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

my $mw = tkinit;

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

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

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

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

my %pends;


#make a prototype pendulum easily at (0,0) coords
$pends{0}{'pendulum'} = $canvas->add('group',1,-visible=> 1);

# all lines are curves....of course!! it's relativity :-)
my $line = $canvas->add('curve',$pends{0}{'pendulum'},
                          [0 ,0, 0 ,$py_new], 
                          -linewidth => 3,
			  -tags => ['line'],
                          -fillcolor => 'white',
			  -linecolor => 'white',
			  );

my $ball = $canvas->add('arc',$pends{0}{'pendulum'}, 
                             [-15,$py_new,15,$py_new+30], 
			    -tags => ['ball'],
			    -filled=> 1,
			    -fillcolor => 'orange',
			    );

$canvas->translate($pends{0}{'pendulum'},240,0);
$pends{0}{'center_rot'} = [240,0];
#end of first prototype

#now clone and position the other pendulums
for(1..4){
$pends{$_}{'pendulum'} = $canvas->clone( $pends{0}{'pendulum'} );
$canvas->translate($pends{$_}{'pendulum'}, $_*30, 0);
$pends{$_}{'center_rot'} = [240 + $_ * 30 ,0];
}

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{
 $timer = $canvas->repeat(10,sub{   
         		 &swing(.0175);        
                           });
 }
######################################################
sub swing{
   my $degree = shift;
   $degree = $toggle*$degree;
   $angle = $angle + $degree;
    if( $angle > 1.57 ){$toggle *= -1}
    if( $angle < -1.57 ){$toggle *= -1}
   
  for(0..5){  # rotate( item, rads, [center of rotation ])
    $canvas->rotate($pends{$_}{'pendulum'},
                       $degree,
		       @{$pends{$_}{'center_rot'}});
  }
	
}