Set a single pixel in PHP

<?php//from w  ww .j  a v a 2  s.  co  m

$x = 400;
$y = 400;

$gd = imagecreatetruecolor($x, $y);

$corners[0] = array('x' => 100, 'y' =>  10);
$corners[1] = array('x' =>   0, 'y' => 390);
$corners[2] = array('x' => 400, 'y' => 390);

$red = imagecolorallocate($gd, 255, 0, 0);

for ($i = 0; $i < 100000; $i++) {
  imagesetpixel($gd, round($x),round($y), $red);
  $a = rand(0, 2);
  $x = ($x + $corners[$a]['x']) / 2;
  $y = ($y + $corners[$a]['y']) / 2;
}

header('Content-Type: image/png');
imagepng($gd);

?>