The High Level Shader Language or High Level Shading Language (HLSL) is a proprietary shading language

Shading language

A shading language is a special programming language adapted to map on shader programming. Those kind of languages usually have special data types like color and normal...

 developed by Microsoft

Microsoft

Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...

 for use with the Microsoft Direct3D

Direct3D

Direct3D is part of Microsoft's DirectX application programming interface . Direct3D is available for Microsoft Windows operating systems , and for other platforms through the open source software Wine. It is the base for the graphics API on the Xbox and Xbox 360 console systems...

 API. It is analogous to the GLSL

GLSL

OpenGL Shading Language , is a high-level shading language based on the syntax of the C programming language...

 shading language used with the OpenGL

OpenGL

OpenGL is a standard specification defining a cross-language, cross-platform API for writing applications that produce 2D and 3D computer graphics. The interface consists of over 250 different function calls which can be used to draw complex three-dimensional scenes from simple primitives. OpenGL...

 standard. It is the same as the Nvidia

NVIDIA

Nvidia is an American global technology company based in Santa Clara, California. Nvidia is best known for its graphics processors . Nvidia and chief rival AMD Graphics Techonologies have dominated the high performance GPU market, pushing other manufacturers to smaller, niche roles...

 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

Rasterisation

Rasterisation is the task of taking an image described in a vector graphics format and converting it into a raster image for output on a video display or printer, or for storage in a bitmap file format....

. 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.

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
  GeForce FX
  The GeForce FX or "GeForce 5" series is a line of graphics processing units from the manufacturer NVIDIA.-Overview:...
  
  -optimized model.
• PS 2.0b = ATI Radeon X700, X800, X850
  Radeon R420
  The Radeon R420 core from ATI Technologies was the company's basis for its 3rd-generation DirectX 9.0/OpenGL 2.0-capable graphics cards. Used first on the Radeon X800, R420 was produced on a 0.13 micrometer low-K process and used GDDR-3 memory...
  
   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 Branch predication Branch predication is a strategy in computer architecture design for mitigating the costs usually associated with conditional branches, particularly branches to short sections of code...	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 Geometry instancing In real-time computer graphics, geometry instancing is the practice of rendering multiple copies of the same mesh in a scene at once. This technique is primarily used for objects such as trees, grass, or buildings which can be represented as repeated geometry without appearing unduly repetitive,...  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
  GeForce FX
  The GeForce FX or "GeForce 5" series is a line of graphics processing units from the manufacturer NVIDIA.-Overview:...
  
  -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.
• VS 4.0 = Shader Model 4.

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