#!/usr/bin/perl
use strict;
use warnings;
use Tk;

my ($width, $height) = (1000, 500);
my $cwidth = 3 * $width;
sub func { $_ = shift; $_ / $width * $height % $height; }
my $mw = MainWindow->new(-width => $width, -height => $height);
$mw->packPropagate(0); # keeps MainWindow @ 1000x500
my $c = $mw->Scrolled('Canvas',
                      -width => $cwidth + 2,
                      -height => $height + 2,
                      -scrollbars => 's')->pack;
# draw a simple graph
$c->create(line => $_,     func($_),
                   $_ + 1, func($_ + 1),
           -fill => 'red') for 1..$cwidth-1;
$c->configure(-scrollregion => [ $c->bbox('all') ]); # THIS SOLVED THE PROBLEM
# could also add: -scrollregion => [ 0, 0, 3000, 500 ],
# to the constructor
MainLoop;