This is a shader technique used for approximating specular highlights. Most phong derivatives use a specular power and the power function is one of the more expensive operations in shaders. That's why Christophe Schlick proposed a way to approximate this effect in his paper. He goes into a few other approximations that can be made which are honestly pretty slick, but I'm focusing on the specular here.
Here we have Schlick's specular on the left and phong on the right both with a "specular power" of 40. As you can see the highlight spreads out somewhat but the core follows essentially the same shape as with phong. Some might even find this preferable to phong, as perfectly sharp highlights can seem artificial. The cool thing is this technique could be applied to other things that use power as well, which could save you some instructions to spend elsewhere. For example, this should work equally well for a blinn shader.
Maya CGFX File:
| schlickspecular.cgfx |
Unity SHADER File:
| schlickspecular.shader |
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