javascript 仿百度穿墙特效

原理是判断从上下左右哪个方向移入遮罩层从哪个方向运动进入，从哪个方向移出，遮罩层从哪个方向运动滑出。

这个是圆的角度弧度转换公式:

角度-》弧度
n*PI/180;

弧度-》角度
n*180/PI;

角度-》方向
Math.atan2(y,x)

上js代码

function a2d(a){
    return a*180/Math.PI;
}
//判断移入的方向
function hoverDir(obj,oEvent){
    var x = obj.offsetLeft+obj.offsetWidth/2-oEvent.clientX;
    var y = obj.offsetTop+obj.offsetHeight/2-oEvent.clientY;
    return Math.round((a2d(Math.atan2(y,x))+180)/90)%4;
}
function hoverGo(obj){
    var oS = obj.children[0];
    obj.onmouseover=function(ev){
        var oEvent = ev||event;
        var oFrom = oEvent.fromElement||oEvent.relatedTarget;
        if(obj.contains(oFrom))return;
        var dir = hoverDir(obj,oEvent);
　　　　　//根据方向重新设定遮罩层位置
        switch(dir){
            case 0:
                oS.style.left = '200px';
                oS.style.top = 0;
                break;
            case 1:
                oS.style.left = 0;
                oS.style.top = '200px';
                break;
            case 2:
                oS.style.left = '-200px';
                oS.style.top = 0;
                break;
            case 3:
                oS.style.left = 0;
                oS.style.top = '-200px';
                break;
        }
        startMove(oS,{top:0,left:0});
    };
    obj.onmouseout=function(ev){
        var oEvent = ev||event;
        var oTo = oEvent.toElement||oEvent.relatedTarget;
        if(obj.contains(oTo))return;
        var dir = hoverDir(obj,oEvent);
　　　　　//根据移除的方向遮罩层进行相应的运动
        switch(dir){
            case 0:
                startMove(oS,{left:200,top:0});
                break;
            case 1:
                startMove(oS,{left:0,top:200});
                break;
            case 2:
                startMove(oS,{left:-200,top:0});
                break;
            case 3:
                startMove(oS,{left:0,top:-200});
                break;
        }
    };
}
window.onload=function(){
    var oUl = document.body.children[0];
    var aLi = oUl.children;
    for(var i=0;i<aLi.length;i++){
        hoverGo(aLi[i]);
    }
};

function getStyle(obj,sName){
    return (obj.currentStyle||getComputedStyle(obj,false))[sName];
}
//运动框架
function startMove(obj,json,options){
    options=options||{};
    options.time = options.time||700;
    options.type = options.type||'ease-out';
    var start = {};
    var dis = {};
    for(var name in json){
        start[name] = parseFloat(getStyle(obj,name));
        if(isNaN(start[name])){
            switch(name){
                case 'top':
                    start[name] = obj.offsetTop;
                    break;
                case 'left':
                    start[name] = obj.offsetLeft;
                    break;
                case 'width':
                    start[name] = obj.offsetWidth;
                    break;
                case 'height':
                    start[name] = obj.offsetHeight;
                    break;
                case 'opacity':
                    start[name] = 1;
                    break;
                case 'borderWidth':
                    start[name] = 0;
                    break;
            }
        }
        dis[name] = json[name]-start[name];
    }
    var count = Math.floor(options.time/30);
    var n = 0;
    clearInterval(obj.timer);
    obj.timer = setInterval(function(){
        n++;
        for(var name in json){
            switch(options.type){
                case 'linear':
                    var cur = start[name]+dis[name]*n/count;
                    break;
                case 'ease-in':
                    var a = n/count;
                    var cur = start[name]+dis[name]*Math.pow(a,3);
                    break;
                case 'ease-out':
                    var a = 1-n/count;
                    var cur = start[name]+dis[name]*(1-Math.pow(a,3));
                    break;
            }
            if(name=='opacity'){
                obj.style.opacity=cur;
                obj.style.filter='alpha(opacity:'+cur*100+')';
            }else{
                obj.style[name] = cur+'px';
            }
        }
        if(n==count){
            clearInterval(obj.timer);
            options.end&&options.end();
        }
    },30);
}

<ul>
    <li><span>模块1</span></li>
    <li><span>模块2</span></li>
    <li><span>模块3</span></li>
    <li><span>模块4</span></li>
    <li><span>模块5</span></li>
    <li><span>模块6</span></li>
</ul>

*{margin:0; padding:0;}
ul{overflow:hidden; width:630px; margin:100px auto;}
li{width:200px; height:200px; background:#ccc; font-size:30px; font-weight:bold; line-height:200px; overflow:hidden; float:left; margin:5px; position:relative; top:0; left:0;}
li span{position:absolute; top:0; left:-200px; width:100%; height:100%; background:red; opacity:0.4; filter:alpha(opacity:40);}