Tweaking Raphael easing function ">"

gistfile1.js

// send first ball from (0, 0) to (200, 0)
animate(firstBall, 0, 200)();

// send second ball from (0, 0) to (100, 0) but with the tempo like it was sent to (200, 0)
animateWithTweak(secondBall, 0, 100, 200)();

function animate(ball, start, intended) {
  return function () {
      ball.animate({cx: intended}, 2000, ">");
  }
}

function animateWithTweak(ball, start, real, intended) {

    var distanceRatio = (real - start) / (intended - start);
    var timeRatio = 1 - Math.pow(1 - distanceRatio, 1/3);
    
    Raphael.easing_formulas["custom"] = function(n) {
        var f = Raphael.easing_formulas[">"];
        return (1 / distanceRatio) * f(timeRatio * n);
    }
    
    return function () {
        ball.animate({cx: real}, 2000 * timeRatio, "custom");
    };
}