package Image::Info::GIF;
# Copyright 1999-2000, Gisle Aas.
#
# This library is free software; you can redistribute it and/or
# modify it under the same terms as Perl itself.
=begin register
MAGIC: /^GIF8[79]a/
Both GIF87a and GIF89a are supported and the version number is found
as C for the first image. GIF files can contain multiple
images, and information for all images will be returned if
image_info() is called in list context. The Netscape-2.0 extention to
loop animation sequences is represented by the C key for the
first image. The value is either "forever" or a number indicating
loop count.
=end register
=cut
use strict;
sub my_read
{
my($source, $len) = @_;
my $buf;
my $n = read($source, $buf, $len);
die "read failed: $!" unless defined $n;
die "short read ($len/$n)" unless $n == $len;
$buf;
}
sub read_data_blocks
{
my $source = shift;
my @data;
while (my $len = ord(my_read($source, 1))) {
push(@data, my_read($source, $len));
}
join("", @data);
}
sub process_file
{
my($info, $fh) = @_;
my $header = my_read($fh, 13);
die "Bad GIF signature"
unless $header =~ s/^GIF(8[79]a)//;
my $version = $1;
$info->push_info(0, "GIF_Version" => $version);
# process logical screen descriptor
my($sw, $sh, $packed, $bg, $aspect) = unpack("vvCCC", $header);
$info->push_info(0, "ScreenWidth" => $sw);
$info->push_info(0, "ScreenHeight" => $sh);
my $color_table_size = 1 $info->push_info(0, "ColorTableSize" => $color_table_size);
$info->push_info(0, "SortedColors" => ($packed & 0x08) ? 1 : 0)
if $version eq "89a";
$info->push_info(0, "ColorResolution", (($packed & 0x70) >> 4) + 1);
my $global_color_table = $packed & 0x80;
$info->push_info(0, "GlobalColorTableFlag" => $global_color_table ? 1 : 0);
if ($global_color_table) {
$info->push_info(0, "BackgroundColor", $bg);
}
if ($aspect) {
$aspect = ($aspect + 15) / 64;
$info->push_info(0, "PixelAspectRatio" => $aspect);
# XXX is this correct????
$info->push_info(0, "resolution", "1/$aspect");
}
else {
$info->push_info(0, "resolution", "1/1");
}
$info->push_info(0, "file_media_type" => "image/gif");
$info->push_info(0, "file_ext" => "gif");
# more??
if ($global_color_table) {
my $color_table = my_read($fh, $color_table_size * 3);
#$info->push_info(0, "GlobalColorTable", color_table($color_table));
}
my $img_no = 0;
my @comments;
my @warnings;
while (1) {
my $intro = ord(my_read($fh, 1));
if ($intro == 0x3B) { # trailer (end of image)
last;
}
elsif ($intro == 0x2C) { # new image
if (@comments) {
for (@comments) {
$info->push_info(0, "Comment", $_);
}
@comments = ();
}
$info->push_info($img_no, "color_type" => "Indexed-RGB");
my($x_pos, $y_pos, $w, $h, $packed) =
unpack("vvvvC", my_read($fh, 9));
$info->push_info($img_no, "XPosition", $x_pos);
$info->push_info($img_no, "YPosition", $y_pos);
$info->push_info($img_no, "width", $w);
$info->push_info($img_no, "height", $h);
if ($packed & 0x80) {
# yes, we have a local color table
my $ct_size = 1 $info->push_info($img_no, "LColorTableSize" => $ct_size);
my $color_table = my_read($fh, $ct_size * 3);
}
$info->push_info($img_no, "Interlace" => "GIF")
if $packed & 0x40;
my $lzw_code_size = ord(my_read($fh, 1));
#$info->push_info($img_no, "LZW_MininmCodeSize", $lzw_code_size);
read_data_blocks($fh); # skip image data
$img_no++;
}
elsif ($intro == 0x21) { # GIF89a extension
push(@warnings, "GIF 89a extensions in 87a")
if $version eq "87a";
my $label = ord(my_read($fh, 1));
my $data = read_data_blocks($fh);
if ($label == 0xF9 && length($data) == 4) { # Graphic Control
my($packed, $delay, $trans_color) = unpack("CvC", $data);
my $disposal_method = ($packed >> 2) & 0x07;
$info->push_info($img_no, "DisposalMethod", $disposal_method)
if $disposal_method;
$info->push_info($img_no, "UserInput", 1)
if $packed & 0x02;
$info->push_info($img_no, "Delay" => $delay/100) if $delay;
$info->push_info($img_no, "TransparencyIndex" => $trans_color)
if $packed & 0x01;
}
elsif ($label == 0xFE) { # Comment
$data =~ s/\0+$//; # is often NUL-terminated
push(@comments, $data);
}
elsif ($label == 0xFF) { # Application
my $app = substr($data, 0, 11, "");
my $auth = substr($app, -3, 3, "");
if ($app eq "NETSCAPE" && $auth eq "2.0"
&& $data =~ /^\01/) {
my $loop = unpack("xv", $data);
$loop = "forever" unless $loop;
$info->push_info($img_no, "GIF_Loop" => $loop);
} else {
$info->push_info($img_no, "APP-$app-$auth" => $data);
}
}
else {
$info->push_info($img_no, "GIF_Extension-$label" => $data);
}
}
else {
die "Unknown introduced code $intro, bad GIF";
}
}
for (@comments) {
$info->push_info(0, "Comment", $_);
}
for (@warnings) {
$info->push_info(0, "Warn", $_);
}
}
sub color_table
{
my @n = unpack("C*", shift);
die "Color table not a multiple of 3" if @n % 3;
my @table;
while (@n) {
my @triple = splice(@n, -3);
push(@table, sprintf("#%02x%02x%02x", @triple));
}
[reverse @table];
}
1;
