reflectance model is a mathematical description of how incoming light is
reflected from a surface.
fairly general form is the bidirectional reflectance
BRDF is a four-dimensional function that models the amount of light reflected
at an opaque surface point. The BRDF
returns the ratio of reflected radiance exiting along a
direction ωo to
the irradiance incident on the surface from direction ωi.
that each direction ω is itself parameterized by azimuth
angle ϕ and zenith angle θ.
4D model is rather complex for a real-time computer game. We would prefer a simpler model, and numerous
have been proposed in the field of computer graphics.Source: dlib.org