Hello I found how to render using cel-shading (http://www.gamedev.net/reference/programming/features/celshading/) but there were some thinks in the algorithm that i didn't completly like. 1- You have to paint 2 timers every primitive. 2- You have to do lighting in the CPU, when GPU can handle it perfectly well. So, now that I've just started learning GLSL i'll try to code this in a shader. So... - how can I find if I'm at font face or at back face? - how can I increase the line width? (When I'm in a back face)

Strictly speaking, you're talking about edge determination or detection, not cel shading. Cel shading generally refers more to the color quantization process involving (typically) the diffuse lighting term as a lookup into a quantization texture.

Here's a paper on hardware-determined feature edges by Morgan McGuire. It's a pretty good basic technique.

well... I didn't understand it so much... (I'm not english, so some tech papers are hard to understand for me)

I've tried



in my vertex shader, but it doesn't seems to work... what should I do?