rem: BRect screenFrame = (BScreen(window).Frame());
add: BRect screenFrame = BScreen(window).Frame();
context: center_on_screen(BRect rect, BWindow *window = NULL){	BRect screenFrame = (BScreen(window).Frame());	BPoint point((screenFrame.Width() - rect.Width()) / 2.0,		(screenFrame.Height() - rect.Height()) / 2.0);	if(!screenFrame.Contains(point))		point.Set(0, 0);		return point;}