Dr' Scott Schaefer

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Programmable Shaders

• Dr. Scott Schaefer

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Graphics Cards Performance

• Nvidia Geforce 6800 GTX1
• 6.4 billion pixels/sec
• Nvidia Geforce 7900 GTX2
• 15.6 billion pixels/sec
• Xbox 3603
• 16 billion pixels/sec (4X AA)
• Nvidia Geforce 8800 GTX4
• 36.8 billion pixels/sec

1 http//www.nvidia.com/page/geforce_6800.html 2
http//www.nvidia.com/page/geforce_7900.html 3
http//news.com.com/Xboxspecsrevealed/2100-1043_
3-5705372.html 4 http//www.nvidia.com/page/gefo
rce_8800.html
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Parallel Processing Power

• Nvidia Geforce 8800 GTX
• 128 programmable processors
• 1.35 GHz each
• 86.4 GB/s memory bandwidth
• 768MB memory

http//www.nvidia.com/page/geforce_8800.html
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Graphics Pipeline
Vertices
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Graphics Pipeline
Vertices
Vertex Transformation/Lighting
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Graphics Pipeline
Vertices
Vertex Transformation/Lighting
Transformed Vertices
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Graphics Pipeline
Vertices
Vertex Transformation/Lighting
Transformed Vertices
Viewport Transformation
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Graphics Pipeline
Vertices
Vertex Transformation/Lighting
Vertex Index Stream
Transformed Vertices
Viewport Transformation
Triangle Setup
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Graphics Pipeline
Vertices
Vertex Transformation/Lighting
Vertex Index Stream
Transformed Vertices
Viewport Transformation
Triangle Setup
Backface Culling
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Graphics Pipeline
Vertices
Vertex Transformation/Lighting
Vertex Index Stream
Transformed Vertices
Viewport Transformation
Triangle Setup
Backface Culling
Clipping
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Graphics Pipeline
Vertices
Vertex Transformation/Lighting
Vertex Index Stream
Transformed Vertices
Viewport Transformation
Triangle Setup
Backface Culling
Clipping
Interpolation/Rasterization
12
Graphics Pipeline
Vertices
Vertex Transformation/Lighting
Vertex Index Stream
Transformed Vertices
Viewport Transformation
Triangle Setup
Backface Culling
Clipping
Interpolation/Rasterization
Pixel Location/Color/Depth
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Graphics Pipeline
Vertices
Vertex Transformation/Lighting
Vertex Index Stream
Transformed Vertices
Viewport Transformation
Triangle Setup
Backface Culling
Clipping
Interpolation/Rasterization
Pixel Location/Color/Depth
Visibility Determination
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Graphics Pipeline
Vertices
Vertex Transformation/Lighting
Vertex Index Stream
Transformed Vertices
Viewport Transformation
Triangle Setup
Backface Culling
Clipping
Interpolation/Rasterization
Pixel Location/Color/Depth
Visibility Determination
Frame Buffer
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Programmable Graphics Pipeline
Vertices
Vertex Shader
Vertex Index Stream
Transformed Vertices/ Normals/Texture coords/
Viewport Transformation
Triangle Setup
Backface Culling
Clipping
Interpolated Vertex Data
Interpolation/Rasterization
Pixel Shader
Pixel Location
Visibility Determination
Color/Depth
Frame Buffer
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Graphics Cards

• Nvidia Geforce 6800 GTX1
• 6 vertex shaders
• 16 pixel shaders
• Nvidia Geforce 7900 GTX2
• 8 vertex shaders
• 24 pixel shaders
• Xbox 3603
• 48 general purpose shaders
• Nvidia Geforce 8800 GTX4
• 128 stream processors

1 http//www.nvidia.com/page/geforce_6800.html 2
http//www.nvidia.com/page/geforce_7900.html 3
http//news.com.com/Xboxspecsrevealed/2100-1043_
3-5705372.html 4 http//www.nvidia.com/page/gefo
rce_8800.html
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Shader Programming

• Many different languages
• Assembly
• OpenGL Shading Language
• Nvidias CG
• Microsofts HLSL
• Different capabilities based on shader model
• Register count
• Instructions
• Maximum number of instructions

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Vertex Shaders

• Input anything associated with vertices
• Position, normal, texture coordinates, etc
• Output transformed vertices
• MUST output position
• Can produce color, normal, texture coordinates,
  etc

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Vertex Shaders

• // vertex shader output structure
• struct VS_OUTPUT
• float4 Pos POSITION

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Vertex Shaders

• VS_OUTPUT VS(
• float3 InPos POSITION // Vertex position
  in model space
• )
• VS_OUTPUT Out (VS_OUTPUT)0
• // transform the position
• float3 transformedPos mul(float4(InPos, 1),
  (float4x3)World)
• Out.Pos mul(float4(transformedPos,1),
  ViewProjection)
• return Out

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Pixel Shaders

• Input Vertex data produced from vertex shader
• Output
• MUST output color
• Can output depth as well
• Cannot change location of pixel on screen

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Pixel Shaders

• float4 PS ( VS_OUTPUT In ) COLOR
• // may perform texture lookup, depth effects,
  fog, etc
• return float4 ( 1, 1, 1, 1 )

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Gouraud Shading Example

• // vertex shader output structure
• struct VS_OUTPUT
• float4 Pos POSITION
• float4 Color COLOR

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Gouraud Shading Example

• VS_OUTPUT VS(
• float3 InPos POSITION, // Vertex
  position in model space
• float3 InNormal NORMAL // Vertex normal in
  model space
• )
• VS_OUTPUT Out (VS_OUTPUT)0
• // transform the position and normal
• float3 transformedPos mul(float4(InPos, 1),
  (float4x3)World)
• Out.Pos mul(float4(transformedPos,1),
  ViewProjection)
• float3 transNormal mul(InNormal,
  (float3x3)World) // normal (view space)
• Out.Color float4 ( calcColor ( normalize (
  lightPos transformedPos ), transNormal,
• 
  normalize ( eyePos transformedPos ) ), 1 )
• return Out

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Gouraud Shading Example

• float3 calcColor ( float3 lightVec, float3
  normal, float3 eyeToVertex )
• float3 color 0
• color lightColor MaterialAmbient
• color lightColor MaterialDiffuse max
  ( 0, dot ( normal, lightVec ) )
• float3 R normalize ( reflect ( lightVec,
  normal ) )
• color lightColor MaterialSpecular pow
  ( max ( 0, dot ( R,
• eyeToVertex ) ),
  MaterialSpecularPower )
• return color

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Gouraud Shading Example

• float4 PS ( VS_OUTPUT In ) COLOR
• return In.Color

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Phong Shading Example

• // vertex shader output structure
• struct VS_OUTPUT
• float4 Pos POSITION
• float3 Normal TEXCOORD0
• float3 TransformedPos TEXCOORD1

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Phong Shading Example

• VS_OUTPUT VS(
• float3 InPos POSITION, // Vertex
  position in model space
• float3 InNormal NORMAL // Vertex normal in
  model space
• )
• VS_OUTPUT Out (VS_OUTPUT)0
• // transform the position and normal
• Out.TransformedPos mul(float4(InPos, 1),
  (float4x3)World)
• Out.Pos mul(float4(Out.TransformedPos,1),
  ViewProjection)
• Out.Normal mul(InNormal, (float3x3)World)
  // normal (view space)
• return Out

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Phong Shading Example

• float4 PS ( VS_OUTPUT In ) COLOR
• // vector from vertex towards eye
• float3 EyeToVertex normalize (
  In.TransformedPos - EyePos )
• float3 normal normalize ( In.Normal )
• float4 color calcColor ( normalize (
  lightPos In.TransformedPos ), normal,
• 
  EyeToVertex )
• return color

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General Purpose GPU Programming

• Limited success because problems must be crammed
  into graphics pipeline
• General purpose computation starting to become
  available
• Nvidias CUDA
• Peakstream