Tween functions

tween.js

/*!
 *  TERMS OF USE - EASING EQUATIONS
 *  Open source under the BSD License.
 *  Easing Equations (c) 2003 Robert Penner, all rights reserved.
 */


  function easeInQuad(pos) {
    return Math.pow(pos, 2);
  }

  function easeOutQuad(pos) {
    return -(Math.pow((pos - 1), 2) - 1);
  }

  function easeInOutQuad(pos) {
    if ((pos /= 0.5) < 1) {
      return 0.5 * Math.pow(pos,2);
    }
    return -0.5 * ((pos -= 2) * pos - 2);
  }

  function easeInCubic(pos) {
    return Math.pow(pos, 3);
  }

  function easeOutCubic(pos) {
    return (Math.pow((pos - 1), 3) + 1);
  }

  function easeInOutCubic(pos) {
    if ((pos /= 0.5) < 1) {
      return 0.5 * Math.pow(pos, 3);
    }
    return 0.5 * (Math.pow((pos - 2), 3) + 2);
  }

  function easeInQuart(pos) {
    return Math.pow(pos, 4);
  }

  function easeOutQuart(pos) {
    return -(Math.pow((pos - 1), 4) - 1);
  }

  function easeInOutQuart(pos) {
    if ((pos /= 0.5) < 1) {
      return 0.5 * Math.pow(pos, 4);
    }
    return -0.5 * ((pos -= 2) * Math.pow(pos, 3) - 2);
  }

  function easeInQuint(pos) {
    return Math.pow(pos, 5);
  }

  function easeOutQuint(pos) {
    return (Math.pow((pos - 1), 5) + 1);
  }

  function easeInOutQuint(pos) {
    if ((pos /= 0.5) < 1) {
      return 0.5 * Math.pow(pos, 5);
    }
    return 0.5 * (Math.pow((pos - 2), 5) + 2);
  }

  function easeInSine(pos) {
    return -Math.cos(pos * (Math.PI / 2)) + 1;
  }

  function easeOutSine(pos) {
    return Math.sin(pos * (Math.PI / 2));
  }

  function easeInOutSine(pos) {
    return (-0.5 * (Math.cos(Math.PI * pos) - 1));
  }

  function easeInExpo(pos) {
    return (pos === 0) ? 0 : Math.pow(2, 10 * (pos - 1));
  }

  function easeOutExpo(pos) {
    return (pos === 1) ? 1 : -Math.pow(2, -10 * pos) + 1;
  }

  function easeInOutExpo(pos) {
    if (pos === 0) {
      return 0;
    }
    if (pos === 1) {
      return 1;
    }
    if ((pos /= 0.5) < 1) {
      return 0.5 * Math.pow(2, 10 * (pos - 1));
    }
    return 0.5 * (-Math.pow(2, -10 * --pos) + 2);
  }

  function easeInCirc(pos) {
    return -(Math.sqrt(1 - (pos * pos)) - 1);
  }

  function easeOutCirc(pos) {
    return Math.sqrt(1 - Math.pow((pos - 1), 2));
  }

  function easeInOutCirc(pos) {
    if ((pos /= 0.5) < 1) {
      return -0.5 * (Math.sqrt(1 - pos * pos) - 1);
    }
    return 0.5 * (Math.sqrt(1 - (pos -= 2) * pos) + 1);
  }

  function easeOutBounce(pos) {
    if ((pos) < (1 / 2.75)) {
      return (7.5625 * pos * pos);
    } else if (pos < (2 / 2.75)) {
      return (7.5625 * (pos -= (1.5 / 2.75)) * pos + 0.75);
    } else if (pos < (2.5 / 2.75)) {
      return (7.5625 * (pos -= (2.25 / 2.75)) * pos + 0.9375);
    } else {
      return (7.5625 * (pos -= (2.625 / 2.75)) * pos + 0.984375);
    }
  }

  function easeInBack(pos) {
    var s = 1.70158;
    return (pos) * pos * ((s + 1) * pos - s);
  }

  function easeOutBack(pos) {
    var s = 1.70158;
    return (pos = pos - 1) * pos * ((s + 1) * pos + s) + 1;
  }

  function easeInOutBack(pos) {
    var s = 1.70158;
    if ((pos /= 0.5) < 1) {
      return 0.5 * (pos * pos * (((s *= (1.525)) + 1) * pos - s));
    }
    return 0.5 * ((pos -= 2) * pos * (((s *= (1.525)) + 1) * pos + s) + 2);
  }

  function elastic(pos) {
    return -1 * Math.pow(4,-8 * pos) * Math.sin((pos * 6 - 1) * (2 * Math.PI) / 2) + 1;
  }

  function swingFromTo(pos) {
    var s = 1.70158;
    return ((pos /= 0.5) < 1) ? 0.5 * (pos * pos * (((s *= (1.525)) + 1) * pos - s)) :
                                0.5 * ((pos -= 2) * pos * (((s *= (1.525)) + 1) * pos + s) + 2);
  }

  function swingFrom(pos) {
    var s = 1.70158;
    return pos * pos * ((s + 1) * pos - s);
  }

  function swingTo(pos) {
    var s = 1.70158;
    return (pos -= 1) * pos * ((s + 1) * pos + s) + 1;
  }

  function bounce(pos) {
    if (pos < (1 / 2.75)) {
      return (7.5625 * pos * pos);
    } else if (pos < (2 / 2.75)) {
      return (7.5625 * (pos -= (1.5 / 2.75)) * pos + 0.75);
    } else if (pos < (2.5 / 2.75)) {
      return (7.5625 * (pos -= (2.25 / 2.75)) * pos + 0.9375);
    } else {
      return (7.5625 * (pos -= (2.625 / 2.75)) * pos + 0.984375);
    }
  }

  function bouncePast(pos) {
    if (pos < (1 / 2.75)) {
      return (7.5625 * pos * pos);
    } else if (pos < (2 / 2.75)) {
      return 2 - (7.5625 * (pos -= (1.5 / 2.75)) * pos + 0.75);
    } else if (pos < (2.5 / 2.75)) {
      return 2 - (7.5625 * (pos -= (2.25 / 2.75)) * pos + 0.9375);
    } else {
      return 2 - (7.5625 * (pos -= (2.625 / 2.75)) * pos + 0.984375);
    }
  }

  function easeFromTo(pos) {
    if ((pos /= 0.5) < 1) {
      return 0.5 * Math.pow(pos, 4);
    }
    return -0.5 * ((pos -= 2) * Math.pow(pos, 3) - 2);
  }

  function easeFrom(pos) {
    return Math.pow(pos, 4);
  }

  function easeTo(pos) {
    return Math.pow(pos, 0.25);
  }

  function linear(pos) {
    return pos;
  }