【Phong Shading】

　　The most serious problem with Gouraud shading occurs when specular highlights are found in the middle of a large polygon. Since these specular highlights are absent from the polygon‘s vertices and Gouraud shading interpolates based on the vertex colors, the specular highlight will be missing from the polygon‘s interior. This problem is fixed by Phong shading.

　　相比Gouraud，Phong Shading能更好地解决镜面照问题。

　　Unlike Gouraud shading, which interpolates colors across polygons, in Phong shading a normal vector is linearly interpolated across the surface of the polygon from the polygon‘s vertex normals. The surface normal is interpolated and normalized at each pixel and then used in a reflection model, e.g. the Phong reflection model, to obtain the final pixel color. Phong shading is more computationally expensive than Gouraud shading since the reflection model must be computed at each pixel instead of at each vertex.

　　顶点色＝GlobalAmbient*kAmbientColor + LiVec*Normal*kDiffuseColor + RefVec*ViewVec*kSpecularColor

【Blinn-Phong】

　　相比于Phong，镜面光照公式改为下面这个：

　　MidVec*Normal*kSpecularColor。

　　MidVec指LiVec和ViewVec的中间向量。Blinn-Phong比Phong略快。

参考：

1、http://en.wikipedia.org/wiki/Phong_shading

2、http://en.wikipedia.org/wiki/Phong_reflection_model

3、http://en.wikipedia.org/wiki/Blinn%E2%80%93Phong_shading_model