You could probably use TBitmap.Scanline - I'm not sure how glBitmap works, though, so I can't give you much more info . Make sure that you set your bitmap's PixelFormat to the relevant value too (pf32Bit or whatever is required for glBitmap) - ScanLine gets a bit annoyed if the pixelformat is the default, pfDevice.

You'd want to pass in the address of the first pixel of the first scanline, I suppose. I'm not sure how the bitmap's orientation (top-down or bottom-up scanlines) would come into the equation either.

I'm sure someone else around here has more insight than me on this. I'll defer to the next poster. Huzzah for vague posts!