可逆缓动功能

Question

我有以下功能:

Math.easeIn = function (val, min, max) {
  strength = 4;
  val /= max;
  return (max-1)*Math.pow(val, strength) + min;
};

给定Math.easeIn(5, 1, 10)，我得到1.5625。我想要一个函数，给定1.5625的值，它返回5。

。Math.easeOut(1.5625, 1, 10) -> 5

我的数学很差

Answer 1

Math.easeIn = function (val, min, max) {
  strength = 4;
  val /= max;
  return (max-1)*Math.pow(val, strength) + min;
};
Math.easeOut = function (val, min, max) {
  var strength = 4, res;
  res = (val-min)/(max-1);
  res = Math.pow(res, 1/strength);
  return max*res;
};
document.body.innerHTML = '<p>easeIn : ' + Math.easeIn(5, 1, 10) + '</p>';
document.body.innerHTML += '<p>easeOut : ' + Math.easeOut(1.5625, 1, 10) + '</p>';

我通过反转你的easeIn函数获得了这个:

res = (max - 1) * Math.pow(val/max, strength) + min     // Your easeIn function
res - min = (max - 1) * Math.pow(val/max, strength)
(res - min)/(max - 1) = Math.pow(val/max, strength)
Math.pow( (res - min)/(max - 1), 1/strength ) = val / max
Math.pow( (res - min)/(max - 1), 1/strength ) * max = val   // Your easeOut function