NAME

Image::PNG::Cairo - extract PNG data from a Cairo::ImageSurface

SYNOPSIS

use Image::PNG::Cairo 'cairo_to_png';
use Cairo;
my $surface = Cairo::ImageSurface->new ('argb32', 100, 100);
# Draw something on surface.
my $png = cairo_to_png ($surface);
# Now can use the methods of Image::PNG::Libpng on the PNG,
# e.g. write to file.

(This example is included as synopsis.pl in the distribution.)

VERSION

This documents Image::PNG::Cairo version 0.09 corresponding to git commit 615fa499479dd235024385a5f4d09f558e3d1ec8 released on Thu Oct 5 13:15:48 2017 +0900.

DESCRIPTION

This is a bridge between Cairo and Image::PNG::Libpng which allows the user to extract the image data from a Cairo::ImageSurface into a structure which can then be manipulated to add other kinds of data.

FUNCTIONS

cairo_to_png

my $png = cairo_to_png ($surface);

The input, $surface, is a Cairo::ImageSurface object. Only Cairo surfaces of type 'argb32' are supported. The return value is an Image::PNG::Libpng object, with its image dimensions, bit depth, colour type, and image data taken from $surface. $png corresponds to the return value of the Image::PNG::Libpng method create_write_struct with the methods set_IHDR and set_rows and set_transforms applied to it using data extracted from $surface.

$png is set up using the Image::PNG::Libpng method set_transforms such that the PNG image data is transformed on writing from the Cairo image data format to the PNG format.

EXAMPLES

Captcha

This example CGI program makes a captcha from random letters. It also includes the captcha text and the date and time of creation of the image in the PNG.

use lib '/home/protected/lib';
use CGI::Carp 'fatalsToBrowser';
use Cairo;
use Image::PNG::Cairo 'cairo_to_png';
use Image::PNG::Libpng ':all';
use Image::PNG::Const ':all';
use constant { M_PI => 3.14159265 };
my $xsize = 200;
my $ysize = 50;
my $surface = Cairo::ImageSurface->create ('argb32', $xsize, $ysize);
my $cr = Cairo::Context->create ($surface);

# Make a background

$cr->set_source_rgb (0, 0, 0);
$cr->rectangle (0, 0, $xsize, $ysize);
$cr->fill ();

# Get six randomly-chosen letters

my $captcha = random_letters (6);

# Draw the captcha text in white
my $gap = 10;
$cr->set_source_rgb (1, 1, 1);
$cr->set_font_size ($ysize - $gap);
$cr->move_to ($gap, $ysize - $gap);
$cr->show_text ($captcha);
$cr->fill ();

# Obscure the text with translucent circles in random colours.

for (0..50) {
    $cr->set_source_rgba (random_colours (), 0.4);
    $cr->arc (rand ($xsize), rand ($ysize), rand (25), 0, 2 * M_PI);
    $cr->fill ();
}

# Get the PNG data out of it.

my $png = cairo_to_png ($surface);

# Put the captcha into the PNG itself, and set a modification time.

$png->set_text ([{compression => PNG_TEXT_COMPRESSION_NONE,
                  key => 'captcha', text => $captcha}]);
$png->set_tIME ();

# Get the PNG data from $png and print it out.

my $data = write_to_scalar ($png);
binmode STDOUT;
print "Content-Type: image/png\r\n\r\n$data";
exit;

sub random_colours
{
    my @r;
    for (1..3) {
        push @r, rand (1);
    }
    return @r;
}

sub random_letters
{
    my ($length) = @_;
    my @letters = ('0' .. '9', 'a' .. 'z', 'A' .. 'Z');
    my $r = '';
    for (1..$length) {
        $r .= $letters[rand (@letters)];
    }
    return $r;
} 

(This example is included as captcha.pl in the distribution.)

Please do not use this example program in the stead of a real captcha.

SEE ALSO

Cairo

Cairo is a general-purpose drawing program.

Image::PNG::Libpng

Image::PNG::Libpng is a Perl wrapper to the C PNG library libpng.

AUTHOR

Ben Bullock, <bkb@cpan.org>

COPYRIGHT & LICENCE

This package and associated files are copyright (C) 2014-2017 Ben Bullock.

You can use, copy, modify and redistribute this package and associated files under the Perl Artistic Licence or the GNU General Public Licence.