Implementing per-vertex ambient, diffuse, and specular (ADS) shading

The OpenGL fixed function pipeline implemented a default shading technique which is very similar to the one presented here. It models the light-surface interaction as a combination of three components: ambient, diffuse, and specular. The ambient component is intended to model light that has been reflected so many times that it appears to be emanating uniformly from all directions. The diffuse component was discussed in the previous recipe, and represents omnidirectional reflection. The specular component models the shininess of the surface and represents reflection around a preferred direction. Combining these three components together can model a nice (but limited) variety of surface types. This shading model is also sometimes called the Phong reflection model (or Phong shading model), after Bui Tuong Phong.

An example of a torus rendered with the ADS shading model is shown in the following screenshot:

The ADS model is...