Another tangent (pun intended) before we look at wrinkle maps, is how to implement specular lighting—also known as specular highlight. So far I’ve only shown you how diffuse lighting works. Now with the normal maps in place it really pays off to also implement a specular lighting model. Specular lighting in real life is actually reflections of the light source on a surface. The shinier a surface is, the more the light source will reflect in it.
A specular highlight is dependent on where the viewer or camera is located in the world. The specular highlight will appear on the model where the surface normal is pointing halfway between the incoming light and the incoming view direction, as shown in Figure 12.10.