Testing Cooperative Levels
Developers often use messages such as WM_ACTIVATE as notification that their applications should restore or re-create the surfaces being used. In some cases, applications take action when they do not need to, or do not take action when they should.
The IDirectDraw::TestCooperativeLevel method makes it possible for your application to retrieve more information about the DirectDraw object's cooperative level and take appropriate steps to continue execution without mishap.
The TestCooperativeLevel method succeeds, returning DD_OK, if your application can restore its surfaces (if it has not already done so) and continue to execute. Failure codes, on the other hand, are interpreted differently depending on the cooperative-level your application uses.
Windowed applications
Windowed applications (those that use the normal cooperative level) receive DDERR_EXCLUSIVEMODEALREADYSET if another application has taken exclusive device access.
In this case, no action should be taken until the application with exclusive access loses it.
This situation is similar to the case for a full-screen application; a windowed application might loop until TestCooperativeLevel returns DD_OK before restoring and reloading its surfaces. As mentioned previously, in a loop like this applications should avoid unnecessarily using CPU cycles by relinquishing CPU control periodically during the loop.
The TestCooperativeLevel method returns DDERR_WRONGMODE to windowed applications when the display mode has changed. In this case, the application should destroy and re-create any surfaces before continuing execution.
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