Introduction to Programmable Hardware

Traditional Graphics Pipeline

frame-bufferanti-aliasingframe-bufferanti-aliasing

textureblendingtexture

blending

setuprasterizer

setuprasterizer

transform &lighting

transform &lighting

(per vertex operations)

(per primitive operation)

(per fragment operation)

Programmable features

• Vertex Programming • Pixel Shader

– Texture shader – Register combiner

• Based on nVIDIA architecture

Vertex Program (cont’d)

Vertex Programming offers programmable T&L unit

User-definedVertex

Processing

User-definedVertex

Processing

frame-bufferanti-aliasingframe-bufferanti-aliasing

textureblendingtexture

blending

setuprasterizer

setuprasterizer

transform &lighting

transform &lighting

Gives the programmer total control of vertex processing.

Vertex Program (cont’d)

frame-bufferanti-aliasingframe-bufferanti-aliasing

textureblendingtexture

blending

setuprasterizer

setuprasterizer

transform &lighting

transform &lighting

VertexProgramVertex

Program

Vertex Program (cont’d)

Vertex Program– Assembly language interface to T&L unit– GPU instruction set to perform all vertex math– Reads an untransformed, unlit vertex– Creates a transformed vertex– Optionally creates

• Lights a vertex• Creates texture coordinates• Creates fog coordinates• Creates point sizes

Create Vertex Program

Programs (assembly) are defined inline as Programs (assembly) are defined inline as

character stringscharacter strings

static const GLubyte vpgm[] = “\!!VP1. 0\ DP4 o[HPOS].x, c[0], v[0]; \ DP4 o[HPOS].y, c[1], v[0]; \ DP4 o[HPOS].z, c[2], v[0]; \ DP4 o[HPOS].w, c[3], v[0]; \ MOV o[COL0],v[3]; \END";

Vertex Source

Vertex Program

Vertex Output

Program Constants

Temporary Registers

16x4 registers

128 instructions

96x4 registers

12x4 registers

15x4 registers

Programming ModelProgramming Model

V[0] …V[15] c[0]

…c[96]

R0 …R11

O[HPOS]O[COL0]O[COL1]O[FOGP]O[PSIZ]O[TEX0] …O[TEX7]

All quad floats

Instruction Set: The ops

• 17 instructions total

• MOV, MUL, ADD, MAD, DST

• DP3, DP4

• MIN, MAX, SLT, SGE

• RCP, RSQ, LOG, EXP, LIT

• ARL

Pixel Shader

frame-bufferanti-aliasingframe-bufferanti-aliasing

textureblendingtexture

blending

setuprasterizer

setuprasterizer

transform &lighting

transform &lighting

User-defined perpixel shading

Texture Mapping/Blending

Traditional OpenGL texture mapping/blending

Texture Coordinate Texture Unit

Fragment color

Blend colors

Fragment color output

Vertex colors Gouraud Shading

Multitexturing

An optional extension of OpenGL 1.2

texture unit 0 blend colors

texture unit 0 blend colors

texture unit 0 blend colors

texture unit 0 blend colors

fragment color input

fragment color output

Texture Compositing

OpenGL 1.2

TextureEnvironment

0 TextureEnvironment

1

TextureEnvironment

1

TextureFetching

SpecularColorSum

SpecularColorSum Fog

Application

Tex0

Tex1

Fragment Color

Fog Color/Factor

Specular Color

Choice of 5 set functions for RGB and Alpha:

Ct: texture color; At: texture alpha Cf: incoming fragment color; Af: incoming fragment alpha Cc: color assigned to GL_TEXTURE_ENV_COLOR

Post-environment specular color addition and fog application

Function RGB Alpha

Replace Ct At

Modulate Cf Ct Af At

Decal Cf (1 – At) + Ct At Af

Blend Cf (1 – Ct) + Cc Ct Af At

Add Cf + Ct Af At

Compositing Operator

Pixel Shader (cont’d)

Texture shader– 4 texture units– 23 different texture shader operations

• Conventional (1D, 2D, 3D, texture rectangle, cube map)• Special case (none, pass through, cull fragment)• Dependent texture fetches (result of one texture lookup

affects texture coords for subsequent unit)• Dependent textures fetches with dot product (and optional

reflection) calculations

Register combiners– 8 stages (general combiners) on GeForce3/4– Per-stage constants

Based on nVIDIA’s GF3/4 architecture

Pixel Shader Based on nVIDIA’s GF3/4 architecture Texture shader + register combiner

texture unit 0 texture program

texture unit 1 texture program

texture unit 2 texture program

texture unit 3 texture program

fragment color input

register combinerfragment color output

texture shader

Texture Shader

TexTex##

Texture Coords(S,T,R,Q)

ShaderOperations

TextureFetch

Texture 2D

2DAny Format

( , )

Bound Texture Target/Format

Qi

Si

Qi

Ti(Si,Ti,Ri,Qi)ii

OutputColor

(R,G,B,A)

Texture program example: conventional 2D texture

Texture Shader (cont’d)

Texture program example: pass through

ShaderOperations

TextureFetch

OutputColor

(Si,Ti,Ri,Qi) None

Bound Texture Target/Format

(R,G,B,A)None

R = Clamp0to1(Si)

G = Clamp0to1(Ti)

B = Clamp0to1(Ri)

A = Clamp0to1(Qi)

Texture Shader (cont’d)

00

TexTex##

Texture Coords(S,T,R,Q)

ShaderOperations

TextureFetch

App specific Texture specific

Any type Unsigned RGB[A]

R0G0B0A0

11 (A0,R0)

Texture specific

Bound Texture Target/Format

R1G1B1A1Ignored None

2D RGBA

Texture program example: dependent texture

Register Combiner

GeForce 2 (only 2 general combiner stages)

Spare 0

Fragment Color

TextureFetching

GeneralCombiner

0

4 RGB Inputs

Texture 0

Texture 1

Fog Color/Factor

Reg

iste

r S

etR

egis

ter

Set

6 RGB Inputs

Specular Color

4 Alpha Inputs

3 RGB Outputs

3 Alpha Outputs

GeneralCombiner

1

4 RGB Inputs

4 Alpha Inputs

3 RGB Outputs

3 Alpha Outputs

FinalCombiner

1 Alpha Input

Specular Color

Register-based programming– All textures and colors available for each and every

texture blending stage– 8 Stages of blending in hardware, plus specular and

fog• Note that GeForce3 has 8 combiners, and 4

textures.– Signed color arithmetic

Register Combiner (cont’d)

Diagram of a General Combiner

Input RGB, Alpha Registers

Input Alpha, Blue Registers

InputMappings

InputMappings

A

B

C

D

A op1 B

C op2 D

AB op3 CD

RGB Function

A

B

C

D

AB

CD

AB op4 CD

Alpha Function

RGBScale/Bias

AlphaScale/Bias

Next Combiner’sRGB Registers

Next Combiner’sAlpha Registers

RGBPortion

AlphaPortion

General Combiner Input Registers

Input RGB, Alpha Registers

Input Alpha, Blue Registers

InputMappings

InputMappings

A

B

C

D

A op1 B

C op2 D

AB op3 CD

RGB Function

A

B

C

D

AB

CD

AB op4 CD

Alpha Function

RGBScale/Bias

AlphaScale/Bias

Next Combiner’sRGB Registers

Next Combiner’sAlpha Registers

RGBPortion

AlphaPortion

The Register Set

Primary (diffuse) color• initialized to RGBA of fragment’s primary color

Secondary (specular) color• initialized to RGB of fragment’s secondary/specular color• alpha not initialized

Texture 0 and Texture 1 colors• initialized to fragment’s filtered RGBA texel from numbered texture unit• not initialized if numbered texture unit is disabled or non-existent

Spare 0 and Spare 1• Alpha of Spare 0 is initialized to alpha of Texture 0 color (if enabled)• RGB of Spare 0 and all of Spare 1 is not initialized

Fog• RGB is current fog color• alpha is fragment’s fog factor (only available in final combiner)• read-only

Constant color 0 and Constant color 1• initialized to user-defined RGBA value• read-only

Zero• constant, read-only value of zero

General Combiner Input Mappings

Input RGB, Alpha Registers

Input Alpha, Blue Registers

InputMappings

InputMappings

A

B

C

D

A op1 B

C op2 D

AB op3 CD

RGB Function

A

B

C

D

AB

CD

AB op4 CD

Alpha Function

RGBScale/Bias

AlphaScale/Bias

Next Combiner’sRGB Registers

Next Combiner’sAlpha Registers

RGBPortion

AlphaPortion

General Combiner Input Mappings

Signed Identity

f(x) = x

[-1, 1] [-1, 1]

Unsigned Identity

f(x) = max(0, x)

[0, 1] [0, 1]

Expand Normal

f(x) = 2 * max(0, x) - 1

[0, 1] [-1, 1]

Half Bias Normal

f(x) = max(0, x) – ½

[0, 1] [-½, ½]

Signed Negate

f(x) = -x

[-1, 1] [1, -1]

Unsigned Invert

f(x) = 1-min(max(0,x),1)

[0, 1] [1, 0]

Expand Negate

f(x) = -2 * max(0, x) + 1

[0, 1] [1, -1]

Half Bias Negate

f(x) = -max(0, x) + ½

[0, 1] [½, -½]

-1

0

1

-1 0 1

-1

0

1

-1 0 1

-1

0

1

-1 0 1

-1

0

1

-1 0 1

-1

0

1

-1 0 1

-1

0

1

-1 0 1

-1

0

1

-1 0 1

-1

0

1

-1 0 1

General Combiner RGB Function

Input RGB, Alpha Registers

Input Alpha, Blue Registers

InputMappings

InputMappings

A

B

C

D

A op1 B

C op2 D

AB op3 CD

RGB Function

A

B

C

D

AB

CD

AB op4 CD

Alpha Function

RGBScale/Bias

AlphaScale/Bias

Next Combiner’sRGB Registers

Next Combiner’sAlpha Registers

RGBPortion

AlphaPortion

General Combiner RGB Functions

A

B

C

D

AB

CD

AB + CD

A

B

C

D

AB

CD

mux(AB, CD)

A

B

C

D

A • B

C • D

Dot / Dot / Discard

A

B

C

D

A • B

CD

A

B

C

D

AB

C • D

Dot / Mult / Discard Mult / Dot / Discard

Mult / Mult / SumMult / Mult / Mux

mux(AB, CD) = (Spare0[Alpha] ½) ? AB : CD

Dot products on RGB registers: A • B = (A[red] * B[red] + A[green] * B[green] + A[blue] * B[blue],

A[red] * B[red] + A[green] * B[green] + A[blue] * B[blue],A[red] * B[red] + A[green] * B[green] + A[blue] * B[blue])

Multiplication on RGB registers: AB = (A[red] * B[red], A[green] * B[green], A[blue] * B[blue])

Diagram of the Final Combiner (OpenGL only)

Input RGB, Alpha Registers

Input Alpha, Blue Registers

InputMappings

InputMapping

A

B

C

D

AB + (1-A)C + D

RGB Function

RGBPortion

AlphaPortion

RGBOut

AvailableRGB Inputs

AlphaOut

E

F

EF

Spare0

2nd-aryColor

Sum

Clamp to [0, 1]

InputMappings

Color Sum Unit

Multiplier