#!/usr/bin/perl -w
# Example 7-3. The bouncing ball.

use strict;
use XML::Writer;    # Used to write the SVG output

my ($width, $height) = (300, 300);

my $writer = XML::Writer->new();
$writer->setDataMode(1);     # Auto insert newlines
$writer->setDataIndent(2);   # Auto indent
$writer->startTag('svg',
                  height => $height,
                  width  => $width,
                  'xmlns:xlink' => 'http://www.w3.org/1999/Xlink');


$writer->startTag('circle',
                  id => 'ball',
                  r => 10,
                  fill   => '#FF0000');
$writer->emptyTag('animateMotion',
                  calcMode=> 'spline',
		  dur => "10s",
		  path => make_bounce_path(300, 200, 4),
		  repeatCount => "indefinite");
$writer->emptyTag('animate',
                  attributeName => "r",
                  from => 10, 
                  to => 50,
                  dur  => "10s",
                  repeatCount => "indefinite"
                 );
$writer->endTag('circle'); 
$writer->endTag('svg');

sub make_bounce_path { 
    my ($ground, $bounce_height, $bounces) = @_;
    my $pi = atan2(1,1) * 4;  
    my $points = "M0,$height ";
    my $y;

    for (my $x=1; $x < $width; $x+=5) {
        $y = int($ground - abs(($bounce_height * 
               sin(($x/($width*2/$bounces)) * 2 * $pi))));
        $points .= "L$x,$y ";    
        $ground -= 40/($width/5);
        $height -= 40/($width/5);
    }
    return $points;
}