/**

 * 显示弹出图片。

 * @param tag 目标元素。弹出的框将显示在其旁边

 * @param url 需要弹出的图片的URL

 * @param pos 弹出位置。0=右，1=上，2=左，3=下，缺省为自动选择最佳方位。

 */

if(!document.getElementById("_showImage"))

{

 document.write('<img id="_showImage" style="z-index:999; display:none; position:absolute; border:1 solid black" onmouseout="style.display=&quot;none&quot;">');

}

function showImage(tag,url,pos) {

    tag.attachEvent("onmouseout",mouseout);

    var helper = document.getElementById("_showImage");

    helper.removeAttribute("src");

    helper.removeAttribute("width");

    helper.removeAttribute("height");

    helper.onload=showImage_show;

    helper.src = url;



    function mouseout() {

        //注释本行将使鼠标移出原图时弹出图立即关闭

        helper.onmouseout();

        helper.onload = null;

        helper.removeAttribute("src");

        tag.detachEvent("onmouoseout",arguments.callee);

    }

    function showImage_show() {

        var rc = tag.getBoundingClientRect();

        helper.style.display = '';

        var rc2 = helper.getBoundingClientRect();   

        var documentElement = document.documentElement;

        var l = rc.left;

        var t = rc.top;

        var r = documentElement.clientWidth-rc.right;

        var b = documentElement.clientHeight-rc.bottom;

        var ratio = (rc2.bottom-rc2.top) / (rc2.right-rc2.left);



        var pos = typeof(pos)!='undefined'?pos:-1;

        if(pos >= 0) { //指定了显示方位

            var w = pos==1||pos==3?documentElement.clientWidth : pos==0?r:l;

            var h = pos==0||pos==2?documentElement.clientHeight : pos==1?t:b;

            if(h < w*ratio) w = h/ratio;

            else if(w < h/ratio) h = w*ratio;



        } else { //未指定显示方位，自动选择

            var pos0_2 = l < r ? 0 : 2;

            var pos1_3 = t < b ? 3 : 1;

            var w = l < r ? r : l;

            var h = t < b ? b : t;

            var h1 = w*ratio; if(h1 > documentElement.clientHeight) h1 = documentElement.clientHeight;

            var h2 = documentElement.clientWidth*ratio; if(h2 > h) h2 = h;

            if(h1 > h2) {

                var pos = pos0_2;

                h = h1;

                w = h1 / ratio;

            } else {

                var pos = pos1_3;

                h = h2;

                w = h2 / ratio;

            }

        }



        if(rc2.bottom-rc2.top > h || rc2.right-rc2.left > w) {

            helper.width = w;

            helper.height = h;

        }



        var rc2 = helper.getBoundingClientRect();

        l = (pos==1||pos==3?rc.left:pos==0?rc.right:rc.left-(rc2.right-rc2.left));

        t = (pos==0||pos==2?rc.top:pos==3?rc.bottom:rc.top-(rc2.bottom-rc2.top));

        var k = documentElement.clientWidth-(l+rc2.right-rc2.left);

        if(k < 0) l += k;

        var k = documentElement.clientHeight-(t+rc2.bottom-rc2.top);

        if(k < 0) t += k;



        helper.style.left = -2+documentElement.scrollLeft+l;

        helper.style.top = -2+documentElement.scrollTop+t;

    }



}