What blending mode should I use for transparent fog? I set the fog color to 1.0, 1.0, 1.0, 0.0, then:

glClear
Translate camera
draw skybox with fog disabled
draw terrain with fog enabled

OpenGL fog doesn't require blending to be enabled, and isn't affected by the blend function.

Are you referring to the different fog functions that OpenGL gives you? I would start with GL_LINEAR (I think it's faster.) It'll probably look fine. But if things bother you about it, or you are concerned with approximating the physical world, then it might be worth looking at the two exponential functions. I just found a good explanation of them here:

http://www.sgi.com/software/opengl/advan...de122.html