Cooperative levels describe how DirectDraw interacts with the display and how it reacts to events that might affect the display. Use the IDirectDraw2::SetCooperativeLevel method to set cooperative level of DirectDraw. For the most part, you use DirectDraw cooperative levels to determine whether your application runs as a full screen program with exclusive access to the display or as a windowed application. However, DirectDraw cooperative levels can also have the following effects:
·Enable DirectDraw to use Mode X resolutions. For more information, see Mode X and Mode 13 Display Modes.
·Prevent DirectDraw from releasing exclusive control of the display or rebooting if the user presses CTRL + ALT + DEL (exclusive mode only).
·Enable DirectDraw to minimize or maximize the application in response to activation events.
The normal cooperative level indicates that your DirectDraw application will operate as a windowed application. At this cooperative level you won't be able to change the primary surface's palette or perform page flipping. Additionally, you won't be able to call some methods that drastically affect the display or video memory, such as IDirectDraw2::Compact.
At the full screen and exclusive cooperative level, you can use the hardware to its fullest. In this mode, you can set custom and dynamic palettes, change display resolutions, compact memory, and implement page flipping. The exclusive (full-screen) mode does not prevent other applications from allocating surfaces, nor does it exclude them from using DirectDraw or GDI. However, it does prevent applications other than the one currently with exclusive access from changing the display mode or palette.
Because applications can use DirectDraw with multiple windows, IDirectDraw2::SetCooperativeLevel does not require a window handle to be specified if the application is requesting the DDSCL_NORMAL mode. By passing a NULL to the window handle, all of the windows can be used simultaneously in normal Windows mode.
IDirectDraw2::SetCooperativeLevel maintains a binding between a process and a window handle. If IDirectDraw2::SetCooperativeLevel is called once in a process, a binding is established between the process and the window. If it is called again in the same process with a different non-null window handle, it returns the DDERR_HWNDALREADYSET error value. Some applications may receive this error value when DirectSound® specifies a different window handle than DirectDraw¾they should specify the same, top-level application window handle.
See also, Multiple Monitor Systems.