Implementing the Phong reflection model

In this recipe, we'll implement the well-known Phong reflection model. The OpenGL fixed-function pipeline's default shading technique was 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 glossy reflection around a preferred direction. Combining these three components together can model a nice (but limited) variety of surface types. This shading model is called the Phong reflection model (or Phong shading...