$fill_x->configure(-command => sub {
    $_->configure(-state => 'disabled') for $fill_x, $fill_y;
    my $ms = 50 * (1 + int rand 10);
    my $iters = 1 + int rand 100;
    my $iter = 0;
    my $id;
    my $label = 'LABEL';
    $id = $mw->repeat($ms, sub {
        if (++$iter <= $iters) {
            text_show($text,
                sprintf "\r%s%4d/%4d [%s]",
                    $label, $iter, $iters, '=' x $iter
            );
        }
        else {
            text_show($text, "\nDone!\n");
            $id->cancel;
            $_->configure(-state => 'normal') for $fill_x, $fill_y;
        }
    });
});

##</code><code>##

{
    my ($line, $char); BEGIN { ($line, $char) = (1, 0) }

    sub text_show {
        my ($text, $str) = @_;

        if (0 == index $str, "\r") {
            $str = substr $str, 1;
            $text->delete("$line.0", "$line.$char");
            $char = 0;
        }

        $text->insert("$line.$char" => $str);

        if (-1 < index $str, "\n") {
            $line += $str =~ y/\n//;
            $char = length(substr $str, rindex $str, "\n") - 1;
        }
        else {
            $char += length $str;
        }

        $text->see("$line.$char");
    }
}