DirectX 8 and GeForce3

1
DirectX 8 and GeForce3
Christian Schär Sacha Saxer
2
Overview

• DirectX
• Direct3D 8
• Vertex Shader
• Pixel Shader
• Hardware Support
• Conclusions
• Future

3
DirectX Components

• DirectDraw
• Direct3D
• DirectSound
• DirectMusic
• DirectShow
• DirectInput
• DirectPlay

2D Graphics API 3D Graphics API Sound
API Music API Multimedia Streams API Input
API Network API
4
Direct3D

• Hardware Abstraction Layer
• Classic Rendering Pipeline
• Vertex Shader
• Pixel Shader
• D3DX

5
Hardware Abstraction Layer
6
Classic Rendering Pipeline
CreateVertexBuffer() SetVertexShader() SetStream
Source() DrawPrimitive()
7
Vertex Shader

• Small assembly language program
• Replaces the Transformation and Lighting Engine
• Responsible for World and View transformations
• Is executed once per vertex
• Has no neighborhood information
• Prepares data for the Pixel Shader

8
Modified Rendering Pipeline
9
Vertex Shader Architecture
16 Input registers (r/o) 96 Constant registers
(r/o) 12 Temp registers (r/w) 1 Address register
(w/o) Output registers Max. 128 instructions
10
Vertex Shader Assembly
Output oPos Position oTn Texture oDn Color oFog/o
Pts

• Input
• vn
• Vertex
• cn
• Constants
• an
• Address
• rn
• Temp

11
Vertex Shader Instructions

• mov r, s0
• add r, s0, s1
• sub r, s0, s1
• mul r, s0, s1
• mad r, s0, s1, s2
• rcp r, s0.w
• rsq r, s0.w

• copy
• sum
• difference
• multiply
• multiply-add
• reciprocal
• reciprocal sqrt

12
Vertex Shader Instructions

• dp3 r, s0, s1
• dp4 r, s0, s1
• min r, s0, s1
• max r, s0, s1
• slt r, s0, s1
• sge r, s0, s1

• 3D dot product
• 4D dot product
• per component
• per component
• 1.0 if less than
• 1.0 if greater/equal

13
Vertex Shader Instructions

• expp r, s0.w
• logp r, s0.w
• lit r, s0, s1
• dst r, s0, s1

• partial prec.
• partial prec.
• lighting fn
• distance fn

14
Register modifier

• Component Modifier
• r.x y z w
• r.xyzwxyzwxyzwxyzw
• -r

• Description
• Destination mask
• Source swizzle
• Source negation

15
Sample Vertex Shader

• vs.1.1
• m4x4 r0, v0, cCV_WORLD_0
• m4x4 oPos, r0, cCV_VIEWPROJ_0
• m3x3 r1, v3, cCV_WORLD_0
• dp3 r1.x, r1, cCV_LIGHT
• max r1.1, r1.x, cCV_ZERO.x
• mul r1, r1.x, cCV_DIFUSE
• add r1, r1, cCV_AMBIENT
• min r1, r1, cCV_ONE.x
• mov oD0.x, r1.x
• mov oD0.y, r1.x
• mov oD0.z, r1.x

16
Pixel Shader

• Small assembly language program
• Replaces the Texturing and Lighting Engine
• Is executed once per pixel
• Has no neighborhood information
• Does further calculations on the Vertex Shaders
  output
• The output is the color of the pixel

17
Modified Rendering Pipeline
18
Pixel Shader Architecture
Specular / Fog Computed
Dx8 Pixel Shaders
TexAddrOp 0
TexAddrOp 1
Alpha Blending
Triangle Rasterizer
8 Texture Blend Ops
TexAddrOp 2
TexAddrOp 3
19
Pixel Shader Assembly
Output rn Temp r0 Output color

• Input
• vn
• Vertex color
• tn
• Texture
• cn
• Constants

20
Pixel Shader Instructions

• mov r, s0
• add r, s0, s1
• sub r, s0, s1
• mul r, s0, s1
• mad r, s0, s1, s2

• copy
• sum
• difference
• multiply
• multiply-add

21
Pixel Shader Instructions

• dp3 r, s0, s1
• lrp r, s0, s1, s2
• cnd r, r0.a, s1, s2
• sub r0, v0, v1_biascnd r0, r0.a, c0, c1

• 3D dot product
• lin. interp. blend
• r r0.agt0.5 ? s1 s2
• r v0 gt v1 ? c0 c1

22
Texture Instructions

• tex t
• texbem t
• texbeml t, s
• texcoord t
• texkill t
• texm3x2pad t, s
• texm3x2tex t, s
• texm3x3pad t, s
• texm3x3tex t, s
• texm3x3spec t, s0, s1
• texm3x3vspec t, s
• texreg2ar t, s
• texreg2gb t, s

• normal sample
• bumped env. mapping
• with Luminance
• sample tex. coords.
• black, if coords lt 0
• Matrix multiplications
• refl. env. map.
• use s.ar as coords.
• use s.gb as coords.

23
Sample Texture Instructions

• tex t
• texm3x2pad t0, s
• texm3x2tex t1, s
• tex t0
• texm3x3pad t1, t0
• texm3x3pad t2, t0
• texm3x3spec t3, t0, c0
• mov r0, t3

• put texture col. into t
• 3x2 matrix multiplication
• get normal vector from t0
• eye-ray vector from c0
• cube env. texture from t3
• do env. mapping
• output color

24
Modifiers

• Component Modifier
• r.a rgb
• 1-r
• -r
• r_bias
• r_bx2

• Description
• Source/Destination mask
• Invert
• Negate
• -0.5
• -0.5, 2

25
Modifiers

• Instruction Modifier
• _x2
• _x4
• _d2
• _sat

• Description
• multiply result by 2
• multiply result by 4
• divide result by 2
• cramp result

26
Sample Pixel Shader

• ps.1.1
• tex t1
• mov r0, t1 use texture color
• mov r0.a, v0 get diffuse lighting from
• vertex interpolation

27
D3DX Mesh Optimizing

• adjacency required
• sort by attribute
• compact
• progressive meshes

28
D3DX Progressive Meshes

• different levels of detail (LOD)
• half edge collapse
• cloning by sharing of vertex buffers
• streamable
• save method
• OptimizeBaseLOD
• TrimByVertices/TrimByFaces

29
D3DX Skinned Meshes

• vertex data, bone data with vertex indices
• support for .X files
• export filters for Maya, 3D Studio Max available
• up to 4 indices per vertex
• up to 12 indices per face
• up to 256 bone palettes
• ConvertToBlendedMesh() reduces to this
  constraints
• ConvertToIndexBlendedMesh() same, but less
  subsets
• Uses GeForces restricted skinning support by
  rendering a prefix in hardware.

30
Conclusions

• very flexible tool
• hardware accelerated
• low level interface (assembly)
• vertex shaders theoretically applicable to
  point-sampled geometry
• rendering of shadows needs lots of work

31
Whats next?

• subdivision surfaces in hardware
• (TruForm technology by ATI)
• displacement maps

32
References

• MSDN (Microsoft Developer Network)
• NVIDIA Whitepapers
• Introduction to Vertex Shaders
• Introdction to Pixel Shaders
• http//msdn.microsoft.com/directx
• http//partners.nvidia.com/Developer