Mgccl's Ivory Towerso tired

$n = 200;
$image = imagecreate($n,$n);
imagecolorallocate($image, 255,255,255);
$color = imagecolorallocate($image, 0,0,0);
$sn=$n*$n;
$prime = esprime($sn);
$y=$x=$n/2;
$color2 = imagecolorallocate($image, 255,0,0);
imagesetpixel($image,$x,$y,$color2);
$remain = 2;
$distance = 1;
$direction = 1;
		for ($count = 2; $count <= $sn; ++$count) {
			if (--$remain == 0) {
				switch ($direction) {
					case 0: $distance++; $direction = 3; break;
					case 2: $distance++;
					default: $direction--; break;
				}
				$remain = $distance;
			}
			switch ($direction) {
				case 3: --$x; break;
				case 1: ++$x; break;
				case 0: --$y; break;
				case 2: ++$y; break;
			}
			if($prime[0] == $count){
				array_splice($prime, 0, 1);
				imagesetpixel($image,$x,$y,$color);
			}
			if(isset($prime[0])){
 
				if($prime[0]-$count+1<$remain){
					switch ($direction) {
						case 3: $x-=$prime[0]-$count-1; break;
						case 1: $x+=$prime[0]-$count-1; break;
						case 0: $y-=$prime[0]-$count-1; break;
						case 2: $y+=$prime[0]-$count-1; break;
					}
					$remain -= $prime[0]-$count-1;
					$count +=$prime[0]-$count-1;
				}elseif($prime[0]-$count+1>=$remain){
					switch ($direction) {
						case 3: $x-=$remain-1; break;
						case 1: $x+=$remain-1; break;
						case 0: $y-=$remain-1; break;
						case 2: $y+=$remain-1; break;
					}
					$count +=$remain-1;
					$remain = 1;
				}
			}
		}
header("Content-type: image/png");
imagepng($image);