Easing 関数

easing.js

// Predefine list of available timing functions
  // If you need more, tween js is full of great examples
  // https://github.com/tweenjs/tween.js/blob/master/src/Tween.js#L421-L737
  const easings = {
    linear(t) {
      return t;
    },
    easeInQuad(t) {
      return t * t;
    },
    easeOutQuad(t) {
      return t * (2 - t);
    },
    easeInOutQuad(t) {
      return t < 0.5 ? 2 * t * t : -1 + (4 - 2 * t) * t;
    },
    easeInCubic(t) {
      return t * t * t;
    },
    easeOutCubic(t) {
      return (--t) * t * t + 1;
    },
    easeInOutCubic(t) {
      return t < 0.5 ? 4 * t * t * t : (t - 1) * (2 * t - 2) * (2 * t - 2) + 1;
    },
    easeInQuart(t) {
      return t * t * t * t;
    },
    easeOutQuart(t) {
      return 1 - (--t) * t * t * t;
    },
    easeInOutQuart(t) {
      return t < 0.5 ? 8 * t * t * t * t : 1 - 8 * (--t) * t * t * t;
    },
    easeInQuint(t) {
      return t * t * t * t * t;
    },
    easeOutQuint(t) {
      return 1 + (--t) * t * t * t * t;
    },
    easeInOutQuint(t) {
      return t < 0.5 ? 16 * t * t * t * t * t : 1 + 16 * (--t) * t * t * t * t;
    }
  };