Try something like this:

use strict;
use warnings;
use Tk;

my $main = new MainWindow;

my $c = $main->Canvas(
    -width       => 200,
    -height      => 200,
    -relief      => 'sunken',
    -borderwidth => 2,
)->pack(
    -expand => 1,
    -fill   => 'both',
);

$c->CanvasBind( '<1>' => sub {
        my ($c) = @_;
        my $e = $c->XEvent;
        my $x = $c->canvasx( $e->x );
        my $y = $c->canvasy( $e->y );
        print "$x,$y\n";
    }
);

MainLoop;
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And it's better not to use Perl's reserved words for variable names or hash keys, in this case 'ref'.