I use CreateOffscreenPlainSurface(), GetBackBuffer(), and StretchRect(). I wrote Render() function. It creates bitmap into surface. Use StretchRect() to copy from surface to backbuffer before Present() displays the backbuffer to the screen. What happen if I press ALT-TAB? The full screen lost the focus when it is now in the windowed screen. I tried to use TestCooperativeLevel() and Reset(). The windowed screen won't switch to the full screen. The entire black rect is still in windowed border. My question is. Do I have to release backbuffer and surface before invokes Reset() and then recreate surface and backbuffer? Correct? Thanks...