Flip swaps the primary surface and the backbuffer surface.
void __fastcall Flip();
Description
Use Flip to copy the backbuffer surface to the screen. In exclusive mode, Flip swaps the primary and the backbuffer surfaces. In debug mode, Flip just copies the backbuffer surface to the screen. So the function does two different things in the two different modes.
In most cases, you will just want to copy the backbuffer to the screen, and forget about the fact that in exclusive mode Flip changes the primary and the backbuffer surfaces. Therefore you usually need to call BackSurface->Paint(), which repaints the backbuffer surface, between two calls to Flip. If you're doing so, the behavior of the exclusive mode and the debug mode are gonna be the same.
Sometimes, however, you really want to change between the two surfaces. In this case, first paint the first surface, then call Flip. Next, paint the second surface. Finally, call Flip to change between the two surfaces. This can only be done in exclusive mode.