Basic OpenGL lighting question

4
votes

I think this is an extremely stupid and newbie question, but then I am a newbie in graphics and openGL. Having drawn a sphere and put a light source nearby, also having specified ambient light, I started experimenting with light and material values and came to a surprising conclusion: the colors which we specify with glColor* do not matter at all when lighting is enabled. Instead, the equivalent is the material's ambient component. Is this conclusion correct? Thanks

2
c++opengllighting

2 Answers

5
votes

If the lighting is enabled, then instead of the vertex color, the material color (well, colors - there are several of them for different types of response to light) is used. Material colors are specified by glMaterial* functions.

If you want to reuse your code, you can use glEnable(GL_COLOR_MATERIAL) and glColorMaterial(GL_AMBIENT_AND_DIFFUSE) to have your old glColor* calls mapped to material color automatically.

(And please switch to shaders as fast as possible - the shader approach is both easier and more powerful)

3
votes

I suppose you don't use fragment shader yet. From glprogramming.com:

vertex color =
    the material emission at that vertex + 
    the global ambient light scaled by the materials ambient
    property at that vertex + 
    the ambient, diffuse, and specular contributions from all the
    light sources, properly attenuated

So yes, vertex color is not used.

Edit: You can also look for GL lightning equation in GL specification (you have one nearby, do you? ^^)