High Level Shader Language
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The High Level Shader Language or High Level Shading Language (HLSL) is a proprietary shading language developed by Microsoft for use with the Microsoft Direct3D API. It is analogous to the GLSL shading language used with the OpenGL standard. It is very similar to the NVIDIA Cg shading language, as it was developed alongside it.[1]
HLSL programs come in three forms, vertex shaders, geometry shaders, and pixel (or fragment) shaders. A vertex shader is executed for each vertex that is submitted by the application, and is primarily responsible for transforming the vertex from object space to view space, generating texture coordinates, and calculating lighting coefficents such as the vertex's tangent, binormal and normal vectors. When a group of vertices (normally 3, to form a triangle) come through the vertex shader, their output position is interpolated to form pixels within its area, this process is known as rasterisation. Each of these pixels comes through the pixel shader, whereby the resultant screen colour is calculated.
Optionally, an application using a Direct3D10 interface and Direct3D10 hardware may also specify a geometry shader. This shader takes as its input the three vertices of a triangle and uses this data to generate (or tessellate) additional triangles, which are each then sent to the rasterizer.
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[edit] Shader model comparison
[edit] Pixel shader comparison
| Pixel shader version | 2.0 | 2.0a | 2.0b | 3.0[2] | 4.0[3] |
|---|---|---|---|---|---|
| Dependent texture limit | 8 | No Limit | 8 | No Limit | No Limit |
| Texture instruction limit | 32 | Unlimited | Unlimited | Unlimited | Unlimited |
| Position register | No | No | No | Yes | Yes |
| Instruction slots | 32 + 64 | 512 | 512 | ≥ 512 | ≥ 65536 |
| Executed instructions | 32 + 64 | 512 | 512 | 65536 | Unlimited |
| Texture indirections | 4 | No limit | 4 | No Limit | No Limit |
| Interpolated registers | 2 + 8 | 2 + 8 | 2 + 8 | 10 | 32 |
| Instruction predication | No | Yes | No | Yes | No |
| Index input registers | No | No | No | Yes | Yes |
| Temp registers | 12 | 22 | 32 | 32 | 4096 |
| Constant registers | 32 | 32 | 32 | 224 | 16x4096 |
| Arbitrary swizzling | No | Yes | No | Yes | Yes |
| Gradient instructions | No | Yes | No | Yes | Yes |
| Loop count register | No | No | No | Yes | Yes |
| Face register (2-sided lighting) | No | No | No | Yes | Yes |
| Dynamic flow control | No | No | No | 24 | Yes |
| Bitwise Operators | No | No | No | No | Yes |
| Native Integers | No | No | No | No | Yes |
- PS 2.0 = DirectX 9.0 original Shader Model 2 specification.
- PS 2.0a = NVIDIA GeForce FX-optimized model.
- PS 2.0b = ATI Radeon X700, X800, X850 shader model, DirectX 9.0b.
- PS 3.0 = Shader Model 3.
- PS 4.0 = Shader Model 4.
"32 + 64" for Executed Instructions means "32 texture instructions and 64 arithmetic instructions."
[edit] Vertex shader comparison
| Vertex shader version | VS 2.0 | VS 2.0a | VS 3.0[2] | VS 4.0[3] |
|---|---|---|---|---|
| # of instruction slots | 256 | 256 | ≥ 512 | 4096 |
| Max # of instructions executed | 65536 | 65536 | 65536 | 65536 |
| Instruction Predication | No | Yes | Yes | Yes |
| Temp Registers | 12 | 13 | 32 | 4096 |
| # constant registers | ≥ 256 | ≥ 256 | ≥ 256 | 16x4096 |
| Static Flow Control | Yes | Yes | Yes | Yes |
| Dynamic Flow Control | No | Yes | Yes | Yes |
| Dynamic Flow Control Depth | No | 24 | 24 | Yes |
| Vertex Texture Fetch | No | No | Yes | Yes |
| # of texture samplers | N/A | N/A | 4 | 128 |
| Geometry instancing support | No | No | Yes | Yes |
| Bitwise Operators | No | No | No | Yes |
| Native Integers | No | No | No | Yes |
- VS 2.0 = DirectX 9.0 original Shader Model 2 specification.
- VS 2.0a = NVIDIA GeForce FX-optimized model.
- VS 3.0 = Shader Model 3.
- VS 4.0 = Shader Model 4.
