1. Tween

/*
 * Tween.js
 * t: current time（当前时间）；
 * b: beginning value（初始值）；
 * c: change in value（变化量）；
 * d: duration（持续时间）。
 * you can visit 'http://easings.net/zh-cn' to get effect
*/
var Tween = {
  Linear: function(t, b, c, d) {
    return c * t / d + b;
  },
  Quad: {
    easeIn: function(t, b, c, d) {
      return c * (t /= d) * t + b;
    },
    easeOut: function(t, b, c, d) {
      return -c * (t /= d) * (t - 2) + b;
    },
    easeInOut: function(t, b, c, d) {
      if ((t /= d / 2) < 1) return c / 2 * t * t + b;
      return -c / 2 * (--t * (t - 2) - 1) + b;
    },
  },
  Cubic: {
    easeIn: function(t, b, c, d) {
      return c * (t /= d) * t * t + b;
    },
    easeOut: function(t, b, c, d) {
      return c * ((t = t / d - 1) * t * t + 1) + b;
    },
    easeInOut: function(t, b, c, d) {
      if ((t /= d / 2) < 1) return c / 2 * t * t * t + b;
      return c / 2 * ((t -= 2) * t * t + 2) + b;
    },
  },
  Quart: {
    easeIn: function(t, b, c, d) {
      return c * (t /= d) * t * t * t + b;
    },
    easeOut: function(t, b, c, d) {
      return -c * ((t = t / d - 1) * t * t * t - 1) + b;
    },
    easeInOut: function(t, b, c, d) {
      if ((t /= d / 2) < 1) return c / 2 * t * t * t * t + b;
      return -c / 2 * ((t -= 2) * t * t * t - 2) + b;
    },
  },
  Quint: {
    easeIn: function(t, b, c, d) {
      return c * (t /= d) * t * t * t * t + b;
    },
    easeOut: function(t, b, c, d) {
      return c * ((t = t / d - 1) * t * t * t * t + 1) + b;
    },
    easeInOut: function(t, b, c, d) {
      if ((t /= d / 2) < 1) return c / 2 * t * t * t * t * t + b;
      return c / 2 * ((t -= 2) * t * t * t * t + 2) + b;
    },
  },
  Sine: {
    easeIn: function(t, b, c, d) {
      return -c * Math.cos(t / d * (Math.PI / 2)) + c + b;
    },
    easeOut: function(t, b, c, d) {
      return c * Math.sin(t / d * (Math.PI / 2)) + b;
    },
    easeInOut: function(t, b, c, d) {
      return -c / 2 * (Math.cos(Math.PI * t / d) - 1) + b;
    },
  },
  Expo: {
    easeIn: function(t, b, c, d) {
      return t == 0 ? b : c * Math.pow(2, 10 * (t / d - 1)) + b;
    },
    easeOut: function(t, b, c, d) {
      return t == d ? b + c : c * (-Math.pow(2, -10 * t / d) + 1) + b;
    },
    easeInOut: function(t, b, c, d) {
      if (t == 0) return b;
      if (t == d) return b + c;
      if ((t /= d / 2) < 1) return c / 2 * Math.pow(2, 10 * (t - 1)) + b;
      return c / 2 * (-Math.pow(2, -10 * --t) + 2) + b;
    },
  },
  Circ: {
    easeIn: function(t, b, c, d) {
      return -c * (Math.sqrt(1 - (t /= d) * t) - 1) + b;
    },
    easeOut: function(t, b, c, d) {
      return c * Math.sqrt(1 - (t = t / d - 1) * t) + b;
    },
    easeInOut: function(t, b, c, d) {
      if ((t /= d / 2) < 1) return -c / 2 * (Math.sqrt(1 - t * t) - 1) + b;
      return c / 2 * (Math.sqrt(1 - (t -= 2) * t) + 1) + b;
    },
  },
  Elastic: {
    easeIn: function(t, b, c, d, a, p) {
      var s;
      if (t == 0) return b;
      if ((t /= d) == 1) return b + c;
      if (typeof p == 'undefined') p = d * 0.3;
      if (!a || a < Math.abs(c)) {
        s = p / 4;
        a = c;
      } else {
        s = p / (2 * Math.PI) * Math.asin(c / a);
      }
      return -(a * Math.pow(2, 10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p)) + b;
    },
    easeOut: function(t, b, c, d, a, p) {
      var s;
      if (t == 0) return b;
      if ((t /= d) == 1) return b + c;
      if (typeof p == 'undefined') p = d * 0.3;
      if (!a || a < Math.abs(c)) {
        a = c;
        s = p / 4;
      } else {
        s = p / (2 * Math.PI) * Math.asin(c / a);
      }
      return a * Math.pow(2, -10 * t) * Math.sin((t * d - s) * (2 * Math.PI) / p) + c + b;
    },
    easeInOut: function(t, b, c, d, a, p) {
      var s;
      if (t == 0) return b;
      if ((t /= d / 2) == 2) return b + c;
      if (typeof p == 'undefined') p = d * (0.3 * 1.5);
      if (!a || a < Math.abs(c)) {
        a = c;
        s = p / 4;
      } else {
        s = p / (2 * Math.PI) * Math.asin(c / a);
      }
      if (t < 1)
        return (
          -0.5 * (a * Math.pow(2, 10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p)) + b
        );
      return (
        a * Math.pow(2, -10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p) * 0.5 + c + b
      );
    },
  },
  Back: {
    easeIn: function(t, b, c, d, s) {
      if (typeof s == 'undefined') s = 1.70158;
      return c * (t /= d) * t * ((s + 1) * t - s) + b;
    },
    easeOut: function(t, b, c, d, s) {
      if (typeof s == 'undefined') s = 1.70158;
      return c * ((t = t / d - 1) * t * ((s + 1) * t + s) + 1) + b;
    },
    easeInOut: function(t, b, c, d, s) {
      if (typeof s == 'undefined') s = 1.70158;
      if ((t /= d / 2) < 1) return c / 2 * (t * t * (((s *= 1.525) + 1) * t - s)) + b;
      return c / 2 * ((t -= 2) * t * (((s *= 1.525) + 1) * t + s) + 2) + b;
    },
  },
  Bounce: {
    easeIn: function(t, b, c, d) {
      return c - Tween.Bounce.easeOut(d - t, 0, c, d) + b;
    },
    easeOut: function(t, b, c, d) {
      if ((t /= d) < 1 / 2.75) {
        return c * (7.5625 * t * t) + b;
      } else if (t < 2 / 2.75) {
        return c * (7.5625 * (t -= 1.5 / 2.75) * t + 0.75) + b;
      } else if (t < 2.5 / 2.75) {
        return c * (7.5625 * (t -= 2.25 / 2.75) * t + 0.9375) + b;
      } else {
        return c * (7.5625 * (t -= 2.625 / 2.75) * t + 0.984375) + b;
      }
    },
    easeInOut: function(t, b, c, d) {
      if (t < d / 2) {
        return Tween.Bounce.easeIn(t * 2, 0, c, d) * 0.5 + b;
      } else {
        return Tween.Bounce.easeOut(t * 2 - d, 0, c, d) * 0.5 + c * 0.5 + b;
      }
    },
  },
};
Math.tween = Tween;