Evolutionary Design of BRDFs

Abstract

The look of a non-transparent material is determined by its bidirectional reflection distribution function (BRDF). To design 3-D objects for example for games or animation films thus includes to design BRDFs. However, as functions defined on a four-dimensional domain, these form a vast space that is very difficult to explore interactively. Typically, the infinite number of degrees of freedom is reduced to a tractable handful of parameters by introducing simplified physical models or heuristic approximations such as Phongs. As the complexity of such approaches increases, they become difficult to master for a human operator. Even if many parameters are made accessible, an infinite variety of useful and/or interesting BRDFs remains hidden and inaccessible. We therefore propose a method of constructing BRDFs through genetic programming with a human operator making choices based on his or her preferences. With the pixel shader programmability of modern graphics cards this can be performed in real time.