//使用方法
//$(function () { setFloatBackgroundByID("adplay"); });
//$(window).resize(function () { setFloatBackgroundByID("adplay"); });
function setFloatBackgroundByID(id){
    var $objId=$("#"+id);//整张大图片的id
    $objId.css({"overflow":"hidden","position":"relative"});
    var $html=$("<div class=\"flow\" style=\"width:"+$objId.width()+"px;height:"+$objId.height()+"px;left:0;top:0;display:none;position:absolute;opacity:0.5;z-index:1\">");
     $objId.children().each(function(){   //为了防止append重复添加
        if (!$objId.is(‘:has(".flow")‘) ) {
             $objId.append($html);
         }
     })
    var $mainImg=$objId.css("background-image"); //获取大图的url地址
    var $divEach=$("div",$objId).not(".flow");
    $divEach.css({"position":"absolute","overflow":"hidden","z-index":"100"});
    $divEach.each(function(){
        var $this=$(this);
        $(this).css({"left":parseInt($this.attr("top"))+"px","top":parseInt($this.attr("left"))+"px"});
        $(this).hover(function(){
            var top=parseInt($(this).css("top"))+"px";  //定位
            var left=parseInt($(this).css("left"))+"px";
           var $Img=$mainImg + " -" + top + " -" + left; //注意top和left前面必须有一个空格，否则显示失败
            //$this.css("background","none");
            $html.css("display","");
            $this.css({"background":$Img});

        },function(){
            $html.css("display","none")
            $divEach.css("background","none");
        })
    })
}
下面是html代码
//<div style="width: 960px; height: 508px; background: url(pic/swhw.jpg); overflow: hidden;" id="swimgbox">
//    <a href="http://www.fsmjj.com/Product/Furniture/0a714b5c22144620815afc82b6069be0.shtml" target="_blank">
//        <div style="width: 190px; height: 160px;" top="0" left="0">
//        </div>
//    </a><a href="http://www.fsmjj.com/Product/Furniture/18ea613c68af47ab9370a2886c3be9b4.shtml" target="_blank">
//        <div style="width: 190px; height: 160px;" top="0" left="196">
//        </div>
//    </a>
//</div>

遮罩层（鼠标移到指定区域时，该区域显示，其他地方为半透明，移动时全部显示）