Pixel Shader

Fragment shaders

Fragment shaders, also known as pixel shaders, compute color and other attributes of each "fragment": a unit of rendering work affecting at most a single output pixel. The simplest kinds of pixel shaders output one screen pixel as a color value; more complex shaders with multiple inputs/outputs are also possible. Pixel shaders range from simply always outputting the same color, to applying a lighting value, to doing bump mapping, shadows, specular highlights, translucency and other phenomena. They can alter the depth of the fragment (for Z-buffering), or output more than one color if multiple render targets are active. In 3D graphics, a pixel shader alone cannot produce some kinds of complex effects because it operates only on a single fragment, without knowledge of a scene's geometry (i.e. vertex data). However, pixel shaders do have knowledge of the screen coordinate being drawn, and can sample the screen and nearby pixels if the contents of the entire screen are passed as a texture to the shader. This technique can enable a wide variety of two-dimensional postprocessing effects such as blur, or edge detection/enhancement for cartoon/cel shaders. Pixel shaders may also be applied in intermediate stages to any two-dimensional images—sprites or textures—in the pipeline, whereas vertex shaders always require a 3D scene. For instance, a pixel shader is the only kind of shader that can act as a postprocessor or filter for a video stream after it has been rasterized.