You can set the display mode by using the IDirectDraw2::SetDisplayMode method. The SetDisplayMode method accepts four parameters that describe the dimensions, bit depth, and refresh rate of the mode to be set. The method uses a fifth parameter to indicate special options for the given mode; this is currently only used to differentiate between Mode 13 and the Mode X 320x200x8 display mode.
Although you can specify the desired display mode's bit depth, you cannot specify the pixel format that the display hardware will use for that bit depth. To determine the RGB bit masks that the display hardware uses for the current bit depth, call IDirectDraw2::GetDisplayMode after setting the display mode. If the current display mode is not palettized, you can examine the mask values in the dwRBitMask, dwGBitMask, and dwBBitMask members to determine the correct red, green, and blue bits. For more information, see Pixel Format Masks.
Modes can be changed by more than one application as long as they are all sharing a display card. You can change the bit depth of the display mode only if your application has exclusive access to the DirectDraw object. All DirectDrawSurface objects lose surface memory and become inoperative when the mode is changed. A surface's memory must be reallocated by using the IDirectDrawSurface3::Restore method.
The DirectDraw exclusive (full-screen) mode does not bar other applications from allocating DirectDrawSurface objects, nor does it exclude them from using DirectDraw or GDI functionality. However, it does prevent applications other than the one that obtained exclusive access from changing the display mode or palette.