The position and color ( hue, saturation, brightness, and contrast) of all pixels, vertices, and/or textures used to construct a final rendered image can be altered using algorithms defined in a shader, and can be modified by external variables or textures introduced by the computer program calling the shader. Shading languages are used to program the GPU's rendering pipeline, which has mostly superseded the fixed-function pipeline of the past that only allowed for common geometry transforming and pixel-shading functions with shaders, customized effects can be used. Most shaders are coded for (and run on) a graphics processing unit (GPU), though this is not a strict requirement. Traditional shaders calculate rendering effects on graphics hardware with a high degree of flexibility. They now perform a variety of specialized functions in various fields within the category of computer graphics special effects, or else do video post-processing unrelated to shading, or even perform functions unrelated to graphics. In computer graphics, a shader is a type of computer program originally used for shading in 3D scenes (the production of appropriate levels of light, darkness, and color in a rendered image). This shader works by replacing all light areas of the image with white, and all dark areas with a brightly colored texture. The unaltered, unshaded image is on the left, and the same image has a shader applied on the right. Another use of shaders is for special effects, even on 2D images, e.g.

Shader model 3.0 graphics card