internal override void Invalidate(IntPtr handle, Rectangle rc, bool clear) {
Hwnd hwnd;
hwnd = Hwnd.ObjectFromHandle(handle);
if (clear) {
AddExpose (hwnd, true, hwnd.X, hwnd.Y, hwnd.Width, hwnd.Height);
} else {
AddExpose (hwnd, true, rc.X, rc.Y, rc.Width, rc.Height);
}
}