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package Image::JpegMinimal; |
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use strict; |
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use Imager; |
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46871
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use Carp qw(croak carp); |
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use MIME::Base64 'encode_base64'; |
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use vars '$VERSION'; |
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$VERSION = '0.01'; |
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=head1 NAME |
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Image::JpegMinimal - create JPEG previews without headers |
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=head1 SYNOPSIS |
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my $compressor = Image::JpegMinimal->new( |
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xmax => 42, |
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ymax => 42, |
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jpegquality => 20, |
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); |
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sub gen_img { |
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my @tags; |
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for my $file (@_) { |
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my $imager = Imager->new( file => $file ); |
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my $preview = $compressor->data_preview( $file ); |
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my ($w, $h ) = ($imager->getwidth,$imager->getheight); |
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my $html = <
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data-preview="$preview" |
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src="$file" |
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/> |
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HTML |
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push @tags, $html; |
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}; |
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return @tags |
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} |
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# This goes into your HTML |
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print join "\n", gen_img(@ARGV); |
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44
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# The headers accumulate in $compressor |
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my %headers = $compressor->headers; |
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47
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# This goes into your Javascript |
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print $headers{l}; |
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print $headers{p}; |
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51
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=head1 DESCRIPTION |
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53
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This module implements the ideas from |
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L |
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to create the data needed for inline previews of images that can be served |
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within the HTML page while keeping a low overhead of around 250 bytes per |
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image preview. This is achieved by splitting up the preview image into |
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a JPEG header which is common to all images and the JPEG image data. |
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With a Javascript-enabled browser, these previews will be shown until |
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the request for the real image has finished loading the data. This reduces |
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the latency and bandwidth needed until the user sees an image. |
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63
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It turns the following image |
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=for html |
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68
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into 250 bytes of image data representing this image: |
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70
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=for html |
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73
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The Javascript on the client side then scales and blurs that preview |
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image to create a very blurry placeholder until the real image data |
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arrives from the server. |
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=for html |
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79
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80
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See below for the Javascript needed to reassemble the image data |
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from the split header and scan data. |
82
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83
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=head1 METHODS |
84
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85
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=head2 C<< Image::JpegMinimal->new( %OPTIONS ) >> |
86
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87
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my $compressor = Image::JpegMinimal->new( |
88
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xmax => 42, |
89
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ymax => 42, |
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jpegquality => 20, |
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); |
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93
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Creates a new compressor object. The C and C values |
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give the maximum dimensions for the size of the preview image. |
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It is suggested that the preview image is heavily blurred when |
96
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presenting the preview image to the user to hide the JPEG artifacts. |
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98
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=cut |
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100
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sub new { |
101
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1
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27
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my( $class, %options ) = @_; |
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103
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# We really need Jpeg-support |
104
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croak "We really need jpeg support but your version of Imager doesn't support it" |
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1
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18
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unless $Imager::formats{'jpeg'}; |
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107
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$options{ jpegquality } ||= 20; |
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$options{ xmax } ||= 42; |
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$options{ ymax } ||= 42; |
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111
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bless \%options => $class |
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} |
113
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114
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sub get_imager { |
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my( $self, $file ) = @_; |
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# We should check that Imager can write jpeg images |
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0
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Imager->new( file => $file ) |
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or croak "Couldn't read $file: " . Imager->errstr(); |
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} |
120
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121
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sub compress_image { |
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my( $self, $file, $xmax, $ymax, $jpegquality ) = @_; |
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$xmax ||= $self->{xmax}; |
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$ymax ||= $self->{ymax}; |
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$jpegquality ||= $self->{jpegquality}; |
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0
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my $imager = $self->get_imager( $file ); |
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128
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# Rotate if EXIF data indicates portrait, this wrecks our headers, |
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# so disabled :-(( |
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# We need two headers, one for portrait and one for landscape |
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if( my $orientation = $imager->tags(name => 'exif_orientation')) { |
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my %rotate = ( |
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1 => 0, |
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#2 => 180, |
135
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3 => 180, |
136
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#4 => 0, |
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#5 => 90, |
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6 => 270, |
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#7 => 0, |
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8 => 90, |
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); |
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my $deg = $rotate{ $orientation }; |
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$imager = $imager->rotate( right => $deg ); |
144
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}; |
145
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146
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# Resize |
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$imager = $imager->scale(xpixels=> $xmax, ypixels=> $ymax, type=>'min') |
148
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or die Imager->errstr; |
149
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# Write with Q20 |
150
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$imager->write(type => 'jpeg', data => \my $data, jpegquality => $jpegquality); |
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152
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# Debug output for checking the original and reconstruction |
153
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# of the image data in base64 |
154
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#(my $data64 = encode_base64($data)) =~ s!\s+!!g; |
155
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#print $data64,"\n"; |
156
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157
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my( $width,$height ) = ($imager->getheight, $imager->getwidth); |
158
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return ($width,$height,$data); |
159
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} |
160
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161
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sub strip_header { |
162
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my( $self,$width,$height,$jpeg ) = @_; |
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164
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# Deparse the JPEG file into its sections |
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# Maybe some other module already provides a JPEG header parser? |
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0
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my @sections; |
167
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0
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while($jpeg =~ /\G(((\x{ff}[^\0\x{d8}\x{d9}])(..))|\x{ff}\x{d8}|\x{ff}\x{d9})/csg) { |
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my $header = $3 || $1; |
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my $payload; |
170
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if( $header eq "\x{ff}\x{da}" ) { |
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0
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171
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# Start of scan |
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0
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$payload = substr( $jpeg, pos($jpeg)-2, length($jpeg)-pos($jpeg)+2); |
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0
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pos($jpeg) = pos($jpeg) + length $payload; |
174
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} elsif( $header eq "\x{ff}\x{d8}" ) { |
175
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# Start of image |
176
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0
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$payload = ""; |
177
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} elsif( $header eq "\x{ff}\x{d9}" ) { |
178
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# End of Image |
179
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0
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$payload = ""; |
180
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} else { |
181
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0
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my $length = unpack "n", $4; |
182
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0
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$payload = substr( $jpeg, pos($jpeg)-2, $length ); |
183
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0
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pos($jpeg) = pos($jpeg) + $length -2; |
184
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}; |
185
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0
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push @sections, { type => $header, payload => $payload } |
186
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}; |
187
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188
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0
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my %priority = ( |
189
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"\x{ff}\x{d8}" => 0, |
190
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"\x{ff}\x{c4}" => 1, |
191
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"\x{ff}\x{db}" => 2, |
192
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"\x{ff}\x{c0}" => 50, |
193
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"\x{ff}\x{da}" => 98, |
194
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"\x{ff}\x{d9}" => 99, |
195
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); |
196
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197
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# Only keep the important sections |
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0
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@sections = grep { exists $priority{ $_->{type}}} @sections; |
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199
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# Reorder them so that the image dimensions are at the end |
200
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0
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@sections = sort {$priority{$a->{type}} <=> $priority{$b->{type}}} @sections; |
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0
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201
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202
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#for my $s (@sections) { |
203
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# print sprintf "%02x%02x - %04d\n", unpack( "CC", $s->{type}), length $s->{payload}; |
204
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#}; |
205
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206
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# Reassemble the (relevant) sections |
207
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my $header = join "", |
208
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0
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map { $_->{type}, $_->{payload }} |
209
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0
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0
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grep { $_->{type} ne "\x{ff}\x{da}" and $_->{type} ne "\x{ff}\x{d9}" } |
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210
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@sections; |
211
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212
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my $payload = join "", |
213
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0
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map { $_->{type}, $_->{payload }} |
214
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0
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0
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grep { $_->{type} eq "\x{ff}\x{da}" or $_->{type} eq "\x{ff}\x{d9}" } |
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0
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215
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@sections; |
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my $min_header = $header; |
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# Do the actual packing |
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my $stripped = pack "CCA*", $width, $height, $payload; |
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($stripped,$min_header) |
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}; |
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sub btoa { |
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my( $self, $data ) = @_; |
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(my $res64 = encode_base64($data)) =~ s!\s+!!g; |
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$res64 |
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} |
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sub split_image { |
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my( $self, $file, $xmax, $ymax ) = @_; |
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$xmax ||= $self->{xmax}; |
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$ymax ||= $self->{ymax}; |
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my($width,$height, $data) = $self->compress_image( $file, $xmax, $ymax ); |
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my $orientation = $self->get_orientation( $width, $height ); |
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my( $payload, $min_header ) = $self->strip_header( $width,$height,$data ); |
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$self->{header}->{$orientation} ||= $self->btoa( $min_header ); |
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carp "Inconsistent header data" |
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if $self->{header}->{$orientation} ne $self->btoa( $min_header ); |
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return ($payload, $min_header) |
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}; |
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=head2 C<< $compressor->data_preview >> |
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my $data_preview = $compressor->data_preview( $file ); |
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Reads the JPEG data from a file and returns a base64 encoded string of |
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the reduced image data. You stuff this into the C<< data-preview >> |
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attribute of the C<< img >> tag in your HTML. |
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254
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=cut |
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256
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sub data_preview { |
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1
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my( $self, $file, $xmax, $ymax ) = @_; |
258
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$xmax ||= $self->{xmax}; |
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$ymax ||= $self->{ymax}; |
260
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261
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my( $payload, $min_header ) = $self->split_image( $file, $xmax, $ymax ); |
262
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263
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my $payload64 = $self->btoa($payload); |
264
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265
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return $payload64; |
266
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} |
267
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268
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sub get_orientation { |
269
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my( $self, $w, $h ) = @_; |
270
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0
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0
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if( $w < $h ) { |
271
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return 'p' # portrait |
272
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} else { |
273
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return 'l' # landscape |
274
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}; |
275
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}; |
276
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277
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=head2 C<< $compressor->headers >> |
278
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279
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my %headers = $compressor->headers; |
280
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281
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After processing all files, this method |
282
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returns the headers that are common to the images. |
283
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You need to pass this to your Javascript. |
284
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285
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=cut |
286
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287
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sub headers { |
288
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0
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0
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1
|
|
my( $self, $file, $xmax, $ymax ) = @_; |
289
|
0
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0
|
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|
|
$xmax ||= $self->{xmax}; |
290
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0
|
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0
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|
|
$ymax ||= $self->{ymax}; |
291
|
|
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292
|
0
|
0
|
|
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|
|
if( 2 != scalar values %{ $self->{ header }}) { |
|
0
|
|
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|
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|
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293
|
|
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|
|
|
|
# We need to extract at least one header from the image |
294
|
0
|
|
|
|
|
|
my( $data, $header) = $self->split_image( $file, $xmax, $ymax ); |
295
|
|
|
|
|
|
|
# sets one entry in $self->{header} as a side effect |
296
|
|
|
|
|
|
|
}; |
297
|
|
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298
|
0
|
|
|
|
|
|
%{ $self->{header} }; |
|
0
|
|
|
|
|
|
|
299
|
|
|
|
|
|
|
} |
300
|
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301
|
|
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|
|
=head1 HTML |
302
|
|
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|
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303
|
|
|
|
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|
|
Each image that has a pre-preview placeholder will need to store the |
304
|
|
|
|
|
|
|
placeholder data in the C<< data-preview >> attribute. That is all |
305
|
|
|
|
|
|
|
the modification you need. You should also set the C<< width >> |
306
|
|
|
|
|
|
|
and C<< height >> attributes of the image so that no ugly image-popping |
307
|
|
|
|
|
|
|
occurs when the real data arrives. The C<< $payload64 >> is the data |
308
|
|
|
|
|
|
|
that is returned from the C<< ->data_preview >> call. |
309
|
|
|
|
|
|
|
|
310
|
|
|
|
|
|
|
|
311
|
|
|
|
|
|
|
data-preview="$payload64" |
312
|
|
|
|
|
|
|
src="$file" |
313
|
|
|
|
|
|
|
/> |
314
|
|
|
|
|
|
|
|
315
|
|
|
|
|
|
|
=head1 JAVASCRIPT |
316
|
|
|
|
|
|
|
|
317
|
|
|
|
|
|
|
You will need to include some Javascript like the following in your |
318
|
|
|
|
|
|
|
page, preferrably near the end so the code runs right after |
319
|
|
|
|
|
|
|
the HTML has loaded completely but image loading has not yet fired. |
320
|
|
|
|
|
|
|
|
321
|
|
|
|
|
|
|
The hash C<%headers> should be set to the base64 |
322
|
|
|
|
|
|
|
encoded fixed headers as returned by the C<< ->headers( $file ) >> call. |
323
|
|
|
|
|
|
|
The image HTML should have been constructed as outlined above. |
324
|
|
|
|
|
|
|
|
325
|
|
|
|
|
|
|
"use strict"; |
326
|
|
|
|
|
|
|
|
327
|
|
|
|
|
|
|
var header = { |
328
|
|
|
|
|
|
|
l : atob("$headers{l}"), |
329
|
|
|
|
|
|
|
h : atob("$headers{p}"), |
330
|
|
|
|
|
|
|
}; |
331
|
|
|
|
|
|
|
function reconstruct(data) { |
332
|
|
|
|
|
|
|
// Reconstruct a JPEG header from our special data structure |
333
|
|
|
|
|
|
|
var raw = atob(data); |
334
|
|
|
|
|
|
|
// Keep as "char" so we don't have to bother with Unicode vs. ASCII |
335
|
|
|
|
|
|
|
var width = raw.charAt(0); |
336
|
|
|
|
|
|
|
var height = raw.charAt(1); |
337
|
|
|
|
|
|
|
var payload = raw.substring(2,raw.length); |
338
|
|
|
|
|
|
|
var head; |
339
|
|
|
|
|
|
|
if( width < height ) { |
340
|
|
|
|
|
|
|
head = header["p"] |
341
|
|
|
|
|
|
|
} else { |
342
|
|
|
|
|
|
|
head = header["l"] |
343
|
|
|
|
|
|
|
}; |
344
|
|
|
|
|
|
|
var dimension_patch = width+height; |
345
|
|
|
|
|
|
|
var patched_header = head.substring(0,head.length-13) |
346
|
|
|
|
|
|
|
+ width |
347
|
|
|
|
|
|
|
+ head.substring(head.length-12,head.length-11) |
348
|
|
|
|
|
|
|
+ height |
349
|
|
|
|
|
|
|
+ head.substring(head.length-10,head.length); |
350
|
|
|
|
|
|
|
var reconstructed = patched_header+payload; |
351
|
|
|
|
|
|
|
var encoded = "data:image/jpeg;base64,"+btoa(reconstructed); |
352
|
|
|
|
|
|
|
return encoded; |
353
|
|
|
|
|
|
|
} |
354
|
|
|
|
|
|
|
|
355
|
|
|
|
|
|
|
var image_it = document.evaluate("//img[\@data-preview]",document, null, XPathResult.ANY_TYPE, null); |
356
|
|
|
|
|
|
|
var images = []; |
357
|
|
|
|
|
|
|
var el = image_it.iterateNext(); |
358
|
|
|
|
|
|
|
while( el ) { |
359
|
|
|
|
|
|
|
images.push(el); |
360
|
|
|
|
|
|
|
el = image_it.iterateNext(); |
361
|
|
|
|
|
|
|
}; |
362
|
|
|
|
|
|
|
|
363
|
|
|
|
|
|
|
for( var i = 0; i < images.length; i++ ) { |
364
|
|
|
|
|
|
|
var el = images[ i ]; |
365
|
|
|
|
|
|
|
if( !el.complete || el.naturalWidth == 0 || el.naturalHeight == 0) { |
366
|
|
|
|
|
|
|
|
367
|
|
|
|
|
|
|
var fullsrc = el.src; |
368
|
|
|
|
|
|
|
var loadsrc = reconstruct( el.getAttribute("data-preview")); |
369
|
|
|
|
|
|
|
var container = document.createElement('div'); |
370
|
|
|
|
|
|
|
container.style.overflow = "hidden"; |
371
|
|
|
|
|
|
|
container.style.display = "inline"; |
372
|
|
|
|
|
|
|
container.style.position = "relative"; |
373
|
|
|
|
|
|
|
|
374
|
|
|
|
|
|
|
var parent = el.parentNode; |
375
|
|
|
|
|
|
|
parent.insertBefore(container, el); |
376
|
|
|
|
|
|
|
container.appendChild(el); |
377
|
|
|
|
|
|
|
|
378
|
|
|
|
|
|
|
// Set up the placeholder data |
379
|
|
|
|
|
|
|
el.src = loadsrc; |
380
|
|
|
|
|
|
|
el.style.filter = "blur(8px)"; |
381
|
|
|
|
|
|
|
var img = document.createElement('img'); |
382
|
|
|
|
|
|
|
img.width = el.width; |
383
|
|
|
|
|
|
|
img.height = el.height; |
384
|
|
|
|
|
|
|
// Shouldn't we also copy the style and maybe even some events?! |
385
|
|
|
|
|
|
|
// img = el.cloneNode(true); // except this doesn't copy the eventListeners etc. Duh. |
386
|
|
|
|
|
|
|
(function(img,container,src) { |
387
|
|
|
|
|
|
|
img.onload = function() { |
388
|
|
|
|
|
|
|
// Put the loaded child in the place of the preloaded data |
389
|
|
|
|
|
|
|
parent.replaceChild(img,container); |
390
|
|
|
|
|
|
|
}; |
391
|
|
|
|
|
|
|
var timeout = 1000+Math.random()*3000; |
392
|
|
|
|
|
|
|
// Kick off the loading |
393
|
|
|
|
|
|
|
// The timeout is just for demonstration purposes |
394
|
|
|
|
|
|
|
// window.setTimeout(function() { |
395
|
|
|
|
|
|
|
img.src = src; |
396
|
|
|
|
|
|
|
//}, timeout); |
397
|
|
|
|
|
|
|
}(img,container,fullsrc)); |
398
|
|
|
|
|
|
|
} else { |
399
|
|
|
|
|
|
|
// Image has already been loaded (from cache), nothing to do here |
400
|
|
|
|
|
|
|
}; |
401
|
|
|
|
|
|
|
}; |
402
|
|
|
|
|
|
|
|
403
|
|
|
|
|
|
|
=head1 REPOSITORY |
404
|
|
|
|
|
|
|
|
405
|
|
|
|
|
|
|
The public repository of this module is |
406
|
|
|
|
|
|
|
L. |
407
|
|
|
|
|
|
|
|
408
|
|
|
|
|
|
|
=head1 SUPPORT |
409
|
|
|
|
|
|
|
|
410
|
|
|
|
|
|
|
The public support forum of this module is |
411
|
|
|
|
|
|
|
L. |
412
|
|
|
|
|
|
|
|
413
|
|
|
|
|
|
|
=head1 BUG TRACKER |
414
|
|
|
|
|
|
|
|
415
|
|
|
|
|
|
|
Please report bugs in this module via the RT CPAN bug queue at |
416
|
|
|
|
|
|
|
L |
417
|
|
|
|
|
|
|
or via mail to L. |
418
|
|
|
|
|
|
|
|
419
|
|
|
|
|
|
|
=head1 AUTHOR |
420
|
|
|
|
|
|
|
|
421
|
|
|
|
|
|
|
Max Maischein C |
422
|
|
|
|
|
|
|
|
423
|
|
|
|
|
|
|
=head1 COPYRIGHT (c) |
424
|
|
|
|
|
|
|
|
425
|
|
|
|
|
|
|
Copyright 2015 by Max Maischein C. |
426
|
|
|
|
|
|
|
|
427
|
|
|
|
|
|
|
=head1 LICENSE |
428
|
|
|
|
|
|
|
|
429
|
|
|
|
|
|
|
This module is released under the same terms as Perl itself. |
430
|
|
|
|
|
|
|
|
431
|
|
|
|
|
|
|
=cut |
432
|
|
|
|
|
|
|
|
433
|
|
|
|
|
|
|
1; |