Subdivision shading

The idea of Phong Shading is applied to subdivision surfaces: normals are associated with vertices and the same construction is used for both locations and normals. This creates vertex positions and normals. The vertex normals are smoother than the normals of the subdivision surface and using vertex normals for shading attenuates the well known visual artifacts of many subdivision schemes. We demonstrate how to apply subdivision to normals and how blend and combine different normals for achieving a variety of effects.