#!/usr/bin/perl

use strict;
use warnings;
use Tk;

my @lines;

my $mw = MainWindow->new;
my $c = $mw->Canvas(-width => 900, -height => 900,)->pack(-side => 'bottom');
$mw->Button(-text => $_->[0], -command => $_->[1])->pack(-side => 'right') for
  [ Exit         => sub { $mw->destroy } ],
  [ 'Clear Last' => sub { pop @lines; redraw() } ],
  [ 'Clear All'  => sub { @lines = (); redraw() } ];

$c->Tk::bind('<1>' => sub
  {
  push @lines, [ &xy ];
  redraw();
  $c->Tk::bind('<Motion>' => sub { push @{ $lines[-1] }, &xy; redraw() } );
  } );
$c->Tk::bind('<ButtonRelease-1>' => sub { $c->Tk::bind('<Motion>' => '') } );

MainLoop;

sub xy { $_[0]->XEvent->x, $_[0]->XEvent->y }

sub redraw
  {
  $c->delete('pen');
  @$_ >= 4 and $c->createLine(@$_, -smooth => 1, -width => 5, -tag => 'pen') 
    for @lines;
  }