var floatImg2 = document.getElementById("img2");
    var delay = 50; //控制每次执行间隔的时间，做越大移动得越慢；
    var speed = 1; //控制每次执行移动的距离，值越大移动得越快；
    var flagX2 = 0;
    var flagY2 = 0;
    
    function toPixel2(str1) {
    //该函数用于去掉数值后面的px，并将之转化为数字。
        var oldLen = str1.length;
        var newLen = oldLen - 2;
        
        str2 = str1.slice(0, newLen);
        str3 = parseInt(str2);
        
        return str3;
    }
    
    function flowImg2() {
        var bWidth = document.body.clientWidth;
        var bHeight = document.body.scrollTop + 600;
        var bLeft = document.body.scrollLeft;
        var bTop = document.body.scrollTop;
        
        var iWidth = floatImg2.offsetWidth;
        var iHeight = floatImg2.offsetHeight;
        var iLeft = toPixel2(floatImg2.style.left);
        var iTop = toPixel2(floatImg2.style.top);
        
        //下面一段控制横向移动
        if(iLeft < (bWidth - iWidth) && flagX2 == 0) {
            floatImg2.style.left = (iLeft + speed) + "px";
        }
        else if(iLeft >= (bWidth - iWidth) && flagX2 ==0) {
            flagX2 = 1;
        }
        else if(iLeft > 0 && flagX2 == 1) {
            floatImg2.style.left = (iLeft - speed) + "px";
        }
        else if(0 >= iLeft && flagX2 == 1) {
            flagX2 = 0;
        }
        
        //下面一段控制纵向移动
        if(iTop < (bHeight - iHeight) && flagY2 == 0) {
            floatImg2.style.top = (iTop + speed) + "px";
        }
        else if(iTop >= (bHeight - iHeight) && flagY2 ==0) {
            flagY2 = 1;
        }
        else if(iTop > 0 && flagY2 == 1) {
            floatImg2.style.top = (iTop - speed) + "px";
        }
        else if(0 >= iTop && flagY2 == 1) {
            flagY2 = 0;
        }
    }
    
    var imgInterval2 = setInterval("flowImg2()", delay);
    floatImg2.onmouseover = function() {clearInterval(imgInterval2);}
    floatImg2.onmouseout = function() {imgInterval2 = setInterval("flowImg2()", delay);}