#!/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 => ['left'] );
$canvas->createOval( 60, 50, 70, 60, -fill => 'red', -tags => ['left iris'] );
$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;