The framework calls this member function when the mouse cursor moves.
If the mouse is not captured, the WM_MOUSEMOVE message is received by the CWnd object beneath the mouse cursor; otherwise, the message goes to the window that has captured the mouse.
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.