....this almost smells of homework..... so here is some starter code .....for it to work on Tk, it needs window focus .... and you will see the problem as you move the window around...... you could make a full-screen Tk app and use this code to drive balls on a canvas widget.... that would be easy..... but it's your homework ;-)

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

my $mw= tkinit;

$mw->bind('<Motion>' => [\&show_position,$mw]);

MainLoop;

sub show_position{
  my $widget = shift;
  my $x = $widget->pointerx;
  my $y = $widget->pointery;
  print "$x $y\n";
  # ($x, $y) = $widget->pointerxy;
}
[download]

i'm no good at maths

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

use Tk 8;

my $mw = tkinit( -width => 500, -height => 500 );

my $canvas = $mw->Canvas()->pack( -expand => 'yes', );
$canvas->createOval( 50, 50, 100, 100, -fill => 'white', -tags => ['le
+ft'] );
$canvas->createOval( 60, 50, 70, 60, -fill => 'red', -tags => ['left i
+ris'] );
$canvas->createOval(
    100 + 50, 50, 100 + 100, 100,
    -fill => 'white',
    -tags => ['right']
);
$canvas->createOval(
    100 + 80, 80, 100 + 90, 90,
    -fill => 'red',
    -tags => ['right iris']
);

$mw->bind( 'Tk::Canvas', '<Motion>' => [ \&marine, Ev('x'), Ev('y') ] 
+);

use Math::Trig qw' atan pi ';

sub marine {
    my ( $w, $x, $y ) = @_;

    my $iris = 'left iris';
    my $r    = 25;
    my $cx   = 75;
    my $cy   = 75;

    my $angle = eval { atan( ( $cy - $y ) / ( $cx - $x ) ) };
    $angle += pi if ( $cx - $x ) >= 0;

    my ( $x1, $y1, $x2, $y2 ) = $w->coords($iris);
    $x1 = ( ( $r * cos($angle) + $cx ) );
    $y1 = ( ( $r * sin($angle) + $cy ) );
    $x2 = $x1 + 10;
    $y2 = $y1 + 10;

    $w->coords( $iris, $x1, $y1, $x2, $y2 );
}

MainLoop;
[download]

The application you used is xeyes. You can get the source code for the ubuntu package from http://archive.ubuntu.com/ubuntu/pool/main/x/xeyes/xeyes_1.0.1.orig.tar.gz, which might give you a clue as to some of the mechanics involved.

@_=qw;
Just another Perl hacker,;
;$_=q=print
"@_"= and eval;
[download]

That is an excellent idea, so I did just that. The source is included in the x11-apps package. I got the 8.04/hardy source http://packages.ubuntu.com/hardy/x11-apps.

My crude analysis is that xeyes polls the mouse position. It polls frequently when there is mouse activity but then backs off on the polling interval when there is no activity. There is no hook into a mouse handler.

Thanks to everyone. I will pursue this further.

Try the module X11::GUITest. It may help you get the cursor's position in X11. From the readme...

    GetMousePos
            Returns an array containing the position of the mouse curs
+or.

              my ($x, $y) = GetMousePos();
[download]

Combine this with a simple Tk window for drawing the eyes, and X11::GUITest should help ya get the cursor position so you don't need Tk to handle that part. Of course this approach is only good for X11 systems and isn't cross platform to Windows or OS X.