Shader

In computer graphics, a shader is a type of computer program that was originally used for shading (the production of appropriate levels of light, darkness, and color within an image) but which now performs a variety of specialized functions in various fields of computer graphics special effects or does video post-processing unrelated to shading, or even functions unrelated to graphics at all. In computer graphics, a shader is a type of computer program that was originally used for shading (the production of appropriate levels of light, darkness, and color within an image) but which now performs a variety of specialized functions in various fields of computer graphics special effects or does video post-processing unrelated to shading, or even functions unrelated to graphics at all. Shaders calculate rendering effects on graphics hardware with a high degree of flexibility. Most shaders are coded for a graphics processing unit (GPU), though this is not a strict requirement. Shading languages are usually used to program the programmable GPU rendering pipeline, which has mostly superseded the fixed-function pipeline that allowed only common geometry transformation and pixel-shading functions; with shaders, customized effects can be used. The position, hue, saturation, brightness, and contrast of all pixels, vertices, or textures used to construct a final image can be altered on the fly, using algorithms defined in the shader, and can be modified by external variables or textures introduced by the program calling the shader. Shaders are used widely in cinema postprocessing, computer-generated imagery, and video games to produce a very wide range of effects. Beyond just simple lighting models, more complex uses include altering the hue, saturation, brightness or contrast of an image, producing blur, light bloom, volumetric lighting, normal mapping for depth effects, bokeh, cel shading, posterization, bump mapping, distortion, chroma keying (so-called 'bluescreen/greenscreen' effects), edge detection and motion detection, psychedelic effects, and many others. The modern use of 'shader' was introduced to the public by Pixar with their 'RenderMan Interface Specification, Version 3.0' originally published in May 1988. As graphics processing units evolved, major graphics software libraries such as OpenGL and Direct3D began to support shaders. The first shader-capable GPUs only supported pixel shading, but vertex shaders were quickly introduced once developers realized the power of shaders. The first video card with programmable pixel shader was the Nvidia GeForce 3 (NV20), released in 2001. Geometry shaders were introduced with Direct3D 10 and OpenGL 3.2. Eventually graphics hardware evolved toward a unified shader model. Shaders are simple programs that describe the traits of either a vertex or a pixel. Vertex shaders describe the traits (position, texture coordinates, colors, etc.) of a vertex, while pixel shaders describe the traits (color, z-depth and alpha value) of a pixel. A vertex shader is called for each vertex in a primitive (possibly after tessellation); thus one vertex in, one (updated) vertex out. Each vertex is then rendered as a series of pixels onto a surface (block of memory) that will eventually be sent to the screen. Shaders replace a section of the graphics hardware typically called the Fixed Function Pipeline (FFP), so-called because it performs lighting and texture mapping in a hard-coded manner. Shaders provide a programmable alternative to this hard-coded approach. The basic graphics pipeline is as follows: The graphic pipeline uses these steps in order to transform three-dimensional (or two-dimensional) data into useful two-dimensional data for displaying. In general, this is a large pixel matrix or 'frame buffer'.