High Level Shader Language

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The High Level Shader Language (HLSL) is a proprietary shading language developed by Microsoft for use with the Microsoft Direct3D API. It is in competition with GLSL shading language, but is not compatible with the OpenGL standard. It is very similar to the NVIDIA Cg shading language.

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 tesselate) additional triangles, which are each then sent to the rasterizer.

1 Shader model comparison
- 1.1 Pixel shader comparison
- 1.2 Vertex shader comparison
2 External links
3 Footnotes

[edit] Shader model comparison

[edit] Pixel shader comparison

	PS_2_0	PS_2_a	PS_2_b	PS_3_0	PS_4_0^[1]
Dependent texture limit	4	No Limit	4	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	Yes
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

PS_2_0 = DirectX 9.0 original Shader Model 2 specification.
PS_2_a = NVIDIA GeForce FX-optimized model.
PS_2_b = 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

	VS_2_0	VS_2_a	VS_3_0	VS_4_0^[1]
# 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	No	No	4	128
Geometry Instancing Support	No	No	Yes	Yes