internal override void ScreenToClient(IntPtr handle, ref int x, ref int y) {
int dest_x_return;
int dest_y_return;
IntPtr child;
Hwnd hwnd;
hwnd = Hwnd.ObjectFromHandle(handle);
lock (XlibLock) {
XTranslateCoordinates (DisplayHandle, RootWindow, hwnd.client_window, x, y, out dest_x_return, out dest_y_return, out child);
}
x = dest_x_return;
y = dest_y_return;
}