What exactly does the doflip option in dxdraw do? I assume it enables the double buffering so everything is drawn offscreen before a dxdraw.flip call is performed.

However I have a problem on one machine (on vista but works okay on another with vista) in fullscreen mode.

My tile based game scrolls super smoothly in fullscreen without doflip switched on but with it on significally slows down the scrolling and makes it jerky. In windowed mode they are both pretty smooth.

Any ideas what could cause this?