This message is sent when Windows or an application makes a request to repaint a portion of an application's window. The message is sent either when the UpdateWindow function is called or by the DispatchMessage function when the application obtains a WM_PAINT message by using the GetMessage or PeekMessage function.
wParam
This parameter is not used.
lParam
This parameter is not used.
DispatchMessage, GetMessage, PeekMessage, UpdateWindow