The framework calls this member function for a minimized (iconic) CWnd object when the background of the icon must be filled before painting the icon.
CWnd receives this call only if a class icon is defined for the window default implementation; otherwise OnEraseBkgnd is called.
The DefWindowProc member function fills the icon background with the background brush of the parent window.
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.