preparing sushi - amd

Preparing Sushi - ATI Research, Inc. EGDC 2001 11

Alex VlachosAlex VlachosAVlachosAVlachos@@atiati.com.com

EGDC 2001EGDC 2001

Preparing Preparing SushiSushiHow Hardware Guys WriteHow Hardware Guys Write

a 3D Graphics Enginea 3D Graphics Engine


OutlineOutline• What is Sushi?

• Island Demo• Scene Graph• Vertex Storage• Rendering Pipeline• Shader Library• Shadow Volumes• Object Engine

• LifeFX Rachel Demo• Extras• Waterfall Demo

• Water Effects• Future Enhancements


What is Sushi?What is Sushi?• It’s not just a tasty treat…• Project name for ATI’s demo

engine used for the Radeon 8500 demo suite.

• The engine was designed with future rendering technologies in mind.

• Will be used for future ATI product demos.


RADEON 8500 Island DemoRADEON 8500 Island Demo


Sushi Engine GoalsSushi Engine Goals

• Shader Driven• Cross API (DirectX & OpenGL)• Cross Platform (Windows &

Mac)• Future-looking For Several

Product Cycles


Engine HierarchyEngine Hierarchy

Engine

WinD3D

Object

Shader Lib

D3D OGLWinOGL MacOGL

Asset Management


Scene GraphScene Graph• Octree – Serves our goals• Our previous engine (Radeon’s Ark)

used a portal-based visibility algorithm, but that’s over engineered for graphics demos.

• Octree provides enough culling opportunities for our purposes.


Octree DivisionsOctree DivisionsOctree Divisions


Vertex Buffer SizeVertex Buffer Size• Don’t use a single 150MB VB!!!• These days, we assume 64MB AGP

aperture for end-users…so 150MB isn’t going to fit anywhere but system memory!

• Sushi VB’s are kept to a reasonable size (2MB). Since our shaders are so varied, so are our stream mappings, making it difficult to break the 2MB barrier.


Optimize For State ChangeOptimize For State Change• Shared VB’s independent of which

octree leaves the polygon lives in.• Sort by shader change first, then

texture change• For most cases, this sorting works

fine, but there are extreme cases where you may want the opposite. Schedule time for experimentation.


Vertex StorageVertex Storage

VBIB

StreamMapping

MetaBins BinsOctreeLeaves

VBIB

StreamMapping

VBIB

StreamMapping

VBIB

StreamMapping

. . .

MetaBin IDShader ID

Texture IDsMetaBin IDShader ID





Texture IDs

MetaBin IDShader ID

Texture IDs

. . .

Bin IDIB StartIB EndBin ID

IB StartIB EndBin ID





IB StartIB End

Bin IDIB StartIB EndBin ID


IB StartIB End

. . .Within each leaf, render calls are sorted by shader state and then by texture handles


RunRun--Time LightsTime Lights• Run-time lights are additional passes

at run-time over geometry in the light’s frustum

• Cast correct shadows using shadow volumes (later slides)

• Pulse or blink independently and adds/subtracts the correct light contribution


Rendering PipelineRendering Pipeline• Clear Z Buffer & Stencil Buffer• Draw “ambient” geometry (+ZWrites,

+ZTest, -StencilWrites, -StencilTest)• For Each Run-Time Light

• Clear relevant area of stencil buffer, if needed!• Draw shadow volumes into stencil buffer

(-ZWrites, +ZTest, +StencilWrites, -StencilTest)• Draw geometry in light frustum and receive

shadows (-ZWrites, +ZTest, -StencilWrites, +StencilTest)

• Swap Buffers


NonNon--Opaque PolygonsOpaque Polygons• Becomes very difficult with run-time

lights• Tradeoffs lend to giving up some

correctness in rare cases.• Order of drawing lights is very

important! Simple far to near needs to be defined in more detail…


NonNon--Opaque Draw Opaque Draw Order Based on LightsOrder Based on Lights


Shader LibraryShader Library• Abstracts ALL fixed function and

programmable vertex and pixel processing to editable text files!

• Multi-pass shaders• Shader fallbacks for different levels

of hardware support• Provides a shader LOD mechanism


Fixed Function ShaderFixed Function ShaderDefineParam texture tex0 NULL

DefineParam vector4 red ( 0.7, 0.0, 0.0, 0.0 )

StartShader

StartPass

SetRenderState TEXTUREFACTOR red

SetTexture 0 tex0

SetColorOp 0 SELECTARG1 TFACTOR

SetAlphaOp 0 SELECTARG1 TFACTOR

EndPass

EndShader


Programmable ShaderProgrammable ShaderStartVertexShader

vs.1.1

m4x4 oPos, v0, c4

mov oT0, v7

//Vertex in normalized light space

sub r0, v0, c3 //V-L

mul oT1, r0, c1.y //V-L/falloff

//Normalized light vector

sub r0, c3, v0

dp3 r0.w, r0, r0

rsq r0.w, r0.w

mul r0, r0, r0.w

dp3 oD0, r0, v3 //Goraud N.L

EndVertexShader

SetPixelShaderConstant 0 appConst

StartPixelShader

ps.1.4

texcrd r1.rgb, t1 //Vertex in norm light space

dp3 r1, r1, r1 //distance squared from light

phase

texld r0, t0 //Base

texld r1, r1 //Light attenuation

mul r0, r0, r1_x2 //Base*light

mul r0, r0, v0 // " * N.L

mul r0, r0, c0.b // " * pulseScalar

EndPixelShader

EndPass

EndShader

StartShader

Requirement VERTEXSHADERVERSION 1.1

Requirement PIXELSHADERVERSION 1.4

LightType LIGHTTYPE_POINT

StartPass

SetRenderState ZWRITEENABLE FALSE

SetRenderState ALPHABLENDENABLE TRUE

SetRenderState SRCBLEND ONE

SetRenderState DESTBLEND ONE

SetTexture 0 tex0

SetTextureStageState 0 MIPFILTER FILTER_LINEAR

SetTexture 1 lightMap

SetTextureStageState 1 MIPFILTER FILTER_NONE

SetTextureWrap 1 CLAMP CLAMP CLAMP

//SetVertexShaderConstant 0 commonConst

SetVertexShaderConstant 1 appConst

//SetVertexShaderConstant 2 worldSpaceCamPos

SetVertexShaderConstant 3 worldSpaceLightPos

SetVertexShaderConstant 4 wvp


Shadow VolumesShadow Volumes• Dynamic vs. Static

• Static volumes are used when you have non-moving lights and non-moving geometry.

• Dynamic volumes are used if you have either a moving light or animated geometry.


Dynamic Shadow VolumesDynamic Shadow Volumes

Shadow VolumeVisualization


Dynamic Shadow Dynamic Shadow VolumesVolumes

• In Sushi, only animated objects & characters have dynamic volumes.

• Are computed entirely in a vertex shader, so the CPU never touches these vertices! Removes any AGP performance issues.


Shadow VolumeShadow Volume

Sphere Sphere’sShadowVolume


Shadow Volume Shadow Volume Extrusion SetupExtrusion Setup

A

B

A

B

Face NormalsFor Polygon A

Face NormalsFor Polygon B

Infinitely ThinFill Polygons

Original borderingpolygons .

We insert 2 degenerate polygons betweenthe original polygons which share theappropriate face normal encoded in thevertex.


Static Shadow VolumesStatic Shadow Volumes


Static Shadow VolumesStatic Shadow Volumes

• Shadows cast by non-moving light sources

• Scene geometry that doesn’t move• Terrain, rocks, buildings, etc.

• Great opportunity to optimize out the brute-force nature of dynamic shadow volumes!


Shadow Beam AlgorithmShadow Beam Algorithm

Beam Polygon 1Beam Polygon 2 Beam Polygon 3

Below is an example of applying this beam algorithm to thefirst 3 polygons of a given volume.


Shadow Beam AlgorithmShadow Beam Algorithm1. Begin with an empty final table.2. Roughly sort all polygons back to front based on some simple test

(QSort will suffice)3. For each polygon in the rough back to front order:

A. Create a beam from each polygon (4 clip planes), clipping away all polygons inside beam that have already been added to final table. A beam consists of 3 copy planes generated from the light source and each edge of the polygon, and the 4th clip plane is the polygon’s plane equation.

B. If polygons are left in front of beam polygon, recurse only 1 deep for each polygon left in front of the original beam polygon adding polygons to final table. Else, add beam polygon to the final table.

C. Optimize mesh in final table to remove redundant tessellation caused by beam planes.

4. Solve for T-Junctions (from the light’s point of view) in final table.

This algorithm does not lend itself to infinite recursion like the Weiler-Atherton algorithm!


Shadow Beam AlgorithmShadow Beam AlgorithmRecursion StepRecursion Step

Beam Polygon

Beam Frustum

Existing Polygon

RecursiveBeam Frustum

Remaining PolygonsOriginal Beam Recursive Beam


Shadow Beam AlgorithmShadow Beam AlgorithmThis solves for cyclically overlapping polygons!

(Now solve for T-Junctions!)


Object EngineObject Engine• Remember, we’re not designing a game

engine!• Play back animation that consist of:

• Skinning• Tweening (morphing, key-frame)• Skinning & Tweening simultaneously!

• Types of objects:• Globally animated (walking creature)• Locally animated (swaying plant)• Static non-animated (rocks)


RADEON 8500 Rachel DemoRADEON 8500 Rachel Demo


ExtrasExtras

• Anamorphic• Spherical screen projection• High resolution screen shots• Fly through paths


AnamorphicAnamorphic• Sushi has an anamorphic mode for plasma

and HDTV displays• 16:9 aspect ratio isn’t necessarily the pixel

aspect ratio for plasma screens!• As is done in celluloid, draw into a 3:4 render

target with the aspect of your projection matrix set to 16:9 (Kung Fu movies in the 80’s).

• The display stretches the image out to 16:9 with no black letterbox bars on the screen.

• Also be aware of odd aspect ratio display modes. Some notebooks and LCDs are shipping with 1280x768 display modes, for example.


AnamorphicAnamorphic

3:4 Render Target

16:9 Plasma Display


Spherical Projection Spherical Projection ScreensScreens

Viewer

150°°°°

Top View

http://www.elumens.com


Spherical Projection Spherical Projection ScreensScreens

• The visual simulation community has made immersive displays which are like small-scale Omnimax™ screens

• Relatively simple to add to an existing engine which already has renderable texture support

• Great demo opportunities!


High Resolution Screen ShotsHigh Resolution Screen Shots• Hit one button in-engine and dump a

screenshot at higher resolution than the GPU can actually render

• Very useful for printed media which use at least 300 dots per inch (dpi)

• Magazines and printed media usually looks lower resolution than a monitor

• Recently published in Game Programming Gems 2


High Resolution Screen ShotsHigh Resolution Screen Shots


Fly Through PathsFly Through Paths

• Smooth quaternion-based fly through paths provide a very nice demo mode for flying through our scenes.

• Recently published in Game Programming Gems 2


RADEON 8500 Waterfall DemoRADEON 8500 Waterfall Demo


RADEON 8500 Waterfall DemoRADEON 8500 Waterfall DemoReflections Refractions


Water EffectWater Effect• Uses 2 renderable textures: reflections & refractions• Geometry is drawn in screen space into the textures.• The water surface itself is rendered using 4 crossing

sin waves (for per-vertex waves) and 2 addative bump maps (for per-pixel perturbations). Both renderable textures are utilized by fetching with perturbed texture coordinates based on the bump maps.

• A Fresnel term is used to add realism.• Additional specular highlight are added for the sun.• The water is rendered in a single pass utilizing 1.1

vertex shaders and 1.4 pixel shaders.• This allows for objects to be partially in water.


Future EnhancementsFuture Enhancements• Shader library

• Make this even more general• Embed stream mapping and data

mapping into shader file so a recompile is never needed when adding new shaders

• Collision Detection• DX9 Features…


QuestionsQuestionsOops. This hysterical outtake was captured from the Rachel demo when we first rendered this model in real-time. Half her polygons remained in object space accidentally… We soon corrected the problem and she now looks better:

preparing sushi - amd

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