GDI and openGL etc.

Hi guys.

Somtimes i get a black region buffer when i use:
glReadPixels(0, 0, w, h, GL_BGR, GL_UNSIGNED_BYTE, mem);

Anyone ?

Anyone tried to syncronize GDI and opengl.
I hate the GDI flickering and then it would be possible to just blit the window canvas. This would be much faster than glReadPixels.