<?php

    define('DPI', 75);
    define('OBS_DIST', DPI*12);
    define('EYE_SEP', (int)DPI*2.5);
    define('SEP_FACTOR', 0.55);
    define('MAX_SCENE_HEIGHT', 255);
    define('MIN_SCENE_HEIGHT', 0);
    define('MAX_DEPTH', OBS_DIST);
    define('MIN_DEPTH', (int)((SEP_FACTOR*MAX_DEPTH*OBS_DIST)/((1-SEP_FACTOR)*MAX_DEPTH+OBS_DIST)));
    define('HEIGHT_SCALE', 2);

    /* Init Random Number Generator */
    srand(time());
        
    $filename = "depthmap.png";
        
    $depth_img = imagecreatefrompng($filename);
    
    if(!$depth_img) die ("Error -- could not load depth image ($filename)!");
    
    $img_width = imagesx($depth_img);
    $img_height = imagesy($depth_img);
    
    /* Create the image used in the stereogram */
    $stereo_img = imagecreate($img_width, $img_height);
    
    if(!$stereo_img) die("Error -- could not allocate stereo image!");
    
    /* Initialize the colors that will be used in the image */
    for($i = 0; $i < 256; $i++) {
                
        if(isset($_POST['bw'])) {
            
            $rnd_color = rand(0,255);
            $colors[] = imagecolorallocate($stereo_img, 
                                           $rnd_color,
                                           $rnd_color,
                                           $rnd_color);
        } else {
            $colors[] = imagecolorallocate($stereo_img, 
                                           rand(0,255),
                                           rand(0,255),
                                           rand(0,255));
        }
        
    }    
    
    /* Load the img array with the random graphics data */
    for($y = 0; $y < $img_height; $y++) {
        for($x = 0; $x < $img_width; $x++) {

            //$buffer[$x][$y] = $colors[rand(0,255)];
            $temp = imagecolorsforindex($depth_img,imagecolorat($depth_img, $x, $y));
            
            /* Get the current blue element */
            $depth_color = $temp['blue'];
            $height = $depth_color/HEIGHT_SCALE;
            $height = ($height > MAX_SCENE_HEIGHT) ? MAX_SCENE_HEIGHT : $height;
            $height = ($height < MIN_SCENE_HEIGHT) ? MIN_SCENE_HEIGHT : $height;
            $feature_z = MAX_DEPTH-$height*(MAX_DEPTH-MIN_DEPTH)/256;
            $sep = (int)((float)(EYE_SEP*$feature_z)/($feature_z+OBS_DIST));
        
            $left_px = (int)$x-($sep/2);
            $right_px = (int)$x+($sep/2);
        
            if(($left_px >= 0) && ($right_px < $img_width)) {
                
                if(!isset($buffer[$left_px][$y]))
                    $buffer[$left_px][$y] = $colors[rand(1,255)];
                
                $buffer[$right_px][$y] = $buffer[$left_px][$y];    
            }
            
        }
        
        for($x = 0; $x < $img_width;$x++)
            if(!isset($buffer[$x][$y])) 
                $buffer[$x][$y] = $colors[rand(1,255)];
    }
    
    
    
    /* Output PNG File */
    
    for($y = 0; $y < $img_height; $y++) {
        for($x = 0; $x < $img_width; $x++) {
            imagesetpixel($stereo_img,$x, $y, $buffer[$x][$y]);
        }
    }
    
    header("Content-type:  image/png");
    $black = imagecolorclosest($stereo_img, 0,0,0);
    $white = imagecolorclosest($stereo_img, 0xff, 0xff, 0xff);
    imagefilledrectangle($stereo_img, 0, $img_height-20, $img_width, $img_height, $black);
    imagestring($stereo_img, 1, 5, $img_height-10, "Made at http://www.coggeshall.org/stereogram.php", $white);
    
    imagepng($stereo_img);
                        
?>