Hi, I'm having a problem with onscreen and offscreen (double buffered) rendered images under Windows XP.
Whenever a window partially, or entirely overlaps the image glReadPixels returns black pixels, or often just garbage of those areas obscured.
Why does this happen? I thought glReadPixels returns pixels straight from the hardware (thought thats why it was known to be slow). If thats true, could it be a nasty trick from my cards manufacturer to speed up glReadPixels (i.e. not rasterize pixels that are underneath other windows)?
Any alternatives to glReadPixels? Or maybe I have to play some tricks on my window device context?