1. Introduction to Programmable Hardware

2. Traditional Graphics Pipeline
transform &
lighting
(per vertex operations)
setup
rasterizer
(per primitive operation)
texture
blending
(per fragment operation)
frame-buffer
anti-aliasing

3. Programmable features
Vertex Programming
Pixel Shader
Texture shader
Register combiner
Based on nVIDIA architecture

4. Gives the programmer total control of vertex processing.
Vertex Program (cont’d)
Vertex Programming offers programmable T&L unit
User-defined
Vertex
Processing
transform &
lighting
setup
rasterizer
texture
blending
Gives the programmer total control of vertex processing.
frame-buffer
anti-aliasing

5. Vertex Program (cont’d)
transform &
lighting
setup
rasterizer
texture
blending
frame-buffer
anti-aliasing

6. Vertex Program (cont’d)
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

7. Create Vertex Program Programs (assembly) are defined inline as
character 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";

8. Programming Model All quad floats Vertex Source Program Constants…
V[15]
Vertex Source
Program Constants
c[0] …
c[96]
16x4 registers
O[HPOS]
O[COL0]
O[COL1]
O[FOGP]
O[PSIZ]
O[TEX0] …
O[TEX7]
Vertex Program
96x4 registers
128 instructions
Temporary Registers R0 …
R11
12x4 registers
Vertex Output
15x4 registers
All quad floats

9. Instruction Set: The ops
17 instructions total
MOV, MUL, ADD, MAD, DST
DP3, DP4
MIN, MAX, SLT, SGE
RCP, RSQ, LOG, EXP, LIT
ARL

10. Pixel Shader transform & lighting setup rasterizer User-defined per
frame-buffer
anti-aliasing
texture
blending
setup
rasterizer
transform &
lighting
User-defined per
pixel shading

11. Texture Mapping/Blending
Traditional OpenGL texture mapping/blending
Vertex colors
Gouraud Shading
Fragment color
Texture Coordinate
Texture Unit
Blend colors
Fragment color output

12. Multitexturing An optional extension of OpenGL 1.2
fragment color input
texture unit 0
blend colors
texture unit 0
blend colors
texture unit 0
blend colors
texture unit 0
blend colors
fragment color output

13. Texture Compositing OpenGL 1.2 Texture Fetching Texture Environment
Fragment Color
Texture
Environment
Texture
Fetching
Texture
Environment 1
Tex0
Tex1
Specular
Color
Sum
Specular Color
Fog
Application
Fog Color/Factor

14. Compositing Operator 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
Add
Cf + Ct

15. Pixel Shader (cont’d) Based on nVIDIA’s GF3/4 architecture
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

16. Pixel Shader Based on nVIDIA’s GF3/4 architecture
Texture shader + register combiner
texture shader
fragment color input
texture unit 0
texture program
texture unit 1
texture program
texture unit 2
texture program
texture unit 3
texture program
register combiner
fragment color output

17. Bound Texture Target/Format
Texture Shader
Texture program example: conventional 2D texture
Tex #
Texture Coords
(S,T,R,Q)
Shader
Operations
Texture
Fetch
Bound Texture Target/Format
Output
Color 2D
Any Format
Texture 2D Si Ti i
(Si,Ti,Ri,Qi)
( , )
(R,G,B,A) Qi Qi

18. Texture Shader (cont’d)
Texture program example: pass through
Shader
Operations
Texture
Fetch
Output
Color
(Si,Ti,Ri,Qi)
None
Bound Texture Target/Format
(R,G,B,A)
R = Clamp0to1(Si)
G = Clamp0to1(Ti)
B = Clamp0to1(Ri)
A = Clamp0to1(Qi)

19. Texture Shader (cont’d)
Texture program example: dependent texture
Tex #
Texture Coords
(S,T,R,Q)
Shader
Operations
Texture
Fetch
App specific
Texture specific
Any type
Unsigned RGB[A]
R0G0B0A0 1
(A0,R0)
Bound Texture Target/Format
R1G1B1A1
Ignored
None
2D RGBA

20. Register Combiner GeForce 2 (only 2 general combiner stages)
4 RGB Inputs
Fragment Color
4 Alpha Inputs
General
Combiner
3 RGB Outputs
Specular Color
3 Alpha Outputs
Fog Color/Factor
4 RGB Inputs
4 Alpha Inputs
Register Set
General
Combiner 1
Texture 0
Texture
Fetching
3 RGB Outputs
3 Alpha Outputs
Texture 1
Spare 0
Specular Color
Final
Combiner
6 RGB Inputs
1 Alpha Input

21. Register Combiner (cont’d)
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

22. Diagram of a General Combiner
Input RGB, Alpha Registers
Input
Mappings
RGB Function
RGB
Scale/Bias
Next Combiner’s
RGB Registers A
A op1 B B
RGB
Portion
C op2 D C
AB op3 CD D
Input Alpha, Blue Registers
Input
Mappings
Alpha Function
Alpha
Scale/Bias
Next Combiner’s
Alpha Registers A AB
Alpha
Portion B CD C
AB op4 CD D

23. General Combiner Input Registers
Input RGB, Alpha Registers
Input
Mappings
RGB Function
RGB
Scale/Bias
Next Combiner’s
RGB Registers A
A op1 B B
RGB
Portion
C op2 D C
AB op3 CD D
Input Alpha, Blue Registers
Input
Mappings
Alpha Function
Alpha
Scale/Bias
Next Combiner’s
Alpha Registers A AB
Alpha
Portion B CD C
AB op4 CD D

24. 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
Zero
constant, read-only value of zero

25. General Combiner Input Mappings
Input RGB, Alpha Registers
Input
Mappings
RGB Function
RGB
Scale/Bias
Next Combiner’s
RGB Registers A
A op1 B B
RGB
Portion
C op2 D C
AB op3 CD D
Input Alpha, Blue Registers
Input
Mappings
Alpha Function
Alpha
Scale/Bias
Next Combiner’s
Alpha Registers A AB
Alpha
Portion B CD C
AB op4 CD D

26. 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]

27. General Combiner RGB Function
Input RGB, Alpha Registers
Input
Mappings
RGB Function
RGB
Scale/Bias
Next Combiner’s
RGB Registers A
A op1 B B
RGB
Portion
C op2 D C
AB op3 CD D
Input Alpha, Blue Registers
Input
Mappings
Alpha Function
Alpha
Scale/Bias
Next Combiner’s
Alpha Registers A AB
Alpha
Portion B CD C
AB op4 CD D

28. General Combiner RGB Functions
Dot / Dot / Discard
Dot / Mult / Discard
Mult / Dot / Discard A A A
A • B
A • B AB B B B
C • D CD
C • D C C C D D D
Mult / Mult / Mux
Mult / Mult / Sum A A AB AB B B CD CD C C
mux(AB, CD)
AB + CD D D
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])

29. Diagram of the Final Combiner (OpenGL only)
Input RGB, Alpha Registers
Available
RGB Inputs
Input
Mappings
RGB Function
Input
Mappings A
Multiplier E EF B F
RGB
Portion
AB + (1-A)C + D
RGB
Out
Color Sum Unit
Clamp to [0, 1] C
Spare0
Sum
2nd-ary
Color D
Input Alpha, Blue Registers
Input
Mapping
Alpha
Portion
Alpha
Out