var ev_msgbox_id=""; //重要  
  
//弹出对话窗口(msgid-要显示的div的id)  
function ev_modealert(msgid){  
    //创建大大的背景框  
    var bgobj=document.createelement("div");  
    bgobj.setattribute('id','ev_bgmodealertdiv');  
    document.body.appendchild(bgobj);  
    //背景框满窗口显示  
    ev_show_bgdiv();  
    //把要显示的div居中显示  
    ev_msgbox_id=msgid;  
    ev_show_msgdiv();  
}  
  
//关闭对话窗口  
function ev_closealert(){  
    var msgobj=document.getelementbyid(ev_msgbox_id);  
    var bgobj=document.getelementbyid("ev_bgmodealertdiv");  
    msgobj.style.display="none";  
    document.body.removechild(bgobj);  
    ev_msgbox_id="";  
}  

//窗口大小改变时更正显示大小和位置  
window.onresize=function(){
    if (ev_msgbox_id.length>0){
        ev_show_bgdiv();
        ev_show_msgdiv();
    }
}

//窗口滚动条拖动时更正显示大小和位置  
window.onscroll=function(){
    if (ev_msgbox_id.length>0){
        ev_show_bgdiv();
        ev_show_msgdiv();
    }
}  

//把要显示的div居中显示  
function ev_show_msgdiv(){
    var msgobj   = document.getelementbyid(ev_msgbox_id);  
    msgobj.style.display  = "block";  
    var msgwidth = msgobj.scrollwidth;  
    var msgheight= msgobj.scrollheight;
    //todo
//    var bgtop=0;
//    var bgleft=0;
    var bgtop=ev_myscrolltop();
    var bgleft=ev_myscrollleft();
    var bgwidth=ev_myclientwidth();
    var bgheight=ev_myclientheight();
    var msgtop=bgtop+math.round((bgheight-msgheight)/2);  
    var msgleft=bgleft+math.round((bgwidth-msgwidth)/2);
    msgobj.style.position = "absolute";
    msgobj.style.top      = msgtop+"px";  
    msgobj.style.left     = msgleft+"px";  
    msgobj.style.zindex   = "1001";
      
}  
//背景框满窗口显示  
function ev_show_bgdiv(){  
    var bgobj=document.getelementbyid("ev_bgmodealertdiv");  
    var bgwidth=ev_myclientwidth();  
    var bgheight=ev_myclientheight();  
    var bgtop=ev_myscrolltop();  
    var bgleft=ev_myscrollleft();  
    bgobj.style.position   = "absolute";
    bgobj.style.top        = bgtop+"px";  
    bgobj.style.left       = bgleft+"px";  
    bgobj.style.width      = bgwidth + "px";  
    bgobj.style.height     = bgheight + "px";  
    bgobj.style.zindex     = "1000";
    bgobj.style.background = "#444";  
    bgobj.style.filter     = "progid:dximagetransform.microsoft.alpha(style=0,opacity=60,finishopacity=60);";  
    bgobj.style.opacity    = "0.6";  
}  
//网页被卷去的上高度  
function ev_myscrolltop(){  
    var n=window.pageyoffset   
    || document.documentelement.scrolltop   
    || document.body.scrolltop || 0;  
    return n;  
}  
//网页被卷去的左宽度  
function ev_myscrollleft(){  
    var n=window.pagexoffset   
    || document.documentelement.scrollleft   
    || document.body.scrollleft || 0;  
    return n;  
}  
//网页可见区域宽  
function ev_myclientwidth(){  
    var n=document.documentelement.clientwidth   
    || document.body.clientwidth || 0;  
    return n;  
}  
//网页可见区域高  
function ev_myclientheight(){  
    var n=document.documentelement.clientheight   
    || document.body.clientheight || 0;  
    return n;  
}