What's it all about?The fundamental geometry for cosine shading calculations is illustrated here. In this scheme the shading variation depends on the variation in the angle between the surface normal and the impinging light rays. A difficulty arises from the fact that this geometry varies across each polygon in the object. In theory we should perform this calculation at each point on the surface of each polygon. While this may be acceptable under some circumstances, it is desirable to find simplifications for the calculation.
The most straight-forward simplification is to assume that the light source is so far away that we need calculate the angle theta only once.
Last updated: October, 2014