jQuery 实现网页图片动态游走，碰到边框反弹

<html>
<head>
    <title></title>
<script type="text/javascript" src="jquery-1.9.1.min.js"></script>
</head>
<body>
<h2>ShowOrHide</h2>

<META http-equiv="content-type" content="text/html;charset=utf8">
    <input type="button" name="stop" value="咒立停"/>
    <input type="button" name="begin" value="颤抖吧"/>
<div id="song" style="text-align: center; font-size: 100px;width:300px;">
    <img id="gala" alt="我爱罗" src="gala.jpg" style="width:300px;height:300px"/>
</div>
<script type="text/javascript">
    $(function () {
        $("h2").click(function () {
            //隐藏或显示标签
            $("img#gala").slideToggle();
        });
        $("img#gala").mouseenter(function(){
            window.clearInterval(timerlr);
        }).mouseleave(function(){
            window.clearInterval(timerlr);//非第一次使用定时器必须先停止，否则会导致时间混乱
            timerlr=self.setInterval("move()", global.timespan);
        });
        $("[name='stop']").click(function(){
            window.clearInterval(timerlr);
        });
         $("[name='begin']").click(function(){
            window.clearInterval(timerlr);//非第一次使用定时器必须先停止，否则会导致时间混乱
            timerlr=self.setInterval("move()", global.timespan);
        });
    });

    //声明全局变量对象，尽量减少污染
    var global = {
        timespan: 10,//定时器间隔
        vdirect: "down",//垂直滚动方向
        hdirect: "right",//水平滚动方向
        widthspan: 10,//单次宽度变化
        heightspan: 10//单次高度变化
    }
    
    var timerlr = self.setInterval("move()", global.timespan);

    function moveright() {
        $song = $("div#song");
        var offset = $song.offset();
        var left = offset.left + global.widthspan;
        $song.offset({ left: left, top: offset.top });
    }
    function movedown() {
        $song = $("div#song");
        var offset = $song.offset();
        var top = offset.top + global.heightspan;
        $song.offset({ left: offset.left, top: top });
    }
    function moveleft() {
        $song = $("div#song");
        var offset = $song.offset();
        var left = offset.left - global.widthspan;
        $song.offset({ left: left, top: offset.top });
    }
    function moveup() {
        $song = $("div#song");
        var offset = $song.offset();
        var top = offset.top - global.heightspan;
        $song.offset({ left: offset.left, top: top });
    }

    //进行水平和垂直方向的移动
    function move() {
        $height=$(window).height();
        $song = $("div#song");

        //离底部还有10像素的距离时开始回弹
        if ($song.offset().top + $song.height() >= $height-10) {
            global.vdirect = "up";
        }
        else if ($song.offset().top <= 10) {
            global.vdirect = "down";
        }
        if (global.vdirect == "down") {
            movedown();
        }
        else if (global.vdirect == "up") {
            moveup();
        } 
        if ($song.offset().left + $song.width() >= $(window).width()-10) {
            global.hdirect = "left";
        }
        //离右边界还有10像素距离还是回弹
        else if ($song.offset().left <= 10) {
            global.hdirect = "right";
        }
        if (global.hdirect == "right") {
            moveright();
        }
        else if (global.hdirect == "left") {
            moveleft();
        }
    }
</script>
</body>
</html>