#!/usr/bin/perl
use strict;
use warnings;
use Tk;
use Tk::Frame;
use Tk::Scrollbar;
use Tk::Menu;
use Tk::Menubutton;

# marker position
my $markX;
my $markY;

my $main = MainWindow->new;
$main->geometry('800x600');

my $topPanel = $main->Frame(-width => 800, -height => 550)->pack;
$topPanel->Button(-text => 'Quit', -width =>5, -command => [$main => 'destroy'])->pack;

# create scrolled canvas
my $viewPanel = $main->Frame->pack;
my $windowScrol = $viewPanel->Scrolled('Canvas',
    -width => 800, 
    -height => 550, 
    -scrollregion => [0, 0, 2000, 1000],
    -bg => 'white',
    -scrollbars => 'se')->pack;
# get reference to actual underlying canvas
my ($window, undef) = $windowScrol->Subwidget();

# binding to mouse click
$window->Tk::bind("<1>" => [\&marker, Ev('x'), Ev('y')]);

MainLoop();

sub marker{
    my($id, $Mx, $My) = @_;
    my $color = '#800000';
    my @items = $id->find('withtag', 'mark');
    # if marker exists, move it to new position
    if ($items[0]){
        my $Mx = $Mx - $markX;
        my $My = $My - $markY;
        for (@items){$id->move($_, $Mx, $My)}
    # or else create marker
    }else{
        $id->create(('line', $Mx, $My-20, $Mx, $My+20),
            -fill => $color, -tags => ['mark'],);
        $id->create(('line', $Mx-20, $My, $Mx+20, $My),
            -fill => $color, -tags => ['mark'],);
    }
    $markX = $Mx;
    $markY = $My;
}