Shader generation and compilation for a programmable GPU Student: Jordi Roca Monfort Advisor: Agustín Fernández Jiménez Co-advisor: Carlos González Rodríguez

Outline Introduction. Background. Goals. Design and implementation. Conclusions.

Introduction

ATTILA simulation framework Vendor OpenGL API Vendor Driver GLInterceptor OpenGL Application ATTILA OpenGL API ATTILA Driver ATTILA Simulator OpenGL trace Statistics GLPlayer

ATTILA Driver ATTILA Simulator Statistics Simulates last generation of 3D graphics boards (programmable GPUs) My Work ATTILA OpenGL API OpenGL Application OpenGL trace Vendor OpenGL API Vendor driver GLInterceptor GLPlayer Extend/Complete OpenGL API to execute recent/advanced 3D Applications (Doom3, Unreal Tournament, etc)

Background

Renderization (I) ¿What is called renderization? Generate the pixels for a set of images/frames forming an animated scene. Goal: compute each pixel color as fast as possible → determines FPS ¿Which computations are required? Given the scene objects DB, compute the color of the projected objects in the pixel screen area. Each pixel color depends on the scene lighting and the viewer camera position.

Renderization (II) Position View Info Renderization data Geometry info Position, Color Lighting Info Screen area

Renderization approaches For each pixel (x,y) compute physical interaction between the lights and objects in scene: RayTracing, Radiosity, Photon Map Very expensive pixel computation: Global lighting (shadows, indirect reflections among objects) Interaction between objects and lights are computed only in vertices and for each pixel (x,y) the corresponding value is approached. Direct Rendering (3D graphics boards, 3D game consoles, etc.). Only direct illumination from light sources (Each vertex color is independent)

Direct Rendering (I) Position Viewer Info Renderization data Geometry info Position, Color Lighting Info Screen area Color interpolation

Direct Rendering (II) The higher density of vertices, the more realistic lighting. In addition, more vertices are required to improve level of detail in surfaces. Thus: ▲ realism → ▲ vertices → ▲ computation → ▼ FPS Solution: Specify surface using less vertices and Specify surface details using textures.

Textures Renderization data Position Viewer Info Geometry info Position, Color Lighting Info Screen area Textures

Texture mapping Screen area (0.63,0.86) (0.26,0.37) (0.79,0.10)

Texture mapping Screen area (0.63,0.86) (0.26,0.37) (0.79,0.10) Coordinate interpolator (0.40,0.45) Texture sampled value

3D Rendering Pipeline Generate interpolated attributes (color, coordinates) Per-pixel texture mapping Compute: color coordinates vertex position in screen Final screen 3D scene Vertex DB Viewer info Lighting info Textures Vertex processing stage (VERTEX SHADING) Parallelizable process Fragment processing stage (FRAGMENT SHADING) Parallelizable process RASTERIZER

3D RP Implementation Implementations Software: Mesa 3D Graphics Library (OpenGL). Software + hardware acceleration: Vendor OpenGL, Direct3D, Xbox, PlayStation, etc. Work distribution between CPU y graphics board transparently to the applications.

3D accelerators evolution 2D accelerators (pre Voodo) <1996 3D accelerators (3Dfx Voodo) 1996 Graphical Processor Units (GeForce) 1999 Programmable GPUs (GeForce 3) 2001 Rasterizer FS VS Final screen BD CPU VGA Rasterizer FS VS Final screen BD CPU 3D accelerators Rasterizer FS VS Final screen BD CPU GPU Rasterizer FS VS Final screen BD CPU PGPU

GPUs: applying 2 textures Rasterizer (x,y) InterpolatedcolorTexture coordinate 1 Final color F1 Fragment stream Texture coordinate 2 + Fragment Unit 0 Texture Memory * Fixed Function Uses: Per-pixel lighting. Shadow implementation. Bump-mapping.

Programmable GPUs: 2 textures Rasterizer (x,y) InterpolatedcolorTexture coordinate Final color F1 Fragment Stream Texture coordinate Fragment Shader 0 Texture Memory ALU Temporals Shader Processors LDTEX t1, coord1, Text1 LDTEX t2, cood2, Text2 ADD t1, colorIn, t1 MUL t1, t1, t2

Shader Processors SP execute small programs (shaders) using vectorial and scalar instructions, that define the computation in the following stages: Vertex processing: Vertex Shader Lighting computation On-screen vertex projection Texture coordinates generation. Fragment processing: Fragment Shader Texture color fetch and blending. FOG It is like a GPU supporting “infinite visualization effects” not supported in previous graphics boards generations.

Goals

Implement all the necessary modules in the OpenGL API to: Support new real 3D applications using shaders in our simulation framework. Support also for old applications using FF and applications combining both shaders and FF. Idea: Perform Fixed Function emulation through generating equivalent shaders for SP.

Things to do Implement shader support in our OpenGL API: Using the most used shader programming language by 3D apps: ARB_vertex_program y ARB_fragment_program Study how to express FF functions in terms of shaders (pre-study phase).

Design and implementation

Fixed Function emulation

FF Emulation Rasterizer Fragment Shader Vertex Shader Final screen BD !!ARBvp1.0 ATTRIB pos = vertex.position; PARAM mat[4] = { state.matrix.mvp }; # Transform by concatenation of the # MODELVIEW and PROJECTION matrices. DP4 result.position.x, mat[0], pos; DP4 result.position.y, mat[1], pos; DP4 result.position.z, mat[2], pos; DP4 result.position.w, mat[3], pos; # Pass the primary color through # w/o lighting. MOV result.color, vertex.color; END !!ARBfp1.0 #first set of texture coordinates ATTRIB tex = fragment.texcoord; # interpolated color ATTRIB col = fragment.color; OUTPUT outColor = result.color; TEMP tmp; #sample the texture TEX tmp, tex, texture, 2D; #perform the modulation MUL outColor, tmp, col; END

FF emulation Implemented functions (according to OpenGL Spec 2.0): Vertex Shading (85% of total): Per-vertex standard OpenGL lighting: Point, directional and spot lights. Attenuation. Local and infinite viewer. Vertex transformation Automatic texture coordinate generation. Object Plane and Eye Plane Normal Map, Reflection Map and Sphere Map. FOG coordinate. Fragment Shading (90% of total): Multi-texturing and texture combine functions FOG application: Linear, Exponential and Second Order Exponential

FF emulation example FOG application: Algorithm: For each pixel, perform linear interpolation between the original and the fog color, accoding to the distance from the object to the viewer.

FOG emulation FOG exponential mode f = e -density*fogcoord f = 2 -(density * fogcoord)/ln(2) (e = 2 1/ln 2 ) Final color = pixel color * f + fog color * (1 - f)

FOG emulation !!ARBfp1.0 ATTRIB fogCoord = fragment.fogcoord; OUTPUT oColor = result.color; PARAM fogColor = state.fog.color; PARAM fogParams = program.local[0]; # fogParams.x : density/ln(2) TEMP fragmentColor, fogFactor; # Texture applications.... # Fog Factor computing... MUL fogFactor.x, fogParam.x, fogCoord.x; # fogFactor.x = density*fogcoord/ln(2) EX2_SAT fogFactor.x, -fogFactor.x; # fogFactor.x = 2^-(fogFactor.x) # Fog color interpolation LRP oColor, fogFactor.x, fragmentColor, fogColor; END

ARB compilers

!!ARBvp1.0 ATTRIB pos = vertex.position; PARAM mat[4] = { state.matrix.mvp }; # Transform by concatenation of the # MODELVIEW and PROJECTION matrices. DP4 result.position.x, mat[0], pos; DP4 result.position.y, mat[1], pos; DP4 result.position.z, mat[2], pos; DP4 result.position.w, mat[3], pos; # Pass the primary color through # w/o lighting. MOV result.color, vertex.color; END !!ARBfp1.0 #first set of texture coordinates ATTRIB tex = fragment.texcoord; # interpolated color ATTRIB col = fragment.color; OUTPUT outColor = result.color; TEMP tmp; #sample the texture TEX tmp, tex, texture, 2D; #perform the modulation MUL outColor, tmp, col; END

The compilers common architecture !!ARBvp1.0 PARAM arr[5] = { program.env[0..4] }; #ADDRESS addr; ATTRIB v1 = vertex.attrib[1]; PARAM par1 = program.local[0]; OUTPUT oPos = result.position; OUTPUT oCol = result.color.front.primary; OUTPUT oTex = result.texcoord[2]; ARL addr.x, v1.x; MOV res, arr[addr.x - 1]; END Lexical - Syntactic Analysis (Flex + Bison) !!ARBvp1.0 IR Semantic Analysis Symbol table Code generation GPU Specific Generic Line:By0By1By2By3By4By5By6By7By8By9ByAByBByByDByEByF 011: b 6a 00 0f 1b : b 1b b : b 1b b 14 b8 014: b 1b b : b 1b b 04 f8 016: b 1b b : b 1b b : b b 04 d8 019: b b : ae 00 0c 1b : b 04 b8 022: b : c 1b 14 f8 024: a ae 00 0c 1b : b c 1b 14 38

Intermediate Representation Example: !!ARBvp1.0 ATTRIB pos = vertex.position; PARAM mat[4] = { state.matrix.mvp }; # Transform by concatenation of the # MODELVIEW and PROJECTION matrices. DP4 result.position.x, mat[0], pos; DP4 result.position.y, mat[1], pos; DP4 result.position.z, mat[2], pos; DP4 result.position.w, mat[3], pos; # Pass the primary color through # w/o lighting. MOV result.color, vertex.color; END IRProgram header: “!!ARBvp1.0” IRVP1ATTRIBStatement name: pos attrib: vertex.position Program Statements IRInstruction opcode: DP4 destination: result.position IRDstOperand writeMask: x isResultRegister: true source: mat IRSrcOperand swizzleMask: xyzw isInputRegister: false destinationsources source: pos IRSrcOperand swizzleMask: xyzw isInputRegister: false

Semantic analysis and generic code generation Features: Implemented using the visitor pattern. Decouples IR from the different operations involved in each compiler phase. Allows using a common analyzer and a common code generator for both program types.

Code generation Phase 1: Generate an architecture-independent generic code assuming unbounded machine resources. Phase 2: Translate to specific code being aware of the concrete GPU architecture constraints. GenericInstruction GenericCode GenericInstruction Machine File Descriptor GPUInstruction Specific Code GPUInstruction

Conclusions

Achieved goals: Now, the OpenGL API implementation supports: Fixed Function emulation Of almost the entire set of functions of VS and FS stages (the most important ones). Shader compilation for ARB_vertex_program and ARB_fragment_program specifications. Both compilers share most of the implementation. Clear separation between generic and specific stages.

Future work Support/include other 3D RP parts (i.e. interpolation) like programables stages to reduce hardware complexity and power consumption (embedded systems). Implement high-level shading languages compilers (GLSlang, HLSL).

End of the presentation