GPU Shading and Rendering Shading Technology 8:30 Introduction (:30–Olano) 9:00 Direct3D 10 (:45–Blythe) Languages, Systems and Demos 10:30 RapidMind (:50–McCool) 11:20 OpenGL Shading Language (:50–Olano) 1:45 Cg / NVIDIA (:50–Kilgard) 2:35HLSL / ATI (:50–Scheuermann) GPUs in Production Rendering 3:45 GPU Production Animation (:45–Wexler) 4:30 Interactive Cinematic Shading. Where are we? (:45–Pellacini) Wrap Up 5:15Discussion and Q&A (:15–All)

GPU Shading and Rendering: Introduction Marc Olano UMBC

Americas Army GPU GPU: Graphics Processing Unit –Designed for real-time graphics –Present in almost every PC –Increasing realism and complexity

GPU computation Texture / Buffer Texture / Buffer Vertex Geometry Fragment CPU Displayed Pixels Displayed Pixels

Low-level code !!ARBvp1.0 # Transform the normal to view space TEMP Nv,Np; DP3 Nv.x,state.matrix.modelview.invtrans.row[0],vertex.normal; DP3 Nv.y,state.matrix.modelview.invtrans.row[1],vertex.normal; DP3 Nv.z,state.matrix.modelview.invtrans.row[2],vertex.normal; MAD Np,Nv,{.9,.9,.9,0},{0,0,0,1}; # screen position from vertex TEMP Vp; DP4 Vp.x, state.matrix.mvp.row[0], vertex.position; DP4 Vp.y, state.matrix.mvp.row[1], vertex.position; DP4 Vp.z, state.matrix.mvp.row[2], vertex.position; DP4 Vp.w, state.matrix.mvp.row[3], vertex.position; […] # interpolate MAD Np, Np, -vertex.color.x, Np; MAD result.position, Vp, vertex.color.x, Np; END

High-level code void main() { vec4 Kin = gl_Color; // key input // screen position from vertex, texture and normal vec4 Vp = ftransform(); vec4 Tp = vec4(gl_MultiTexCoord0.xy*1.8-.9, 0,1); vec4 Np = vec4(nn*.9,1); // interpolate between Vp, Tp and Np gl_Position = Vp; gl_Position = mix(Tp,gl_Position,pow(1.-Kin.x,8.)); gl_Position = mix(Np,gl_Position,pow(1.-Kin.y,8.)); // copy to output gl_TexCoord[0] = gl_MultiTexCoord0; gl_TexCoord[1] = Vp; gl_TexCoord[3] = Kin; }

Non-real time vs. Real time Not real-time –Developed from General CPU code –Seconds to hours per frame –1000s of lines –“Unlimited” computation, texture, memory, … Real-time –Developed from fixed- function hardware –Tens of frames per second –1000s of instructions –Limited computation, texture, memory, …

Non-real time vs. Real-time Non-real timeReal-time Texture/ Buffer Texture/ Buffer Vertex Geometry Fragment Application Displayed Pixels Displayed Pixels Light Displayed Pixels Displayed Pixels Application Displacement Surface Volume Atmosphere Imager

History (not real-time) Testbed [Whitted and Weimer 1981] Shade Trees [Cook 1984] Image Synthesizer [Perlin 1985] RenderMan [Hanrahan and Lawson 1990] Multi-pass RenderMan [Peercy et al. 2000] GPU acceleration [Wexler et al. 2005]

History (real-time) Custom HW [Olano and Lastra 1998] Multi-pass standard HW [Peercy et al. 2000] Register combiners [NVIDIA 2000] Vertex programs [Lindholm et al. 2001] Compiling to mixed HW [Proudfoot et al. 2001] Fragment programs Standardized languages Geometry shaders [Blythe 2006]

Choices OS: Windows, Mac, Linux API: DirectX, OpenGL Language: HLSL, GLSL, Cg, … Compiler: DirectX, OpenGL, Cg, ASHLI Runtime: CgFX, ASHLI, OSG (& others), sample code

Major Commonalities Vertex & Fragment/Pixel C-like, if/while/for Structs & arrays Float + small vector and matrix –Swizzle & mask (a.xyz = b.xxw) Common math & shading functions

PipelinePipeline Texture / Buffer Texture / Buffer Vertex Geometry Fragment GPU Parallelism

PipelinePipeline SPMD Parallel Fragment Stream Texture / Buffer Texture / Buffer Vertex Geometry Fragment GPU Parallelism

SPMD Parallel Fragment Stream Fragment SIMD Parallel 2x2 Block

Fragment GPU Parallelism Shader Unit Shader Unit Shader Unit Shader Unit Branch Unit Branch Unit Fog Texture Unit Texture Unit L1 Cache L2 Cache Pipeline(NVIDIA)Pipeline(NVIDIA) SIMD Parallel 2x2 Block

GPU Parallelism Shader Unit Shader Unit Shader Unit Shader Unit Branch Unit Branch Unit Fog Texture Unit Texture Unit L1 Cache L2 Cache Pipeline(NVIDIA) Vector Parallel Limited MIMD ALUALUALUALU ALUALUALUALU

Managing GPU Programming Simplified computational model –Bonus: consistent as hardware changes All stages SIMD –Explicit 4-element SIMD vectors Fixed conversion / remapping between each stage Buffer Vertex (stream) Geometry (stream) Fragment (array)

Vertex One element in / one out NO communication Can select fragment address Buffer Vertex (stream) Geometry (stream) Fragment (array)

Geometry More next (Blythe talk) One element in / 0 to ~100 out –Limited by hardware buffer sizes Like vertex: –NO communication –Can select fragment address Buffer Vertex (stream) Geometry (stream) Fragment (array)

Fragment Biggest computational resource One element in / 0 – 1 out Cannot change destination address –I am element x,y in an array, what is my value? Effectively no communication Conditionals expensive –Better if block coherence Buffer Vertex (stream) Geometry (stream) Fragment (array)

Program / Multiple Passes Communication –None in one pass –Arbitrary read addresses between passes Data layout –No persistent per- processor memory –No penalty to change Buffer Vertex (stream) Geometry (stream) Fragment (array)

Multiple passes GPGPU Non-local effects –Shadow maps –Texture space Precomputation –Fix some degrees of freedom –Factor into functions of 1-3D –Project input or output into another space

GPU Shading and Rendering Shading Technology 8:30 Introduction (:30–Olano) 9:00 Direct3D 10 (:45–Blythe) Languages, Systems and Demos 10:30 RapidMind (:50–McCool) 11:20 OpenGL Shading Language (:50–Olano) 1:45 Cg / NVIDIA (:50–Kilgard) 2:35HLSL / ATI (:50–Scheuermann) GPUs in Production Rendering 3:45 GPU Production Animation (:45–Wexler) 4:30 Interactive Cinematic Shading. Where are we? (:45–Pellacini) Wrap Up 5:15Discussion and Q&A (:15–All)