#!/usr/bin/perl
package main;
use strict; use warnings;

use Tk;
use Tk::ProgressBar;

my $mw = MainWindow->new(-title=>"Bug Demo");
my $pb = $mw->ProgressBar(
	-width => 20,
	-length => 200,
	-blocks => 20,
)->pack();

my $button = $mw->Button(
	-text => 'Press this!',
	-command => \&count_up,
)->pack();

MainLoop;

sub count_up {
	$mw->update;
	my $progress = 0;
	$pb->configure(
		-from => 0,
		-to   => 20,
		-variable => \$progress,  ## store the reference.
	);
	
	my $cnt = 0;
	print "\$cnt=$cnt; \$progress=$progress\n";
	
	for (1..20) {
		$progress++;
		$cnt++ unless ($_ % 2);
		$mw->update;
	}
	
	$mw->update;
}

##</code><code>##

$cnt=0; $progress=0
$cnt=0; $progress=20
$cnt=0; $progress=40