tweenjs缓动算法的使用实例分析

本文实例讲述了tweenjs缓动算法的使用。分享给大家供大家参考，具体如下：

这里的tweenjs不是依托于createjs的tewwnjs，而是一系列缓动算法集合。因为本身是算法，可以用在各个业务场景中，这也正是总结学习它的价值所在。tweenjs代码详情：

/*
 * 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 * .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 * .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 * (.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 -.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 ) * .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 + .75) + b;
      } else if (t < (2.5 / 2.75)) {
        return c * (7.5625 * (t -= (2.25 / 2.75)) * t + .9375) + b;
      } else {
        return c * (7.5625 * (t -= (2.625 / 2.75)) * t + .984375) + b;
      }
    },
    easeinout: function(t, b, c, d) {
      if (t < d / 2) {
        return tween.bounce.easein(t * 2, 0, c, d) * .5 + b;
      } else {
        return tween.bounce.easeout(t * 2 - d, 0, c, d) * .5 + c * .5 + b;
      }
    }
  }
}
math.tween = tween;

具体每种算法的操作实例，可以看大神张鑫旭的博客实例：http://www.zhangxinxu.com/study/201612/how-to-use-tween-js.html

当然，以上这些算法仅仅是一个状态，需要配合时间上的变化，才能实现缓动，这里使用的是requestanimationframe，具体代码好吧，也是拿来主义

(function() {
  var lasttime = 0;
  var vendors = ['ms', 'moz', 'webkit', 'o'];
  for(var x = 0; x < vendors.length && !window.requestanimationframe; ++x) {
    window.requestanimationframe = window[vendors[x]+'requestanimationframe'];
    window.cancelanimationframe = window[vendors[x]+'cancelanimationframe']
                  || window[vendors[x]+'cancelrequestanimationframe'];
  }
  if (!window.requestanimationframe)
    window.requestanimationframe = function(callback, element) {
      var currtime = new date().gettime();
      var timetocall = math.max(0, 16 - (currtime - lasttime));
      var id = window.settimeout(function() { callback(currtime + timetocall); },
       timetocall);
      lasttime = currtime + timetocall;
      return id;
    };
  if (!window.cancelanimationframe)
    window.cancelanimationframe = function(id) {
      cleartimeout(id);
    };
}());

最后是简单的实例应用，很简单，

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>使用tweenjs</title>
  <style type="text/css">
  div {
    width: 100px;
    height: 100px;
    border: 1px solid red;
    text-align: center;
    line-height: 100px;
    position: absolute;
  }
  </style>
</head>
<body>
  <div id="test">
    这是测试
  </div>
  <script type="text/javascript" src="requestanimationframe.js"></script>
  <script type="text/javascript" src="tween.js"></script>
  <script type="text/javascript">
    var dom=document.getelementbyid("test");
  var t = 0,//开始时间
    b = 0,//开始位置
    c = 1000,//变化值
    d = 100;//持续时间
  var step = function() {
    var value = tween.bounce.easeout(t, b, c, d);
    dom.style.left = value + 'px';
    t++;
    if (t <= d) {
      // 继续运动
      requestanimationframe(step);
    } else {
      // 动画结束
    }
  };
  step();
  </script>
</body>
</html>

具体使用中，需要参数以及控制好结束条件即可。