Created
August 3, 2010 15:36
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package Gif; | |
use 5.12.1; | |
use strict; | |
use warnings; | |
use Carp; | |
sub new { | |
my ($class, $file) = @_; | |
my $self = bless {}, $class; | |
$self->{file} = $file; | |
return $self; | |
} | |
sub parse { | |
my ($self) = @_; | |
open $self->{fh}, '<', $self->{file} or die "can't read $self->{file}: $@"; | |
binmode($self->{fh}); | |
$self->{position} = 0; | |
$self->parse_header or die "$self->{file} is not GIF89a"; | |
while (my $block = $self->parse_block) { | |
push @{$self->{blocks}}, $block; | |
given ($block->{type}) { | |
when ('graphic control extension') { | |
push @{$self->{images}}, { | |
start => $block->{start}, | |
length => $block->{length}, | |
}; | |
} | |
when ('image') { | |
my $img = $self->{images}->[-1]; | |
$img->{length} += $block->{length}; | |
} | |
when ('trailer') { | |
last; | |
} | |
} | |
} | |
delete $self->{fh}; | |
} | |
sub extract_image { | |
my ($self, $index) = @_; | |
my $image = $self->{images}->[$index] or return; | |
open my $fh, '<', $self->{file} or return; | |
binmode($fh); | |
seek $fh, $image->{start}, 0; | |
read $fh, my $data, $image->{length}; | |
return $self->{header} . | |
$self->{global_color_table} . | |
$data . | |
chr(0x3B); | |
} | |
sub parse_header { | |
my ($self) = @_; | |
$self->{header} = $self->read(13); | |
$self->{header} =~ m{^GIF89a} or return; | |
my ($h, $w, $packed) = unpack('vvC', substr($self->{header},6)); | |
$self->{height} = $h; | |
$self->{width} = $w; | |
my $global_color_table_flag = $packed & 0b10000000; | |
$self->{resolution} = ($packed & 0b01110000 >> 4) + 1; | |
my $sort_flag = 0b00001000; | |
my $size = (2 ** (($packed & 0b00000111) + 1)) * 3; | |
$self->{global_color_table} = $self->read($size); | |
return 1; | |
} | |
sub parse_block { | |
my ($self) = shift; | |
my $pos = $self->{position}; | |
my $intro = $self->readint; | |
my $type = 'unknown'; | |
given ($intro) { | |
when (0x21) { | |
my $label = $self->readint; | |
given ($label) { | |
when (0x01) { | |
$type = 'plain text extension'; | |
} | |
when (0xfe) { | |
$type = 'comment extension'; | |
} | |
when (0xf9) { | |
$type = 'graphic control extension'; | |
} | |
when (0xff) { | |
$type = 'application extension'; | |
} | |
default { | |
confess "unknown extension label: $label"; | |
} | |
} | |
$self->readdataseq; | |
} | |
when (0x2C) { | |
$type = 'image'; | |
$self->read(8); | |
my $b = $self->readint; | |
if ($b & 0b10000000) { | |
my $size = $b & 0b00000111; | |
$self->read((2 ** ($size + 1)) * 3); # local color table | |
} | |
$self->read(1); # lzw minimum code size | |
$self->readdataseq; | |
} | |
when (0x3B) { | |
$type = 'trailer'; | |
} | |
default { | |
die "unknown intro: $intro"; | |
} | |
} | |
my $length = $self->{position} - $pos; | |
return { | |
type => $type, | |
start => $pos, | |
length => $length, | |
}; | |
} | |
sub read { | |
my ($self, $length) = @_; | |
my $size = CORE::read($self->{fh}, my $data, $length); | |
if (! defined $size) { | |
confess "reading error: $@"; | |
} elsif ($size != $length) { | |
confess "reached EOF: $self->{position}"; | |
} | |
$self->{position} += $size; | |
return $data; | |
} | |
sub readint { | |
my ($self) = @_; | |
return ord($self->read(1)); | |
} | |
sub readdataseq { | |
my ($self) = @_; | |
my $i; | |
while (1) { | |
$self->readdata or last; | |
} | |
} | |
sub readdata { | |
my ($self) = @_; | |
my $size = $self->readint or return; | |
return $self->read($size); | |
} | |
1; |
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