Hi I''ve heard that Doom3 uses 4 kinds of textures: Texture Itself, Normal Map, Specular Map, Diffuse Map. What exactly are the Specular and the Diffuse map used for? Thx

Easy: these are textures that maps the specular and diffuse components !

Well if you just overlay those, some parts are brighter but that doesnt make them specular for example

Specular is not a simple texture "added" statically. This is mapped in realtime (just like GL_SPHERE_MAP) so that you really think you''re seing a specular highlight.

You can try it easily by using a radial texture mapped with GL_SPHERE_MAP : it''s pretty impressive the specular feeling it gives.

You can look an example of the sphere map trick in the third demo of this page : http://opengl.nutty.org/extensions

sphere mapping is really a simple mapping and better mappings exist, but I think it''s a very good start.