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

my $mw = tkinit;

my $heightmw = 260;
my $width = 600;
my $height = $heightmw - 60;

$mw->geometry($width.'x'.$heightmw .'+100+100');

my $canvas = $mw->RotCanvas(-width => $width, -height => $height,
                 -bg => 'black')->pack(-fill=>'both',-expand => 1);

my $angle = 0;
my $px0 = 240;
my $py0 = 0;
my $px_new = 240;
my $py_new = $height;

my %pend;

for(0..4){
  $pend{$_}{'line'} = $canvas->createLine(
                          $px0 ,$py0,
			  $px_new ,$py_new, 
                          -smooth => 1,
                          -width => 3,
			  -tags => ['line'.$_],
                          -fill => 'white');

  $pend{$_}{'ball'} = $canvas->createOval($px_new - 15 ,$py_new ,
                            $px_new + 15, $py_new + 30, 
			    -tags => ['ball'.$_],
			    -fill => 'orange',
			    );

  $canvas->move( $pend{$_}{'line'},$_ * 30,0);
  $canvas->move( $pend{$_}{'ball'},$_ * 30,0);
  $pend{$_}{'centerx'} = $px0 + $_ * 30;

}


my $motion = 0;

my $bframe = $mw->Frame()->pack(-fill =>'both');
my $startbut;
my $timer;
my $toggle = -1;
$startbut = $bframe->Button(-text=>'Start',
                 -command =>sub{
                       if($motion == 0){
		           $startbut->configure(-text=>'Stop'); 
		           $motion = 1;
			   &start;
			  }else{
                           $startbut->configure(-text=>'Start'); 
		           $motion = 0;
			   $timer->cancel;
			   }
		    }
		    )->pack(-side => 'left');

$bframe->Button(-text=>'Quit',
              -command =>sub{exit})->pack(-side => 'right');

MainLoop;

sub start{
#cannot set the timer too low or
#the rotate's below don't have enough
#time to complete, so lockups occur 
#so set swing degree higher for more speed

 $timer = $canvas->repeat(50,sub{   
            	 &swing(4);       
                 });             
 }
##########################################################

sub swing{
   my $degree = shift;
   $degree = $toggle*$degree;
   $angle = $angle + $degree;
    if( $angle > 90 ){$toggle *= -1}
    if( $angle < -90 ){$toggle *= -1}

for(0..4){
# can only specify one tag at a time in RotCanvas, 
# and it will not do a group
 $canvas->rotate('line'.$_, $degree, $pend{$_}{'centerx'},$py0); 
 $canvas->rotate('ball'.$_, $degree, $pend{$_}{'centerx'},$py0);
}

 }