The framework calls this member function to notify the window that is losing the mouse capture.
A window receives this message even if it calls ReleaseCapture itself. An application should not attempt to set the mouse capture in response to this message. When it receives this message, a window should redraw itself, if necessary, to reflect the new mouse-capture state.
See the Windows SDK for information on the ReleaseCapture Windows function.
This member function is called by the framework to allow your application to handle a Windows message. The parameters passed to your function reflect the parameters received by the framework when the message was received. If you call the base-class implementation of this function, that implementation will use the parameters originally passed with the message and not the parameters you supply to the function.