Tk runs by MainLoop; it only talks to your app via events. The trick is to bind some event to a subroutine in your app, and then access the coordinates you want (probably via the x and y methods, or possibly rootx and rooty methods, of the Tk::event object your receive).

A simple example

#!/usr/local/bin/perl -w
use strict;
use Tk;

my $mw = new Tk::MainWindow;
my $c = $mw->Canvas->pack;
my $tx = $c->createText(20, 10, -text => 'X: UNKNOWN');
my $ty = $c->createText(20, 25, -text => 'Y: UNKNOWN');
$c->Tk::bind('<Motion>' =>
         [sub {
        my ($e,$x,$y) = (@_);
        $c->itemconfigure($tx, -text => "X: $x");
        $c->itemconfigure($ty, -text => "Y: $y");
          },
          Ev('x'), Ev('y')]);
MainLoop;
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