Preparing Sushi. Alex Vlachos. How Hardware Guys Write a 3D Graphics Engine. ati.com. EGDC 2001

Transcription

1 Preparing Sushi How Hardware Guys Write a 3D Graphics Engine Alex Vlachos AVlachos@ati ati.com EGDC 2001 Preparing Sushi - ATI Research, Inc. EGDC

2 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 Outline Future Enhancements Preparing Sushi - ATI Research, Inc. EGDC

3 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. Preparing Sushi - ATI Research, Inc. EGDC

4 RADEON 8500 Island Demo Preparing Sushi - ATI Research, Inc. EGDC

5 RADEON 8500 Island Demo Preparing Sushi - ATI Research, Inc. EGDC

6 RADEON 8500 Island Demo Preparing Sushi - ATI Research, Inc. EGDC

7 RADEON 8500 Island Demo Preparing Sushi - ATI Research, Inc. EGDC

8 Sushi Engine Goals Shader Driven Cross API (DirectX & OpenGL) Cross Platform (Windows & Mac) Future-looking For Several Product Cycles Preparing Sushi - ATI Research, Inc. EGDC

9 Engine Hierarchy Engine Object Asset Management Shader Lib WinD3D WinOGL MacOGL D3D OGL Preparing Sushi - ATI Research, Inc. EGDC

10 Scene 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. Preparing Sushi - ATI Research, Inc. EGDC

11 Octree Divisions Octree Divisions Preparing Sushi - ATI Research, Inc. EGDC

12 Vertex 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. Preparing Sushi - ATI Research, Inc. EGDC

13 Optimize 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. Preparing Sushi - ATI Research, Inc. EGDC

14 Vertex Storage MetaBins Bins Octree Leaves VB IB Stream Mapping VB IB Stream Mapping VB IB Stream Mapping MetaBin ID Shader ID Texture IDs MetaBin ID Shader ID Texture IDs MetaBin ID Shader ID Texture IDs MetaBin ID Shader ID Texture IDs MetaBin ID Shader ID Texture IDs MetaBin ID Shader ID Texture IDs Bin ID IB Start IB End Bin ID IB Start IB End Bin ID IB Start IB End Bin ID IB Start IB End Bin ID IB Start IB End Bin ID IB Start IB End Bin ID IB Start IB End Within each leaf, render calls are sorted by shader state and then by texture handles VB IB Stream Mapping MetaBin ID Shader ID Texture IDs Bin ID IB Start IB End Bin ID IB Start IB End Bin ID IB Start IB End Preparing Sushi - ATI Research, Inc. EGDC

15 Run-Time 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 Preparing Sushi - ATI Research, Inc. EGDC

16 Rendering Pipeline Rendering 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 Preparing Sushi - ATI Research, Inc. EGDC

17 Non-Opaque 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 Preparing Sushi - ATI Research, Inc. EGDC

18 Non-Opaque Draw Order Based on Lights Preparing Sushi - ATI Research, Inc. EGDC

19 Shader 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 Preparing Sushi - ATI Research, Inc. EGDC

20 Fixed Function Shader DefineParam 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 Preparing Sushi - ATI Research, Inc. EGDC

21 Programmable Shader 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 StartVertexShader 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 //SetVertexShaderConstant 0 commonconst SetVertexShaderConstant 1 appconst //SetVertexShaderConstant 2 worldspacecampos SetVertexShaderConstant 3 worldspacelightpos SetVertexShaderConstant 4 wvp 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 Preparing Sushi - ATI Research, Inc. EGDC

22 Shadow 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. Preparing Sushi - ATI Research, Inc. EGDC

23 Dynamic Shadow Volumes Shadow Volume Visualization Preparing Sushi - ATI Research, Inc. EGDC

24 Dynamic Shadow Volumes 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. Preparing Sushi - ATI Research, Inc. EGDC

25 Shadow Volume Sphere Sphere s Shadow Volume Preparing Sushi - ATI Research, Inc. EGDC

26 Shadow Volume Extrusion Setup A B Face Normals For Polygon A A B Face Normals For Polygon B Infinitely Thin Fill Polygons Original bordering polygons. We insert 2 degenerate polygons between the original polygons which share the appropriate face normal encoded in the vertex. Preparing Sushi - ATI Research, Inc. EGDC

27 Static Shadow Volumes Preparing Sushi - ATI Research, Inc. EGDC

28 Static 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! Preparing Sushi - ATI Research, Inc. EGDC

29 Shadow Beam Algorithm Below is an example of applying this beam algorithm to the first 3 polygons of a given volume. Beam Polygon 1 Beam Polygon 2 Beam Polygon 3 Preparing Sushi - ATI Research, Inc. EGDC

30 Shadow Beam Algorithm 1. 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 4 th 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! Preparing Sushi - ATI Research, Inc. EGDC

31 Shadow Beam Algorithm Recursion Step Original Beam Recursive Beam Remaining Polygons Existing Polygon Beam Polygon Beam Frustum Recursive Beam Frustum Preparing Sushi - ATI Research, Inc. EGDC

32 Shadow Beam Algorithm This solves for cyclically overlapping polygons! (Now solve for T-Junctions!) Preparing Sushi - ATI Research, Inc. EGDC

33 Object 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) Preparing Sushi - ATI Research, Inc. EGDC

34 RADEON 8500 Rachel Demo Preparing Sushi - ATI Research, Inc. EGDC

35 RADEON 8500 Rachel Demo Preparing Sushi - ATI Research, Inc. EGDC

36 Extras Anamorphic Spherical screen projection High resolution screen shots Fly through paths Preparing Sushi - ATI Research, Inc. EGDC

37 Anamorphic 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. Preparing Sushi - ATI Research, Inc. EGDC

38 Anamorphic 3:4 Render Target 16:9 Plasma Display Preparing Sushi - ATI Research, Inc. EGDC

39 Spherical Projection Screens 150 Viewer Top View Preparing Sushi - ATI Research, Inc. EGDC

40 Spherical Projection Screens 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! Preparing Sushi - ATI Research, Inc. EGDC

41 High 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 Preparing Sushi - ATI Research, Inc. EGDC

42 High Resolution Screen Shots Preparing Sushi - ATI Research, Inc. EGDC

43 Fly 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 Preparing Sushi - ATI Research, Inc. EGDC

44 RADEON 8500 Waterfall Demo Preparing Sushi - ATI Research, Inc. EGDC

45 RADEON 8500 Waterfall Demo Reflections Refractions Preparing Sushi - ATI Research, Inc. EGDC

46 Water 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. Preparing Sushi - ATI Research, Inc. EGDC

47 Future 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 Preparing Sushi - ATI Research, Inc. EGDC

48 Questions Oops. 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 - ATI Research, Inc. EGDC