Cg programming language
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Cg or C for Graphics is a High level shader language created by NVIDIA for programming vertex and pixel shaders.
Cg is based on the C programming language and although they share the same syntax, some features of C were modified and new data types were added to make Cg more suitable for programming graphics processing units.
Background
As a result of technical advancements in graphics cards, some areas of 3D graphics programming have become quite complex. To simplify the process, new features were added to graphics cards, including the ability to modify their rendering pipelines using vertex and pixel shaders.In the beginning, vertex and pixel shaders were programmed at a very low level with only the assembly language of the graphics processing unit. Although using the assembly language gave the programmer complete control over code and flexibility, it was fairly hard to use. A portable, higher level language for programming the GPU was needed, so Cg was created to overcome these problems and make shader development easier.
Some of the benefits of using Cg over assembly are:
- High level code is easier to learn, program, read, and understand than assembly code.
- Cg code is portable to a wide range of hardware and platforms, unlike assembly code, which usually depends on hardware and the platforms it's written for.
- The Cg compiler can optimize code and do lower level tasks automatically, which are hard to do and error prone in assembly.
Details
Data types
Cg has six basic data types, some of them are the same as in C, others are especially added for GPU programming, these types are:- float - a 32bit floating point number
- half - a 16bit floating point number
- int - a 32bit integer
- fixed - a 12bit fixed point number
- bool - a boolean variable
- sampler* - represents a texture object
Operators
Cg supports a wide range of operators, including the common arithmetic operators from C, the equivalent arithmetic operators for vector and matrix data types, and the common logical operators.Functions and control structures
Cg shares the basic control structures with C, like if/else, while, and for. It also has a similar way of defining functions.The standard Cg library
As in C, Cg features a set of functions for common tasks in GPU programming. Some of the functions have equivalents in C, like the mathematical functions abs and sin, while others are specialized in GPU programming tasks, like the texture mapping functions tex1D and tex2D.The Cg runtime library
Cg programs are merely vertex and pixel shaders, and they need supporting programs that handle the rest of the rendering process, Cg can be used with two APIs, OpenGL or DirectX, each has its own set of Cg functions to communicate with the Cg program, like setting the current Cg shader, passing parameters, and such tasks.A sample Cg vertex shader
// input vertex struct VertIn ;
// output vertex struct VertOut ;
// vertex shader main entry VertOut main(VertIn IN, uniform float4x4 modelViewProj)
Applications and games that use Cg
- Far Cry
- PlayStation 3 compatibility
- Crystal Space
- OGRE
- Virtools Dev
Further reading
- Randima Fernando, Mark J. Kilgard, The Cg Tutorial: The Definitive Guide to Programmable Real-Time Graphics, Addison-Wesley Professional, ISBN 0-32119-496-9
- Randima Fernando, GPU Gems: Programming Techniques, Tips, and Tricks for Real-Time Graphics, Addison-Wesley Professional, ISBN 0-32122-832-4
- William R. Mark, R. Steven Glanville, Kurt Akeley, Mark J. Kilgard, [Cg: A System for Programming Graphics Hardware in a C-like Language], [Proceedings of SIGGRAPH 2003].
- Mark J. Kilgard, [Cg in Two Pages], 2003.
See also
- Computer programming
- Computer graphics
- Vertex and pixel shaders
- High level shader language
- OpenGL shading language
- Shader Model
- OpenGL
- DirectX
External links
- [Cg in Two Pages]
- [NVIDIA]
- [Cg home page]
- [OpenGL home page]
- [DirectX home page]
- [CgShaders.org]
- [NeHe Cg vertex shader tutorial]
- [Far Cry]
- [A glimpse at Cg Shader Toolkit]
- [Virtools]
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