On Windows the gamma ramp for cards with 2d / 3d hardware can 
in general be set using the Win32 functions SetDeviceGammaRamp 
and GetDeviceGammaRamp.

Some 3dfx cards, however, do not support these functions.  As of
December 1999, this category includes Voodoo 1, 2 and Rush.  The 
current drivers for these cards export the WGL_3DFX_gamma_control
extension; see the documents section of the site for more details.

This code can be used to set gamma values using SetDeviceGammaRamp
or wglSetDeviceGammaRamp3DFX:

(Thanks to Pete Sebor for the original code for this.  Any mistakes
in this version are mine.)

----------------------------------------------------------------------

Gamma is a floating point number in the range (e.g.) 0.0f to 2.0f.

pEntry is a WORD* pointer to one of the component gamma arrays
(red, green or blue)

for (dcSint32 idx=0; idx<256; idx++)
	{
	*pEntry = min(65535, max(0, pow((idx+1) / 256.0, Gamma) * 65535 + 0.5));

	pEntry++;
	}

----------------------------------------------------------------------