So far, we have explored various methods of mapping textures to models. However, eventually, we will meet complex surfaces that move or distort during an animation. In this circumstance, we require the textures to be mapped directly on the faces of the mesh rather than projected from some arbitrary point within the mesh. One area where this is extensively used is the simulation of skin, from the leathery exterior of a dinosaur to the ultimate nirvana of the human head.
Skin shading is one of the most difficult tasks for the 3D materials designer. Firstly, the models tend to be complex in shape with many varying angles that make standard texture projections such as flat, cube, sphere, and tube difficult because of distortion. Secondly, skin has a unique ability to scatter light within its surface, which is tricky to reproduce. Thirdly, when a UV map is wrapped around the object, seams will form where edges of the UV map meet.
Over the course of this chapter, we will work through...