This message is sent to a minimized (iconic) window when the background of the icon must be filled before painting the icon. A window receives this message only if a class icon is defined for the window. Otherwise, WM_ERASEBKGND is sent instead. Passing this message to the DefWindowProc function permits Windows to fill the icon background with the background brush of the parent window.
wParam
Contains the device-context handle of the window.
lParam
This parameter is not used.
WM_ERASEBKGND