$gdkWin = $gtkWin->get_window();
$winXid = $gdkWin->get_xid();
	
$wnckScreen->force_update();
foreach my $wnckWin ($wnckScreen->get_windows()) {
    my $wnckWinXid = $wnckWin->get_xid();
    if ($wnckWinXid && $wnckWinXid eq $winXid) {
        ...
}