土豆(tudou.com)首页的导航条,当鼠标移到到“社区”菜单时，对应的菜单的弹出效果比较有意思，类似于一个弹球落地的效果，对于有意思的东西，当然要研究研究。有兴趣的朋友可以自己先去看看效果，然后再来看文章。
tudou代码
看了tudou的js代码，发现他们也是使用jquery来实现动画效果的，代码如下：
f.style.height=0;
this.style.visibility="visible";
$(f).animate({height:g},500,"easeOutBounce");
$(i).addClass("hover")
最重要的是上面第三行代码，使用jquery的animate的函数，其中重点就是tudou自定义了animate的easing函数，即easeOutBounce函数，easeOutBounce函数如下。
easeOutBounce:function(o,p,n,r,q){
if((p/=q)<(1/2.75)){
return r*(7.5625*p*p)+n
}else{
if(p<(2/2.75)){
return r*(7.5625*(p-=(1.5/2.75))*p+0.75)+n
}else{
if(p<(2.5/2.75)){
return r*(7.5625*(p-=(2.25/2.75))*p+0.9375)+n
}else{
return r*(7.5625*(p-=(2.625/2.75))*p+0.984375)+n
}
}
}
}
DEMO
先不分析代码，先用tudou的easeOutBounce函数做个demo看看效果。
demo(该demo在IE下点击没有效果，可能是跟博客园的其他代码有冲突，不想花时间去解决。要在IE下看效果，请copy后面的代码在本地进行测试)：
代码：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<script type="text/javascript" src="http://common.cnblogs.com/script/jquery.js"></script>
<script type="text/javascript">
jQuery.extend(jQuery.easing,{
def : "easeOutQuad",
swing : function(o, p, n, r, q) {
return jQuery.easing[jQuery.easing.def](o, p, n, r,q)
},
easeOutBounce : function(o, p, n, r, q) {
if ((p /= q) < (1 / 2.75)) {
return r * (7.5625 * p * p) + n
} else {
if (p < (2 / 2.75)) {
return r * (7.5625 * (p -= (1.5 / 2.75)) * p + 0.75) + n
} else {
if (p < (2.5 / 2.75)) {
return r * (7.5625 * (p -= (2.25 / 2.75)) * p + 0.9375) + n
} else {
return r * (7.5625 * (p -= (2.625 / 2.75)) * p + 0.984375) + n
}
}
}
}
});
function showMenu(){
resetMenu();
$("#b_menu").animate({height:100},500,"easeOutBounce");
}
function resetMenu(){
$("#b_menu").show();
$("#b_menu").height(0);
}
</script>
<style type="text/css">
#b_menu{border:1px solid #F56E0B;width:100px;list-style:none;padding:0;height:0;overflow:hidden;display:none;}
#b_menu li{line-height:25px;width:100px;text-align:center;}
</style>
</head>
<body>
<a href="javascript:showMenu();void(0)">我的菜单</a><br />
<ul id="b_menu">
<li>菜单一</li>
<li>菜单二</li>
<li>菜单三</li>
<li>菜单四</li>
</ul>
</body>
</html>
easing函数
jquery默认定义了2个easing函数，分别是swing和linear,easing函数格式如下：function(o, p, n, r, q)
但对于该几个参数的具体说明，jquery官方也没有文档说明(不知道是否是我没有找到)，经过我看源代码和自己的理解，对几个参数理解如下：
o = p/q
p: 当前时间 - animate开始时间的毫秒值
n: 起始值，一直为0
r: 这个个人认为是递增值，一直为1
q: animate中的duration参数，即设置的动画效果运行完毕需要的时间
返回值：返回1个大于0，小于等于1的百分比值，animate方法通过这个百分比去计算各个参数的值
知道这几个参数的含义后，再看看tudou的easeOutBounce，就发现其第一行代码写的有问题，if ((p /= q) < (1 / 2.75)) 其实可以直接写成 if ((o) < (1 / 2.75)) 。
可以看出tudou的开发人员对easing函数的几个参数也不太理解，不然就不会这样写了(也有可能easeOutBounce函数，tudou也是直接从其他地方copy过来的，呵呵)
胡言乱语
在查询jquery的easing参数的时候，无意间发现1个专门做easing效果的网站(http://gsgd.co.uk/sandbox/jquery/easing/)，而土豆的几个easing效果代码跟该网站的easing效果代码是惊人的相似，除了参数名不同外(这也出现我前面copy 代码的猜测),其实是不是copy都无所谓的，偶也是胡言乱语下，大家也别想太多，贴出2段代码，大家自己看看吧。
下面tudou的代码：
jQuery.extend(jQuery.easing,{
def : "easeOutQuad",
swing : function(o, p, n, r, q) {
return jQuery.easing[jQuery.easing.def](o, p, n, r,q)
},
easeInQuad : function(o, p, n, r, q) {
return r * (p /= q) * p + n
},
easeOutQuad : function(o, p, n, r, q) {
return -r * (p /= q) * (p - 2) + n
},
easeInOutQuad : function(o, p, n, r, q) {
if ((p /= q / 2) < 1) {
return r / 2 * p * p * p + n
}
return r / 2 * ((p -= 2) * p * p + 2) + n
},
easeInBack : function(o, p, n, u, r, q) {
if (q == undefined) {
q = 1.70158
}
return u * (p /= r) * p * ((q + 1) * p - q) + n
},
easeOutBack : function(o, p, n, u, r, q) {
if (q == undefined) {
q = 1.70158
}
return u * ((p = p / r - 1) * p * ((q + 1) * p + q) + 1) + n
},
easeOutBounce : function(o, p, n, r, q) {
if ((p /= q) < (1 / 2.75)) {
return r * (7.5625 * p * p) + n
} else {
if (p < (2 / 2.75)) {
return r * (7.5625 * (p -= (1.5 / 2.75)) * p + 0.75) + n
} else {
if (p < (2.5 / 2.75)) {
return r * (7.5625 * (p -= (2.25 / 2.75)) * p + 0.9375) + n
} else {
return r * (7.5625 * (p -= (2.625 / 2.75)) * p + 0.984375) + n
}
}
}
}
});
jQuery.extend( jQuery.easing,{
def: 'easeOutQuad',
swing: function (x, t, b, c, d) {
//alert(jQuery.easing.default);
return jQuery.easing[jQuery.easing.def](x, t, b, c, d);
},
easeInQuad: function (x, t, b, c, d) {
return c*(t/=d)*t + b;
},
easeOutQuad: function (x, t, b, c, d) {
return -c *(t/=d)*(t-2) + b;
},
easeInOutQuad: function (x, t, b, c, d) {
if ((t/=d/2) < 1) return c/2*t*t + b;
return -c/2 * ((--t)*(t-2) - 1) + b;
},
easeInCubic: function (x, t, b, c, d) {
return c*(t/=d)*t*t + b;
},
easeOutCubic: function (x, t, b, c, d) {
return c*((t=t/d-1)*t*t + 1) + b;
},
easeInOutCubic: function (x, 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;
},
easeInQuart: function (x, t, b, c, d) {
return c*(t/=d)*t*t*t + b;
},
easeOutQuart: function (x, t, b, c, d) {
return -c * ((t=t/d-1)*t*t*t - 1) + b;
},
easeInOutQuart: function (x, 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;
},
easeInQuint: function (x, t, b, c, d) {
return c*(t/=d)*t*t*t*t + b;
},
easeOutQuint: function (x, t, b, c, d) {
return c*((t=t/d-1)*t*t*t*t + 1) + b;
},
easeInOutQuint: function (x, 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;
},
easeInSine: function (x, t, b, c, d) {
return -c * Math.cos(t/d * (Math.PI/2)) + c + b;
},
easeOutSine: function (x, t, b, c, d) {
return c * Math.sin(t/d * (Math.PI/2)) + b;
},
easeInOutSine: function (x, t, b, c, d) {
return -c/2 * (Math.cos(Math.PI*t/d) - 1) + b;
},
easeInExpo: function (x, t, b, c, d) {
return (t==0) ? b : c * Math.pow(2, 10 * (t/d - 1)) + b;
},
easeOutExpo: function (x, t, b, c, d) {
return (t==d) ? b+c : c * (-Math.pow(2, -10 * t/d) + 1) + b;
},
easeInOutExpo: function (x, 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;
},
easeInCirc: function (x, t, b, c, d) {
return -c * (Math.sqrt(1 - (t/=d)*t) - 1) + b;
},
easeOutCirc: function (x, t, b, c, d) {
return c * Math.sqrt(1 - (t=t/d-1)*t) + b;
},
easeInOutCirc: function (x, 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;
},
easeInElastic: function (x, t, b, c, d) {
var s=1.70158;var p=0;var a=c;
if (t==0) return b; if ((t/=d)==1) return b+c; if (!p) p=d*.3;
if (a < Math.abs(c)) { a=c; var s=p/4; }
else var 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;
},
easeOutElastic: function (x, t, b, c, d) {
var s=1.70158;var p=0;var a=c;
if (t==0) return b; if ((t/=d)==1) return b+c; if (!p) p=d*.3;
if (a < Math.abs(c)) { a=c; var s=p/4; }
else var 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;
},
easeInOutElastic: function (x, t, b, c, d) {
var s=1.70158;var p=0;var a=c;
if (t==0) return b; if ((t/=d/2)==2) return b+c; if (!p) p=d*(.3*1.5);
if (a < Math.abs(c)) { a=c; var s=p/4; }
else var 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;
},
easeInBack: function (x, t, b, c, d, s) {
if (s == undefined) s = 1.70158;
return c*(t/=d)*t*((s+1)*t - s) + b;
},
easeOutBack: function (x, t, b, c, d, s) {
if (s == undefined) s = 1.70158;
return c*((t=t/d-1)*t*((s+1)*t + s) + 1) + b;
},
easeInOutBack: function (x, t, b, c, d, s) {
if (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;
},
easeInBounce: function (x, t, b, c, d) {
return c - jQuery.easing.easeOutBounce (x, d-t, 0, c, d) + b;
},
easeOutBounce: function (x, 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;
}
},
easeInOutBounce: function (x, t, b, c, d) {
if (t < d/2) return jQuery.easing.easeInBounce (x, t*2, 0, c, d) * .5 + b;
return jQuery.easing.easeOutBounce (x, t*2-d, 0, c, d) * .5 + c*.5 + b;
}
});
相关链接
