use strict;
use warnings;

use Tk;
my $top = MainWindow->new;
my $can = $top->Canvas()->pack();

my @offset = (100, 100);

my $PI = atan2(1,1) * 4;
my $max = 100;
my $radius = 20;

my @coords;

foreach my $i (1..$max-30) {
	push(@coords, _circleCoord($i*2*$PI/$max, $radius));
}

$can->createLine(@coords, -arrow=>'last',
	#-arrowshape=>[10, 15, 9],	# Goofy arrowhead - this  helps
	tags=>['SELFARROW']);
$can->move('SELFARROW', @offset);

MainLoop;

sub _circleCoord {
	my $radians = shift || die "Missing radians";
	my $radius = shift || die "Missing radius";

	my @coords;
	push(@coords, ($radius * sin($radians)));
	push(@coords, ($radius * cos($radians)));
	return(@coords);
}