function displayCoverLay(){//display coverlay and return it
	BafangwangUtil.loadCssFile("/divBox/bg/v1/coverlay.css", "css");
	var obj = document.getElementById("coverlay");
	if(obj==undefined){
		obj= document.createElement("DIV");
		obj.setAttribute("id", "coverlay");
		//obj.onclick = hiddenCoverLay;
		var objBody = document.getElementsByTagName('body')[0];
		objBody.appendChild(obj);
	}
	obj.style.display = "block";
	setTopmostObjVisibility(new Array('select', 'object', 'embed'), "hidden");
	var wh = calculateCurPageWidthHeight();
	obj.style.width = wh[0] +"px";
	obj.style.height = wh[1]+"px";
	return obj;
}
function hiddenCoverLay(){//hidden coverlay
	var obj = document.getElementById("coverlay");
	if(obj!=undefined){
		obj.style.display = "none";
		setTopmostObjVisibility(new Array('select', 'object', 'embed'), "visible");
	}
}
function setTopmostObjVisibility(tagNameList, value){//hidden or display all the topmost obj
	for(var i=0;i<tagNameList.length;i++){
		var objarray = document.getElementsByTagName(tagNameList[i]);
		for(var j=0;objarray!=undefined&&j<objarray.length;j++){
			objarray[j].style.visibility = value;
		}
	}
}
function calculateCurPageWidthHeight() {//calculate current page's width and height
	var xScroll, yScroll;
	if (window.innerHeight && window.scrollMaxY) {//firefox
		xScroll = window.innerWidth + window.scrollMaxX;
		yScroll = window.innerHeight + window.scrollMaxY;
	} else if (document.body.scrollHeight > document.body.offsetHeight){ // all but Explorer Mac
		xScroll = document.body.scrollWidth;
		yScroll = document.body.scrollHeight;
	} else { // Explorer Mac...would also work in Explorer 6 Strict, Mozilla and Safari
		xScroll = document.body.offsetWidth;
		yScroll = document.body.offsetHeight;
	}
	var windowWidth, windowHeight;
	if (self.innerHeight) {	// all except Explorer
		if(document.documentElement.clientWidth){
			windowWidth = document.documentElement.clientWidth; 
		} else {
			windowWidth = self.innerWidth;
		}
		windowHeight = self.innerHeight;
	} else if (document.documentElement && document.documentElement.clientHeight) { // Explorer 6 Strict Mode
		windowWidth = document.documentElement.clientWidth;
		windowHeight = document.documentElement.clientHeight;
	} else if (document.body) { // other Explorers
		windowWidth = document.body.clientWidth;
		windowHeight = document.body.clientHeight;
	}
	// for small pages with total height less then height of the viewport
	if(yScroll < windowHeight){
		pageHeight = windowHeight;
	} else { 
		pageHeight = yScroll;
	}
	// for small pages with total width less then width of the viewport
	if(xScroll < windowWidth){	
		pageWidth = xScroll;		
	} else {
		pageWidth = windowWidth;
	}
	return [pageWidth,pageHeight];
}