#!/usr/bin/perl

use strict;
use Tk;

my $top    = MainWindow->new();
my $canvas = $top->Canvas( width => 300, height => 245 )->pack();

my $origin_x      = 110;
my $origin_y      = 70;
my $PI            = 3.141592635;
my $circle_radius = 5;
my $path_radius   = 0;
my $angle         = 0;

$canvas->repeat(
    1000,
    sub {
        &animate( $origin_x, $origin_y, $PI, \$canvas,
            \$circle_radius, \$path_radius, \$angle );
    }
);

# Could also be done as follows, although there are
# differences in the two methods
# $canvas->repeat(
#     1000,
#     [   \&animate,     $origin_x, $origin_y,
#         $PI,           \$canvas,  \$circle_radius,
#         \$path_radius, \$angle
#     ]
# );

MainLoop();

sub animate {
    my ( $origin_x, $origin_y, $PI, $canvas, $circle_radius,
        $path_radius, $angle )
        = @_;

    $$angle         += 10;
    $$circle_radius += 3;
    $$path_radius   += 7;

    my $path_x =
        $origin_x + $$path_radius * cos( $$angle * $PI / 90 );
    my $path_y =
        $origin_y - $$path_radius * sin( $$angle * $PI / 90 );

    $$canvas->create(
        'oval',
        $path_x - $circle_radius,
        $path_y - $circle_radius,
        $path_x + $circle_radius,
        $path_y + $circle_radius,
        -fill => 'yellow'
    );
    $$canvas->create( 'line', $origin_x, $origin_y, $path_x,
        $path_y, -fill => 'slategray' );

    if ( $$angle > 180 ) {
        $angle          = 0;
        $$circle_radius = 5;
        $$path_radius   = 0;
    }
}