The graphics hardware maintains a graphical state consisting of the actual projection matrices and the actual color and texturing of 3D objects to be rendered. The 3D objects are usually made up from 3D geometric primitives, the most common of which is the triangle mesh.
The geometric primitives are processed in the so called computer graphics pipeline. The tasks of the pipeline is to
- define the scene as sequence of 3D points, the vertices, which have varying attributes like color, texture, normals, etc.
- transform the points from local and world coordinate systems into the camera coordinate system with a uniform model view matrix
- perspectively project the transformed points with a uniform projection matrix
- build geometric primitives from 3 or more consecutive points
- rasterize the projected primitives into so called fragments
- texture and blend the fragments
- display the resulting rgb pixels
The scheme above is called the fixed function pipeline.
Replacing Step 2 and 6 with a freely programmable vertex resp. fragment shader leads to the so called programmable pipeline.