CG pioneer Jim Blinn wrote an excellent article which provides a myriad of ways to do it. http://dl.acm.org/citation.cfm?id=1435623.1436274 http://dl.acm.org/c

CG pioneer Jim Blinn wrote an excellent article which provides a myriad of ways to do it. http://dl.acm.org/citation.cfm?id=1435623.1436274 http://dl.acm.org/citation.cfm?id=1435623.1436274 It was republished in his excellent collection of essays "A Trip down the Graphics Pipeline"