase’s Particle Type on page 130).

To select phases and set up their structures

1. On the Simulation page in the ExplosionOp property editor, select a Phase Activation (any combination): Flame, Smoke, and/or Sparks.

2. For each phase you activate, set its properties on its corresponding property page. For example, if you select Smoke, click the Smoke tab and set the properties there.

Shown in the following image is the Flame page: the pages for the Smoke and Sparks structures are the same except that they don’t have Light parameters.

If you select the Flame phase, an explosion light is generated (in the explorer, you can find it under the Explosion Emitter node). You can constrain the light to the position of the explosion icon; its color, defined frame by frame, is equal to the average RGB of all of the flame’s particles. The light emission is proportional to the particle density.

Since the light emulates flame illumination, it should stay in the same zone of flame particles; by default it is set at the emitter centre, but you can move it.

The light for the Flame only takes into the consideration the color set for the particle type.


The information in the following illustration gives you an overview of the parameters, but for more information on them, see ExplosionOp Property Editor on page 176.

Time it takes to go from the simulation’s start to end. For example, to cut speed in half, use a value of 2.

Angular speed in degrees per second of the structure around its normal axis.

Motion plane of structure’s circular-velocity term (0 is normal radial, 1 is normal-binormal).

End value of radius (in Softimage units) that defines structure’s circular-velocity term.

Start/end values of angular speed (in degrees per second) of structure’s circular-velocity term.

Speed of structure in terms of age, frames, or constant initial speed.

Sets the angle jitter in degrees for the structure's starting direction.

Sets the smoothness of the structure's starting directions. Results depend on the emitter object shape for the explosion (Sphere or Cylinder).

Available only with the Flame structure. The Emission Factor is the value multiplier in the HSV color space for the light, and Min/Max set the available range of values for the light emission.

Value used to scale the intensity of the Gravity force.

Amount of air friction between the air and the structure. A value of 1 makes the structure have the same speed as the applied Wind force.

When the structure particles start to fade out in terms of the percentage of the structure’s life.

Duration of structure’s life.

Movement of particles in direction opposite of the Gravity force. A value of 1 equals (exact opposite of) the strength of the applied Gravity force.

Number of structure particles emitted.

If you find that particles are generated for the explosion but don’t move from the icon, check the Air Friction value for the active phases. A value of 0 means that the particles cannot move with respect to the air, so if there is no wind, they don’t move at all.

The same applies for the Gravity Coefficient: the value must be anything other than 0 (zero) for gravity to have an effect.


Setting Up the Phase Emissions

After you select and set up a phase, you must set up the emission parameters and the particle types associated with it. For example, if you selected the Sparks phase, you must set up the Sparks emission parameters and the Sparks particle type.

To set up the phase’s emission

• In the ExplosionOp property editor, click the Emission tab and set the emission properties for each of the phases you selected.

The information in the following illustration gives you an overview of the parameters, but for more information on them, see Emission on page 178 in the Properties Reference.

Particle type to use for structure.

Emission type used for the structure.

Reference emission speed of structure in Softimage units per second.

Number of structure particles emitted per second.

Duration of structure life in seconds.

Number of particles being emitted per second.

Movement of particles in direction opposite of the Gravity force. When value is 1, the acceleration is equal to (exactly opposite) the Gravity’s force. Adds variation to parameters’ values.

Explosions are a bit different from particles to animate because they have structures (sparks, smoke, and flame) as well as particle types. For example, if you’re animating the Speed on the Emission page here, change the Speed Control parameter on the appropriate structure’s property page (see previous page) to Absolute Frame to see the expected keyed results.


Setting Up the Phase’s Particle Type

After you set up the phase’s emission parameters, you must select and set up the particle types associated with it. For example, if you selected the Sparks phase, you must set up its particle type (Sparks by default).

Setting up the phase’s particle type

1. From the ParType list on the Emissions page in the ExplosionOp property editor, select the particle type to use. By default, the structure’s corresponding particle type is selected (that is, a Flame particle type is created if you selected the Flame phase).

You can also click the New button beside the list to create a new particle type.

2. Click Edit to open the particle type’s property editor in which you can set its properties.

3. Set the properties for the explosion particle types in the Particle Type’s property editor.

You can set any of the properties as you would for any particle type (such as color, size, and mass) on the General, Color, and Envir. pages. See Defining a Particle Type on page 46 for more information.

As well, there are properties that apply only to the Explosion operator on the Explode page in this property editor.

The information in the following illustration gives you an overview of the parameters, but for more information on them, see Explosion on page 218.

Amount of structure speed inherited by particle.

Location of particle emission.

Length or time of particle’s life or death.

Overrides RGB values set on Color page.

Start/end of particle’s angular speed in degrees per second, defining the structure’s circular-velocity term.

When the particles start to fade out (alpha channel value reduces) in terms of the percentage of the particle’s life.

Overrides Alpha values set on Color page.

Start/end of particle’s radius in Softimage units, defining the structure’s circular-velocity term.

Overrides Size values set on General page.


Rendering Explosions

When you render the explosion, you must use the Explosion shader, which is applied by default to the explosion particle cloud. Other particle shaders are not designed to be used with the Explosion operator, so they will not render the appropriate results.

The Explosion shader defines the look of the particles, depending on the phases you have active for the explosion simulator: sparks, smoke, and flame.

For information on each parameter in the Explosion shader’s property editor, see Particle Explosion on page 237.

For information in general about rendering particles and using the render tree, see Rendering Particles and Fluid on page 133.

• Keep all light sources outside the explosion cloud’s bounding area so that the particles render properly.

• Are there unwanted black spots in the explosion when rendering with the default settings? The spots you see are the default sparks particles that can be used to simulate sparks and debris from fires and explosions. Deselect the Sparks phase in the ExplosionOp property editor to prevent the sparks from being generated.


Chapter 5 Rendering Particles and Fluid

In many basic ways, rendering particle and fluid simulations is similar to rendering any other object in Softimage. You can use all standard lighting techniques (including global illumination and final gathering), set shadows, and apply motion blur.

The particle shaders described in this section are not supported for the Explosion simulator so they will not render any results. You can use only the Explosion shader with this simulator. See Rendering Explosions on page 131 for more information.


Unlike any other object in Softimage, however, there are special particle shaders designed specifically for particle-based simulations that let you make particles look the way you want. As well, you can apply shaders to individual particles types to create specific effects or apply shaders to a whole particle cloud to have all its particle types be rendered in the same way.

General Rendering Information

Rendering particles is much like rendering other objects in Softimage when it comes to general things like lighting, shadows, and motion blur.

You can have multiple particle clouds in a scene and they can all render happily, even if the clouds’ volumes intersect one another.

Motion Blur

You can use motion blur on particles in the same way that it is used on any other type of object in Softimage. Motion blur calculates the speed of the particles using the camera shutter speed. The camera motion is mapped as particle motion relative to the camera, so blur vectors are computed in any condition of absolute and relative motion.

To render motion blur on particles, make sure that the whole particle simulation is cached because Softimage stores motion from the last frame to compute the motion blur. See Playing Particle-based Simulations on page 19 for information about caching particles.

If you want to have motion blur only on the particles but not on other objects in the scene, create a group with all the objects on which you don’t want motion blur, apply the motion blur property to the group, and deselect Blur for it.


Using the Particle Shaders

There are special particle shaders for particle and fluid simulations that give you the control to make particles look the way you want. All particle shaders are texture shaders except for the particle renderer shader, which is a volume shader. As well as these special particle shaders, you can plug many other Softimage shaders into a particle’s render tree.

Shaders Per Particle Type

You can apply shaders to each particle type of a particle cloud for specific multi-effect control. For example, if you have one particle type for smoke and one for lava, you can use a different shader for each one, letting you set the correct look for each entity.

Overview of Particle Shaders

There are different types of particle shaders to give a variety of different effects. Because you can use different particle shaders together, as well as throw other Softimage shaders into the mix, the visual possibilities are virtually endless.

When you create a particle or fluid simulation, the particle renderer shader is connected to the cloud’s Material node by default. As well, with Particle clouds, the Billboard and Shape shaders are connected to the particle type; with Fluid, the Blob shader is connected to the particle type.

To apply other shaders to particles, you connect them in the render tree (see Connecting Shaders in a Particle Render Tree on page 140). This gives you more control over which shader is connected to which node. As well, you have access to all other Softimage shaders.

You can find these particle shaders in Softimage by choosing Nodes > Texture > More in the render tree. Then open the Particle_Old folder to see all the texture-based particle shaders (Billboard, Blob, Sphere, etc.). xxx

You can also use the particle shaders designed to be used with ICE particles.

Render region drawn over flame particles to show the effects of the particle color gradient shader.


The Particle Renderer Shader on the Cloud

The Particle Renderer shader is a volume shader that acts as a “meta” shader node controlling how the whole particle cloud is rendered. It offers you rendering control with BSP tree settings that are set exclusively for the particle cloud.

This shader plugs in to the particle cloud’s Material node and accepts inputs from other particle shaders via the particle type. This allows for maximum flexibility when you have multiple particle types on the same cloud.

You must have this shader attached to the particle cloud’s Material for particles to be rendered. As well, you must have a basic render type shader (see below) attached to the particle type for particles to be rendered.

Basic Particle Render Types

The Billboard (2D), Sphere (3D), and Blob (3D) shaders define the basic shape/surface of the particles. You can plug these shaders directly into the particle type or into the Particle Renderer shader that’s on the particle cloud’s material. These shaders are usually used individually on a particle type because they define the basic look of the particles. By default, the Billboard shader is attached to particle types created with the Particle simulator, and the Blob shader is attached to particle types created with the Fluid simulator.

These shaders share many of the same types of parameters for self-shadowing, color burn, global illumination, and shading properties (ambient and specular color settings).

For more information, see The Basic Particle Render Type Shaders on page 141.

Texture Shaders

The Sprite and Shape shaders both define the particle’s shape and can be used in combination with each other.


These shaders are 2D-based, so they are often plugged into the Billboard shader, which provides a 2D surface. You cannot plug these color shaders directly into the particle type or cloud.

You can plug them into the Blob and Sphere (3D) shaders, but the results are less predictable because they are 2D non-repeating textures.

For more information, see Rendering Sprites on page 166.

Color Shaders

The Particle Color and Particle Gradient shaders both allow you to override the particle type’s color for rendering. The Particle Color shader is a simple shader that overrides RGB/alpha values, while the Particle Gradient shader allows you to create sophisticated color/alpha shifts for the particle.

You can plug the Particle Color and Gradient shaders directly into any of the three basic shaders (Billboard, Blob, or Sphere) or into the Sprite or Shape shaders which are, in turn, plugged into a basic shader. You cannot plug these color shaders directly into the particle type or cloud.

For more information, see Rendering the Particle Color on page 151.


Vector and Scalar Shaders

The Particle Vector and Particle Scalar shaders let you override the settings for the particle type and output the particle simulation as vector or scalar values. Vector and Scalar shaders allow you to use particle attributes, such as velocity, rotation, particle index, mass, or radius to drive other parameters in the render tree.

You can plug these shaders directly into any of the three basic render type shaders (Billboard, Blob, or Sphere), or into the Sprite, Shape, or Particle Gradient shaders which are, in turn, plugged into a basic shader. You cannot plug these shaders directly into the particle type or cloud.

Editing a Shader’s Properties

After you’ve applied a shader, you can edit it by setting the properties in its property editor. First draw a render region over the particles (see next section) to view to results of the shader. Then as you edit the shader’s properties, the render region updates to display the changes you make.

For a description of each parameter in a shader’s property editor, click the ? icon in the property editor to open its online help.

To open a particle shader’s property editor

Do one of the following:

• Select the particle cloud and choose Modify > Shader. This opens the property pages for all shaders attached to the Particle Renderer shader.

or

• Select the particle cloud and choose Inspect > Par Types > particle type. This opens the Particle Type property editor, as well as property pages for all shaders attached to this particle type.

or

• In a render tree, double-click on the shader’s node to open its property editor, as well as property pages for all shaders attached to it. See Connecting Shaders in a Particle Render Tree on page 140 for more information.


Previewing Shaders in the Render Region

As you’re tweaking your particles to perfection, you’ll find that the render region is an invaluable friend and ally for checking things. Once you have applied a shader to the particles, you can use the render region to preview a mental ray rendered image of the final look of the particles.

To create a render region

• In a viewport, press Q and drag over the area of the particles you want to preview.

You can resize the render region using the little blue boxes in its corners or on the sides and set the aliasing by dragging the little slider on the right side of the region.

Press Q and drag to create a region.

Inside this region, you see the results of using the Blob shader with a high level of blending and a Color shader on the particles.

Drag the aliasing slider up to set the highest quality image.

Resize the region by dragging its little blue boxes.


Connecting Shaders in a Particle Render Tree

Connecting shaders in a particle system’s render tree gives you full control over which shader you want attached where. You can attach shaders directly to each particle type for ultimate control. This allows for maximum flexibility when you have multiple particle types on the same cloud.

In addition, you have access to the standard Softimage shaders, many of which can be plugged into any particle shader.

Connecting Shaders to a Particle Type

To connect shaders in the particle’s render tree

1. Select some particles or a particle cloud.

2. Open a render tree in a viewport or press 7 to open one in a floating window.

3. Click the Update icon or press F6 to display the render tree for the selected particle cloud. By default, the particle type is displayed.

You can also select any particle type node from the Selection list at the top of the window in the render tree (ParTypes.name of particle type).

4. Choose Nodes > Texture > More in the render tree. Then open the Particle_Old folder to see all available texture-based particle shaders. This folder includes all of the particle shaders except for the Particle Renderer shader, which is a Volume shader.

The basic shaders (Blob, Sphere, and Billboard) are attached by default to get the initial particle surface/shape. You must have one of these basic shaders attached before you can use other shaders, such as Shape, Sprite, or Particle Gradient.

5. Connect the basic shader to the Renderer input of the Particle Type node. For example, the Billboard shader is connected to the particle type, and the Shape shader is connected to the Billboard shader’s Color input. This is the default shader connection when you create a particle cloud.

6. Now you can connect other shaders to the basic shaders, and to the shaders attached to them. For example, the tree below shows how to connect other shaders to the Blob shader to give reflection and incidence to a fluid’s appearance.


The Basic Particle Render Type Shaders

The Billboard, Sphere, and Blob shaders define the overall shape of the particles because they create the particle surface. As a result, you need to have one of these shaders attached to the particle type (or cloud) before you can attach other shaders.

Shown below is the same particle simulation with each of the three shaders applied to show the basic particle surface that is created:

Connecting the Basic Shaders

By default, the Billboard shader is attached to particle types created with the Particle simulator and the Blob shader is attached to particle types created with the Fluid simulator. See Connecting Shaders in a Particle Render Tree on page 140 for more information.

Because these shaders create the basic shading surface for the particle, you must attach one of them to the cloud or particle type to have particles rendered or to use other particle shaders, such as Sprite, Shape, or Color Gradient.

Making Quick Connections to Other Shaders

In any of the Blob, Billboard, and Sphere shader property editors, you can quickly and easily connect some typical shaders to them.

Click the buttons on the Make Connections page to connect that shader to the Color input of the Blob, Billboard, or Sphere shader.

Blob shaderBillboard shader Sphere shader

When you choose Create > Particles > New Particle Type from the Simulation toolbar, you can select which basic shader to attach to it immediately: Billboard, Blob, or Sphere.


For example, the Shape shader is attached to the Billboard shader by default, but you can connect it quickly by clicking the Shape button on the Billboard shader’s Make Connections page.

If something is already plugged in to the basic shader’s Color input, it will be disconnected and the shader you choose takes its place.

Common Parameters The three basic shaders share many of the same parameters for shading and lighting properties, such as self-shadowing, color burn, global illumination, and shading properties (ambient and specular color settings).

For information on:

• Shading properties, see Setting the Ambient and Specular Colors on page 151.

• Transparency, see Setting the Particle Transparency on page 157.

• Static blur, see Static Blur (Interparticle Transparency) on page 159.

• Self-shadows, see Creating Self-Shadows for Particles on page 161.

• Color burn, see Color Burn (Additivity) on page 152.

• Global illumination, see Global Illumination on page 162.


Billboard Shader (2D)

The Billboard shader renders particles as 2D particles instead of 3D, similar to how the Particle (Sparks) shader did in previous versions of Softimage. This shader is attached to the particle type by default (along with the Shape shader) when you create a particle cloud with the Particles simulator.

The Billboard shader provides a good surface for making the particles look as you want, such as by using a sprite with the Sprite shader attached, or using a shape with the Shape shader attached. You can control the particle’s form, how it’s textured, which way it faces (the camera, any ray, or using rotation), and if it rotates (rolls). The smoke shown above is created by rendering the rotation from particles.

For more details on each of the parameters, see Particle Billboard on page 228.

If you have the Shape shader attached to the Billboard shader, its shape type overrides the shape set for the Billboard. For example, the smoke shown on the previous page uses the Turbulence shape type with falloff in the Shape shader, which is attached to the Billboard shader.

Smoke created with the Turbulence shape in the Shape shader attached to the Billboard shader.

Basic shape of particle surface.

Direction of surface normals.

The direction the particles face.

Make particles rotate with the velocity.

How the particles are textured.


Blob Shader (3D)

The Blob shader renders particles as 3D blobby objects that can flow like the semi-liquid wax balls you see in lava lamps. This shader is attached to the particle type by default when you create a fluid cloud.

The Surface Evaluation parameters let you specify how much the particles flow into one another. The Blending Amount slider lets you set no blending (0) to an exaggerated blending (1) where the individual blobs are barely distinguishable. Softimage tries to keep the blob radius constant in accordance to the blending amount you specify, but as the value increases toward 1, the blobs may start to thicken. Keep this value below 0.5 for more consistent blob blending.

The Texture Projection parameters dictate the projection (cylindrical, lollipop, etc.) and blending of the textures. If the particles have 3D rotations on them, you can choose to render them.

For more details on each of the parameters, see Particle Blob on page 232.

While you can’t blend blobs between multiple particle clouds, you can blend between multiple particles types on the same cloud.

Blob shader on Fluid simulator

Blending Amount set to 0.1. Blending Amount set to 0.5.


How much the blobs blend together.

How the blobs are blended.

The texture projection method.

Blends the textures between the blobs.

Renders particles’ 3D rotation.


Sphere Shader (3D)

The Sphere shader basically does as advertised: renders particles as spheres. This is a good starting point for rendering typical effects like bubbles to billowing smoke or even lava spewing from a volcano.

The Face parameter lets you render both faces of the particle or just the front or back. You can select a Texture Projection style (cylindrical, lollipop, etc.); and if the particle types have 3D rotations on them, you can choose to render the rotations.

For more details on each of the parameters, see Particle Sphere on page 248.

Sphere shader with 3D wood texture shader attached.

Renders the particles’ faces.

How the particles are textured.

Renders particles’ 3D rotation.


Setting a Particle’s Color

You can assign color and color variance to emitted particle types. For convenience’s sake, color information appears on the Color page in the Particle Type property editor so that you don’t have to open a shader when setting up the display color of the particles.

Anything you set here is used by the shaders, but you can also override the color with the Particle Color or Particle Gradient shaders. If you want to define the color as a ramp (for doing color shifts), use the Particle Gradient shader. This shader works according to a particle’s Age % by default.

For information on these shaders, see Rendering the Particle Color on page 151.

Setting the Particle Type’s Color

To set color properties for particles

1. Open the particles’ Particle Type property editor.

2. On the Color page, specify the color information of each particle type by using these controls:

You can animate the RGB and Alpha channels like other particle type parameters using the Birth, Age, Absolute, and Age % controls. For more information on this, see Animating Particle Type Parameters on page 52.

Adding Color Variance

The Color - Variance parameters allow you to add variance to the H (hue), L (luminance), S (saturation), and Alpha parameters’ values. The values for parameters define the range in which the random numbers are generated.

The distribution method of the variance can be Uniform or Gaussian:

• With Uniform, random numbers are distributed uniformly around the parameter’s value using the Variance value. The parameter will always be in the range [ Value - Variance; Value + Variance ], never outside of it.

Color applies color to the particles. This is the particle color displayed in the viewport.

Variance specifies the variations to the particles’ HLS color and alpha channel values.

Animation Reference defines the variations to the particles’ RGB and alpha channel values. You can animate these using birth, age, age%, and absolute controls.


• With Gaussian, random numbers are distributed as a bell curve around the parameter's value using the Variance value. Most numbers will be in the range [ Value - Variance; Value + Variance ], but they may be outside of that range with [Value - Variance], and they will be outside of that range with [Value + Variance]. Values using Gaussian distribution will have greater variations than the ones using a Uniform distribution.


The seed parameter (the text box with no label to the right of the Uniform/Gaussian parameter) allows you to change the effect on the variance without changing either the parameter's value or its Var value. The seed defines which numbers will be generated in the range that the Var parameter specifies. It allows you to have very fine control over the parameters, changing them slightly without having to change the parameter’s value or its Var value.

The Seed parameter works only if you have a value other than zero for the Variance parameter to which it is associated.

Original particle color for gold dust. Variance - Hue value set to 1 using the Gaussian distribution method.


Setting the Initial Color of the Emitted Particles

The Map Color option on the Emission property page lets you use the color values from a texture or vertex color map (using an image or sequence) that is connected to this option. When you select Map Color and connect a map, the colors on the map are used to set the initial color of each emitted particle. In this case, the particle color set on the particle type’s Color page is not used.

However, you can use the Jitter parameters (H, L, S and Alpha) on that page to modify the mapped particle colors.

Example: Mapping Colors to Particles

This is a simple example of how to change the emitted particle colors using the colors from a cloud image and a texture map.

1. Create a grid and make it larger than the default.

2. Choose Create > Particles > From Selection and accept the defaults.

3. Select the grid (particle-emitting object) and choose Get > Property > Texture Map > XZ to create the XZ projection and a texture map for this projection.

4. In the explorer, click the Texture Map icon under the grid’s node.

5. In the Texture Map property editor that opens, click the New button and choose New from File.

6. In the browser that appears, navigate to the <Softimage installation>\Data\XSI_SAMPLES\Pictures folder and select the cloud02.pic image to use as the map. Close the property editor.

7. In the Emission property editor, activate the Map Color option.

8. Click its connect icon and choose Connect. In the pop-up explorer, select the texture map you just created.


9. Still in the Emission editor, increase the Rate of particles to a larger amount such as 1000.

10. On the Particle Type > General page, set the Max Life to 10 or more, or select Live Forever so that there is enough time to see the effect of the texture map emerging.

11. In the Top view, select the Shaded or Textured display mode and play the particle simulation to see the colors of the cloud emerging in the particle formation.


Rendering the Particle Color

There are different ways in which you can set the color for particles. You can set the ambient and specular color on the Shading Properties page in any of the three basic shaders’ property editors: Billboard, Blob, and Sphere. You can also add color burn (additivity) for any of these shaders to create specific glow or overexposure effects.

As well, the Particle Color and Particle Gradient shaders both allow you to override the particle type’s color for rendering. The Particle Color shader is a simple shader that overrides RGB/alpha values, while the Particle Gradient shader allows you to create sophisticated color/alpha shifts for the particle using a gradient control.

Setting the Ambient and Specular Colors

You can set the ambient and specular color for the particles using the parameters on the Shading Properties page in any of the three basic shaders’ property editors (Billboard, Blob, and Sphere).

The ambient color is the shadow color and the specular color is the highlight. The ambient color you set here is modified by the scene’s ambience.

If you turn off Apply Shading, the particles have a constant color and ignore any lights in the scene. If there are no lights in the scene and you turn Apply Shading off, the particles revert to their base color (which will look constant).

Uses the lights in the scene for particle shading. If you turn this off, the particles are a constant color and ignore lights in the scene.

Sets the highlight color for the particles.

Sets the shadow color for the particles. This color is modified by the scene’s ambience.

Determines the specular area. High values create a larger area.


To set the ambient and/or specular color

1. Make sure Apply Shading is selected.


- Select Use Ambient Color and/or Use Specular Color from the appropriate Type list. Set the ambient or specular colors using their associated Color sliders. To get luminescent particles, use a high value for the Ambient color.

You can also set the Shininess of the specular color: low values create a larger specular area.

or

- Select % of Base Color from the appropriate Type list to use a percentage of the particles’ diffuse color that is set for the particle type. Set the percentage using the % of Base slider. To “blast” the color, use values higher than 100%.

Color Burn (Additivity) The Burn parameter on the Rendering Properties page for the Blob, Billboard, or Sphere shaders adds the RGB values of the particles when they overlap.

This creates a saturated color, or color burn, which is useful for creating glow or radiant, phosphorescent effects. High values can create “inner glow” effects.

Burn set to 0.5. Burn set to 0.


Creating Particle Color Gradients (Ramps)

The Particle Gradient shader uses the same gradient controls as found in the Gradient Mixer shader but is designed to be “particle friendly” for color shifts based on a particle’s age. As well, it is optimized for working with a large number of particles. The Particle Gradient shader affects the particle colors from their age percentage by default.

To connect the Particle Gradient shader

• Connect the Particle Gradient shader to the Color node of the Billboard, Sphere, or Blob shader.

or

• Connect the Particle Gradient shader to the Shape or Sprite shader’s Input node, which is, in turn, connected to the Billboard, Sphere, or Blob.

Using the Gradient Controls

The gradient slider in the Particle Gradient shader’s property editor is where you create and adjust the gradient. The bar displays the gradient left-to-right that is used from the particle’s birth (Pos of 0) to its death (Pos of 1).

Particle flame rendered using the Particle Gradient shader.


To select color markers

• Click a square marker below the gradient slider. You can then set its color using the color sliders or key its position.

To set the gradient color/alpha values


- Select RGB to use only RGB values. You can also select Show alpha to add the alpha channel to the RGB values.

or

- Select Alpha to use only the alpha values.

2. Click a square marker to select the color you want to adjust.

3. Use the color sliders below the gradient control to set the RGB/alpha values to use for this marker.

To change the gradient composition

• Drag a color marker anywhere along the gradient.

To insert a color marker

• Click at any point along the gradient slider.

By default, the new marker assumes the color at that point in the gradient. You can use up to eight color markers, each with its own color.

To delete a color marker

• Right-click it and choose Delete marker.

Selected square marker shows current color value and Pos (position) value.

Gradient slider displays how the color/alpha values change.

Determines the range of values displayed on the gradient slider.

Round markers indicate the mid-point of the blending between two square color markers.

Click in the gradient slider to add a color marker at that point.

Click one of the Presets buttons to load a specific gradient control setup.


To change the blending between two colors

• Drag a round marker above the gradient slider closer to either square color marker.

Round markers appear between each pair of color markers, indicating the mid-point in the blend between those two colors.

To set the gradient’s interpolation

• Click the Cubic/Linear button to toggle between linear and cubic interpolation of the gradient.

Cubic interpolation results in a smoother transition between alpha values, while linear interpolation results in sharper transitions.

To animate the markers

1. Go to the frame at which you want to set keys.


- Click the Key All RGB/Alpha Markers buttons to key all markers’ positions on the gradient slider (both square and round markers).

or

- Select a square color marker and click the Pos parameter’s animation icon.

To remove the animation on the markers

• At any frame, do one of the following:

- Click the Remove All RGB/Alpha Keys buttons to remove all keys from the markers (both square and round markers).

or

- Select a square color marker and go to a frame where there is a key. Then click the Pos parameter’s animation icon.

To reset the marker positions and remove keys

• Click the Reset Gradient button.

This removes all keys on the RGB and Alpha markers, puts the markers back in their original positions, and disconnects all shaders that are attached to gradient shader parameters.


Overriding the Particle Type’s RGB and/or Alpha Values

You can override the color (and/or alpha values) you’ve set for the particle type by selecting a new color with the Particle Color shader. This is a simple way to keep the particle type’s color constant (such as if you’re using particle types from a library), but change the particle color during rendering

To override the particle color

1. In the render tree, connect the Particle Color shader to the Color inputs on one of the three basic render type shaders (Billboard, Sphere, or Blob).

2. Set the new RGB/alpha values using the New Color color controls.

Overrides the particle type’s RGB values with the ones you set here.

Overrides the particle type’s alpha value with the one you set here.


Setting the Particle Transparency

You can create transparent particles using the Billboard, Blob, and Sphere shaders by setting the alpha value in different places, such as from the particle color, the particle color shader, or the particle gradient shader.

As well, you can load the Raytracing > Transparency or Opaque shaders in the render tree and plug them into the Color input of the Billboard/Blob/Sphere shader.

To use the alpha value from the particle type’s color

1. On the particle’s Particle Type > Color property page, set the Alpha value for the level of transparency you want.

2. On the Shading Properties page in the Billboard/Blob/Sphere shader’s property editor, set the Ambient - Type to Use % of Base Color.

3. Set the % of Base to 100% or more to see the effect better.

See Setting the Ambient and Specular Colors on page 151 for more information.

To use the alpha value from the Particle Color shader

1. In the render tree, select the particle type from the drop-down list.

2. Load the Particle Color shader by choosing Nodes > Texture > More in the render tree. Then open the Particle_Old folder and select Particle_Color.

3. Plug this shader into the Color input of the Billboard/Blob/Sphere shader to override the particle type’s alpha value.

4. In the Particle Color shader’s property editor, select Override Particles - Alpha only (you can deselect RGB if you don’t want to override the particle type color) and set the New Color - Alpha value to the level of transparency you want.


See Rendering the Particle Color on page 151 for more information.

To use the alpha value from the Particle Gradient shader


2. Load the Particle Gradient shader by choosing Nodes > Texture > More in the render tree. Then open the Particle_Old folder and select Particle_Gradient.

3. Plug this shader into the Color input of the Billboard/Blob/Sphere shader to override the particle type alpha value.

4. In the Particle Gradient shader’s property editor, select Alpha and set the alpha value and the gradient control to the level of transparency you want.

See Creating Particle Color Gradients (Ramps) on page 153 for more information.

To use the Transparency shader


2. Load the Transparency shader by choosing Nodes > Raytracing > Transparency.

3. Plug this shader into the Color input of the Billboard/Blob/Sphere shader to override the particle type alpha value.

4. Set the Transparency shader values to an appropriate level of transparency.

Adding Reflections To make the particles reflective


2. Load the Reflection shader by choosing Nodes > Raytracing > Reflection_Diffuse.

3. Deactivate the Apply Shading option on the Shading Properties page in the Billboard/Blob/Sphere shader’s property editor. This lets the Reflection shader take care of color shading too.

4. Plug this shader into the Color input of the Billboard/Blob/Sphere shader.


Set the Reflection shader values to an appropriate level.

Static Blur (Interparticle Transparency)

With the Blob and Sphere (3D) shaders, you can set the interparticle transparency by selecting the Static Blur option on their Rendering Properties page. This value modifies the alpha channel by the distance between the in and out hit points. It makes the particles transparent on the edges and fully opaque through the center.

With the Sphere shader, overlapping particles accumulate so the blur is less obvious if many particles overlap. The Blob shader brings all particles together into one mass when they get close enough to each other, so individual particles don’t really overlap.

You can set the Width, which increases the diameter of each particle by this number of units.

The Falloff rate controls how the transparency decreases as it gets further from the particle center. The rate of falloff increases with larger values.

The transparency is greatest when the particle’s normal is perpendicular to the viewing direction. The transparency is not modified when the normal is coincident.

If you want to control transparency with the Billboard shader (for 2D), you can attach the Shape shader to it and set the Falloff (transparency) controls with it (see Rendering Particle Shapes on page 163).

Particle with Sphere shader attached and no Static Blur.

Particle with Sphere shader attached and Static Blur Width of 0.2.

Activates static blur (transparency).

Sets the width of the blur around each particle.

Sets how quickly the transparency decays.


Using the Textured display mode, you can see the transparency and color burn values for the particles. For more information, see Selecting a Display Type on page 6.


Lighting and Shadows for Particles

You can have particles cast shadows on other objects in the scene as well as on each other. As with anything else in Softimage, casting shadows with particles depends on the number and types of lights you’re using.

When you’re using shadows, make sure you have shadows activated for the lights you want to use.

As well, the Blob, Billboard, and Sphere shaders all support global illumination and final gathering.

Creating Self-Shadows for Particles

You can have particles cast shadows on other objects in the scene as well as on each other, which enhances the illusion of 3D volume.

To do this, set the value for the Self-shadowing slider on the Rendering Properties page for the Blob, Billboard, or Sphere shaders to let particles cast shadows on each other. This slider controls the overall density of the particles for tracing the shadow area.

Lower values makes the particles more transparent to light rays (less pronounced shadows), while higher values make the particles more opaque (darker shadows), all relative to the light settings in the scene.

You can decrease the render time if you set the Self-shadowing option to 0 so that the particles no longer cast shadows onto themselves. The entire particle cloud still receives and cast shadows on other objects.

Self-shadowing controls only the amount of shadows falling on the particles from the particles themselves: it does not control the shadows received from other objects in the scene.

To see shadows on particles, make sure that shadows are activated for the lights in the scene.

Makes particles cast shadows on each other, relative to the lights in the scene.


Global Illumination The Blob, Billboard, and Sphere shaders all support global illumination, which includes final gathering. You can set both the Irradiance and Radiance color values on the Global Illumination page for each of these shaders.

• Irradiance determines how much color the particle type receives from other surfaces during final gathering.

• Radiance determines how much color the particle type transmits onto other surfaces.

To set the irradiance/radiance colors

• Do one of the following:

- Select Use Irradiance Color and/or Use Radiance Color from the appropriate Type list and then set the colors using their associated sliders.

or

- Select % of Base Color from the appropriate Type list to use a percentage of the particles’ diffuse color that is set for the particle type. Set the percentage using the % of Base slider.

Set the color of the light that is received from other surfaces with final gathering.

Set the color of the particle type that transmits to other surfaces.


Rendering Particle Shapes

When you’re defining the look of a particle type, setting its shape plays a significant role. The Shape shader provides a plethora of 2D shapes from which you can choose, including setting the shape’s position within the particle radius and setting its transparency falloff.

To connect the Shape shader

• Connect the Shape shader to the Color input of the Billboard shader.

By default, the Shape shader is already attached to the Billboard shader when you create a particle cloud: these two complement each other nicely because they’re both useful for 2D effects. The Billboard shader creates the 2D surface while the Shape shader provides the actual shape definition and look.

Selecting a Shape In the Shape shader’s property editor, you can choose from these shape types on the Shape page:

• Step uses a ratio (its Width) of the particle size to set the shape in a single step.

Particles using the Turbulence shape pattern in the Shape shader, which is attached to the Billboard shader.

Original particle with no shape specified.

Step Sine Star Beam

FractalTurbulenceNoiseSymmetry


• Sine creates a particle with a number of rings that are equally spaced from one another. The Sine’s Scale controls specify the number of rings used.

• Star creates a particle with a star-like configuration. You can specify the number of branches used (default is 4).

• Beam gives the particle a long beam shape with a bright center surrounded by a glow effect. You can specify the width of the beam.

• Symmetry creates a symmetrical particle shape whose width you can set.

• Noise can be used to create a variety of chaotic effects. Based on one basic pattern, you can modify the spacing and the level of detail using its Time and Size controls.

Time lets you control the animation of the noise over time by connecting a Particle Scalar shader and setting it to Global Time (or particle age).

• Turbulence creates irregular cloud-like patterns. You can control its size and high and low frequency patterns. This is often useful for creating smoke and fog effects. As with the Noise shape, you can set the Time to control the animation of the turbulence.

• Fractal creates iterative fractal-based patterns. You can set its size, granularity, weight of iterations, and number of octaves. As with the Noise shape, you can set the Time to control the animation of the fractal pattern.

Setting the Shape’s Falloff (Transparency)

The falloff for the shape is the rate at which the transparency around each particle decays. For any shape that you select, you can set the type of falloff (transparency), as well as offset it from the particle pattern center. The range defines where you want the falloff to start and end, in relation to the particle pattern center that you specify.

To set the type of falloff

• Select a calculation method from the Type list on the Falloff page in the Shape shader’s property editor.

The type of falloff is the calculation method used to determine the falloff ’s general shape. You can select from square, cubic, linear, smooth, Gaussian (bell-shaped), user-defined, or none.

You can view the shape types in Textured display mode except for the Noise, Turbulence, and Fractal shape patterns.


- If you select User-defined, you can set its Exponent value, which controls the transparency falloff rate. Values less than 1 give a steep falloff from the center. Higher values give a more gradual falloff.

- If you select Gaussian (bell curve-shaped falloff) as the type, you can control the Rate of falloff. Higher values give a more rapid falloff.

To set the falloff pattern center

• Enter a value for the Pattern Center X and/or Y text boxes on the Falloff page in the Shape shader’s property editor.

These values determine the center point for the falloff pattern in X and/or Y according to the particle’s center. This lets you offset the falloff from the particle’s center.

To modulate the RGB/Alpha values

• Select the Modulation RGB and/or Alpha on the Falloff page in the Shape shader’s property editor.

This multiplies the RGB and/or alpha components of the base particle color by the falloff value at the intersection point.

• Select Inverted for the RGB and/or Alpha options to invert the shape value when multiplying the RGB/Alpha components.

To set the range of falloff

• Enter values in the Range Start and End text boxes on the Falloff page in the Shape shader’s property editor.

This is the distance from the pattern center at which the falloff value goes from 0 to 1. The falloff value is interpolated between the Start and End values using the Type of falloff you have selected.

Particle with square falloff on a step shape pattern.

Particle with linear falloff on a step shape pattern.


Rendering Sprites

When you use sprites, you can use any textured image file or animated sequence and apply it to the particle type so that the particles look like that image. For example, you can use any of the sample sprite images from the <Softimage installation>\Data\XSI_Samples\Pictures\Sprites folder that’s installed by default, as shown below.

After you’ve selected a sprite image sequence for the particle type, you attach the Sprite shader to your particle type and render with it.

Using a Single Sprite Image

You should use the Sprite shader only if you are using a sprite image sequence for the particles. If you are using a single image, you can select a Texture > Image shader in the render tree and select the sprite image there. Then connect the Image shader directly to the Billboard shader’s Color node.

Selecting a Sprite Image Sequence

To load a sprite image sequence for the particle shape

1. In the Particle Type property editor, click the Sprite tab.


- Select a sprite image sequence from the list and click Edit to change its settings.

or

- Click New to load a new sprite image sequence from source or file.

Sprite samples available in the Data\XSI Samples\Pictures folder.


3. Select the Animation Control as described in Animating the Sprites on page 167.

4. Render the particles using the Sprite shader (see Rendering with the Sprite Shader on page 168).

Animating the Sprites Using the Animation Control on the Particle Type > Sprite page, you can also control the sprite sequence’s animation the same way as you can for any of the other particle type parameters using the Birth, Age, Absolute, and Age% controls.

For example, this means that you can map image sequences to the particle’s lifetime using the Age control. See Animating Particle Type Parameters on page 52 for more information on these controls.

• Using the Random animation control, a sprite image from the sequence is assigned to the particle at random. This sprite image is assigned to the particle at its birth, and it remains with it for the particle’s lifetime.

• The Var is a variance parameter, as found for other parameters (see Adding Variation to Particles on page 64).

• Render Time lets you control the sprite sequence’s animation when it’s rendered with the Sprite shader. With this option, Softimage stops trying to optimize which frames are sent to mental ray (such as any unused frames), and makes them all available at render time.

Then you can texture the sprite using another shader plugged into the Sprite shader’s Start Sequence % input (see Rendering Sprite Image Sequences on page 170) to control where in the sprite sequence mental ray should evaluate. For example, you can procedurally control the lookup of the frame index using another shader, such as the Particle Scalar shader, which extracts scalar type data on the particle being rendered.


Rendering with the Sprite Shader

The Sprite shader is designed to be used if you have sprites attached to the particle type. Sprites won’t be rendered if you don’t use this shader. And if you use this shader with no sprite attached, the particle’s color is displayed instead.

To connect the Sprite shader


- Select a sprite image sequence from the Sprite page in the Particle Type property editor (see Selecting a Sprite Image Sequence on page 166).

or

- If you don’t have a sprite defined for the particle type, you can also select a Texture > Image shader in the render tree and select the sprite image there. Then connect the Image shader to the Sprite shader’s Input node, as shown here, or directly to the Billboard shader’s Color node.

2. Connect the Sprite shader to the Color node of the Billboard shader, or directly to the Particle Type Renderer node (if you have a basic render type shader attached to the particle cloud’s Material node).

The Billboard shader creates the 2D surface for the Sprite to be applied. If you apply the Sprite shader to the Blob or Sphere shaders (which are 3D), the sprite images are projected onto them as a texture.

Setting the Sprite Color and Alpha

To set the sprite color

• Select Output Color From Sprite in the Sprite shader’s property editor. This uses the color from the sprite image you have attached to the particle type.

• If you deselect this option, the color is taken from whatever shader is connect to the Sprite shader’s Input node. In this case, you can attach an Image shader with the sprite image to the Sprite shader’s Input node.

Particles with a red bubble sprite rendered by the Sprite shader, which is attached to the Billboard shader.


• If nothing is connected to the Sprite shader’s Input with this option off, then the particle type’s color is used.

To modulate the particle’s alpha values

• Select one of the Alpha Modulation options in the Sprite shader’s property editor. This multiplies the alpha channel by the sprite’s alpha channel or RGB intensity, or nothing at all.

• Select Inverted to invert the alpha calculated from the sprite before multiplying with the incoming alpha. For example, if the sprite appears with a border around it, toggling this option usually gets rid of it.

Original bubble sprite image

Color taken from the sprite image. Color taken from the particle type.

Alpha is inverted for this sprite image.

Toggling the Inverted option inverts the alpha value and the border disappears.


Rendering Sprite Image Sequences

If you have attached a sprite sequence, you can decide how the sprite is animated using the animation controls on the Particle Type > Sprite property page (Animating the Sprites on page 167).

Then you can set up how the sprite sequence is rendered in the Sprite shader.

To render the sprite sequence

• Set the Start Sequence (%) value in the Sprite shader’s property editor. This percentage value is where in the sprite sequence you want to evaluate the frame. It uses the value 0 to mean the beginning of the sequence and 1 to mean the end of the sequence. This option is useful to set when you have the Render Time option set in the sprite’s animation controls (see Animating the Sprites on page 167).

• Select or deselect Looping to determine how the Start Sequence % values are marked:

- With Looping on, the fractional value of Start Sequence % indicates the frame. This means that if, for example, you animate the value to go from 0 to 5 over 100 frames, you will see the sprite animation looped five times over those 100 frames.

A whole number (integer value) always marks the first frame, and the last frame is the number just before the next whole number.

- With Looping off, values less than or equal to 0 mark the first frame, and values equal to or greater than 1 mark the last frame.

This means that any values outside the range are clipped to the start/end point for less than 0 and greater than 1 respectively.

• Select an Image Sampling method (Bilinear or Nearest Neighbor) which is the type of sampling method to read pixel values from the sprite image.

• Select Frame Interpolation to interpolate between frames if the frame number is fractional. For example, if a sprite is at frame 1.5, the shader interpolates frames 1 and 2 at 50%.


Rendering Particles in Fields

If you field render a scene with particles, you’ll notice that the particle emission in both fields (for example test.1.1.pic and test.1.2.pic) is similar. However, the particle emission should actually be offset from one field to the next.

The easiest way to detect and view this is by using the diffpic image standalone to produce a pic image which shows differences in pixel values (type diffpic -h in a command prompt or shell for usage help). In the diffpic result, you will not see any difference in the pixel values in the area where the particle emission is visible.

Here’s how you can work around this problem:

1. Scale the entire animation sequence to twice its length (set the Scaling to 2) using the Animation > Sequence Animation > All Scene command in the Animation panel.

2. Render the scene in Softimage .pic format. Remember to change the Start and End frames in the Render Options > Output tab to reflect the new sequence.

3. Interleave the result using the interleave standalone (type interleave -h in a command prompt or shell for usage help) to produce an image sequence that will appear as if the scene was rendered in fields.


Particle Properties


Add ParticleOp Property Editor

To display: Choose Create > Particles > Sketch Particle Setup from the Simulate toolbar, or sketch some particles with Create > Particles > Sketch Particles, select the particles, and press Enter.

General Velocity

Multiplicity Multiplies the number of added particles. A value of 1 means that one particle is added for every sampling point on the curve you sketch.

Radius Sets how the particles are uniformly distributed within spheres centered at each sampling point on the curve. This parameter controls the radius of those spheres: the larger the radius, the more the particles are spread out.

On the Advanced page, you can also set this parameter’s Seed value for random effects (see Particle Variance and Seed Parameters on page 224).


Advanced The parameters on the Advanced page offers Seed values for the Radius, Seed, and Spread parameters on the General page. This allows you to add variation to the value you enter for each of these parameters. See Particle Variance and Seed Parameters on page 224 for more information.

Speed The speed of the particles as determined by the direction and speed at which you drag the Sketch Particles drawing tool. To see the effect of the speed after you’ve sketched the particles, select the sketched particles and choose Create > Particles > From Initial State.

This parameter also has a Var parameter so that you can produce a more random effect on the particles.

On the Advanced page, you can also set this parameter’s Seed value.

See Particle Variance and Seed Parameters on page 224 for more information on these parameters.

Spread Controls the direction of the velocity. If the Spread is zero, particles flow exactly along the velocity vector defined by the stroke you make with the Sketch Particles drawing tool.

With a value higher than zero, the particles’ velocity vector is defined within the angle of a cone (in degrees) whose axis is in line with the stroke at that point. This is similar to the Spread parameter in the Particle Emission Property Editor on page 187. The Spread value is between 0 and 180 degrees.

On the Advanced page, you can also set this parameter’s Seed value for random effects (see Particle Variance and Seed Parameters on page 224).


ExplosionOp Property Editor

| Simulation on page 176 | Output on page 177 | Collisions on page 178 | Emission on page 178 | Sparks on page 183 | Smoke on page 183 | Flame on page 180

Simulation Execution State

Range

You cannot have multiple emitters on an explosion cloud. As well, the Explosion operator works only with the default sphere or cylinder emitter objects.

Mode Not interactive is the default. This doesn’t calculate the particle animation until you move to a different frame (either by clicking the Play button below the timeline or moving the playback cursor). This lets you choose when you want to play back the simulation, especially if your system is a bit slow and you don’t want to wait for each update to be calculated.

Interactive recomputes the animation from start frame as soon as you modify a particle parameter. This is useful for immediately seeing the effects of your changes.

Disconnected doesn’t calculate the particle animation at all. This is useful for setting parameters and moving back and forth on the timeline without having to wait for the particle simulation to update.

Start Frame Initial frame of the simulation

Duration Number of frames of the simulation

Copy from Scene Copies the start and end frame values from the scene’s timeline to the Start Frame and Duration.

Copy to Scene Copies the values you set for the Start Frame and Duration to the scene’s start and end frame values on the timeline.


Multiplicative Factors

Phase Activation

You can have any or all of these structures active as phases of the explosion.

Output

Time Scale Scales the dynamic with respect to time. If, for example, you divide this value in half, the whole dynamic evolves at twice the speed.

Space Scale Scales the dynamic with respect to spatial dimensions. Modifying this parameter changes the space extension of the explosion without changing its shape.

Particles % Percentage of the particles that are emitted. Setting this to a lower value is useful for a quick preview of the particles’ behavior.

Seed Seed for the pseudo-random-number generator.

Sparks Activates the sparks phase of the explosion. You can set the spark structure’s parameters on the Sparks page (see Sparks on page 183), as well as select and edit the particle type to use.

Smoke Activates the smoke phase of the explosion. You can set the smoke structure’s parameters on the Smoke page (see Smoke on page 183), as well as select and edit the particle type to use.

Flame Activates the flame phase of the explosion. You can set the flame structure’s parameters on the Flame page (see Flame on page 180), as well as select and edit the particle type to use.

Output Sequence Directory and path name for the output particles files (a .ptp is generated for each frame). By default, the name is Explosion plus an instance-counter number. If Usr is on, the path is displayed as you entered it. If Res is on, the resolved path is displayed.


Collisions Collision Accuracy

Emission Sets the emission parameters for all structures and their corresponding particles.

For all parameters that have a Var parameter associated with them, see Particle Variance and Seed Parameters on page 224 for more information.

Clean Cached Files

When you exit Softimage, this deletes the .ptp files that were recorded and cached for the particle simulation in the current session.

Use File for Rendering

Activates a flag that tells the Explosion shader to use the PTP files currently specified in the Output Sequence for rendering the simulation. This option is useful if you’re rendering over a number of machines and you want each machine to use the same PTP files as they render the same simulation.

Iterations When a particle collides with an obstacle, its velocity is modified, which could cause a new collision with a different obstacle. To accurately calculate this, any time a collision is detected Explosion checks if a new collision can occur with all the remaining obstacles, iterating this process until no more collisions can be detected. This parameter sets the maximum number of iterations that occur inside a single time step. The higher the number, the more accurate the collision detection (at the cost of more time).

Interframes Sets the number of interframes in which a single frame has to be subdivided for collision detection. The higher the number, the more accurate the collision detection (at the cost of more time).

Check Particles Detects collisions between particles and obstacles and calculates how the particles will respond. If this option is off, only collisions with structures are detected.


Sparks\Smoke\Flame Structures

ParType Name of particle type to use for the emission (smoke, sparks, or flame, by default). Click the New button to create a new particle type, or click the Edit button to open the particle type’s PType (Particle Type) Property Editor on page 210.

Emission Defines the type of emissions used for each structure (flame, smoke, or sparks): structures, particles, structures+flame particles, structures+smoke particles, or structures+sparks particles.

Speed Defines the reference emission speed in SOFTIMAGE units per second of the structures along the emission direction. The actual emission speed is controlled by this value and the Emission shape.

This parameter also has a Var parameter (see Particle Variance and Seed Parameters on page 224) so that you can produce a more random effect on the particles.

Struct. Rate Defines the rate of structure particles emitted per second.


Struct. Life Duration of life (in seconds) of the structure. When the structure dies, all its particles disappear simultaneously.



Flame Sets the parameters for the flame structure of the explosion.

Global Parameters

Structure Parameters

Particle Rate Controls the number of particles emitted per second.


Buoyancy The movement (acceleration) of particles in the direction opposite of gravity. This value is the buoyancy coefficient at any frame for the structures. When 0, there is no buoyancy; when 1, the acceleration is equal (or opposite) to gravity, etc. You must have gravity set for the explosion system for Buoyancy to have an effect.


Evolution Time The number of seconds needed to go from the Start to the End value.

Vorticity Angular speed in degrees per second of the structure around its normal axis. In regard to the direction of the normal axis, if no point of the icon is tagged, the axis is generated randomly. If some points are tagged, they define some “special” directions; when the structure is created, the normal axis is generated so as to be perpendicular to both the radial axis and the closer “special” direction. The overall effect is that each special direction is surrounded by the structures rotating symmetrically with respect to it and with velocities tangential to itself.


Gravity Coeff. The coefficient value used to scale the intensity of gravity.


Rotation

Each of these parameters has a Var parameter associated with them: see Particle Variance and Seed Parameters on page 224 for more information

Controls

Air Friction Amount of air friction between the air and the structures. A value of 0 is no air friction, and 1 is full friction (structures have the same speed as the Wind force). The air resistance is proportional to Air Friction and the difference between the structure’s speed and the wind.

Fading Age % The starting time of fading in terms of the percentage of the structure’s life. When the structure percentage age reaches this value, the alpha channel of the structure and its related particles start reducing, taking it to 0 at the structure’s death time. Use this parameter to avoid the effect of particles suddenly vanishing from the scene.

Plane Coeff. When 0, the structure’s circular-velocity terms lie in the normal radial plane. When 1, the motion plane is the normal-binormal one. Any values between 0 and 1 result in intermediate motion planes.

Radius The ending value of the radius in SOFTIMAGE units defining the structure’s circular-velocity term. The starting radius is always 0 and the time needed to go from the start to end value is defined by the Evolution Time.

Start and End Speed

The start and end value of the angular speed in degrees per second defining the structure’s circular-velocity term. The time needed to go from the start to end value is defined by the Evolution Time.

Speed Absolute frame, structure age, or constant initial speed.

Life Structure death time or structure life duration: Duration of life (in seconds) of the particles.


Structure Spread

Light Parameters

These parameters are associated only with the Flame structure.

When you select the Flame phase, an explosion light is generated (under the Explosion Emitter node). You can constrain the light to the position of the explosion icon. The light emission is proportional to the particle density.

Since the light emulates flame illumination, it should stay in the same zone of flame particles; by default it is set at the emitter centre, but you can move it.

Rate Controls the number of particles emitted per second.

Buoyancy Absolute frame or structure age: The movement (acceleration) of particles in the direction opposite to gravity. This value is the buoyancy coefficient at any frame for the structures. When 0, there is no buoyancy; when 1, the acceleration is equal (or opposite) to gravity, etc. You must have gravity set for the particle system for Buoyancy to have an effect.

Angle Sets the angle jitter in degrees for the structure’s starting directions.

Smoothness Sets the smoothness of the structure’s starting directions. This parameter has different effects, depending on the implicit object you chose for the explosion (Sphere or Cylinder).

At 1, all the starting directions are generated randomly from the sphere; for the cylinder, it’s inside the cylinder basis.

At 0, the structures are generated only along the sphere icon’s main directions or the cylinder basis points.

At any value between 0 and 1, it represents the ratio of structures with a random starting direction (for the sphere) or random emission points (for the cylinder) with respect to the total number of structures generated at any frame.

The light for the Flame only takes into the consideration the color set for the particle type.


Smoke Sets the parameters for the smoke structure of the explosion. The parameters here are the same as for the Flame on page 180, except that there are no Light parameters.

Sparks Sets the parameters for the sparks structure of the explosion. The parameters here are the same as for the Flame on page 180, except that there are no Light parameters.

Emission Factor Value multiplier in the HSV color space for the light.

Emission Min. and Max.

Sets the minimum and maximum values for the light emission.


Fluid Property Editor

| Simulation on page 184 | Output on page 185 | Collisions on page 185


Range

Simulation Factors

You cannot have multiple emitters on a fluid cloud. As well, the Fluid operator works only with the default cube, disc, or square emitter objects.

Mute Toggles the fluid simulation on/off.

Start Frame First frame at which the fluid simulation is calculated.

Duration Number of frames over which the fluid simulation occurs.

Copy from Scene Copies the start and end frame values from the scene’s timeline to the Start Frame and Duration.

Copy to Scene Copies the values you set for the Start Frame and Duration to the scene’s start and end frame values on the timeline.

Accuracy Sets the accuracy of the fluid simulation. Increasing this value controls the simulation more but takes more time.

Slave Ratio The percentage of slave particles in relation to master particles that are set with Mean distance. A value of 1 means that there are as many slave particles as there are master particles. The slave particles are randomly distributed on the surface/volume of the emission.

Mean Distance Density of the particles determined by the distance between them in a set space. This determines the number of master particles. The lower this value (the smaller the space between particles), the greater the density of particles.


Output


Foam % Determines which percentage of the particle density will be used as foam. Particles whose density is lower than the value here and with a value higher than the Foam speed min. are rendered as foam.

Foam Speed Min. Determines which particles may be rendered as foam. Particles whose speed is higher than this value could be rendered as foam. The Foam % is also taken into account: particles with a density lower than that value will probably be rendered as foam; if a particle is not very “quiet,” it will probably be rendered as foam.

Output Sequence Name of file in which you want to save current particle simulation. The file extension is .ptp. By default, these files are saved in the c:\temp folder with the prefix “Fluid.” If Usr is on, the path is displayed as you entered it. If Res is on, the resolved path is displayed.

Clean Cached Files

All the PTP files that were recorded and cached for playback are erased each time you exit Softimage. PTP files record the position of your particles at each frame in the animated scene.

Restart from File Restarts the simulation from a previously selected PTP file. Select the file you want before selecting this option.

Iterations The number of times a particle’s position is calculated per interval. The higher the value, the more accurate the position but the longer the time it takes to calculate.

Interframes The number of times a particle’s position is calculated per frame. The higher the value, the more accurate the position but the longer the time it takes to calculate.


Initial State Property Editor

To display: Select a particle cloud with an initial state and choose Modify > Particles > Edit Initial State Prop from the Simulate toolbar.

Mute Temporarily deactivates the initial state.

Transfer Velocity Transfers the velocity of particles from the selected particle cloud to the initial state cloud. Deselecting this option creates static particles.

Live Forever Makes particles live a very looooong time. They just won’t die.


Particle Emission Property Editor

| Overview on page 187 | Emission on page 187 | Distribution on page 191

Applies general particle emission characteristics to objects, such as particle speed, density, and spread angle. It also gives you access to a property set that lets you define the particle stream (called a particle type) that is emitted, in terms of its rendering characteristics, environmental forces that act on the particles, and particle decay.

To display: Select a particle cloud and choose Modify > Particles > Set Emission from the Simulate toolbar, then pick an emitter object. You can also select a particle emitter object and choose Modify > Particles > Edit Emission.

The Fluid Emission page that appears in the Fluid Property Editor on page 184 when you create a fluid particle cloud contains the same parameters as for this Particle Emission property editor.

Any parameter with a connection icon can have its values modified by a connected weight map (and texture map for color parameters).


Overview This page contains the most frequently used emission parameters, allowing you to quickly set up or view the emission. Each of these parameters are the same ones that are on the Emission page.

You can change the parameter values either on the Overview page or on the Emission page; either way, the parameter of the same name on the other page is immediately updated.

Emission

If you create a particle event with emitted particles, the event’s Emission property page that appears is similar to this one, but with some different parameters. See Event Emissions on page 197 for more information.

Name The name of the emission property. By default, this is the name of the object used as the emitter with an Emission suffix appended.

Mute Temporarily deactivates the particle emission (emission properties).


Particle

ParType Displays the name of the particle stream currently applied to the particle emitter. Click New to define a new type, or click Edit to modify the one listed. Either way, the PType (Particle Type) Property Editor on page 210 appears for that particle.

Generation Specifies where the particles originate from, according to the geometry of the emitter object.

Point: Particles originate from the points of the emitter object.

Line: Particles originate from the edges (for polygons) or U/V isolines and boundaries (for NURBS) of the emitter object.

Surface: Particles originate from the entire surface of the emitter object.

Volume: Particles originate from within the volumetric boundaries of the emitter object.

Fluid: Particles are emitted from the implicit fluid emitter object.

Direction Specifies the direction in which the particle stream is emitted. Emission direction can be relative to the emitter object’s local or global reference or relative to the direction of the emitter object’s normals.


Velocity

These parameters also have Var parameters so that you can produce a more random effect on the particles.

On the Distribution page, you can also set the parameter’s Distribution method (Uniform or Gaussian), as well as set a Seed value.


Rate Controls the number of particles emitted per second.


On the Distribution page, you can also set this parameter’s Distribution method (Uniform or Gaussian), as well as set a Seed value.


Spread Controls the diameter of the aperture through which particles are emitted from the emitter object. Range is 0 to 180 degrees.


On the Distribution page, you can also set this parameter’s Distribution method (Uniform or Gaussian), as well as set a value.



Orientation

Sets the rotation angle (in degrees, counterclockwise) at which the particles are initially emitted. The rotation is updated at every frame using the Rotation Velocity defined on the General on page 210 page in the PType property editor.

These parameters also have Var parameters so that you can produce a more random effect on the particles. On the Distribution page, you can also set the parameter’s Distribution method (Uniform or Gaussian), as well as set a Seed value. See Particle Variance and Seed Parameters on page 224 for more information on these parameters.

Speed Controls the initial speed of emitted particle in SOFTIMAGE units per second.

Inherit Controls the velocity of the particle emissions from an animated 3D object or moving vertices that you are using as a source.

You apply a percentage value that is relative to the velocity of the source; that is, the emitted particles inherit the specified velocity from the moving source.

If you specify a value greater than 100, for example, the particles are emitted at a greater velocity than the source itself, causing them to speed ahead of the emitter. Values of less than 100 cause the particles to trail behind the emitter.

Billboard Sets the rotation of the particles as they’re emitted. The particles are displayed as billboards (2D). The range is -360 to 360 degrees.

Roll Sets the particle’s rotation around its Z axis as it’s emitted. The range is -360 to 360 degrees.

Pitch Sets the particle’s rotation around its X axis as it’s emitted. The range is -360 to 360 degrees.

Yaw Sets the particle’s rotation around its Y axis as it’s emitted. The range is -360 to 360 degrees.


Color

Distribution This page contains the Distribution and Seed parameters for all emission parameters that have accompanying Var parameters. The Var parameter values add variance to their accompanying parameter’s value.

For more information, see Particle Variance and Seed Parameters on page 224.

Distribution

Uniform or Gaussian are methods of how the variance value is distributed.

Seed

Introduces even more variation to the Var parameter values, in case you didn’t already have enough. The Seed allows you to have very fine control over parameters, changing them slightly without having to change the parameter’s value or Var(iance) value.

The Seed parameters work only if you have a value other than zero for its accompanying Var parameter.

Sub-Frame Emission

Adds particles between frames (oversampling) when, for example, you are emitting particles from a fast-moving emitter. When you oversample the particle emission, you can specify how many times per frame you want to emit particles.

Map Color Lets you use the color values from a weight map or texture map (see in the guide) that is connected to this option (click its connection icon and select a map). When you select Map Color and connect a map, the colors on the map are used to set the initial color of each emitted particle. In this case, the particle’s color set on the Color page (see Color on page 220) is not used.

Uniform Numbers are distributed uniformly around the parameter’s value using the Variance value. The parameter will always be in the range [value - variance; value + variance], never outside of it.

Gaussian Numbers are distributed as a Gaussian bell curve around the parameter’s value using the Variance value. Most numbers will be in the range [value - variance; value + variance], but they may be outside of that range with [value - variance], and they will be outside of that range with [value + variance].


Randomize Position

Does a random spreading of the particles between two successive positions of emission. For a given particle, the emission position is computed in 3D space at the current frame (or subframe) and the frame (or subframe) before. The particle is randomly positioned on the line joining these two points.

This lets you do oversampling without much cost to the calculation time, but you have little control as to how the oversampling is done.

Steps Number of emissions to occur per frame (1 is the default). For each subframe, a certain number of particles are emitted at the locations specified by the position of the emitter at this subframe. This lets you spread the particles in a controlled manner and still have some puffs, if you like.

Stratified Emission

Emits particles in distinct strata (layers). If you emit particles with identical speed from a grid, you’ll see distinct planes of particles; if you emit from a sphere, you’ll see concentric spheres of particles, etc.

Because this option takes into consideration the geometry of the emitter, you need to use Surface as the Generation type (on the Emission page in this property editor).


Particle Event Property Editor

| Event on page 193 | Script on page 194 | Advanced on page 196 | Event Emissions on page 197

Lets you set up a particle event by choosing a trigger with a resulting action.

Event

Trigger

Name Name of the event property. By default, this is called Particle_Event but you can/really should rename it.

Mute Temporarily deactivates the event.

Trigger The condition at which the event happen (triggers the Action that you set): Particle Age %, Particle Age, Every N Particle, Every N Frame, XYZ Position, XYZ Speed, Speed, Collision, Interparticle Collision, and Interparticle Avoidance.

When you set an object as an obstacle for particles, an event is automatically created with Collision set as the trigger.

For information on the Var parameter, see Particle Variance and Seed Parameters on page 224 for more information.

Value Value at which the event happens. An event will only do something if the value of the parameter used as a trigger reaches the this Value. For example, if you set this to 50% with Age as the trigger, the specified action happens every time a particle reaches 50% of its age (Max Lifetime value).


Action

Source

Obstacle

Script Runs a script you have created for the event so you can modify the behavior or appearance of particles.

Action The action that happens when the trigger Value is reached. You can make particles Emit (another particle), Disappear, Emit & Disappear, Bounce, Bounce & Emit, Stick, or run a Script.

- If you select Emit, Bounce & Emit, or Emit & Disappear, you must create or select the particle type to be emitted. You do this by defining the Source, below.

- If you select Bounce or Stick, you must define an Obstacle, below.

- If you select Script, you must select a predefined script or write one on the Script page.

Emission Name of the particle type to be emitted.

Create Creates a new particle type to be emitted. You must define its emission properties on the Event Emission page (see Event Emissions on page 197) that appears.

Del Removes the currently emitted particle type from the event.

Edit Opens the PType (Particle Type) Property Editor on page 210 so that you can edit its properties.

Obstacle Name of the obstacle used for the collision.

Pick Initiates a picking session in which you can pick the obstacle object to use in the collision.

Del Removes the current obstacle from the event.

Edit Opens the Obstacle property editor in which you can edit its properties.


Use Script File Activates a predefined script that you must select.

Language Select either VBScript or Jscript as the language for the script.

File File name of the script you want to use. Click the browser button (...) to search for the script.

Proc(edure) Subroutine name that calls the script file. The subroutine must have these three parameters in this order:

• Parameter 1- the particle cloud primitive that triggered the event.

• Parameter 2- An array containing the indices of the particles that triggered the event.

• Parameter 3- The current simulation frame.


Advanced This page contains the Distribution and Seed parameters for all event parameters that have accompanying Var parameters. The Var parameter values add variance to their accompanying parameter’s value.

For more information, see Particle Variance and Seed Parameters on page 224.

Script Context Activates the script in these contexts: Per Trigger Particle (every particle at which the event is triggered), Per Particle (every particle), Per Cloud (for the whole simulation).

Text Box If you don’t use a predefined script, you can write a script directly in this box. The Script Context defines how the script is called:

• Per trigger particle: the script is called once for each particle that triggers the event. In this context, you can use these variables:

- inParticle: One particle that triggered the event.

- inTriggerParticleCnt: The index of the particle within the array of particles that triggered the event.

• Per particle: The script is called once for every particle in the cloud, whether it triggered the event or not. In this context, you can use these variables:

- inParticle: One particle in the cloud

- inParticleCnt: The index of the particle within the cloud

• Per cloud: This script is called once for the cloud. No extra variables are accessible here.

In all three contexts, the following variables are available:

• inParticleCloud : the cloud primitive

• inTriggerParticleIndices: the array of indices of the particles that triggered the event (whatever the context)

• inSimFrame: The current simulation frame when the event occured

• inParticleCollection: The particle collection object


Distribution

Uniform or Gaussian are methods of how the variance value is distributed.

Seed

Introduces even more variation to the Var parameter values, in case you didn’t already have enough. The Seed allows you to have very fine control over parameters, changing them slightly without having to change the parameter’s value or Var(iance) value.

The Seed parameters work only if you have a value other than zero for its accompanying Var parameter.

Event Emissions When you click the Source > Create button on the Event page in this property editor, you must define the new particle type’s emission properties. The options on this page are similar to a regular particle emission (see Emission on page 187), but listed here are some special parameters that are available only for event emissions.

Particle

Uniform Numbers are distributed uniformly around the parameter’s value using the Variance value. The parameter will always be in the range [value - variance; value + variance], never outside of it.

Gaussian Numbers are distributed as a Gaussian bell curve around the parameter’s value using the Variance value. Most numbers will be in the range [value - variance; value + variance], but they may be outside of that range with [value - variance], and they will be outside of that range with [value + variance].

Rate The number of particles emitted at event time. Note that this is different from Rate for regular emissions, which is the number of particles emitted per second.

Azimuth Determines the azimuth vector along which the emitted particle type is generated. Range is 0 to 180 degrees.

Declination Determines the degree of declination of the vector along which the emitted particle is propelled. Range is 0 to 180 degrees.


Birth Offset

Radius Offsets the emitted particle type in a radius around the original particle type. Values are in Softimage units.


Particle Goal Property Editor

| Goal on page 199 | Advanced on page 203

Defines the parameters for the particle goal. A goal is an object to which particles are usually attracted. They can also be repelled from a goal object.

Goal

Behavior

Name Name of the goal object.

Mute Toggles the activeness of the effect of the goal on the particles.

Goal Behavior Determines how the particles react to the goal. Select an option from the list:

• Chase: the particles follow the goal object as if it was a magnet.

• Flee: the particles are repelled from the goal and move in the opposite direction of it.

• Arrive: the particles move gradually toward the goal.

You then set the landing distance in Softimage units and deceleration of the particles. This allows you to prevent the particles from overshooting the goal.

• Spring: the particles are linked to the goal by springs and dampers.

If you set the Spring Constant to positive values, the particles are attracted to the goal; negative values repel the particles. The farther the value is from 0 (either positive or negative), the more “elastic” the particles become.

Viscosity is the amount of resistance applied to the particles as they move through space, as if they were moving through fluid. This is similar to the effect of a drag force. The higher the value, the more the particles are slown down.

• Stick: the particles immediately stick on the goal object as they are born; that is, they do not move from the emitter toward the goal and then stick on it.


Target

Spatial Influence

Determines the goal’s range of influence in which the particles are affected.

Target The component on the goal object’s geometry to which the particles are attracted. Select an option from the list:

• Point: each particle is attracted to a randomly selected point (control vertex) on the goal’s geometry.

• Line: each particle is attracted to a randomly selected position on an edge, isoline, or curve of the goal geometry. If the goal object is a curve, make sure to select this option.

• Surface: each particle is attracted to a randomly selected position (a random U and V value) on a polygon mesh or NURBS surface.

• Volume: each particle is attracted to a randomly selected position inside the target geometry.

• Center: each particle is attracted to the center of the goal object.

If the Target option (geometry component) you select here isn’t supported by the goal object, the object’s Center is used.


Influence Select Global or Local:

• Global: the particles are influenced by the goal wherever they are in space.

• Local: the particles are influenced by the goal only when they come within the distance as set by the Local Radius value.

Local Radius If you selected Local as the Influence, this is the number of Softimage units within which you want the particles to be influenced by the goal.


On the Advanced page, you can also set this parameter’s Distribution method (Uniform or Gaussian), as well as set a Seed value.



Effect

Weight Determines the amount of influence the goal has on the particles that are attracted to it.

Set a value between 0 and 1. A value of 0 means that the goal has no effect on the particles, and a value of 1 means that the goal has full effect (100%) on the particles.

If there is more than one goal, the Weight values are multiplied together.





Advanced These parameters allow you to set more advanced variation for the Local Radius, Weight, and Offset X/Y/Z parameters on the Goal page. You can select the Distribution method for each one (Uniform or Gaussian), as well as set a Seed value.

Offset Reference Determines the reference point from which the target is offset from the goal object using the Offset X/Y/Z options:

• World referential: the target is offset relative to the global center: the reference stays constant regardless of changes to the goal object’s position, orientation, or scale.

• Goal object referential: the target is offset relative to the goal object’s local position, orientation, scale, and shape.

• Goal point referential: the target is offset relative to the local reference frame of the points on the goal object; that is, the offset follows the state of the goal object’s normals and tangents.

Offset X/Y/Z Offsets the target from its position on the goal object in relation to the Offset Reference you have selected. The offset directs the particles to the goal’s target plus the offset.

• With the World referential, the Offset X/Y/Z values are expressed along the X/Y/Z axes of the world (global).

• With the Goal object referential, the Offset X/Y/Z values are expressed along the X/Y/Z axes of the object (local).

• With the Goal point referential, the Offset Y value is the direction along the normals, while the Offset X and Z values are directions along the tangents.





ParticlesOp Property Editor

| Simulation on page 205 | Output on page 207 | Collisions on page 208

Defines the general parameters of the particle simulation. The parameters defined in this editor are associated with the particle simulation’s particle cloud.


Mode Sets the visibility of the particle simulation as follows:

• Live allows you to play a simulation continuously for quick editing and tweaking. You can then view the effect of any modifications in real time. As soon as you skip forward, the simulation is computed from the current frame, for all of the intermediate frames.

If you want to see the effects of motion blur on the particles or do final rendering, switch to Standard Caching or Standard No Caching.

• Standard No Caching is the default. It doesn’t cache any PTP files, and calculates the particle animation only when you click the Simulate button or go to a different frame (either by clicking the Play button below the timeline or moving the playback cursor).

• Standard Caching is the same as Standard No Caching except that it caches one PTP file per frame. These PTP files are saved in the folder you specify on the Output page. Caching PTP files allows you to scrub the simulation and get the correct state, play the simulation backwards, and play PTP files in the Particle Player for previewing.

Mute Cloud Mutes the simulation and temporarily freezes the particle cloud in its current shape (no particle simulation is calculated). This is useful for setting parameters and moving back and forth on the timeline without having to wait for the particle simulation to update

Simulate Recalculates the simulation from the first frame up to the current frame.


Time Management

Source Time Sets the time reference for the simulation:

- Global (default) determines the simulation’s time relative to the scene. All the animated values of the source are read in the scene’s global time. This let you build a simulation between frames n and m by animating the source parameters between frames n and m.

- Local determines the simulation’s time relative to the source. All the animated values of the source are read in local time. Local time extends from frame 1 up to frame 1 + Duration in global time. This lets you build up simulation libraries and offset them as you like without losing any of the source’s animation.

Source - Start and End

The Start and End frames of the simulation source are calculated depending on the Duration. These frames are where the source animation is read from in the scene’s global time. These values are for display only and cannot be changed.

- When the Source Time is local, Start = 1 and End = 1 + Duration value.

- When the Source Time is global, Start = Global Result Start (which is the Offset value) and End = Start + Duration.

Duration The duration, in frames, of the particle simulation.

Time Reference - Offset

The number of frames by which you want to offset the start of the simulation.

With Local time, an Offset affects the place where the simulation is being played, but does not affect the source itself. This means that whatever the offset, the animation on the source is always read between frame 1 and 1+ Duration in the scene’s global time.

Global Result - Start and End

Display at which frames in the scene the simulation will be played. These values are for display only and cannot be changed.


Particle Multiplicator

Simulation

Output

Copy from Scene Copies the scene’s first and last frame defined for the timeline to the simulation. This changes the Offset and Duration so that the simulation is played throughout the scene’s timespan.

Copy to Scene Copies the Global Result > Start and End frames to the scene timeline’s first and last frame.

Particles % Specifies how much of the total particle simulation will be generated.

Seed Adds an overall variation to all Var parameter values in the simulation. This means that any of the Emission or PType parameters whose Var parameters have values other than zero are modified by this Seed value.

See Particle Variance and Seed Parameters on page 224 for more information.

Fuzzy Force Distribution

Applies the forces for a specific amount of time on a per-particle basis at each update cycle. This helps eliminate the problem of stratified particles when large forces are applied to the cloud.

Output Sequence The file name and location of the particle animation PTP files that allow you to play back a simulation. PTP files are saved when you play the simulation in Standard Caching mode. The default folder for this sequence is c:\temp. By default, the name is Particles plus an instance-counter number. If Usr is on, the path is displayed as you entered it. If Res is on, the resolved path is displayed.

Clean Cached Files

When on, all the PTP files that were recorded and cached for playback are erased each time you exit, PTP files record the position of your particles at each frame in the animated scene.



Iterations The number of times a particle’s position is calculated per interval.

Interframes The number of times a particle’s position is calculated per frame.


Particle Player Property Editor

Plays back PTP files that you have cached for a particle, fluid, or explosion simulation.

Simulation

Input

Output

Start Frame Frame at which the PTP sequence starts.

Duration Number of frames over which the PTP sequence is played.

Input Sequence Specify the first PTP file in the simulation sequence that you want to play back. The subsequent PTP files in that sequence are then played.

Write Output Sequence

Saves the current PTP sequence as another sequence.

Output Sequence Name and location of the output sequence you want to save.


PType (Particle Type) Property Editor

| Overview on page 210 | General on page 210 | Events on page 212 | User Parameters on page 213 | Goals on page 213 | Envir. on page 214 | Noise on page 215 | Interpart. on page 216 | Fluid on page 217 | Explosion on page 218 | Color on page 220 | Sprite on page 222 | Instancing on page 223

Defines the characteristics of particles after they are emitted from its source object. The values you set here can be saved as a single entity called a particle type, which can be given its own name and retrieved and applied to any emitter object.


Overview This page contains the most frequently used emission parameters, allowing you to quickly set up or view the emission. The Color parameters are the same ones that are on the Color page, and the remaining parameters are the same as on the General page.

You can change the parameter values either on the Overview page or on the Color/General pages; either way, the parameter of the same name on the other page is immediately updated.

General

Life

Particle Type ID Displays the ID of the current particle type. This is only for information purposes and cannot be modified.

Name Specifies the name assigned to the particle type defined in this editor.

Max. Life Controls the amount of time, in seconds, a particle exists once it is emitted.

Live Forever Makes particles live for a very long time (many many seconds). The particles do not die off during the simulation.


Characteristics at Birth

Mass Specifies the mass of particles. The mass of a particle is an indication of how swiftly it reacts to forces applied to it.

Gravity is a force directly proportional to the particle mass. The more massive the particle, the stronger the gravity force applied to it. As a result, several particles of different masses will all have the same identical motion if the only force acting upon them is gravity.

Possible value types are Birth, Age, and Abs(olute) - see below.

This parameter has associated Var parameters that let you add variation (see Particle Variance and Seed Parameters on page 224).

Size Controls the size of the emitted particle in Softimage units. Particle size is only computed when the scene is rendered. The size of the rendered particles is affected by the perspective transformation; i.e., the farther away a particle appears in the viewport, the smaller it appears when rendered.

Possible value types are Birth, Age, and Abs(olute), where:

Birth: The size of the particle remains constant throughout its lifetime (no parameter animation).

Age: The size of the particle may change over its lifetime, depending on how the parameter’s function curve is modified.

Abs: The size of all particles are identical throughout the simulation.

Age%: The size of particles change over the particle’s life percentage, depending on how the parameter’s function curve is modified. In this case, parameter animation between the start and end frames is mapped to the whole particle life.

This parameter has associated Var parameters that let you add variation (see Particle Variance and Seed Parameters on page 224).


Rotation Velocity

Determines the speed of the particles’ rotation over the duration of the simulation. The values set here take into consideration the Orientation values at emission time set in the Particle Emission property editor (see Particle Emission Property Editor on page 187).

You can set these value types for each parameter:

• Birth: The size of the particle remains constant throughout its lifetime (no parameter animation).

• Age: The size of the particle may change over its lifetime, depending on how the parameter’s function curve is modified.

• Abs: The size of all particles are identical throughout the simulation.

As well, each parameter has associated Var parameters that let you add variation (see Particle Variance and Seed Parameters on page 224).

Allowed Velocity Range

Events Events are available only for the Particle operator (not Fluid or Explosion).

Billboard The angle in degrees (counterclockwise) that the billboard particle rotates per second.

Roll The angle in degrees (counterclockwise) that the particle rotates per second around its Z axis.

Pitch The angle in degrees (counterclockwise) that the particle rotates per second around its X axis.

Yaw The angle in degrees (counterclockwise) that the particle rotates per second around its Y axis.

Align On Velocity Aligns the particle rotation along the particle’s velocity vector instead of from cloud’s reference frame. This is useful for controlling local rotations on particles.

Min Controls the minimum speed particles are emitted from their source. Possible value types are Birth, Age, and Abs(olute) - see above.

Max Controls the maximum speed particles are emitted from their source. Possible value types are Birth, Age, and Abs(olute) - see above.


User Parameters Lets you create your own custom parameters per particle type on a cloud, providing more flexibility when building custom particle behaviors. You can then use the Object Model and C API.

See the SDK Object Model documentation for ParticleAttribute, ParticleType, and ParticleTypecollection for more information.

Parameter Creation

Goals Lets you set a goal for this particle type. If the particle cloud already has a goal set for it, you can change the goal for this particle type.

New Event Creates a new event to be defined for the particle type. This opens the Particle Event property editor in which you specify an event trigger and action.

Event Table Displays the name of the event and the trigger value, which can be animated. When you set an obstacle, a collision event is created by default.

Name Name of the custom parameter.

Type Select a type of parameter:

• Vector 4 (float)

• Vector 3 (float)

• Float

• Integer

• Unsigned Long

• Unsigned Short

• Bool

New Parameter Click this button to create the new parameter you have specified.

The new parameter is added to the bottom of this property page and becomes a property of the particle type.

In the explorer, you can find all custom parameters in the Parameters folder under the PType node. Make sure to use the All Nodes filter to see them.


Envir. These parameters control how natural forces and obstacles affect this particle type in the simulation.





All parameters have Var and Seed parameters associated with them: see Particle Variance and Seed Parameters on page 224 for more information.

Sensitivity to Forces

These parameters control the amount of influence each natural force has on the particles. For particles to be affected, the appropriate force must be applied to the emitter object. Using the values here, you can increase or decrease the effect that the forces have on each particle type while keeping the force’s values the same.

A force has no effect on the particles unless a value other than 0 has been set for its corresponding parameter here.

New Goal Click this button, then pick the object you want as a goal. Right-click to end picking. A new goal property is created for this particle type and you can edit it using the parameters in the Goal Table below.

Goal Table Displays the goal’s parameters:

• Name of the goal, which you can change by clicking its cell and entering a new name.

• Weight value, which you can edit by clicking its cell and entering a new value (0 to 1). You can then animate the values by clicking its animation icon to set keys at different frames.

• Mute the goal by clicking in the cell so there’s a check mark.

• Right-click on the PType.goal name cell and choose Select Item to select the goal object. You can also choose Inspect Item open the Particle Goal property editor.


Obstacles

Noise Adds mathematical randomness to the particles. Noise is available only for the Particle operator (not Fluid or Explosion).

Intensity

You can animate each of these parameters using these variables:

• Birth: Noise parameter acting on the particles remains constant throughout their lifetimes (no parameter animation).

• Age: Noise parameter acting on the particles may change over their lifetime, depending on how the parameter’s function curve is modified.

• Abs: Noise parameter is identical for all particles throughout the simulation.

Elasticity Controls the amount of influence gravity has on the particles as they bounce off obstacles. Possible value types are Birth, Age, and Abs(olute).

When connected to a Particles or Fluid cloud, the Age animation mode behaves like the Abs animation mode.

Friction Controls the amount of influence surface friction has on the particles as they strike obstacles. Possible value types are Birth, Age, and Abs(olute).

When connected to a Particles cloud, the Age animation mode behaves like the Abs animation mode.

Use size for collision

Considers the particle size when the particles collide with an obstacle. This works for standard particles as well as fluid and explosions.

Position Amount of noise to be added to the particle’s position (in SOFTIMAGE spatial units).

Velocity Amount of noise to be added to the particle’s velocity (in [SOFTIMAGE spatial units]/[SOFTIMAGE time units]).

Acceleration Amount of noise to be added to the particle’s acceleration (in [SOFTIMAGE spatial units]/[SOFTIMAGE time units]) ^2).


Pattern

Interpart. Interparticle Avoidance and Collision is available only for the Particle operator (not Fluid or Explosion).






Interparticle Avoidance

Type Select from Brownian (not correlated in space or time so it’s more random) or Perlin (spatially correlated as defined by turbulence parameters) noise. If you select Perlin, you can also set its Iteration, Scale, and Power.

Iteration Number of iterations of the turbulence algorithm (if 1 it coincides with a simple Perlin function).

Scale Spatial correlation scale of Perlin noise.

Power Amount of turbulence in Perlin noise.

Enable Toggles on/off the ability for current particle type to avoid collisions with other particle types.

Intensity Maximum avoidance force intensity. The total avoidance force between two particles depends on the product of each of their Intensity values.

Radius Distance from the particle at which avoidance Intensity force vanishes.

Enable avoidance with same Ptype

Toggles on/off the ability for the current particle type to avoid collisions with itself.


Interparticle Collision

Fluid Fluid properties are available only for the Fluid operator (not Particles or Explosion).






Enable Toggles on/off the ability for current particle type to collide with other particle types.

Probability Probability of collision (between 0 and 100). The total collision probability between two particles depends on the product of each of their Probability values.

Radius Minimum distance from particle at which collision takes place.

Elasticity The amount of elasticity in the collision. If 0, the collision is inelastic; if 1, the normal speed component is fully reversed. The actual elasticity coefficient between two particles is the product of each of their Collision Elasticity values.

Enable collision with same Ptype

Toggles on/off the ability for the current particle type to collide with itself.


Explosion Explosion properties are available only for the Explosion operator (not Fluid or Particles).

Particle Parameters

Viscosity Sets the level of resistance to flow in a fluid. Lower values, like 0.07, simulates the flow of a liquid such as water. A high value, such as 1 (maximum), produces behavior similar to that of syrup. Heavier fluids also depend on gravity to define their behavior. By decreasing the gravity, you slow down the fluid dynamic (the result is similar to increasing the Viscosity), and vice-versa.

Surface Tension Sets the degree of liquid tension on the particle’s surface. Particles that simulate liquid in the shape of a cube, for example, will tend to transform into a spherical shape as they fall to the ground. A high level of surface tension will cause the particles to hold their original shape longer.

Coriolis Sets the angular speed of a Coriolis force. A Coriolis force is the rotational motion of fluid, such as that of water emptying down a drain. The higher that value of this parameter, the stronger the Coriolis force.

Compressibility Sets the compressibility factor of fluid as it strikes and bounces off obstacles.

Inherit Coeff Defines the amount of structure speed inherited by the particle (0 means no speed inherited, 1 means the full speed inherited). Note that forces like gravity, buoyancy, wind, fans and air friction affect the structure’s velocity only; therefore, their action is lost when this parameter is set to 0.

Fading Age % Sets the starting time (in terms of percentage particle life) of the automatic fading. When the particle percentage age reach this value, Softimage starts reducing the particle alpha channel, taking it to 0 at particle death time. It can be useful for preventing particles from vanishing suddenly from the scene.

Emission From By default, a particle’s starting position is the structure’s current position. You can force the particles to emit from the cloud icon’s center by selecting Icon in this list.


Particle Controls

Life Particle Death time on Abs frame: Particle death time is set, depending on the absolute generation frame.

Particle Life Length on Abs frame: Particle life length is set, depending on the absolute generation frame.

Particle Death time on Structure age: Particle death time is set, depending on the structure age.

Particle Life Length on Structure age: Particle life length is set, depending on the structure age.

RGB Overrides the same value set on the Color page (see Color on page 220).

Absolute frame: RGB values are identical for all particles throughout the simulation.

Structure Percentage Age: RGB values change over the structure’s life percentage, depending on how the parameter’s function curve is modified. In this case, parameter animation between 0 and 100 is mapped to the whole structure life

Particle Percentage Age: RGB values change over the particle’s life percentage, depending on how the parameter’s function curve is modified. In this case, parameter animation between 0 and 100 is mapped to the whole particle life.

Alpha Overrides the same value set on the Color page (see Color on page 220).

Same as RGB except for the alpha component.

Size Overrides the same value set on the General page (see General on page 210).

Absolute frame: Particle size depends on current frame only.

Structure age: Particle size depends on related structure age.

Particle age: Particle size depends on its age.

Constant: Particle size is set at its birth and remains constant throughout its lifetime (no parameter animation).


Radius

Rotation Speed

Color

Start and End The start and end value of the particle’s radius in SOFTIMAGE units defining the structure’s circular-velocity term. The starting radius is always 0 and the time needed to go from the start to end value is defined by the Evolution Time.

This parameter has an associated Var parameter parameter that let you add variation (see Particle Variance and Seed Parameters on page 224).

Start and End The start and end value of the particle’s angular speed in degrees per second defining the structure’s circular-velocity term. The time needed to go from the start to end value is defined by the Evolution Time.

This parameter has an associated Var parameter parameter that let you add variation (see Particle Variance and Seed Parameters on page 224).

Color Adds a color to the particle using RGBA or HLSA color values. This color is also displayed for the particle wireframe color in the viewport. You can override these values with the Particle Color and Particle Gradient shaders.


Animation Reference

Variance

For information on Uniform and Gaussian distribution, see Particle Variance and Seed Parameters on page 224.

RGB Birth: A particle’s RGB values remain constant throughout its lifetime (no color animation).

Age: RGB values change over the particle’s lifetime, depending on how the parameter’s function curve is modified.

Abs: RGB values are identical for all particles throughout the simulation.

Age%: RGB values change over the particle’s life percentage, depending on how the parameter’s function curve is modified. In this case parameter animation between the start and end frames is mapped to the whole particle life.

When you’re animating the Color, key its values first, then set the animation reference mode to Age%.

Alpha Birth: A particle’s Alpha values remain constant throughout its lifetime (no color animation).

Age: Alpha values may change over the particle’s lifetime, depending on how the parameter’s function curve is modified.

Abs: Alpha values are identical for all particles throughout the simulation.

Age%: Alpha values may change over the particle’s life percentage, depending on how the parameter’s function curve is modified. In this case parameter animation between the start and end frames is mapped to the whole particle life.

When you’re animating the Color, key its values first, then set the animation reference mode to Age%.


Sprite Attaches sprite image sequences to the particles. Sprites are available only for the Particle operator (not Fluid or Explosion).

H Controls the amount of variance to the hue in a particle’s color. The distribution can be Uniform or Gaussian.

L Controls the amount of variance to the luminance in a particle’s color. The distribution can be Uniform or Gaussian.

S Controls the amount of variance to the saturation in a particle’s color. The distribution can be Uniform or Gaussian.

Alpha Controls the amount of variance to the alpha value in a particle’s color. The distribution can be Uniform or Gaussian.

Sprite Image Lets you choose the texture or image file sequence that will serve as the particle shape.

When an image is loaded, you can edit it in the Image Clip property editor, whose pages appear below in the PType property editor.

Window and Playback Controls

Displays a list of texture or image files. When highlighted, this will be the texture or image on the particle shape. Use the playback controls to play, pause, loop, and stop an image sequence.

Clear Clears the currently selected sprite image from the window.

Edit Modifies parameters of the selected sprite in the list.

New Opens a browser in which you can select a new sprite image file to create a new sprite.

Animation Control

Animates the sprite per particle based on one of the following conditions:

Birth: the current sprite is assigned to particle at its birth, and will remain the same for all particle life.

Age: sprite is animated following particle age (in frame).


Instancing The options allow you to create instances of objects attached to each particle at render time.

Abs: sprite is animated following the absolute frame (i.e. the time bar); it is the default value, and it corresponds to the old implementation.

Age% sprite is animated following particle percentage age.

Random: a random sprite of the sequence is assigned to particle at its birth, and will remain the same for all particle life.

Var: adds variation to the sprite over the duration of the simulation.

Render Time: controls the sprite sequence’s animation when it’s rendered with the Particle Sprite shader. With this option, Softimage stops trying to optimize what frames are sent to mental ray (such as any unused frames) and makes them all available at render time.

Enable Activates particle instancing.

Instance Group Group of objects from which to create the instances. These objects must be part of a group (select the objects and press Ctrl+g).

Click the Pick button and pick the instance group from the explorer.

Click the Remove button to remove the group from the text box.

Rotation If the particle has rotation applied, you can have the instances inherit it (select From Particle), or you can have no rotation (None).


Particle Variance and Seed Parameters

Many parameters in the Particle Emission Property Editor on page 187, PType (Particle Type) Property Editor on page 210, Particle Goal Property Editor on page 199, and ExplosionOp Property Editor on page 176 property editors (as well as a few others) have Var (Variance) parameters, which allow you to add variance to their associated parameter’s value.

In addition, some of these parameters also have a Seed parameter, which allows you to change the effect on the variance without changing either the parameter’s value or its Var value.

Var Parameters

The Var parameters define the range in which the random numbers are generated. Variance can be animated, allowing you to have different animations for the parameter’s variance and its value.

Variance is animated using two different Distribution methods: Uniform and Gaussian.

• With Uniform distribution, random numbers are distributed uniformly around the parameter’s value using the Variance value. The parameter will always be in the range [Value - Variance; Value + Variance], never outside of it.

Scaling The instanced objects can inherit the scaling from the particle:

By particle size scales the object uniformly by taking the size of the particle and scaling by that.

Non-uniform to particle scales the object to fit the particle’s bounding box using non-uniform scaling. This makes the object completely fill in the bounding box.

Uniform to particle scales the object to fit the particle’s bounding box using uniform scaling. This makes the object fit in the bounding box but without changing its shape.

None: the instanced object stays its current size, and is not influenced by the particle size.

OGL Display Select from either Nulls or Bounding Boxes as a display type for the instanced objects in the viewport.


This generates a random number between -1 and 1 depending on the seed, and then scale it and offset it so it ends up being distributed according to the variance we chose and around the average we set.

• With Gaussian distribution, random numbers are distributed as a bell curve around the parameter’s value using the Variance value. Most numbers will be in the range [Value - Variance; Value + Variance], but they may be outside of that range with [Value - Variance], and they will be outside of that range with [Value + Variance].


Seed Parameters

The seed defines which numbers will be generated in the range that the Var parameter specifies. The Seed parameters are available for some of the parameters that have a Var parameter. These parameters usually appear as text boxes without a label to the right of a Var parameter. They allow you to have very fine control over parameters, changing them slightly without having to change the parameter’s value or Var value.

All Seed parameters work only if you have a value other than zero for the Variance parameter to which it is associated.

To have an overall control over the whole simulation, you can set the Simulation Seed value in the ParticlesOp Property Editor on page 205. This adds an overall variance factor to all the parameters of the simulation that have a Var parameter, except for the size and color of the particles. Using this you can, for example, create identical particle clouds and test different results achieved by changing only the simulator seed value.


Particle Shaders

• Particle Billboard on page 228

• Particle Blob on page 232

• Particle Color on page 236

• Particle Explosion on page 237

• Particle Gradient on page 240

• Particle Renderer on page 243

• Particle Scalar on page 244

• Particle Shape on page 245

• Particle Sphere on page 248

• Particle Sprite on page 252

• Particle Vector on page 253


Particle Billboard

| Rendering Properties | Shading Properties | Global Illumination | Make Connections | Making Transparent Particles

Shader Type: Particle (texture)

Output: Color (RGB) value

Renders particles as a 2D surface (a billboard) upon which you can create many different effects.

Rendering Properties Geometry

Name The shader’s name. Enter any name you like, or leave the default.

Shape The outline shape of the billboards:

• Square is a square shape that is circumscribed by the particle’s radius.

• Rectangular is the same as Square except that its aspect ratio is the same as the sprite that’s applied to the particle.

• Circular is a circle shape with the same radius as the particle.

Surface Normal Type

The calculated normal for lighting calculations: Billboard or Spherical.

Face Direction Direction that the billboard faces:

• Camera: the billboard faces the camera.

• Incoming ray: billboard faces the camera unless there are reflections. If so, the billboard tries to orient itself so that it faces the reflected/refracted ray as well.

• Camera and Lights: the billboard faces the camera unless shadows are being cast. If so, the billboard faces each shadow casting light. This ensures that the billboard’s Shape doesn’t appear flat, giving the illusion that it is three-dimensional.

• Use Rotation: billboard uses the particle’s Orientation values set in the Particle Emission property editor.


Effects

Shading Properties

Ambient

Rotation Follow Velocity

Particle billboard rotates in the direction of the velocity. This is disabled if the billboard Face Direction is set to Use Rotation.

Texture Coordinates

Controls which texture coordinates are generated for the particle.

• Planar is a straight planar UV mapping with origin in the lower-left corner.

• Particle’s Local Space is the hit point in the particle’s own local space.

• Cloud’s Local Space is a hit point in the local space of the particle cloud.

• World Space is the hit point in the world coordinate space.

Burn Adds the particle’s RGB values together when particles overlap in space (sometimes called color burn or additivity). This lets you create bright spots of colors and glows where many particles are on top of each other.

Self-Shadowing Factor

Shadows cast by the particles onto themselves are attenuated by this factor.

Apply Shading Applies a simple shading model to the particles. If not selected, only shadows are calculated, and the particles are still visible even if no lights are applied to the cloud.

Type The way in which the ambient color is calculated: % of Base Color (particle type color), Use Ambient Color (the values of the Color sliders below), or None.


Specular

Global Illumination Irradiance

Irradiance determines how much color the particle type receives from other surfaces during final gathering.

Color When you select Use Ambient Color as the Type, this is the surface’s underlying ambient color, which gets modified by the scene’s ambience. To get luminescent particles, use a high value for this parameter.

% of Base When you select % of Base Color as the Type, this is the percentage of the particle type’s color (the base color) to use as the ambient color. To “blast” the base color, enter values higher than 100%.

Type The way in which the specular color is calculated: % of Base Color (particle type color), Use Specular Color (the values of the Color sliders below), or None.

Color When you select Use Specular Color as the Type, this is the color of the surface specular highlight.

% of Base When you select % of Base Color as the Type, this is the percentage of particle type (base) color to use as the specular color.

Shininess Shininess of the specular highlight. Lower values result in a larger highlight.

Type The way in which the irradiance modifier color is calculated: % of Base Color (particle type color), Use Irradiance Color (the values of the Color sliders below), or None.

Color When you select Use Irradiance Color as the Type, this is the color received by the particles.

% of Base When you select % of Base Color as the Type, this is the percentage of the color received from the particle type.


Radiance

Radiance determines how much color the particle type transmits onto other surfaces.

Make Connections Connects different shaders to this one.

Connect To

Making Transparent Particles

There are three basic ways in which you can create transparent particles with the Billboard shader:

• On the Particle Type > Color page, set the Alpha value for the level of transparency you want. Then on the Shading Properties on page 229 page in the Billboard shader, set the Ambient - Type to Use % of Base Color and set the % of Base to 100% or more to see the effect better.

• Plug the Particle Color on page 236 shader into the Color input of the Billboard shader to override the particle type color. In the Particle Color shader property editor, select Override Particles - Alpha and set the New Color - Alpha value to the level of transparency you want.

• Plug the Particle Gradient on page 240 shader into the Color input of the Billboard shader to override the particle type color. In the Particle Gradient shader property editor, select Alpha and set the alpha value and the gradient control to the level of transparency you want.

As well, you can plug the Raytracing > Transparency or Opaque shaders into the Color input of the Billboard shader and set their values to an appropriate level of transparency.

Type The way in which the radiance modifier color is calculated: % of Base Color (particle type color), Use Radiance Color (the values of the Color sliders below), or None.

Color When you select Use Radiance Color as the Type, this is the color transmitted by the particles.

% of Base When you select % of Base Color as the Type, the color that is transmitted is this percentage of the particle type’s color.

Sprite Connects the sprite shader to this one.

Shape Connects the shape shader to this one.

Color Gradient on age

Connects the particle color gradient shader to this one. The gradient shader works on the particle’s age % by default.


Particle Blob

| Render Properties on page 232 | Shading Properties on page 233 | Global Illumination on page 234 | Make Connections on page 235 | Making Transparent Particles on page 235



Renders particles as 3D blobs that can blend into each other. By default, this shader is attached to the Fluid operator.

Render Properties Geometry

Surface Evaluation:

Texture Projection


Blending Amount The frequency at which individual particles merge with others. A value of 0 prevents a particle from merging with its neighbor, while 1 is full blending.

Blending The attributes of the particles, color, and bumps are blended using the selected algorithm: Blend using weighted influence, Sample from greatest influence, Averaging.

While you cannot blend blobs between multiple particle clouds, you can blend between multiple blob particle types on the same particle cloud.

Type Texture projection type generated for the spheres: Spherical, Cylindrical, Lollipop, Particle Local, Cloud Local, or World Coordinates.

Blend Texture Coordinates

Instead of using separate texture coordinates for each texture lookup, this option adds the texture coordinates together using the blobs’ influences.

Use Particle Rotation

Applies a particle’s rotation on the texture projection.


Effects

Static Blur

Shading Properties

Ambient




Static Blur Adds extra transparency as the normal gets more perpendicular to the viewing direction. This makes the spheres transparent on the edges and fully opaque through the center.

Width Inflates the diameter of each particle by this number of units.

Falloff rate Controls the transparency falloff rate. Rate of falloff increases with larger values.






Specular



Radiance












Connect To


There are three basic ways in which you can create transparent particles with the Blob shader:

• On the Particle Type > Color page, set the Alpha value for the level of transparency you want. Then on the Shading Properties on page 233 page in the Blob shader, set the Ambient - Type to Use % of Base Color and set the % of Base to 100% or more to see the effect better.

• Plug the Particle Color on page 236 shader into the Color input of the Blob shader to override the particle type color. In the Particle Color shader property editor, select Override Particles - Alpha and set the New Color - Alpha value to the level of transparency you want.

• Plug the Particle Gradient on page 240 shader into the Color input of the Blob shader to override the particle type color. In the Particle Gradient shader property editor, select Alpha and set the alpha value and the gradient control to the level of transparency you want.

As well, you can plug the Raytracing > Transparency or Opaque shaders into the Color input of the Blob shader and set their values to an appropriate level of transparency.








Particle Color



Renders the color of the particle.

Overrides


Override Particle RGB/Alpha

Select these options to use the New Color RGB and/or alpha values instead of those given with the particle. If you deselect these options, the particle type’s color and/or alpha values are used.

New Color If you select Override Particle RGB and/or Alpha, you can set the new color and/or alpha values for the particle using these sliders. If those options are deselected, this color is ignored.


Particle Explosion

| General Property Page on page 237 | Sparks Property Page on page 237 | Smoke and Flame Property Pages on page 239

Shader Type: Particle (material)


When applied to a particle cloud, this shader renders particles according to their explosion structures and particle types (smoke, flame, and sparks).

General Property Page

Integration

Sparks Property Page


Get File Name from User Data

Name of the PTP file to be used.

Ray steps Number of steps in the ray marching phase. High values produce better results but take longer to calculate. Try a value of 20 for previews, and 40 for final renders. If artifacts appear in the image in the parts rendered by Explosion, they may be caused by an insufficient number of steps. If so, raise this value to 40 or 50, or more.

ID For PTP files generated by particles, you must associate the appropriate ID of each phase. The phase ID numbers are given in the Sparks property editor (Particle ID). If you don’t want this phase to be rendered, enter -1 in this box.

Radius Jitter The radius of the particles is taken from the PTP file. If this parameter is 0, the particles are rendered as spheres. Higher values introduce a noise in the size, varying with the radial directions, so each particle assumes a non-spherical form. The deviation from the sphere shape increases with higher values.


Light Emission

Light Diffusion

Get RGB from Particle Type

Uses the RGB values defined for the current particle type.

Get Alpha from Particle Type

Uses the alpha value defined for the current particle type.

Emission color Color of the emission for this phase. The check boxes below the color sliders let you replace this color (RGB values and/or Alpha value) with the corresponding values read from the PTP file.

In the file, there is only one color for each particle, so if you use both the Diffuse and Emission color and read them from the file, the same color is used. When tuning the Flame phase, you should focus on the Emission component; for Smoke, use only the Diffuse component.

Emission intensity

The coefficient that is a multiplier for the emission color. This changes the overall intensity of the emitted light without opening the Explosion property editor and recalculating the PTP files, if you only want to modify the emission intensity (in case you are reading this color from the files).

Emission turbulence

Amount of noise in the emission color.

Diffusion intensity

The coefficient that is a multiplier for the diffuse color (as read from the file). This allows you to change the overall intensity of the diffused light without interference from the ambient light. Also, you don’t need to open the Explosion property editor and recalculate the PTP files if you only want to modify the diffuse intensity (in case you are reading this color from the files).

Ambient The coefficient that indicates which fraction of the diffuse color (as read from the file) is to be used for ambient illumination. 0 = no ambient light; 1 = an ambient color is equal to the diffuse color.

Diffusion turbulence

Amount of noise in the diffuse color.


Turbulence

Smoke and Flame Property Pages

The parameters are the same as on the Sparks Property Page on page 237 except for:

Turbulence pattern

Displays a menu for different patterns of noise: Classic, Wired, Galaxy, Rocher, Virus, or Amoeba.

Iterations Number of iterations in the computation of the turbulence.

Scale Scaling factor of the pattern used to obtain the noise effect. It is the granularity of the turbulence pattern; the higher the value, the smaller the size of visible details.

Power Multiplication factor of the noise between two consecutive iterations.

Time shift If this value is 0, the turbulence pattern is static; if you want the pattern to vary with time, use a value greater than 0. Higher values mean a faster change in the pattern.

Scale Turbulence with Structures

Scales the noise pattern according to the size of the Explosion structures (Sparks, Smoke, or Flame structures).

Density Each particle gives a contribution to the density of the media (flame, smoke). The contribution is proportional to the density; the light absorbed, diffused, or emitted by each elemental volume is proportional to its density.


Particle Gradient



Renders the particle’s color using a color ramp (gradient). The gradient is determined by the particle’s age % by default.

This is similar to the Gradient Mixer shader except that it is designed for particles.

Evaluation Range

Gradient


Minimum/Maximum

Minimum/maximum points on the gradient to evaluate for color.

Show Alpha Displays the alpha channel in the gradient control if you have RGB selected. Deselect this option if you want to display only RGB values.

RGB Displays only the RGB values in the gradient control if Show Alpha is off.

Alpha Displays only the Alpha values in the gradient control.


Presets

Gradient Control The gradient slider is where you create and adjust the gradient. The bar displays the gradient left-to-right from beginning (0.00) to end (1.00).

Square markers on the bottom of the gradient bar are color markers. You can use up to 8 color markers, each with its own color. Clicking on the gradient bar inserts a color marker at the click-point. By default, the new marker assumes the color of that point in the gradient. To delete a color marker, right-click it and choose Delete marker from the menu.

A round marker on the top of the gradient bar appears between each pair of color markers, indicating the mid-point in the blend between those two colors. Moving the round marker closer to either color marker causes less of that color, and more of the other, to appear in that “sub-gradient”. The net effect is a sharper blend and a larger portion of the dominant color.

Color Controls the R, G, B, and alpha values for the selected color marker.

Pos Controls the position of markers on the gradient:

Color Markers: If a color marker is selected, the Pos value indicates its position, on a scale of 0.00-1.00, within the entire gradient.

Interpolation Markers: If an interpolation marker is selected, the Pos value indicates its position, on a scale of 0.00-1.00, between its associated pair of color markers.

Cubic/Linear Switches between linear and cubic interpolation of the gradient. Cubic interpolation results in a smoother transition between alpha values, while linear interpolation results in sharper transitions.

Black/White Loads a preset using black and white values in the gradient control.


Animation

Flame Loads a preset using a color spectrum going from blue to yellow, orange, and then black in the gradient control.

Smoke Loads a preset using only white and the alpha channel in the gradient control.

Key All RGB/Alpha Markers

Keys all current RGB or Alpha marker values on the gradient control at this frame.

Remove All RGB/Alpha Keys

Removes all keys on RGB or Alpha markers.

Reset Gradient Removes all keys on to the RGB and Alpha markers, puts the markers back in their original positions, and disconnects all shaders that are attached to gradient shader parameters.


Particle Renderer

Shader Type: Particle (volume)


Renders the output for all shaders attached to the particle cloud. This includes all particles types that are attached to the cloud.

BSP Tree Settings


Maximum Tree Depth

Maximum number of branches down the tree until it stops splitting into further branches. Range is 1 to 50.

Maximum Leaf Size

Maximum number of particles each leaf on the tree can hold before converting that leaf into a branch to allow for further splitting. Range is 1 to 30.

Maximum Number of Trees

When using motion blur, instead of generating one tree for the whole traversal of particles through time, the open/close shutter time interval is split into a maximum of this number and that many trees generated for each time slice. This speeds up rendering, and may even increase memory for fast moving particles. Your mileage may vary. Range is 1 to 20.


Particle Scalar


Output: Scalar value

Output the particles as a scalar value.


Output Type Type of particle data to output as a scalar.

Normalize Returns a normalized value for a data type.


Particle Shape

| Falloff on page 245 | Shape on page 246



Renders the shape of the particles, including the way the falloff (transparency) is calculated around the shape.

Falloff

Pattern Center

Modulation

Range

User-defined Falloff


Type Radial falloff type: Linear, Square, Smooth, Cubic, Gaussian, User-defined, or None. If you select User-defined, you can set its Exponent value below; if you select Gaussian, you can set its falloff Rate below.

X, Y Center point for falloff pattern in X and/or Y.

RGB, Alpha Multiplies the RGB and/or Alpha component of the base color by the falloff value at the intersection point.

RGB/Alpha Inverted

Inverts the shape value when multiplying the RGB/Alpha components.

Start, End The distance from the given center at which the falloff value goes to 1 (Start) and 0 (End). The falloff value is interpolated between the Start and End values using the Falloff Type selected.

Exponent If you select User-defined as the Type, you can control the transparency falloff rate with this value. Values less than 1 give a steep falloff from the center. Higher values give a more gradual falloff.


Gaussian Falloff

Shape

Pattern Center

Modulation

Step

Sine

Rate If you select Gaussian as the Type, you can control the rate of falloff for this interpolation. Higher values give a more rapid falloff.

Type Lets you choose a geometric shape pattern for emitted particles.

None uses no predefined shape for emitted particles.

Step is the ratio of the size of the particle set in a single step.

Sine creates a particle with an editable number of rings that are equally spaced from one another.

Star creates a particle with a star-like configuration.

Beam gives the particle a long beam shape with a bright center surrounded by a glow effect.

Symmetry creates symmetrical particles.

Noise creates an infinite variety of patterned effects.

Turbulence creates chaotic movement.

Fractal creates a fractal pattern.

X, Y Center point for the shape pattern in X and/or Y.

RGB, Alpha Multiplies the RGB and/or Alpha component of the base color by the shape value at the intersection point.

Width Width of step, which is a ratio of the particle size. Range is 0 to 1.

Scale Scale of sine. Range is 0 to 30.


Star

Beam

Symmetry

Noise

Turbulence

Fractal

Branches Number of branches in star. Range is 0 to 20.

Width Width of beam. Range is 0 to 1.

Width Width of symmetry. Range is 0 to 2.

Time Evaluation time of noise pattern over time. Range is 0 to 10.

Scale Scale of the noise pattern. Range is 0 to 5.

Time Evaluation time for turbulence pattern over time. Range is 0 to 10.

Scale Scale of turbulence pattern. Range is 0 to 5.

Low Frequency Low frequency of turbulence pattern. Range is 0 to 10.

High Frequency High frequency of turbulence pattern. Range is 0 to 10.

Time Evaluation time for fractal pattern over time. Range is 0 to 10.

Scale Scale of fractal pattern. Range is 0 to 5.

Weight Iteration weight for fractal pattern. Range is 0 to 1.

Granularity Granularity of fractal pattern. Range is 0 to 5.

Octaves Number of octaves (iterations) of noise in fractal pattern. Range is 0 to 8.


Particle Sphere

Render Properties on page 248 | Shading Properties on page 249 | Global Illumination on page 250 | Make Connections on page 250 | Making Transparent Particles on page 251



Renders particles with a basic 3D sphere shape.

Render Properties Geometry

Texture Projection

Effects


Face Renders the faces of the sphere: front, back, or both faces.

Type Texture projection type generated for the spheres: Spherical, Cylindrical, Lollipop, Particle Local, Cloud Local, or World Coordinates.

Use Particle Rotation

Applies a particle’s rotation on the texture projection.





Static Blur

Shading Properties

Ambient

Specular

Static Blur Adds extra transparency as the normal gets more perpendicular to the viewing direction. This makes the spheres transparent on the edges and fully opaque through the center.

Width Inflates the diameter of each particle by this number of units.

Falloff rate Controls the transparency falloff rate. Rate of falloff increases with larger values.










Radiance



Connect To












There are three basic ways in which you can create transparent particles with the Sphere shader:

• On the Particle Type > Color page, set the Alpha value for the level of transparency you want. Then on the Shading Properties on page 249 page in the Sphere shader, set the Ambient - Type to Use % of Base Color and set the % of Base to 100% or more to see the effect better.

• Plug the Particle Color on page 236 shader into the Color input of the Sphere shader to override the particle type color. In the Particle Color shader property editor, select Override Particles - Alpha and set the New Color - Alpha value to the level of transparency you want.

• Plug the Particle Gradient on page 240 shader into the Color input of the Sphere shader to override the particle type color. In the Particle Gradient shader property editor, select Alpha and set the alpha value and the gradient control to the level of transparency you want.

As well, you can plug the Raytracing > Transparency or Opaque shaders into the Color input of the Blob shader and set their values to an appropriate level of transparency.





Particle Sprite



Renders sprite image sequences that are used for the particle shape. Sprite image sequences are loaded on the Sprite page in the particle type’s PType property editor.

You should use the Sprite shader only if you are using a sprite image sequence for the particles. If you are using a single image, you can select a Texture > Image shader in the render tree and select the sprite image there. Then connect the Image shader directly to the Billboard shader’s Color node.

Output Color


Start Sequence (%)

Where in the sprite sequence you want to evaluate the frame.

Looping With looping off, values less than or equal to zero mark the first frame, and values equal to or greater than 1 mark the last frame.

With looping on, a whole number (integer value) always marks the first frame and the last frame is the number just before the next whole number.

Image Sampling Type of sampling method to read pixel values from texture: Bi-linear or Nearest Neighbor.

Frame Interpolation

Interpolation between frames if the frame number is fractional.

From Sprite Uses the color from the sprite; otherwise, the color is taken from the input (if there is no connection to the input, then the particle’s color is used).

Alpha Modulation

Controls how the particle alpha is modulated. Multiplies the alpha channel by the sprite’s alpha channel or RGB Intensity, or None.

Inverted Inverts the alpha calculated from the sprite before multiplying with the incoming alpha.


Particle Vector


Output: Vector value

Outputs the particles as a vector value.

Vector Overrides

Vector value to use instead of the supplied one.


Output Type Type of particle data to output as a vector.

Override X, Y, Z Overrides the particle data vector’s X, Y, Z component.

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