Making GIF Images

#!/usr/local/bin/perl
 
# script: circle.pl
use GD;
use CGI::Pretty qw/:standard :imagemap/;
use strict vars;
use vars qw/$draw $circle_color $mag %COLORS/;
 
use constant RECTSIZE     => 100;
use constant CIRCLE_RADIUS  => 40;
%COLORS = (
 	   'white' => [255,255,255],
 	   'red'   => [255,0,0],
 	   'green' => [0,255,0],
 	   'blue'  => [0,0,255],
 	   'black' => [0,0,0],
 	   'bisque'=> [255,228,196],
 	   'papaya whip' => [255,239,113],
 	   'sienna' => [160,82,45]
 	   );
$draw          = param('draw');
$circle_color  = param('color') || 'bisque';
$mag           = param('magnification') || 1;

if ($draw) {
    draw_image();
} else {
    make_page();
}
         
sub draw_image {
    # create a new image
    my $im = new GD::Image(RECTSIZE*$mag,RECTSIZE*$mag);
    
    # allocate some colors
    my $white = $im->colorAllocate(@{$COLORS{'white'}});
    my $black = $im->colorAllocate(@{$COLORS{'black'}});       
    my $circlecolor = $im->colorAllocate(@{$COLORS{$circle_color}});
    
    # make the background transparent and interlaced
    $im->transparent($white);
    $im->interlaced('true');
    
    # Put a black frame around the picture
    $im->rectangle(0,0,RECTSIZE*$mag-1,RECTSIZE*$mag-1,$black);
    
    # Draw the circle
    $im->arc(RECTSIZE*$mag/2,RECTSIZE*$mag/2,CIRCLE_RADIUS*$mag*2,CIRCLE_RADIUS*$mag*2,0,360,$black);
    
    # And fill it with circlecolor
    $im->fill(RECTSIZE*$mag/2,RECTSIZE*$mag/2,$circlecolor);
    
     # Convert the image to GIF and print it
    print header('image/gif'),$im->gif;
}

sub make_page {
    print header(),
    start_html(-title=>'Feeling Circular',-bgcolor=>'white'),
    h1('A Circle is as a Circle Does'),
    start_form,
    "Magnification: ",radio_group(-name=>'magnification',-values=>[1..4]),br,
    "Color: ",popup_menu(-name=>'color',-values=>[sort keys %COLORS]),
    submit(-value=>'Change'),
    end_form;
    print em(param('message')) if param('message');

    my $url = url(-relative=>1,-query_string=>1);
    $url .= '?' unless param();
    $url .= '&draw=1';

    print p(
	img({-src=>$url,
	     -align=>'LEFT',
	     -usemap=>'#map',
	     -border=>0}));

    print Map({-name=>'map'},
 	      Area({-shape=>'CIRCLE',
 		    -href=>param(-name=>'message',-value=>"You clicked in the circle") 
			&& url(-relative=>1,-query_string=>1),
		    -coords=>join(',',RECTSIZE*$mag/2,RECTSIZE*$mag/2,CIRCLE_RADIUS*$mag),
		    -alt=>'Circle'}),
 	      Area({-shape=>'RECT',
 		    -href=>param(-name=>'message',-value=>"You clicked in the square") 
			&& url(-relative=>1,-query_string=>1),
		    -coords=>join(',',0,0,RECTSIZE*$mag,RECTSIZE*$mag),
		    -alt=>'Square'}));
    print end_html;
}