High-level shader language

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 the same as the Nvidia Cg shading language, as it was developed alongside it.

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 coefficients 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 Direct3D 10 interface and Direct3D 10 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.

Shader model comparison

Pixel shader comparison

Pixel shader version	1.0 to 1.3	1.4	2.0	2.0a	2.0b	3.0	4.0
Dependent texture limit	4	6	8	Unlimited	8	Unlimited	Unlimited
Texture instruction limit	4	6*2	32	Unlimited	Unlimited	Unlimited	Unlimited
Position register	No	No	No	No	No	Yes	Yes
Instruction slots	8+4	8+4	32 + 64	512	512	≥ 512	≥ 65536
Executed instructions	8+4	6*2+8*2	32 + 64	512	512	65536	Unlimited
Texture indirections	4	4	4	Unlimited	4	Unlimited	Unlimited
Interpolated registers	2 + 8	2 + 8	2 + 8	2 + 8	2 + 8	10	32
Instruction predication	No	No	No	Yes	No	Yes	No
Index input registers	No	No	No	No	No	Yes	Yes
Temp registers	2	6	12 to 32	22	32	32	4096
Constant registers	8	8	32	32	32	224	16x4096
Arbitrary swizzling	No	No	No	Yes	No	Yes	Yes
Gradient instructions	No	No	No	Yes	No	Yes	Yes
Loop count register	No	No	No	No	No	Yes	Yes
Face register (2-sided lighting)	No	No	No	No	No	Yes	Yes
Dynamic flow control	No	No	No	No	No	24	Yes
Bitwise Operators	No	No	No	No	No	No	Yes
Native Integers	No	No	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."

Vertex shader comparison

Vertex shader version	VS 1.1	VS 2.0	VS 2.0a	VS 3.0	VS 4.0
# of instruction slots	128	256	256	≥ 512	4096
Max # of instructions executed	Unknown	65536	65536	65536	65536
Instruction predication	No	No	Yes	Yes	Yes
Temp registers	12	12	13	32	4096
# constant registers	≥ 96	≥ 256	≥ 256	≥ 256	16x4096
Static flow control	???	Yes	Yes	Yes	Yes
Dynamic flow control	No	No	Yes	Yes	Yes
Dynamic flow control depth	No	No	24	24	Yes
Vertex texture fetch	No	No	No	Yes	Yes
# of texture samplers	N/A	N/A	N/A	4	128
Geometry instancing support	No	No	No	Yes	Yes
Bitwise operators	No	No	No	No	Yes
Native integers	No	No	No	No	Yes

• VS 2.0 = DirectX 9.0 original Shader Model specification.
• VS 2.0a = NVIDIA GeForce FX-optimized model.
• VS 3.0 = Shader Model 3.
  • Note that ATI X1000 series cards (e.g. X1900) does not support Vertex Texture Fetch, hence it does not fully comply with the VS 3.0 model. Instead, they offer a feature called "Render to Vertex Buffer (R2VB)" that provides functionality that is a superset of Vertex Texture Fetch.^{[citation needed]}
• VS 4.0 = Shader Model 4.

See also

• GLSL

External links

• Programming Guide for HLSL, from Microsoft
• Introduction to the DirectX 9 High Level Shading Language, (ATI) AMD developer central
• Riemer's HLSL Introduction & Tutorial (includes sample code)
• Simple HLSL Shader Tutorial
• HLSL Introduction