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Cooperative levels describe how DirectDraw interacts with the display and how it reacts to events that might affect the display. Use the IDirectDraw4::SetCooperativeLevelmethod 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:
- Prevent DirectDraw from releasing exclusive control of the display.
- 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.
Because applications can use DirectDraw with multiple windows, IDirectDraw4::SetCooperativeLeveldoes 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.
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, 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 palette.
DirectDraw takes control of window activation events for full-screen, exclusive mode applications, sending WM_ACTIVATE messages to the window handle registered through the SetCooperativeLevelmethod as needed. DirectDraw only sends activation events to the top-level window. If your application creates child windows that require activation event messages, it is your responsibility to subclass the child windows.
SetCooperativeLevelmaintains a binding between a process and a window handle. If SetCooperativeLevelis 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 DirectDrawthey should specify the same, top-level application window handle.
See Also
Last updated on Tuesday, May 18, 2004