Task: Julia set
C#: using System.Drawing;



using System.Linq;

namespace RosettaJuliaSet
{
    class Program
    {
        static void Main(string[] args)
        {
            const int w = 800;
            const int h = 600;
            const int zoom = 1;
            const int maxiter = 255;
            const int moveX = 0;
            const int moveY = 0;
            const double cX = -0.7;
            const double cY = 0.27015;
            double zx, zy, tmp;
            int i;

            var colors = (from c in Enumerable.Range(0, 256)
                          select Color.FromArgb((c >> 5) * 36, (c >> 3 & 7) * 36, (c & 3) * 85)).ToArray();

            var bitmap = new Bitmap(w, h);
            for (int x = 0; x < w; x++)
            {
                for (int y = 0; y < h; y++)
                {
                    zx = 1.5 * (x - w / 2) / (0.5 * zoom * w) + moveX;
                    zy = 1.0 * (y - h / 2) / (0.5 * zoom * h) + moveY;
                    i = maxiter;
                    while (zx * zx + zy * zy < 4 && i > 1)
                    {
                        tmp = zx * zx - zy * zy + cX;
                        zy = 2.0 * zx * zy + cY;
                        zx = tmp;
                        i -= 1;
                    }
                    bitmap.SetPixel(x, y, colors[i]);
                }
            }
            bitmap.Save("julia-set.png");
        }
    }
}

PHP: set_time_limit(300);
header("Content-Type: image/png");

class Julia {
	
	static private $started = false;
	
	public static function start() {
		if (!self::$started) {
			self::$started = true;
			new self;
		}
	}
	
	const AXIS_REAL 	= 0;
	const AXIS_IMAGINARY 	= 1;
	const C 		= [-0.75, 0.1];
	const RADII 		= [1, 0.5];
	const CENTER 		= [0, 0];
	const MAX_ITERATIONS 	= 100;
	const TICK_SPACING 	= 0.001;
	
	private $maxDistance;
	private $imageResource;
	private $whiteColorResource;
	private $z0 = [];
	
	private function __construct() {
		$this->maxDistance = max($this->distance(self::C), 2);
		$this->imageResource = imagecreate(
			$this->coordinateToPixel(self::RADII[self::AXIS_REAL], self::AXIS_REAL),
			$this->coordinateToPixel(self::RADII[self::AXIS_IMAGINARY], self::AXIS_IMAGINARY)
		);
		imagecolorallocate($this->imageResource, 0, 0, 0);
		$this->whiteColorResource = imagecolorallocate($this->imageResource, 255, 255, 255);
		
		for ($x = self::CENTER[self::AXIS_REAL] - self::RADII[self::AXIS_REAL];
		$x <= self::CENTER[self::AXIS_REAL] + self::RADII[self::AXIS_REAL]; $x += self::TICK_SPACING) {
			$z0[self::AXIS_REAL] = $x;
			
			for ($y = self::CENTER[self::AXIS_IMAGINARY] - self::RADII[self::AXIS_IMAGINARY];
			$y <= self::CENTER[self::AXIS_IMAGINARY] + self::RADII[self::AXIS_IMAGINARY]; $y += self::TICK_SPACING) {
				$z0[self::AXIS_IMAGINARY] = $y;
				$iterations = 1;
				do {
					$z0 = $this->q($z0);
					$iterations++;
				} while($iterations < self::MAX_ITERATIONS && $this->distance($z0) <= $this->maxDistance);
				
				if ($iterations !== self::MAX_ITERATIONS) {
					imagesetpixel(
						$this->imageResource,
						$this->coordinateToPixel($x, self::AXIS_REAL),
						$this->coordinateToPixel($y, self::AXIS_IMAGINARY),
						$this->whiteColorResource
					);
				}
				$z0[self::AXIS_REAL] = $x;
			}
		}
	}
	
	public function __destruct() {
		imagepng($this->imageResource);
		imagedestroy($this->imageResource);
	}
	
	private function q($z) {
		return [ ($z[self::AXIS_REAL] ** 2) - ($z[self::AXIS_IMAGINARY] ** 2) + self::C[self::AXIS_REAL],
                       (2 * $z[self::AXIS_REAL] * $z[self::AXIS_IMAGINARY]) + self::C[self::AXIS_IMAGINARY] ];
	}
	
	private function distance($z) {
		return sqrt( ($z[self::AXIS_REAL] ** 2) + ($z[self::AXIS_IMAGINARY] ** 2) );
	}
	
	private function coordinateToPixel($coordinate, $axis) {
		return ($coordinate + self::RADII[$axis]) * (self::TICK_SPACING ** -1);
	}
}

Julia::start();