http://nehe.gamedev.net/lesson.asp?index=08 Here's Nehe's code for cel shading, it's lesson 37 http://www.gamedev.net/reference/programming/features/celshading The gamedev article it's based on. http://www.red3d.com/cwr/npr/ NPR rendering theory. There's also a reference to a book that supposedly takes the cel shading further in its NPR chapter, but covers all kinds of real time rendering.