Shaders can be thought of as a sequence of programming codes that tells a computer how an image should be drawn. Different shaders govern different properties of an image. For example, Vertex Shaders give properties such as position, color, and UV coordinates for individual vertices. Another important purpose of vertex shaders is to transform vertices with 3D coordinates into the 2D screen space for display. Pixel shaders processes pixels to provide color, z-depth, and alpha value information. Geometry shader is responsible for processing data at the level of a primitive (triangle, line, and vertex).
Data information from an image is passed from one shader to the next for processing before they are finally output through a frame buffer.
Shaders are also used to incorporate post-processing effects such as Volumetric Lighting, HDR, and Bloom effects to accentuate images in a game.
The language which shaders are programmed in depends on the target environment. For Direct3D, the official...