ogl-problem

hi

i have a problem (ogl)
i have win xp and riva tnt

when i change resolution (changedisplaysettings) to 32 bpp i have acceleration and everything i ok
but when i change resolution to 24 bpp or 16 bpp i have no acceleration ogl (1 frame /20 sec)!
why?

i always setup ogl like this:

(pfd.dwFlags & PFD_SUPPORT_OPENGL) &&
(pfd.dwFlags & PFD_DRAW_TO_WINDOW) &&
(pfd.dwFlags & PFD_DOUBLEBUFFER) &&
(pfd.iPixelType == PFD_TYPE_RGBA) &&
(pfd.cColorBits >= 16) &&
(pfd.cStencilBits >= 8)

thanks

If you use stencil, only the 32 bit color resolution gives you 24 bits depth and 8 bits stencil in hardware with that chip.