mandelbrot.js

function countIterations(x, y) {
    var count = 0;
    var t = x;
    x=-y;
    y=t;
    var zx = x;
    var zy = y;
    var n = 100;
    var p = 200;
    while (count < maxIterations && zx*zx + zy*zy < 20) {
        if (0==(count+1)%n) {
            x += zx*count/p;
            y += zy*count/p;
            n--;
            p++;
        }
        var new_zx = zx*zx - zy*zy + x;
        zy = 2*zx*zy + y;
        zx = new_zx;
        count++;
    }
    return count < maxIterations ? count : Math.floor((Math.atan(zy/zx)+Math.PI/2)/Math.PI*count);
}