IdentiFrac Class Reference
[IdentiFrac]

This is a class to generate so called identifrac image. More...

List of all members.

Public Member Functions
	__construct ($hash, $size=100)
	Constructor.
	get_as_string ()
	Returns the image as a string of biaray data.
	output_image ()
	Prints the image and sends cache related headers.
	send_headers ()
	Sends content-type and cache related headers so the browsers caches the image for about two months.
Public Attributes
const	ITERATIONS = 50
Protected Member Functions
	create ($final_size, $hash)
	Create the image.
	draw_antialiasing ($img, $img_size, $final_size)
	Antialiasing.
	draw_border ($img, $img_size, &$hash)
	Draw the border.
	draw_frac ($img, $img_size, $img_colors, &$hash)
	Plots the Julia Set.
	get_colors ($img, &$hash)
	Create all the colors used.
	get_iterations ()
	Returns number of iterations.
	get_nibbles (&$hex_stream, $num_nibbles)
Protected Attributes
	$hash
	$size

---

Detailed Description

This is a class to generate so called identifrac image.

An identifrac is similar to Don Park's "identicon", only that is uses fractal functions to generate the image.

This code is based upon Identifrac v0.9! A Visually Unique Identification System by Jesse Dubay (jesse@thefortytwo.net) Once available at adb.thefortytwo.net, it now can only be retrievend from archive.org: http://web.archive.org/web/20071212034846/adb.thefortytwo.net/projects/identifrac/

The code has been changed in several ways:

• Less options: No alpha blending, no saturation, no brightness.
• Use more bytes from hash so color changes from color one to color two, rather than from black to color one
• Draws a border
• It's a class now

Requires the PHP GD extension to be installed

See also:

http://php.net/manual/en/book.image.php

Example usage:

 // This could be a page called as e.g. example.php?identity=Gerd+Riesselmann 
 $identifrac = new IdentiFrac(md5($_GET['identity']), 100);
 $identifrac->output_image(); 

 // Some more advanced usage, same invocation
 $identifrac = new IdentiFrac(md5($_GET['identity']), 100);
 $result = $identifrac->get_as_string();
 // Do some etag checking
 $etag = md5($result);
 if (isset($_SERVER['IF_NONE_MATCH']) && $_SERVER['IF_NONE_MATCH'] == $etag) {
   if (substr(php_sapi_name(), 0, 3) == 'cgi') {
        header('Status: 304 Not Modified');
   }
   else {
     header('HTTP/1.x 304 Not Modified');
   }
   exit; 
 }
 header('ETag: ' . $etag);
 $identifrac->send_headers();
 print $result;

The class is overloadable in many ways, so it should be possible to change behavior without needing to touch the original code.

Report bugs here: http://www.gyro-php.org/bugreport.html

Licensed under the GPL (http://www.gnu.org/licenses/gpl.txt)

Author:

Gerd Riesselmann

Version:

0.8

Definition at line 63 of file identifrac.cls.php.

---

Constructor & Destructor Documentation

IdentiFrac::__construct	(	$	hash,
		$	size = 100
	)

Constructor.

Parameters:

	string	$hash A Hash (SHA1, MD5) value, hexadecimal and at least 30 characters long
	int	$size Size in pixel.

Definition at line 75 of file identifrac.cls.php.

                                                        {
                $this->size = $size;
                $this->hash = $hash;
        }

---

Member Function Documentation

IdentiFrac::create	(	$	final_size,
		$	hash
	)			[protected]

Create the image.

Returns:

handle Handle to image.

Attention:

Calling code is resposible to call imagedestroy()!

Definition at line 199 of file identifrac.cls.php.

                                                      {
                // We want to generate more data than necessary, so when we
                // resize the image at the very end, we have some cushion for the
                // "poor man's antialiasing" algorithm
                $img_size = $final_size * 2;
                $img = imagecreate($img_size, $img_size);
                
                $img_colors = $this->get_colors($img, $hash);
                $this->draw_frac($img, $img_size, $img_colors, $hash);
                $this->draw_border($img, $img_size, $hash);
                
                $img_final = $this->draw_antialiasing($img, $img_size, $final_size);
                imagedestroy($img);
                
                return $img_final;
        }

IdentiFrac::draw_antialiasing	(	$	img,
		$	img_size,
		$	final_size
	)			[protected]

Antialiasing.

Definition at line 180 of file identifrac.cls.php.

                                                                           {
            // "Poor Man's Antialiasing" inspired by Don Park
            // Take the slightly-oversized image and scale it down to the specified size.
            $img_final = imagecreatetruecolor($final_size, $final_size);
        imagecopyresampled(
                $img_final, $img, 
                0, 0, 0, 0, 
                $final_size, $final_size, $img_size, $img_size
        );
                return $img_final;
        }

IdentiFrac::draw_border	(	$	img,
		$	img_size,
		&$	hash
	)			[protected]

Draw the border.

Definition at line 170 of file identifrac.cls.php.

                                                                {
                $border_color = imagecolorallocate($img, $this->get_nibbles($hash, 2), $this->get_nibbles($hash, 2), $this->get_nibbles($hash, 2));
                imagerectangle($img, 0, 0, $img_size - 1, $img_size - 1, $border_color);
                imagerectangle($img, 1, 1, $img_size - 2, $img_size - 2, $border_color);
                imagerectangle($img, 2, 2, $img_size - 3, $img_size - 3, $border_color);                                
        }

IdentiFrac::draw_frac	(	$	img,
		$	img_size,
		$	img_colors,
		&$	hash
	)			[protected]

Plots the Julia Set.

Definition at line 132 of file identifrac.cls.php.

                                                                           {
                // Pull some data out and generate a constant for the Julia polynomial
                $a = ($this->get_nibbles($hash, 6) - pow(2, 23)) / pow(2, 23); // Real coefficient
                $b = ($this->get_nibbles($hash, 6) - pow(2, 23)) / pow(2, 23); // Imaginary coefficient

                // This algorithm is heavily based off of BASIC code found at
                // http://library.thinkquest.org/26242/full/progs/a2.html
                for($screen_y = 0; $screen_y < $img_size; $screen_y++) {
                    for($screen_x = 0; $screen_x < $img_size; $screen_x++) {
                        // Map the canvas coords to complex plane, range -1.5..1.5
                        // These are our initial coordinates
                        $x = (($screen_x / $img_size) * 3) - 1.5;
                        $y = (($screen_y / $img_size) * 3) - 1.5;
                        
                        // Time to iterate.
                        $max = $this->get_iterations();
                        for ($iterations = 0; $iterations < $max; $iterations++) {
                            // If it leaves the boundary, it's not in the Julia set
                            if ($x * $x + $y * $y > 4) {
                                break;
                            }
                            
                            // The polynomial itself
                            $new_x = $x * $x - $y * $y + $a;
                            $new_y = 2 * $x * $y + $b;
                            
                            $x = $new_x;
                            $y = $new_y;
                        }
                        // Plot the point, referencing the color table
                        imagesetpixel($img, $screen_x, $screen_y, $img_colors[$iterations]);
                    }
                }
        }

IdentiFrac::get_as_string

(

)

Returns the image as a string of biaray data.

Returns:

string

Definition at line 221 of file identifrac.cls.php.

                                        {
                $img = $this->create($this->size, $this->hash);
                $file = tempnam("/tmp", "IFR");
                imagepng($img, $file);
                imagedestroy($img);
                
                // Writing and reading to a file is done, since ob_* may already be used
                $ret = file_get_contents($file);
                unlink($file);

                return $ret;
        }

IdentiFrac::get_colors	(	$	img,
		&$	hash
	)			[protected]

Create all the colors used.

Definition at line 103 of file identifrac.cls.php.

                                                    {
                $ret = array();
                $color = array();
                // Pull two RRGGBB colors from the stream
                for ($i = 0; $i < 6; $i++) {
                    $color[$i] = $this->get_nibbles($hash, 2);
                }
                // This is new code. GR
                $color_delta = array();
                for ($i = 0; $i < 3; $i++) {
                        $d = 0 - $color[$i+3] * $color[$i];
                    $color_delta[$i] = $d;
                }

                // Build the color table
                $max = $this->get_iterations();
                for($i = 0; $i < $max; $i++) {
                        // Tis part has been changed. GR
                        $ret[] = imagecolorallocate($img, ($color[0] + ($i / $max) * $color_delta[0]) & 0x00ff,
                                                  ($color[1] + ($i / $max) * $color_delta[1]) & 0x00ff,
                                                  ($color[2] + ($i / $max) * $color_delta[2]) & 0x00ff);
                }
                
                return $ret;            
        }

IdentiFrac::get_iterations

(

)

[protected]

Returns number of iterations.

Returns:

int

Definition at line 96 of file identifrac.cls.php.

                                            {
                return self::ITERATIONS;
        }

IdentiFrac::get_nibbles	(	&$	hex_stream,
		$	num_nibbles
	)			[protected]

Definition at line 84 of file identifrac.cls.php.

                                                                   {
            if (strlen($hex_stream) < $num_nibbles) return -1;
            $data = hexdec(substr($hex_stream, 0, $num_nibbles));
            $hex_stream = substr($hex_stream, $num_nibbles);
            return $data;
        }

IdentiFrac::output_image

(

)

Prints the image and sends cache related headers.

Returns:

void

Definition at line 239 of file identifrac.cls.php.

                                       {
                $this->send_headers();
                $img = $this->create($this->size, $this->hash);
                imagepng($img);
                imagedestroy($img);
        }

IdentiFrac::send_headers

(

)

Sends content-type and cache related headers so the browsers caches the image for about two months.

This reduces traffic.

Definition at line 250 of file identifrac.cls.php.

                                       {
                header('Content-Type: image/png');
                header('Cache-Control: public');
                header('Pragma:');
                header('Expires: ' . gmdate('D, d M Y H:i:s \G\M\T', time() + 62 * 24 * 60 * 60 )); // Expire 2 months          
        }

---

Member Data Documentation

IdentiFrac::$hash [protected]

Definition at line 65 of file identifrac.cls.php.

IdentiFrac::$size [protected]

Definition at line 64 of file identifrac.cls.php.

const IdentiFrac::ITERATIONS = 50

Definition at line 67 of file identifrac.cls.php.

---

The documentation for this class was generated from the following file:

• contributions/lib.identifrac/lib/components/identifrac.cls.php