A reflectance model is a mathematical description of how incoming light is reflected from a surface.

A fairly general form is the bidirectional reflectance distribution function (BRDF)

• The 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.
• Note that each direction ω is itself parameterized by azimuth angle ϕ and zenith angle θ.

This 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

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