We introduce a physically plausible mathematical model for a large
class of BRDFs. The new model is as simple as the well-known Phong
model, but eliminates its disadvantages. It gives a good visual
approximation for many practical materials: coated metals, plastics,
ceramics, retro-reflective paints, anisotropic and retro-reflective
materials, etc. Because of its illustrative properties it can be used
easily in most commercial software and because of its low computational
cost it is practical for virtual reality. The model is based on a
special basic BRDF definition, which meets the requirements of
reciprocity and of energy conservation. Then a class of BRDFs is
constructed from this basic BRDF with different ent weight functions,
The definition of such weight functions requires the user to specify
the profile of the highlights,from which the weight function is
obtained by derivation. It is also demonstrated how importance sampling
can be used with the new BRDFs.
