problem with linear fog - can't set the start and the end value

The fog works OK in GL_LINEAR mode. But if I modify the frustum the GL_FOG_END and GL_FOG_START parameters dont work! What ever I do the fog-end and fog-start are not realy setted to the values. Sometimes there is everywhere a little bit fog but no end and sometimes there is a thick wall of fog what hide my polys behind a short distance.

How can I configurate the end and start with my modified frustum? (or is the problem somewhere else?)

Well, do you want the fog to anways end at the far clipping plane, and always start at the near plane, or what?

If so, then aftear each call to glFrustum, you call…

glFogf(GL_FOG_END, far);

… where near is the near plane, and far is the far plane, as specified in glFurstum(). Then you will always have the fog starting at the near plane, and end at the far plane.