#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper qw/Dumper/;
use Tk;

my $mw = tkinit(-width => 640, -height => 480);
$mw->packPropagate(0);

my $btn = $mw->Button(-text => 'show / hide left pane')->pack();

my $pane = $mw->Panedwindow()->pack(-fill => 'both', -expand => 1,);
my $frame1 = $pane->Frame(-bg => 'blue');
my $canvas = $pane->Scrolled('Canvas', -bg => 'red', -scrollbars => 'se',);
$pane->add($frame1, -width => 100,);
$pane->add($canvas, -width => 400,);

# -- canvas resize binding
$canvas->Tk::bind('<Configure>' => sub{
        my @bbox = $canvas->bbox("all");
        $canvas->configure(-scrollregion => [ @bbox ]);
});

$btn->configure(-command => sub{ toogle_frame($frame1, $canvas, $pane); return 1; });

$mw->MainLoop();

sub toogle_frame {
        my $frame1 = shift or die('Missing frame');
        my $frame2 = shift or die('Missing frame');
        my $pane = shift or die('Missing pane');
        
        if( scalar( @{$pane->panes()} ) == 2 ) {
                $pane->forget($frame1);
        }else{
                $pane->add($frame1, -before => $frame2, -width => 100);
        }
        
} # /toogle_frame