cs 4363/6353 other things you should know. overview matrix stacks raytracing and npr physics engines...

CS 4363/6353

OTHER THINGS YOU SHOULD KNOW

OVERVIEW• Matrix Stacks

• Raytracing and NPR

• Physics Engines

• Common File Formats

MATRIX STACKS• Typically, matrices are stored in a stack to avoid this

• Stacks give us the ability to rotate one body around another

• Stacks are also how (character) animation is done

• Let’s say we wanted to fly through the solar system

• You still have a camera matrix

• The sun has been translated (but probably not rotated)

MATRIX STACK EXAMPLE

Camera matrix


Camera matrix

“Push” the camera matrix.Note: everything is rotated by our camera matrix…


Camera matrix

“Push” the translation of the sun

Sun trans matrix


Camera matrix

“Push” the translation of the sun

Sun trans matrixCombine everything on the stack into one MV matrix, then drawthe sun. Trans first, then camera!

mMV

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ns


Camera matrix

Sun trans matrix

The Earth is both translated

Note: yes, yes… I know it’s not to scale…


Camera matrix

Sun trans matrix

The Earth is both translated

Earth trans matrix


Camera matrix

Sun trans matrix

The Earth is both translatedand rotated (in that order), sowe push those on a separateframe… Earth trans matrix

Earth rot matrix


Camera matrix

Sun trans matrix

WRONG! The matrices aremultiplied TOP DOWN!

Earth trans matrixEarth rot matrix


Camera matrix

Sun trans matrix

WRONG! The matrices aremultiplied TOP DOWN!

Earth rot matrixEarth trans matrix


Camera matrix

Sun trans matrix

Combine everything on thestack into one MV matrix,then draw the Earth!

mMVEarth rot matrix

Earth trans matrix

Ord

er


Camera matrix

Sun trans matrix

What about the moon?



Camera matrix

Sun trans matrix

Well, the moon has a translation… Moon trans matrix



Camera matrix

Sun trans matrix

Well, the moon has a translation… as well asa rotation…

Moon trans matrixMoon rot matrix



Camera matrix

Sun trans matrix

Well, the moon has a translation… as well asa rotation…

Moon rot matrixMoon trans matrix



Camera matrix

Sun trans matrix

So we combine everythingon the stack into one MVmatrix, then draw the moon

mMV Earth rot matrixEarth trans matrix


Ord

er


Camera matrix

Sun trans matrix

What if we want to draw a little independent spaceship?




Camera matrix

Sun trans matrix

POP the Moon stuff!



Camera matrix

Sun trans matrix

POP the Earth stuff!



Camera matrix

Sun trans matrix

POP the Sun stuff!


Camera matrix

…Leaving us with just thecamera matrix. Then, wecan add the spaceshipmatrices on top of that.


Camera matrix

Push the spaceship trans first!

Ship trans matrix


Camera matrix

Then the rotation! Why?

Ship trans matrixShip rot matrix


Camera matrix

Now that you have your MV,draw the ship…

Ship trans matrixShip rot matrix

mMV

RAYTRACING• Easy to read article at http://en.wikipedia.org/wiki/Ray_tracing_(graphics)

Note: there are independent reflection, refraction and shadow rays

EXAMPLES(AGAIN, FROM WIKIPEDIA.ORG)

RAYTRACING• Advantages:

• Realistic simulation of lighting

• Natural shadows

• Simple to implement (but not trivial)

• Heavily parallelizable

• Disadvantages

• Still an approximation

• not truly photorealistic

• Must limit depth

• Recursively adds up light values of rays

• Ssssssssssssslllllllllllllllloooooooooooooooowwwwwwwwwwwwww

• “…holds that when human replicas look and act almost, but not perfectly, like actual human beings, it causes a response of revulsion among human observers”

THE UNCANNY VALLEY…

http://en.wikipedia.org/wiki/Uncanny_valleyFinal Fantasy: The Spirits Within

NPR(NON-PHOTOREALISTIC RENDERING)

• Stylistic

• Water color

• Impressionism

• Example: Toon Shading

• Geometry remains the same

• Shading changes

• Commonly seen in video games

• Borderlands

http://en.wikipedia.org/wiki/File:Toon_Shader.jpg

WORKING WITH PHYSICS ENGINES• There are several out there:

• Tokamak (open source, no longer maintained)

• Bullet (open source – several commercial games and movies like “2012” and “Bolt”)

• Havok (commercial – Ireland, loads of commercial games)

• PhysX (commercial – Ageia/NVDIA, CUDA, uses PPU, tons of games as well)

• Usually provide:

• Gravity

• Collision (between static and dynamic bodies)

• Soft-body physics

• Ragdoll physics

• Vehicle dynamics

• Fluid simulations

• Cloth simulations

HOW WE USE THEM…• Physics engine is a black box

• We “load” the physics engine

• Tell it which objects are dynamic

• Tell it which are static

• Define parameters, such as gravity, bounce and so on

• During each frame of animation:

• Update the physics engine by a delta time

• Ask the physics engine for:

• The location of each dynamic object

• The orientation of each dynamic object

TOKAMAK EXAMPLE• Typically have a limited number of basic shapes

• Cube

• Capsule

• Sphere

• Must declare variables to hold all of the objects in your scene

#include <tokamak.h>

neSimulator* gSim = NULL; neRigidBody* gCubes[NUM_CUBES]; neRigidBody* sphere; neAnimatedBody* floor1 = NULL; neT3 t;

void setupPhysicsEngine() {// This will define the size and shape of each cubeneGeometry* geom;// length, width and height of the cubeneV3 boxSize1; neV3 gravity;neV3 pos;float mass;float fmass = 0.2f;// The number of total objects the simulator has to keep track of...neSimulatorSizeInfo sizeInfo;

// Fill in the size info about the environmentsizeInfo.rigidBodiesCount = NUM_CUBES+1;sizeInfo.animatedBodiesCount = 1;// total number of objectssizeInfo.geometriesCount = sizeInfo.rigidBodiesCount + sizeInfo.animatedBodiesCount;// total number of collisions possible n*(n-1)/2sizeInfo.overlappedPairsCount = sizeInfo.geometriesCount*(sizeInfo.geometriesCount-1)/2;sizeInfo.rigidParticleCount = 0;sizeInfo.constraintsCount = 0;sizeInfo.terrainNodesStartCount = 0;

gravity.Set(0.0f, -3.0f, 0.0f);gSim = neSimulator::CreateSimulator(sizeInfo, NULL, &gravity);

// Setup a box - using loopfor (int i = 0; i < NUM_CUBES; i++) {gCubes[i] = gSim->CreateRigidBody();// Get the geometry object from the cubegeom = gCubes[i]->AddGeometry();boxSize1.Set(1.0f, 1.0f, 1.0f);geom->SetBoxSize(boxSize1[0], boxSize1[1], boxSize1[2]);gCubes[i]->UpdateBoundingInfo();mass = 1.0f;gCubes[i]->SetInertiaTensor(neBoxInertiaTensor(boxSize1[0], boxSize1[1], boxSize1[2], mass));gCubes[i]->SetMass(mass);pos.Set(i%10-5, i/10+0.5, -30);gCubes[i]->SetPos(pos);

}

// Create the spheresphere = gSim->CreateRigidBody();geom = sphere->AddGeometry();geom->SetSphereDiameter(2);sphere->UpdateBoundingInfo();sphere->SetInertiaTensor(neSphereInertiaTensor(2, fmass));sphere->SetMass(fmass);pos.Set(0, 1, -4);sphere->SetPos(pos);sphere->SetAngularDamping(0.01f);

// Create the floorfloor1 = gSim->CreateAnimatedBody();geom = floor1->AddGeometry();boxSize1.Set(100, 0.001, 100);geom->SetBoxSize(boxSize1[0], boxSize1[1], boxSize1[2]);floor1->UpdateBoundingInfo();pos.Set(0, 0, 0);floor1->SetPos(pos);

}

void display () { degree += 0.1f; glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); gSim->Advance(0.015);

//Cubes for (int i = 0; i < NUM_CUBES; i++) {

t = gCubes[i]->GetTransform();cube_state[0][0] = t.rot[0][0]; cube_state[1][0] = t.rot[1][0]; cube_state[2][0] = t.rot[2][0]; cube_state[3][0] = t.pos[0];cube_state[0][1] = t.rot[0][1]; cube_state[1][1] = t.rot[1][1]; cube_state[2][1] = t.rot[2][1]; cube_state[3][1] = t.pos[1];cube_state[0][2] = t.rot[0][2]; cube_state[1][2] = t.rot[1][2]; cube_state[2][2] = t.rot[2][2]; cube_state[3][2] = t.pos[2];cube_state[0][3] = 0.0f; cube_state[1][3] = 0.0f; cube_state[2][3] = 0.0f; cube_state[3][3] = 1.0f;

drawCube(…); }

// Sphere t = sphere->GetTransform(); sphere_state[0][0] = t.rot[0][0]; sphere_state[1][0] = t.rot[1][0]; sphere_state[2][0] = t.rot[2][0]; sphere_state[3][0] = t.pos[0]; sphere_state[0][1] = t.rot[0][1]; sphere_state[1][1] = t.rot[1][1]; sphere_state[2][1] = t.rot[2][1]; sphere_state[3][1] = t.pos[1]; sphere_state[0][2] = t.rot[0][2]; sphere_state[1][2] = t.rot[1][2]; sphere_state[2][2] = t.rot[2][2]; sphere_state[3][2] = t.pos[2]; sphere_state[0][3] = 0.0f; sphere_state[1][3] = 0.0f; sphere_state[2][3] = 0.0f; sphere_state[3][3] = 1.0f; drawSphere(…);

glutSwapBuffers(); glutPostRedisplay();}

COMMON FILE FORMATS• .3ds – AutoDesk 3DS Max (legacy)

• .blend - Blender

• .c4d – Cinema 4D

• .dae – COLLADA (xml)

• .fbx – AutoDesk

• .lwo – LightWave Object

• .ma/.mb – AutoDesk Maya

• .max – AutoDesk 3DS Max

• .md2/.md3 – Quake 2/Quake 3

• .pov – POV ray file

• .skp – Google Sketchup

• .sldasm – SolidWorlds Assembly

• .smd – Valve’s format

• .u3D – Universal 3D (3D Industry Consortium - xml)

THE .OBJ FILE FORMAT• Also called WaveFront OBJ

• Text-based

• Easy to work with and widely accepted

• File specifies:

• Position of each vertex

• UVs of each vertex

• Normals of each vertex

• List of faces (triangles)

EXAMPLE(HTTP://EN.WIKIPEDIA.ORG/WIKI/WAVEFRONT_.OBJ_FILE)

# List of Vertices, with (x,y,z[,w]) coordinates, w is optional. v 0.123 0.234 0.345 1.0 v ... ...

# Texture coordinates, in (u,v[,w]) coordinates, w is optional. vt 0.500 -1.352 [0.234] vt ... ...

# Normals in (x,y,z) form; normals might not be unit. vn 0.707 0.000 0.707 vn ... ...

# Face Definitions (see below) f 1 2 3 # Vertices only f 3/1 4/2 5/3 # Vertices/Texture coords f 6/4/1 3/5/3 7/6/5 # Vertices/Textures/Normals f ... ...

OTHER OPTIONS• Smooth shading

• s 1 – smoothing is true

• s off – no smoothing

• Materials may be put into a separate .mtl file

• newmtl myMat

• Ka 1.000 1.000 1.000 #ambient white

• Kd 1.000 1.000 1.000 #diffuse white

• Ks 0.000 0.000 0.000 #specular off

• Ns 50.000 # size of spec (s from our lighting equation)

• Tr 0.9 #transparency

cs 4363/6353 other things you should know. overview matrix stacks raytracing and npr physics engines...

Documents

spaceship trans

sunsun trans matrixcombine

earth stuff

moon stuff

mv matrix

thecamera matrix

translated note

matrices aremultiplied