Robert L. Cook
Shade trees
Proceedings of the 11th annual conference on Computer graphics and interactive techniques, p.223-231, V18, #3, January 1984, pp 223-231.
ABSTRACT
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.