Before learning the full Phong reflection model, we'll start with just one part: diffuse reflection. It is a simple reflection model that makes the assumption that the surface exhibits purely diffuse reflection. That is to say that the surface appears to scatter light in all directions equally, regardless of direction.
Incoming light strikes the surface and penetrates slightly before being reradiated in all directions. Of course, the incoming light interacts with the surface before it is scattered, causing some wavelengths to be fully or partially absorbed and others to be scattered. A typical example of a diffuse surface is a surface that has been painted with a matte paint. The surface has a dull look with no shine at all.
The following image shows a torus rendered with diffuse shading:
The mathematical...
