#!/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);
}

 }
           
__END__

###########################################################
##########################################################
#and now with Zinc
##########################################################
#########################################################

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

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);    # 1 degree in radians      
                           });
 }
######################################################
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'}});
  }
   
}
           
__END__