[sdlgit/SDL_perl.git] / lib / SDL / Tutorial / Images.pm

#!/usr/bin/env perl
#
# Images.pm
#
# Copyright (C) 2005 David J. Goehrig <dgoehrig@cpan.org>
#
# ------------------------------------------------------------------------------
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
# 
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# Lesser General Public License for more details.
# 
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
#
# ------------------------------------------------------------------------------
#
# Please feel free to send questions, suggestions or improvements to:
#
#	David J. Goehrig
#	dgoehrig@cpan.org
#

package SDL::Tutorial::Images;

use strict;
use SDL;
use warnings;

my %images;
BEGIN
{
	%images = (
	left => [qw(
		47 49 46 38 37 61 10 00 10 00 E7 00 00 00 00 00 01 01 01 02 02 02 03 03
		03 04 04 04 05 05 05 06 06 06 07 07 07 08 08 08 09 09 09 0A 0A 0A 0B 0B
		0B 0C 0C 0C 0D 0D 0D 0E 0E 0E 0F 0F 0F 10 10 10 11 11 11 12 12 12 13 13
		13 14 14 14 15 15 15 16 16 16 17 17 17 18 18 18 19 19 19 1A 1A 1A 1B 1B
		1B 1C 1C 1C 1D 1D 1D 1E 1E 1E 1F 1F 1F 20 20 20 21 21 21 22 22 22 23 23
		23 24 24 24 25 25 25 26 26 26 27 27 27 28 28 28 29 29 29 2A 2A 2A 2B 2B
		2B 2C 2C 2C 2D 2D 2D 2E 2E 2E 2F 2F 2F 30 30 30 31 31 31 32 32 32 33 33
		33 34 34 34 35 35 35 36 36 36 37 37 37 38 38 38 39 39 39 3A 3A 3A 3B 3B
		3B 3C 3C 3C 3D 3D 3D 3E 3E 3E 3F 3F 3F 40 40 40 41 41 41 42 42 42 43 43
		43 44 44 44 45 45 45 46 46 46 47 47 47 48 48 48 49 49 49 4A 4A 4A 4B 4B
		4B 4C 4C 4C 4D 4D 4D 4E 4E 4E 4F 4F 4F 50 50 50 51 51 51 52 52 52 53 53
		53 54 54 54 55 55 55 56 56 56 57 57 57 58 58 58 59 59 59 5A 5A 5A 5B 5B
		5B 5C 5C 5C 5D 5D 5D 5E 5E 5E 5F 5F 5F 60 60 60 61 61 61 62 62 62 63 63
		63 64 64 64 65 65 65 66 66 66 67 67 67 68 68 68 69 69 69 6A 6A 6A 6B 6B
		6B 6C 6C 6C 6D 6D 6D 6E 6E 6E 6F 6F 6F 70 70 70 71 71 71 72 72 72 73 73
		73 74 74 74 75 75 75 76 76 76 77 77 77 78 78 78 79 79 79 7A 7A 7A 7B 7B
		7B 7C 7C 7C 7D 7D 7D 7E 7E 7E 7F 7F 7F 80 80 80 81 81 81 82 82 82 83 83
		83 84 84 84 85 85 85 86 86 86 87 87 87 88 88 88 89 89 89 8A 8A 8A 8B 8B
		8B 8C 8C 8C 8D 8D 8D 8E 8E 8E 8F 8F 8F 90 90 90 91 91 91 92 92 92 93 93
		93 94 94 94 95 95 95 96 96 96 97 97 97 98 98 98 99 99 99 9A 9A 9A 9B 9B
		9B 9C 9C 9C 9D 9D 9D 9E 9E 9E 9F 9F 9F A0 A0 A0 A1 A1 A1 A2 A2 A2 A3 A3
		A3 A4 A4 A4 A5 A5 A5 A6 A6 A6 A7 A7 A7 A8 A8 A8 A9 A9 A9 AA AA AA AB AB
		AB AC AC AC AD AD AD AE AE AE AF AF AF B0 B0 B0 B1 B1 B1 B2 B2 B2 B3 B3
		B3 B4 B4 B4 B5 B5 B5 B6 B6 B6 B7 B7 B7 B8 B8 B8 B9 B9 B9 BA BA BA BB BB
		BB BC BC BC BD BD BD BE BE BE BF BF BF C0 C0 C0 C1 C1 C1 C2 C2 C2 C3 C3
		C3 C4 C4 C4 C5 C5 C5 C6 C6 C6 C7 C7 C7 C8 C8 C8 C9 C9 C9 CA CA CA CB CB
		CB CC CC CC CD CD CD CE CE CE CF CF CF D0 D0 D0 D1 D1 D1 D2 D2 D2 D3 D3
		D3 D4 D4 D4 D5 D5 D5 D6 D6 D6 D7 D7 D7 D8 D8 D8 D9 D9 D9 DA DA DA DB DB
		DB DC DC DC DD DD DD DE DE DE DF DF DF E0 E0 E0 E1 E1 E1 E2 E2 E2 E3 E3
		E3 E4 E4 E4 E5 E5 E5 E6 E6 E6 E7 E7 E7 E8 E8 E8 E9 E9 E9 EA EA EA EB EB
		EB EC EC EC ED ED ED EE EE EE EF EF EF F0 F0 F0 F1 F1 F1 F2 F2 F2 F3 F3
		F3 F4 F4 F4 F5 F5 F5 F6 F6 F6 F7 F7 F7 F8 F8 F8 F9 F9 F9 FA FA FA FB FB
		FB FC FC FC FD FD FD FE FE FE FF FF FF 2C 00 00 00 00 10 00 10 00 00 08
		36 00 FF 09 1C 48 B0 A0 C1 83 08 13 22 04 C0 10 80 C2 7F 0C 05 46 4C E8
		70 60 C5 85 15 27 52 6C A8 30 E3 45 8C 0D 39 76 FC 38 F2 A1 44 91 1B 4F
		82 24 88 D2 64 C1 80 00 3B
	)],
	center => [qw(
		47 49 46 38 37 61 10 00 10 00 E7 00 00 00 00 00 01 01 01 02 02 02 03 03
		03 04 04 04 05 05 05 06 06 06 07 07 07 08 08 08 09 09 09 0A 0A 0A 0B 0B
		0B 0C 0C 0C 0D 0D 0D 0E 0E 0E 0F 0F 0F 10 10 10 11 11 11 12 12 12 13 13
		13 14 14 14 15 15 15 16 16 16 17 17 17 18 18 18 19 19 19 1A 1A 1A 1B 1B
		1B 1C 1C 1C 1D 1D 1D 1E 1E 1E 1F 1F 1F 20 20 20 21 21 21 22 22 22 23 23
		23 24 24 24 25 25 25 26 26 26 27 27 27 28 28 28 29 29 29 2A 2A 2A 2B 2B
		2B 2C 2C 2C 2D 2D 2D 2E 2E 2E 2F 2F 2F 30 30 30 31 31 31 32 32 32 33 33
		33 34 34 34 35 35 35 36 36 36 37 37 37 38 38 38 39 39 39 3A 3A 3A 3B 3B
		3B 3C 3C 3C 3D 3D 3D 3E 3E 3E 3F 3F 3F 40 40 40 41 41 41 42 42 42 43 43
		43 44 44 44 45 45 45 46 46 46 47 47 47 48 48 48 49 49 49 4A 4A 4A 4B 4B
		4B 4C 4C 4C 4D 4D 4D 4E 4E 4E 4F 4F 4F 50 50 50 51 51 51 52 52 52 53 53
		53 54 54 54 55 55 55 56 56 56 57 57 57 58 58 58 59 59 59 5A 5A 5A 5B 5B
		5B 5C 5C 5C 5D 5D 5D 5E 5E 5E 5F 5F 5F 60 60 60 61 61 61 62 62 62 63 63
		63 64 64 64 65 65 65 66 66 66 67 67 67 68 68 68 69 69 69 6A 6A 6A 6B 6B
		6B 6C 6C 6C 6D 6D 6D 6E 6E 6E 6F 6F 6F 70 70 70 71 71 71 72 72 72 73 73
		73 74 74 74 75 75 75 76 76 76 77 77 77 78 78 78 79 79 79 7A 7A 7A 7B 7B
		7B 7C 7C 7C 7D 7D 7D 7E 7E 7E 7F 7F 7F 80 80 80 81 81 81 82 82 82 83 83
		83 84 84 84 85 85 85 86 86 86 87 87 87 88 88 88 89 89 89 8A 8A 8A 8B 8B
		8B 8C 8C 8C 8D 8D 8D 8E 8E 8E 8F 8F 8F 90 90 90 91 91 91 92 92 92 93 93
		93 94 94 94 95 95 95 96 96 96 97 97 97 98 98 98 99 99 99 9A 9A 9A 9B 9B
		9B 9C 9C 9C 9D 9D 9D 9E 9E 9E 9F 9F 9F A0 A0 A0 A1 A1 A1 A2 A2 A2 A3 A3
		A3 A4 A4 A4 A5 A5 A5 A6 A6 A6 A7 A7 A7 A8 A8 A8 A9 A9 A9 AA AA AA AB AB
		AB AC AC AC AD AD AD AE AE AE AF AF AF B0 B0 B0 B1 B1 B1 B2 B2 B2 B3 B3
		B3 B4 B4 B4 B5 B5 B5 B6 B6 B6 B7 B7 B7 B8 B8 B8 B9 B9 B9 BA BA BA BB BB
		BB BC BC BC BD BD BD BE BE BE BF BF BF C0 C0 C0 C1 C1 C1 C2 C2 C2 C3 C3
		C3 C4 C4 C4 C5 C5 C5 C6 C6 C6 C7 C7 C7 C8 C8 C8 C9 C9 C9 CA CA CA CB CB
		CB CC CC CC CD CD CD CE CE CE CF CF CF D0 D0 D0 D1 D1 D1 D2 D2 D2 D3 D3
		D3 D4 D4 D4 D5 D5 D5 D6 D6 D6 D7 D7 D7 D8 D8 D8 D9 D9 D9 DA DA DA DB DB
		DB DC DC DC DD DD DD DE DE DE DF DF DF E0 E0 E0 E1 E1 E1 E2 E2 E2 E3 E3
		E3 E4 E4 E4 E5 E5 E5 E6 E6 E6 E7 E7 E7 E8 E8 E8 E9 E9 E9 EA EA EA EB EB
		EB EC EC EC ED ED ED EE EE EE EF EF EF F0 F0 F0 F1 F1 F1 F2 F2 F2 F3 F3
		F3 F4 F4 F4 F5 F5 F5 F6 F6 F6 F7 F7 F7 F8 F8 F8 F9 F9 F9 FA FA FA FB FB
		FB FC FC FC FD FD FD FE FE FE FF FF FF 2C 00 00 00 00 10 00 10 00 00 08
		36 00 FF 09 1C 48 B0 A0 C1 83 08 13 26 04 C0 10 80 C2 7F 0C 05 46 5C 48
		D0 E1 42 8B 13 2F 66 54 B8 F1 60 C3 8F 16 2F 3E 1C D8 11 E1 C7 87 13 4B
		4A DC D8 70 E4 C1 80 00 3B
	)],
	right => [qw(
		47 49 46 38 37 61 10 00 10 00 E7 00 00 00 00 00 01 01 01 02 02 02 03 03
		03 04 04 04 05 05 05 06 06 06 07 07 07 08 08 08 09 09 09 0A 0A 0A 0B 0B
		0B 0C 0C 0C 0D 0D 0D 0E 0E 0E 0F 0F 0F 10 10 10 11 11 11 12 12 12 13 13
		13 14 14 14 15 15 15 16 16 16 17 17 17 18 18 18 19 19 19 1A 1A 1A 1B 1B
		1B 1C 1C 1C 1D 1D 1D 1E 1E 1E 1F 1F 1F 20 20 20 21 21 21 22 22 22 23 23
		23 24 24 24 25 25 25 26 26 26 27 27 27 28 28 28 29 29 29 2A 2A 2A 2B 2B
		2B 2C 2C 2C 2D 2D 2D 2E 2E 2E 2F 2F 2F 30 30 30 31 31 31 32 32 32 33 33
		33 34 34 34 35 35 35 36 36 36 37 37 37 38 38 38 39 39 39 3A 3A 3A 3B 3B
		3B 3C 3C 3C 3D 3D 3D 3E 3E 3E 3F 3F 3F 40 40 40 41 41 41 42 42 42 43 43
		43 44 44 44 45 45 45 46 46 46 47 47 47 48 48 48 49 49 49 4A 4A 4A 4B 4B
		4B 4C 4C 4C 4D 4D 4D 4E 4E 4E 4F 4F 4F 50 50 50 51 51 51 52 52 52 53 53
		53 54 54 54 55 55 55 56 56 56 57 57 57 58 58 58 59 59 59 5A 5A 5A 5B 5B
		5B 5C 5C 5C 5D 5D 5D 5E 5E 5E 5F 5F 5F 60 60 60 61 61 61 62 62 62 63 63
		63 64 64 64 65 65 65 66 66 66 67 67 67 68 68 68 69 69 69 6A 6A 6A 6B 6B
		6B 6C 6C 6C 6D 6D 6D 6E 6E 6E 6F 6F 6F 70 70 70 71 71 71 72 72 72 73 73
		73 74 74 74 75 75 75 76 76 76 77 77 77 78 78 78 79 79 79 7A 7A 7A 7B 7B
		7B 7C 7C 7C 7D 7D 7D 7E 7E 7E 7F 7F 7F 80 80 80 81 81 81 82 82 82 83 83
		83 84 84 84 85 85 85 86 86 86 87 87 87 88 88 88 89 89 89 8A 8A 8A 8B 8B
		8B 8C 8C 8C 8D 8D 8D 8E 8E 8E 8F 8F 8F 90 90 90 91 91 91 92 92 92 93 93
		93 94 94 94 95 95 95 96 96 96 97 97 97 98 98 98 99 99 99 9A 9A 9A 9B 9B
		9B 9C 9C 9C 9D 9D 9D 9E 9E 9E 9F 9F 9F A0 A0 A0 A1 A1 A1 A2 A2 A2 A3 A3
		A3 A4 A4 A4 A5 A5 A5 A6 A6 A6 A7 A7 A7 A8 A8 A8 A9 A9 A9 AA AA AA AB AB
		AB AC AC AC AD AD AD AE AE AE AF AF AF B0 B0 B0 B1 B1 B1 B2 B2 B2 B3 B3
		B3 B4 B4 B4 B5 B5 B5 B6 B6 B6 B7 B7 B7 B8 B8 B8 B9 B9 B9 BA BA BA BB BB
		BB BC BC BC BD BD BD BE BE BE BF BF BF C0 C0 C0 C1 C1 C1 C2 C2 C2 C3 C3
		C3 C4 C4 C4 C5 C5 C5 C6 C6 C6 C7 C7 C7 C8 C8 C8 C9 C9 C9 CA CA CA CB CB
		CB CC CC CC CD CD CD CE CE CE CF CF CF D0 D0 D0 D1 D1 D1 D2 D2 D2 D3 D3
		D3 D4 D4 D4 D5 D5 D5 D6 D6 D6 D7 D7 D7 D8 D8 D8 D9 D9 D9 DA DA DA DB DB
		DB DC DC DC DD DD DD DE DE DE DF DF DF E0 E0 E0 E1 E1 E1 E2 E2 E2 E3 E3
		E3 E4 E4 E4 E5 E5 E5 E6 E6 E6 E7 E7 E7 E8 E8 E8 E9 E9 E9 EA EA EA EB EB
		EB EC EC EC ED ED ED EE EE EE EF EF EF F0 F0 F0 F1 F1 F1 F2 F2 F2 F3 F3
		F3 F4 F4 F4 F5 F5 F5 F6 F6 F6 F7 F7 F7 F8 F8 F8 F9 F9 F9 FA FA FA FB FB
		FB FC FC FC FD FD FD FE FE FE FF FF FF 2C 00 00 00 00 10 00 10 00 00 08
		3A 00 FF 09 1C 48 B0 A0 C1 83 08 13 2A 04 C0 10 80 C2 7F 0C 05 46 4C E8
		70 60 45 84 13 27 52 6C F8 50 62 C5 8B 05 1B 8A 04 79 50 E3 43 93 1B 51
		1A CC 48 D2 A2 49 8E 1D 0B 06 04 00 3B
	)],
);
}

use Pod::ToDemo sub
{
	(undef, my $filename) = @_;
	(my $imagebase        = $filename) =~ s/\.\w+$//;
	my @img_files         = map { $imagebase . "_$_.gif" }
		qw( left center right );
	my $demo_source       = <<'END_HERE';
package Walker;

sub new
{
	my ($class, @images) = @_;
	my @frames           = map { SDL::Surface->new( -name => $_ ) } @images;
	my $frame_rect       = SDL::Rect->new(
		-height => $frames[0]->height(),
		-width  => $frames[0]->width(),
		-x      => 0,
		-y      => 0,
	);
	my $self             = 
	{
		frames      => \@frames,
		frame_rect  => $frame_rect,
	};
	bless $self, $class;
}

sub frames
{
	my $self        = shift;
	$self->{frames} = shift if @_;
	$self->{frames};
}

sub frame_rect
{
	my $self            = shift;
	$self->{frame_rect} = shift if @_;
	$self->{frame_rect};
}

sub next_frame
{
	my $self   = shift;
	my $frames = $self->frames();
	my $frame  = shift @$frames;

	push @$frames, $frame;
	$self->frames( $frames );

	return $frame;
}

package main;

use strict;

use SDL;
use SDL::App;
use SDL::Surface;
use SDL::Color;

# change these values as necessary
my $title                                = 'My SDL Animation';
my ($width,      $height,      $depth)   = (  640,  480,   16 );
my ($bg_r,       $bg_g,        $bg_b)    = ( 0xff, 0xff, 0xff );
my ($start_x,    $end_x)                 = (   20,  600       );
my $sleep_msec                           = 0.05;

my $app = SDL::App->new(
	-width  => $width,
	-height => $height,
	-depth  => $depth,
);

my $bg_color = SDL::Color->new(
	-r => $bg_r,
	-g => $bg_g,
	-b => $bg_b,
);

my $background = SDL::Rect->new(
	-width  => $width,
	-height => $height,
);

my $pos = SDL::Rect->new(
	-width  => 16,
	-height => 16,
	-x      => 0,
	-y      => 240,
);

my $walker = Walker->new(qw(
END_HERE

$demo_source .= join( ' ', @img_files ) . "));" . <<'END_HERE';

for my $x ( $start_x .. $end_x )
{
	draw_background( $app, $background, $bg_color );
	$pos->x( $x );
	draw_walker( $walker, $app, $pos );
	$app->update( $background );
	select( undef, undef, undef, $sleep_msec );
}

# you'll want to remove this
sleep 2;

sub draw_background
{
	my ($app, $background, $bg_color) = @_;
	$app->fill( $background, $bg_color );
}

sub draw_walker
{
	my ($walker, $app, $pos) = @_;
	my $frame                = $walker->next_frame();
	my $frame_rect           = $walker->frame_rect();
	$frame->blit( $frame_rect, $app, $pos );
}
END_HERE

	Pod::ToDemo::write_demo( $filename, "#$^X\n$demo_source" );
	write_files( $imagebase );
};
		
sub write_files
{
	my $imagebase = shift;

	for my $image (qw( left center right ))
	{
		my $file = join('', map { chr( hex( $_ ) ) } @{ $images{ $image } });
		write_file( $imagebase . "_$image" . '.gif', $file );
	}
}

sub write_file
{
    my ($file, $contents) = @_;

	die "Cowardly refusing to overwrite '$file'\n" if -e $file;
	open my $out, '>', $file or die "Cannot write '$file': $!\n";
	binmode $out;
	print $out $contents;
}

__END__

=head1 NAME

SDL::Tutorial::Images

=head1 SYNOPSIS

	# to read this tutorial
	$ perldoc SDL::Tutorial::Images

	# to create a demo animation program based on this tutorial
	$ perl -MSDL::Tutorial::Images=sdl_images.pl -e 1

=head1 ANIMATING IMAGES

Since you're already familiar with the concepts behind animation, it's time to
learn how to work with images.  As usual, the important point is that computer animation is just I<simulating> motion by painting several slightly different frames to the screen every second.

There are two ways to vary an image on screen.  One is to change its
coordinates so it's at a slightly different position.  This is very easy to do;
it's just like animating a rectangle.  The other way is to change the image
itself so it's slightly different.  This is a little more difficult, as you'll
need to draw the alternate image beforehand somehow.

=head2 Loading Images

As usual, start with an L<SDL::App> object representing the image window.  Then
preload the image file.  This is easy; just pass the C<name> parameter to the
L<SDL::Surface> constructor:

	use SDL::Surface;

	my $frame = SDL::Surface->new( -name => 'frame1.png' );

B<Note:> you'll need to have compiled SDL Perl (and probably SDL) to support
JPEG and PNG files for this to work.

That's it; now you have an SDL::Surface object containing the image.  You can
use the C<height()>, C<width()>, and C<bpp()> methods to retrieve its height,
width, and bits per pixel, if you need them.

=head2 Displaying Images

Drawing an image onto the screen requires blitting it from one surface to
another.  (Remember, "blitting" means copying bits in memory.)  The C<blit()>
method of SDL::Surface objects comes in handy.  Its arguments are a little odd,
though.  Assuming C<$app> is the SDL::App object, as usual:

	use SDL::Rect;

	my $frame_rect = SDL::Rect->new(
		-height => $frame->height(),
		-width  => $frame->width(),
		-x      => 0,
		-y      => 0,
	);

	my $dest_rect  = SDL::Rect->new(
		-height => $frame->height(),
		-width  => $frame->width(),
		-x      => 0,
		-y      => 0,
	);

	$frame->blit( $frame_rect, $app, $dest_rect );
	$app->update( $dest_rect );

Here we have two L<SDL::Rect> objects which represent rectangular regions of a
Surface.  C<$frame_rect> represents the entire area of C<$frame>, while
C<$dest_rect> represents the area of the main window in which to blit the
frame.  This may be clearer with more descriptive variable names:

	$source_surface->blit(
		$area_of_source_to_blit,
		$destination_surface,
		$destination_area
	);

As usual, call C<update()> on C<$app> to see the change.

Requiring the source and destination Rect objects may seem tedious in this
simple example, but it's highly useful for copying only part of surface to part
of another.  For example, animating this image is a matter of changing the C<x>
and C<y> coordinates of C<$dest_rect>:

	for my $x ( 1 .. 100 )
	{
		$dest_rect->x( $x );
		$frame->blit( $frame_rect, $app, $dest_rect );
		$app->update( $dest_rect );
	}

Of course, you'll have to redraw all or part of the screen to avoid artifacts,
as discussed in the previous tutorial.

=head2 Multi-Image Animation

That covers moving a single image around the screen.  What if you want
something more?  For example, what if you want to animate a stick figure
walking?

You'll need several frames, just as in a flip-book.  Each frame should be slightly different than the one before it.  It's probably handy to encapsulate all of this in a C<Walker> class:

	package Walker;

	use SDL::Surface;

	sub new
	{
		my ($class, @images) = @_;
		my $self = [ map { SDL::Surface->new( -name => $_ ) } @images ];

		bless $self, $class;
	}

	sub next_frame
	{
		my $self  = shift;
		my $frame = shift @$self;

		push @$self, $frame;
		return $frame;
	}

To use this class, instantiate an object:

	my $walker = Walker->new( 'frame1.png', 'frame2.png', 'frame3.png' );

Then call C<next_frame()> within the loop:

	for my $x ( 1 .. 100 )
	{
		my $frame = $walker->next_frame();

		$dest_rect->x( $x );
		$frame->blit( $frame_rect, $app, $dest_rect );
		$app->update( $dest_rect );
	}

Again, the rest of the frame drawing is missing from this example so as not to
distract from this technique.  You'll probably want to abstract the undrawing
and redrawing into a separate subroutine so you don't have to worry about it
every time.

It'd be easy to make C<next_frame()> much smarter, selecting an image
appropriate to the direction of travel, using a bored animation when the
character is no longer moving, or adding other characteristics to the
character.  As you can see, the hard part of this technique is generating the
images beforehand.  That can add up to a tremendous amount of art and that's
one reason for the popularity of 3D models... but that's another tutorial much
further down the road.

More importantly, it's time to discuss how to make these animations run more
smoothly.  More on that next time.

=head1 SEE ALSO

=over 4

=item L<SDL::Tutorial>

basic SDL tutorial

=item L<SDL::Tutorial::Animation>

non-image animation

=back

=head1 AUTHOR

chromatic, E<lt>chromatic@wgz.orgE<gt>

Written for and maintained by the Perl SDL project, L<http://sdl.perl.org/>.

=head1 BUGS

No known bugs.

=head1 COPYRIGHT

Copyright (c) 2004, chromatic.  All rights reserved.  This module is
distributed under the same terms as Perl itself, in the hope that it is useful
but certainly under no guarantee.
Commit	Line	Data
bfd90409	1	#!/usr/bin/env perl
	2	#
	3	# Images.pm
	4	#
	5	# Copyright (C) 2005 David J. Goehrig <dgoehrig@cpan.org>
	6	#
	7	# ------------------------------------------------------------------------------
	8	#
	9	# This library is free software; you can redistribute it and/or
	10	# modify it under the terms of the GNU Lesser General Public
	11	# License as published by the Free Software Foundation; either
	12	# version 2.1 of the License, or (at your option) any later version.
	13	#
	14	# This library is distributed in the hope that it will be useful,
	15	# but WITHOUT ANY WARRANTY; without even the implied warranty of
	16	# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	17	# Lesser General Public License for more details.
	18	#
	19	# You should have received a copy of the GNU Lesser General Public
	20	# License along with this library; if not, write to the Free Software
	21	# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
	22	#
	23	# ------------------------------------------------------------------------------
	24	#
	25	# Please feel free to send questions, suggestions or improvements to:
	26	#
	27	# David J. Goehrig
	28	# dgoehrig@cpan.org
	29	#
	30
	31	package SDL::Tutorial::Images;
	32
	33	use strict;
	34	use SDL;
	35	use warnings;
	36
	37	my %images;
	38	BEGIN
	39	{
	40	%images = (
	41	left => [qw(
	42	47 49 46 38 37 61 10 00 10 00 E7 00 00 00 00 00 01 01 01 02 02 02 03 03
	43	03 04 04 04 05 05 05 06 06 06 07 07 07 08 08 08 09 09 09 0A 0A 0A 0B 0B
	44	0B 0C 0C 0C 0D 0D 0D 0E 0E 0E 0F 0F 0F 10 10 10 11 11 11 12 12 12 13 13
	45	13 14 14 14 15 15 15 16 16 16 17 17 17 18 18 18 19 19 19 1A 1A 1A 1B 1B
	46	1B 1C 1C 1C 1D 1D 1D 1E 1E 1E 1F 1F 1F 20 20 20 21 21 21 22 22 22 23 23
	47	23 24 24 24 25 25 25 26 26 26 27 27 27 28 28 28 29 29 29 2A 2A 2A 2B 2B
	48	2B 2C 2C 2C 2D 2D 2D 2E 2E 2E 2F 2F 2F 30 30 30 31 31 31 32 32 32 33 33
	49	33 34 34 34 35 35 35 36 36 36 37 37 37 38 38 38 39 39 39 3A 3A 3A 3B 3B
	50	3B 3C 3C 3C 3D 3D 3D 3E 3E 3E 3F 3F 3F 40 40 40 41 41 41 42 42 42 43 43
	51	43 44 44 44 45 45 45 46 46 46 47 47 47 48 48 48 49 49 49 4A 4A 4A 4B 4B
	52	4B 4C 4C 4C 4D 4D 4D 4E 4E 4E 4F 4F 4F 50 50 50 51 51 51 52 52 52 53 53
	53	53 54 54 54 55 55 55 56 56 56 57 57 57 58 58 58 59 59 59 5A 5A 5A 5B 5B
	54	5B 5C 5C 5C 5D 5D 5D 5E 5E 5E 5F 5F 5F 60 60 60 61 61 61 62 62 62 63 63
	55	63 64 64 64 65 65 65 66 66 66 67 67 67 68 68 68 69 69 69 6A 6A 6A 6B 6B
	56	6B 6C 6C 6C 6D 6D 6D 6E 6E 6E 6F 6F 6F 70 70 70 71 71 71 72 72 72 73 73
	57	73 74 74 74 75 75 75 76 76 76 77 77 77 78 78 78 79 79 79 7A 7A 7A 7B 7B
	58	7B 7C 7C 7C 7D 7D 7D 7E 7E 7E 7F 7F 7F 80 80 80 81 81 81 82 82 82 83 83
	59	83 84 84 84 85 85 85 86 86 86 87 87 87 88 88 88 89 89 89 8A 8A 8A 8B 8B
	60	8B 8C 8C 8C 8D 8D 8D 8E 8E 8E 8F 8F 8F 90 90 90 91 91 91 92 92 92 93 93
	61	93 94 94 94 95 95 95 96 96 96 97 97 97 98 98 98 99 99 99 9A 9A 9A 9B 9B
	62	9B 9C 9C 9C 9D 9D 9D 9E 9E 9E 9F 9F 9F A0 A0 A0 A1 A1 A1 A2 A2 A2 A3 A3
	63	A3 A4 A4 A4 A5 A5 A5 A6 A6 A6 A7 A7 A7 A8 A8 A8 A9 A9 A9 AA AA AA AB AB
	64	AB AC AC AC AD AD AD AE AE AE AF AF AF B0 B0 B0 B1 B1 B1 B2 B2 B2 B3 B3
65	B3 B4 B4 B4 B5 B5 B5 B6 B6 B6 B7 B7 B7 B8 B8 B8 B9 B9 B9 BA BA BA BB BB
66	BB BC BC BC BD BD BD BE BE BE BF BF BF C0 C0 C0 C1 C1 C1 C2 C2 C2 C3 C3
67	C3 C4 C4 C4 C5 C5 C5 C6 C6 C6 C7 C7 C7 C8 C8 C8 C9 C9 C9 CA CA CA CB CB
68	CB CC CC CC CD CD CD CE CE CE CF CF CF D0 D0 D0 D1 D1 D1 D2 D2 D2 D3 D3
69	D3 D4 D4 D4 D5 D5 D5 D6 D6 D6 D7 D7 D7 D8 D8 D8 D9 D9 D9 DA DA DA DB DB
70	DB DC DC DC DD DD DD DE DE DE DF DF DF E0 E0 E0 E1 E1 E1 E2 E2 E2 E3 E3
71	E3 E4 E4 E4 E5 E5 E5 E6 E6 E6 E7 E7 E7 E8 E8 E8 E9 E9 E9 EA EA EA EB EB
72	EB EC EC EC ED ED ED EE EE EE EF EF EF F0 F0 F0 F1 F1 F1 F2 F2 F2 F3 F3
73	F3 F4 F4 F4 F5 F5 F5 F6 F6 F6 F7 F7 F7 F8 F8 F8 F9 F9 F9 FA FA FA FB FB
74	FB FC FC FC FD FD FD FE FE FE FF FF FF 2C 00 00 00 00 10 00 10 00 00 08
75	36 00 FF 09 1C 48 B0 A0 C1 83 08 13 22 04 C0 10 80 C2 7F 0C 05 46 4C E8
76	70 60 C5 85 15 27 52 6C A8 30 E3 45 8C 0D 39 76 FC 38 F2 A1 44 91 1B 4F
77	82 24 88 D2 64 C1 80 00 3B
78	)],
79	center => [qw(
80	47 49 46 38 37 61 10 00 10 00 E7 00 00 00 00 00 01 01 01 02 02 02 03 03
81	03 04 04 04 05 05 05 06 06 06 07 07 07 08 08 08 09 09 09 0A 0A 0A 0B 0B
82	0B 0C 0C 0C 0D 0D 0D 0E 0E 0E 0F 0F 0F 10 10 10 11 11 11 12 12 12 13 13
83	13 14 14 14 15 15 15 16 16 16 17 17 17 18 18 18 19 19 19 1A 1A 1A 1B 1B
84	1B 1C 1C 1C 1D 1D 1D 1E 1E 1E 1F 1F 1F 20 20 20 21 21 21 22 22 22 23 23
85	23 24 24 24 25 25 25 26 26 26 27 27 27 28 28 28 29 29 29 2A 2A 2A 2B 2B
86	2B 2C 2C 2C 2D 2D 2D 2E 2E 2E 2F 2F 2F 30 30 30 31 31 31 32 32 32 33 33
87	33 34 34 34 35 35 35 36 36 36 37 37 37 38 38 38 39 39 39 3A 3A 3A 3B 3B
88	3B 3C 3C 3C 3D 3D 3D 3E 3E 3E 3F 3F 3F 40 40 40 41 41 41 42 42 42 43 43
89	43 44 44 44 45 45 45 46 46 46 47 47 47 48 48 48 49 49 49 4A 4A 4A 4B 4B
90	4B 4C 4C 4C 4D 4D 4D 4E 4E 4E 4F 4F 4F 50 50 50 51 51 51 52 52 52 53 53
91	53 54 54 54 55 55 55 56 56 56 57 57 57 58 58 58 59 59 59 5A 5A 5A 5B 5B
92	5B 5C 5C 5C 5D 5D 5D 5E 5E 5E 5F 5F 5F 60 60 60 61 61 61 62 62 62 63 63
93	63 64 64 64 65 65 65 66 66 66 67 67 67 68 68 68 69 69 69 6A 6A 6A 6B 6B
94	6B 6C 6C 6C 6D 6D 6D 6E 6E 6E 6F 6F 6F 70 70 70 71 71 71 72 72 72 73 73
95	73 74 74 74 75 75 75 76 76 76 77 77 77 78 78 78 79 79 79 7A 7A 7A 7B 7B
96	7B 7C 7C 7C 7D 7D 7D 7E 7E 7E 7F 7F 7F 80 80 80 81 81 81 82 82 82 83 83
97	83 84 84 84 85 85 85 86 86 86 87 87 87 88 88 88 89 89 89 8A 8A 8A 8B 8B
98	8B 8C 8C 8C 8D 8D 8D 8E 8E 8E 8F 8F 8F 90 90 90 91 91 91 92 92 92 93 93
99	93 94 94 94 95 95 95 96 96 96 97 97 97 98 98 98 99 99 99 9A 9A 9A 9B 9B
100	9B 9C 9C 9C 9D 9D 9D 9E 9E 9E 9F 9F 9F A0 A0 A0 A1 A1 A1 A2 A2 A2 A3 A3
101	A3 A4 A4 A4 A5 A5 A5 A6 A6 A6 A7 A7 A7 A8 A8 A8 A9 A9 A9 AA AA AA AB AB
102	AB AC AC AC AD AD AD AE AE AE AF AF AF B0 B0 B0 B1 B1 B1 B2 B2 B2 B3 B3
103	B3 B4 B4 B4 B5 B5 B5 B6 B6 B6 B7 B7 B7 B8 B8 B8 B9 B9 B9 BA BA BA BB BB
104	BB BC BC BC BD BD BD BE BE BE BF BF BF C0 C0 C0 C1 C1 C1 C2 C2 C2 C3 C3
105	C3 C4 C4 C4 C5 C5 C5 C6 C6 C6 C7 C7 C7 C8 C8 C8 C9 C9 C9 CA CA CA CB CB
106	CB CC CC CC CD CD CD CE CE CE CF CF CF D0 D0 D0 D1 D1 D1 D2 D2 D2 D3 D3
107	D3 D4 D4 D4 D5 D5 D5 D6 D6 D6 D7 D7 D7 D8 D8 D8 D9 D9 D9 DA DA DA DB DB
108	DB DC DC DC DD DD DD DE DE DE DF DF DF E0 E0 E0 E1 E1 E1 E2 E2 E2 E3 E3
109	E3 E4 E4 E4 E5 E5 E5 E6 E6 E6 E7 E7 E7 E8 E8 E8 E9 E9 E9 EA EA EA EB EB
110	EB EC EC EC ED ED ED EE EE EE EF EF EF F0 F0 F0 F1 F1 F1 F2 F2 F2 F3 F3
111	F3 F4 F4 F4 F5 F5 F5 F6 F6 F6 F7 F7 F7 F8 F8 F8 F9 F9 F9 FA FA FA FB FB
112	FB FC FC FC FD FD FD FE FE FE FF FF FF 2C 00 00 00 00 10 00 10 00 00 08
113	36 00 FF 09 1C 48 B0 A0 C1 83 08 13 26 04 C0 10 80 C2 7F 0C 05 46 5C 48
114	D0 E1 42 8B 13 2F 66 54 B8 F1 60 C3 8F 16 2F 3E 1C D8 11 E1 C7 87 13 4B
115	4A DC D8 70 E4 C1 80 00 3B
116	)],
117	right => [qw(
118	47 49 46 38 37 61 10 00 10 00 E7 00 00 00 00 00 01 01 01 02 02 02 03 03
119	03 04 04 04 05 05 05 06 06 06 07 07 07 08 08 08 09 09 09 0A 0A 0A 0B 0B
120	0B 0C 0C 0C 0D 0D 0D 0E 0E 0E 0F 0F 0F 10 10 10 11 11 11 12 12 12 13 13
121	13 14 14 14 15 15 15 16 16 16 17 17 17 18 18 18 19 19 19 1A 1A 1A 1B 1B
122	1B 1C 1C 1C 1D 1D 1D 1E 1E 1E 1F 1F 1F 20 20 20 21 21 21 22 22 22 23 23
123	23 24 24 24 25 25 25 26 26 26 27 27 27 28 28 28 29 29 29 2A 2A 2A 2B 2B
124	2B 2C 2C 2C 2D 2D 2D 2E 2E 2E 2F 2F 2F 30 30 30 31 31 31 32 32 32 33 33
125	33 34 34 34 35 35 35 36 36 36 37 37 37 38 38 38 39 39 39 3A 3A 3A 3B 3B
126	3B 3C 3C 3C 3D 3D 3D 3E 3E 3E 3F 3F 3F 40 40 40 41 41 41 42 42 42 43 43
127	43 44 44 44 45 45 45 46 46 46 47 47 47 48 48 48 49 49 49 4A 4A 4A 4B 4B
128	4B 4C 4C 4C 4D 4D 4D 4E 4E 4E 4F 4F 4F 50 50 50 51 51 51 52 52 52 53 53
129	53 54 54 54 55 55 55 56 56 56 57 57 57 58 58 58 59 59 59 5A 5A 5A 5B 5B
130	5B 5C 5C 5C 5D 5D 5D 5E 5E 5E 5F 5F 5F 60 60 60 61 61 61 62 62 62 63 63
131	63 64 64 64 65 65 65 66 66 66 67 67 67 68 68 68 69 69 69 6A 6A 6A 6B 6B
132	6B 6C 6C 6C 6D 6D 6D 6E 6E 6E 6F 6F 6F 70 70 70 71 71 71 72 72 72 73 73
133	73 74 74 74 75 75 75 76 76 76 77 77 77 78 78 78 79 79 79 7A 7A 7A 7B 7B
134	7B 7C 7C 7C 7D 7D 7D 7E 7E 7E 7F 7F 7F 80 80 80 81 81 81 82 82 82 83 83
135	83 84 84 84 85 85 85 86 86 86 87 87 87 88 88 88 89 89 89 8A 8A 8A 8B 8B
136	8B 8C 8C 8C 8D 8D 8D 8E 8E 8E 8F 8F 8F 90 90 90 91 91 91 92 92 92 93 93
137	93 94 94 94 95 95 95 96 96 96 97 97 97 98 98 98 99 99 99 9A 9A 9A 9B 9B
138	9B 9C 9C 9C 9D 9D 9D 9E 9E 9E 9F 9F 9F A0 A0 A0 A1 A1 A1 A2 A2 A2 A3 A3
139	A3 A4 A4 A4 A5 A5 A5 A6 A6 A6 A7 A7 A7 A8 A8 A8 A9 A9 A9 AA AA AA AB AB
140	AB AC AC AC AD AD AD AE AE AE AF AF AF B0 B0 B0 B1 B1 B1 B2 B2 B2 B3 B3
141	B3 B4 B4 B4 B5 B5 B5 B6 B6 B6 B7 B7 B7 B8 B8 B8 B9 B9 B9 BA BA BA BB BB
142	BB BC BC BC BD BD BD BE BE BE BF BF BF C0 C0 C0 C1 C1 C1 C2 C2 C2 C3 C3
143	C3 C4 C4 C4 C5 C5 C5 C6 C6 C6 C7 C7 C7 C8 C8 C8 C9 C9 C9 CA CA CA CB CB
144	CB CC CC CC CD CD CD CE CE CE CF CF CF D0 D0 D0 D1 D1 D1 D2 D2 D2 D3 D3
145	D3 D4 D4 D4 D5 D5 D5 D6 D6 D6 D7 D7 D7 D8 D8 D8 D9 D9 D9 DA DA DA DB DB
146	DB DC DC DC DD DD DD DE DE DE DF DF DF E0 E0 E0 E1 E1 E1 E2 E2 E2 E3 E3
147	E3 E4 E4 E4 E5 E5 E5 E6 E6 E6 E7 E7 E7 E8 E8 E8 E9 E9 E9 EA EA EA EB EB
148	EB EC EC EC ED ED ED EE EE EE EF EF EF F0 F0 F0 F1 F1 F1 F2 F2 F2 F3 F3
149	F3 F4 F4 F4 F5 F5 F5 F6 F6 F6 F7 F7 F7 F8 F8 F8 F9 F9 F9 FA FA FA FB FB
150	FB FC FC FC FD FD FD FE FE FE FF FF FF 2C 00 00 00 00 10 00 10 00 00 08
151	3A 00 FF 09 1C 48 B0 A0 C1 83 08 13 2A 04 C0 10 80 C2 7F 0C 05 46 4C E8
152	70 60 45 84 13 27 52 6C F8 50 62 C5 8B 05 1B 8A 04 79 50 E3 43 93 1B 51
153	1A CC 48 D2 A2 49 8E 1D 0B 06 04 00 3B
154	)],
155	);
156	}
157
158	use Pod::ToDemo sub
159	{
160	(undef, my $filename) = @_;
161	(my $imagebase = $filename) =~ s/\.\w+$//;
162	my @img_files = map { $imagebase . "_$_.gif" }
163	qw( left center right );
164	my $demo_source = <<'END_HERE';
165	package Walker;
166
167	sub new
168	{
169	my ($class, @images) = @_;
170	my @frames = map { SDL::Surface->new( -name => $_ ) } @images;
171	my $frame_rect = SDL::Rect->new(
172	-height => $frames[0]->height(),
173	-width => $frames[0]->width(),
174	-x => 0,
175	-y => 0,
176	);
177	my $self =
178	{
179	frames => \@frames,
180	frame_rect => $frame_rect,
181	};
182	bless $self, $class;
183	}
184
185	sub frames
186	{
187	my $self = shift;
188	$self->{frames} = shift if @_;
189	$self->{frames};
190	}
191
192	sub frame_rect
193	{
194	my $self = shift;
195	$self->{frame_rect} = shift if @_;
196	$self->{frame_rect};
197	}
198
199	sub next_frame
200	{
201	my $self = shift;
202	my $frames = $self->frames();
203	my $frame = shift @$frames;
204
205	push @$frames, $frame;
206	$self->frames( $frames );
207
208	return $frame;
209	}
210
211	package main;
212
213	use strict;
214
215	use SDL;
216	use SDL::App;
217	use SDL::Surface;
218	use SDL::Color;
219
220	# change these values as necessary
221	my $title = 'My SDL Animation';
222	my ($width, $height, $depth) = ( 640, 480, 16 );
223	my ($bg_r, $bg_g, $bg_b) = ( 0xff, 0xff, 0xff );
224	my ($start_x, $end_x) = ( 20, 600 );
225	my $sleep_msec = 0.05;
226
227	my $app = SDL::App->new(
228	-width => $width,
229	-height => $height,
230	-depth => $depth,
231	);
232
233	my $bg_color = SDL::Color->new(
234	-r => $bg_r,
235	-g => $bg_g,
236	-b => $bg_b,
237	);
238
239	my $background = SDL::Rect->new(
240	-width => $width,
241	-height => $height,
242	);
243
244	my $pos = SDL::Rect->new(
245	-width => 16,
246	-height => 16,
247	-x => 0,
248	-y => 240,
249	);
250
251	my $walker = Walker->new(qw(
252	END_HERE
253
254	$demo_source .= join( ' ', @img_files ) . "));" . <<'END_HERE';
255
256	for my $x ( $start_x .. $end_x )
257	{
258	draw_background( $app, $background, $bg_color );
259	$pos->x( $x );
260	draw_walker( $walker, $app, $pos );
261	$app->update( $background );
262	select( undef, undef, undef, $sleep_msec );
263	}
264
265	# you'll want to remove this
266	sleep 2;
267
268	sub draw_background
269	{
270	my ($app, $background, $bg_color) = @_;
271	$app->fill( $background, $bg_color );
272	}
273
274	sub draw_walker
275	{
276	my ($walker, $app, $pos) = @_;
277	my $frame = $walker->next_frame();
278	my $frame_rect = $walker->frame_rect();
279	$frame->blit( $frame_rect, $app, $pos );
280	}
281	END_HERE
282
283	Pod::ToDemo::write_demo( $filename, "#$^X\n$demo_source" );
284	write_files( $imagebase );
285	};
286
287	sub write_files
288	{
289	my $imagebase = shift;
290
291	for my $image (qw( left center right ))
292	{
293	my $file = join('', map { chr( hex( $_ ) ) } @{ $images{ $image } });
294	write_file( $imagebase . "_$image" . '.gif', $file );
295	}
296	}
297
298	sub write_file
299	{
300	my ($file, $contents) = @_;
301
302	die "Cowardly refusing to overwrite '$file'\n" if -e $file;
303	open my $out, '>', $file or die "Cannot write '$file': $!\n";
304	binmode $out;
305	print $out $contents;
306	}
307
308	__END__
309
310	=head1 NAME
311
312	SDL::Tutorial::Images
313
314	=head1 SYNOPSIS
315
316	# to read this tutorial
317	$ perldoc SDL::Tutorial::Images
318
319	# to create a demo animation program based on this tutorial
320	$ perl -MSDL::Tutorial::Images=sdl_images.pl -e 1
321
322	=head1 ANIMATING IMAGES
323
324	Since you're already familiar with the concepts behind animation, it's time to
325	learn how to work with images. As usual, the important point is that computer animation is just I<simulating> motion by painting several slightly different frames to the screen every second.
326
327	There are two ways to vary an image on screen. One is to change its
328	coordinates so it's at a slightly different position. This is very easy to do;
329	it's just like animating a rectangle. The other way is to change the image
330	itself so it's slightly different. This is a little more difficult, as you'll
331	need to draw the alternate image beforehand somehow.
332
333	=head2 Loading Images
334
335	As usual, start with an L<SDL::App> object representing the image window. Then
336	preload the image file. This is easy; just pass the C<name> parameter to the
337	L<SDL::Surface> constructor:
338
339	use SDL::Surface;
340
341	my $frame = SDL::Surface->new( -name => 'frame1.png' );
342
343	B<Note:> you'll need to have compiled SDL Perl (and probably SDL) to support
344	JPEG and PNG files for this to work.
345
346	That's it; now you have an SDL::Surface object containing the image. You can
347	use the C<height()>, C<width()>, and C<bpp()> methods to retrieve its height,
348	width, and bits per pixel, if you need them.
349
350	=head2 Displaying Images
351
352	Drawing an image onto the screen requires blitting it from one surface to
353	another. (Remember, "blitting" means copying bits in memory.) The C<blit()>
354	method of SDL::Surface objects comes in handy. Its arguments are a little odd,
355	though. Assuming C<$app> is the SDL::App object, as usual:
356
357	use SDL::Rect;
358
359	my $frame_rect = SDL::Rect->new(
360	-height => $frame->height(),
361	-width => $frame->width(),
362	-x => 0,
363	-y => 0,
364	);
365
366	my $dest_rect = SDL::Rect->new(
367	-height => $frame->height(),
368	-width => $frame->width(),
369	-x => 0,
370	-y => 0,
371	);
372
373	$frame->blit( $frame_rect, $app, $dest_rect );
374	$app->update( $dest_rect );
375
376	Here we have two L<SDL::Rect> objects which represent rectangular regions of a
377	Surface. C<$frame_rect> represents the entire area of C<$frame>, while
378	C<$dest_rect> represents the area of the main window in which to blit the
379	frame. This may be clearer with more descriptive variable names:
380
381	$source_surface->blit(
382	$area_of_source_to_blit,
383	$destination_surface,
384	$destination_area
385	);
386
387	As usual, call C<update()> on C<$app> to see the change.
388
389	Requiring the source and destination Rect objects may seem tedious in this
390	simple example, but it's highly useful for copying only part of surface to part
391	of another. For example, animating this image is a matter of changing the C<x>
392	and C<y> coordinates of C<$dest_rect>:
393
394	for my $x ( 1 .. 100 )
395	{
396	$dest_rect->x( $x );
397	$frame->blit( $frame_rect, $app, $dest_rect );
398	$app->update( $dest_rect );
399	}
400
401	Of course, you'll have to redraw all or part of the screen to avoid artifacts,
402	as discussed in the previous tutorial.
403
404	=head2 Multi-Image Animation
405
406	That covers moving a single image around the screen. What if you want
407	something more? For example, what if you want to animate a stick figure
408	walking?
409
410	You'll need several frames, just as in a flip-book. Each frame should be slightly different than the one before it. It's probably handy to encapsulate all of this in a C<Walker> class:
411
412	package Walker;
413
414	use SDL::Surface;
415
416	sub new
417	{
418	my ($class, @images) = @_;
419	my $self = [ map { SDL::Surface->new( -name => $_ ) } @images ];
420
421	bless $self, $class;
422	}
423
424	sub next_frame
425	{
426	my $self = shift;
427	my $frame = shift @$self;
428
429	push @$self, $frame;
430	return $frame;
431	}
432
433	To use this class, instantiate an object:
434
435	my $walker = Walker->new( 'frame1.png', 'frame2.png', 'frame3.png' );
436
437	Then call C<next_frame()> within the loop:
438
439	for my $x ( 1 .. 100 )
440	{
441	my $frame = $walker->next_frame();
442
443	$dest_rect->x( $x );
444	$frame->blit( $frame_rect, $app, $dest_rect );
445	$app->update( $dest_rect );
446	}
447
448	Again, the rest of the frame drawing is missing from this example so as not to
449	distract from this technique. You'll probably want to abstract the undrawing
450	and redrawing into a separate subroutine so you don't have to worry about it
451	every time.
452
453	It'd be easy to make C<next_frame()> much smarter, selecting an image
454	appropriate to the direction of travel, using a bored animation when the
455	character is no longer moving, or adding other characteristics to the
456	character. As you can see, the hard part of this technique is generating the
457	images beforehand. That can add up to a tremendous amount of art and that's
458	one reason for the popularity of 3D models... but that's another tutorial much
459	further down the road.
460
461	More importantly, it's time to discuss how to make these animations run more
462	smoothly. More on that next time.
463
464	=head1 SEE ALSO
465
466	=over 4
467
468	=item L<SDL::Tutorial>
469
470	basic SDL tutorial
471
472	=item L<SDL::Tutorial::Animation>
473
474	non-image animation
475
476	=back
477
478	=head1 AUTHOR
479
480	chromatic, E<lt>chromatic@wgz.orgE<gt>
481
482	Written for and maintained by the Perl SDL project, L<http://sdl.perl.org/>.
483
484	=head1 BUGS
485
486	No known bugs.
487
488	=head1 COPYRIGHT
489
490	Copyright (c) 2004, chromatic. All rights reserved. This module is
491	distributed under the same terms as Perl itself, in the hope that it is useful
492	but certainly under no guarantee.