|Microsoft DirectX 9.0|
The IVideoWindow plug-in distributor (PID) in the filter graph manages full-screen playback. It will swap a video renderer out for a specialist full-screen renderer, stretch a window of a renderer to full screen, or have the renderer implement full-screen playback directly. To interact in full-screen protocols, a video renderer should send an EC_ACTIVATE notification whenever its window is either activated or deactivated. In other words, an EC_ACTIVATE notification should be sent for each WM_ACTIVATEAPP message a renderer receives.
When a renderer is being used in full-screen mode, these notifications manage the switching into and out of that full-screen mode. Window deactivation typically occurs when a user presses ALT+TAB to switch to another window, which the DirectShow full-screen renderer uses as a cue to return to typical rendering mode.
When the EC_ACTIVATE notification is sent to the Filter Graph Manager upon switching out of full-screen mode, the Filter Graph Manager sends an EC_FULLSCREEN_LOST notification to the controlling application. The application might use this notification to restore the state of a full-screen button, for example. The EC_ACTIVATE notifications are used internally by DirectShow to manage full-screen switching on cues from the video renderers.