Robert L. Cook
Shading is an important part of computer imagery, but shaders have been based on fixed
models to which all surfaces must conform. As computer imagery becomes more
sophisticated, surfaces have more complex shading characteristics and thus require a less
rigid shading model. This paper presents a flexible tree-structured shading model that
can represent a wide range of shading characteristics. The model provides an easy
means for specifying complex shading characteristics. It is also efficient because
it can tailor the shading calculations to each type of surface.
Available in the Proceedings of SIGGRAPH 1984.