<?php
set_time_limit(0);

$width = $_GET["width"];
$height = $_GET["height"];
$x_min = $_GET["xmin"]; //-1.5
$x_max = $_GET["xmax"]; //0.5
$y_min = $_GET["ymin"]; //-1
$y_max = $_GET["ymax"]; //1
$max_iterations = $_GET["maxiterations"]; //200

header("Content-type: image/png");
$image = imagecreate($width, $height);

//farbpalette aus png lesen:
$colours = array();
$colours['inside'] = imagecolorallocate($image, 0, 0, 0);
$palette = imagecreatefrompng("palette2.png");
for ($i=0; $i<imagesx($palette); $i++) {
$rgb = imagecolorat($palette, $i, 0);
$colours[$i] = imagecolorallocate($image, ($rgb >> 16) & 0xFF, ($rgb >> 8) & 0xFF, $rgb & 0xFF);}

for ($i=0; $i<$width; $i++) {
for ($j=0; $j<$height; $j++) {

$x = $x_min+$i*(($x_max - $x_min) / ($width-1)); //c realteil
$y = $y_min+$j*(($y_max - $y_min) / ($height-1)); //c imaginärteil

$iteration = 0;
$z = array(0,0); // initial 0+0i

$x2 = 0; //x quadrat
$y2 = 0; // y quadrat

while ($iteration <= $max_iterations && $x2+$y2 <= 4) {

$k = $z; //z = k*k+c

$z[0] = $x2 - $y2; //real teil (x*x+y*y)
$z[1] = 2 * $k[0] * $k[1]; //imaginärteil ( 2*x*y)

// c dazuadieren:
$z[0] = $z[0] + $x;
$z[1] = $z[1] + $y;

$x2 = $z[0]*$z[0];
$y2 = $z[1]*$z[1];

++$iteration; }

if ($iteration == $max_iterations) {
imagesetpixel($image, $i, $j, $colors['inside']);
} else {
imagesetpixel($image, $i, $j, $colours[$iteration]);
}}}

imagepng($image);
?>