The current mode for drawing the alpha map (black to white indicating alpha values) is endian-dependent, causing problems on non-ppc computers. In those cases, the red component is used, rather than the alpha component.

This (rather hackish) patch draws a white image alpha-blended over a black image, simulating the drawing of the alpha channel as luminance. It works, but it involves a lot of openGL state changes.

Right now, it's basically drawing the original image, with scale and bias settings to make it draw black / white when needed. I figured it was faster than trying to extract the alpha chanel.