// JavaScript Document

	//创建遮罩层
	function LoginMsg(){
	   /**第一步：创建DIV遮罩层。*/
		var sWidth,sHeight;
		//sWidth = window.screen.availWidth;
		sWidth =   document.body.scrollWidth;
		//屏幕可用工作区高度： window.screen.availHeight;
		//屏幕可用工作区宽度： window.screen.availWidth;
		//网页正文全文宽：     document.body.scrollWidth;
		//网页正文全文高：     document.body.scrollHeight;
		if(window.screen.availHeight > document.body.scrollHeight){  //当高度少于一屏
			sHeight = window.screen.availHeight;
		}else{//当高度大于一屏
			sHeight = document.body.scrollHeight;   
		}
		//创建遮罩背景
		var maskObj = document.createElement("div");
		maskObj.setAttribute('id','BigDiv');
		maskObj.style.position = "absolute";
		maskObj.style.top = "0";
		maskObj.style.left = "0";
		maskObj.style.background = "#777";
		maskObj.style.filter = "Alpha(opacity=30);";
		maskObj.style.opacity = "0.3";
		maskObj.style.width = sWidth + "px";
		maskObj.style.height = sHeight + "px";
		maskObj.style.zIndex = "10000";
		document.body.appendChild(maskObj);
		
        /**第二步：动态设置div的上边距和左边距，使弹出div居中打开。*/
        var MyDiv =document.getElementById("LoginDiv");
		var MyDiv_w = getStyle(MyDiv,"width");
		var MyDiv_h = getStyle(MyDiv,"height");
	    
		MyDiv_w = parseInt(MyDiv_w); //去掉 单位 "px"
		MyDiv_h = parseInt(MyDiv_h);

		var width = pageWidth(); 
		var height = pageHeight();
		var left = leftPosition();
		var top = topPosition();

		var Div_topposition = top + (height / 2) - (MyDiv_h / 2); //计算上边距
		var Div_leftposition = left + (width / 2) - (MyDiv_w / 2); //计算左边距

		MyDiv.style.left = Div_leftposition + "px";  //拼接上 单位"px"
		MyDiv.style.top =  Div_topposition + "px";
		MyDiv.style.display = "block";  //设置弹出div显示
	}

		/**第三步：关闭窗口和遮罩层。*/
	function CloseDiv(){
		var Bigdiv = document.getElementById("BigDiv");
		var Mydiv = document.getElementById("LoginDiv");
		if(document.body) document.body.removeChild(Bigdiv); 
		else document.documentElement.removeChild(Bigdiv); 
		Mydiv.style.display="none";
	}
/**
下面都是常用函数，已经收录在我的jsskep.js中。可以在里面找到。
工程地址：http://code.google.com/p/jsskep/
**/
// 计算当前窗口的宽度 //
function pageWidth(){
			 return window.innerWidth != null ? window.innerWidth : document.documentElement && document.documentElement.clientWidth ? document.documentElement.clientWidth : document.body != null ? document.body.clientWidth : null;
}

// 计算当前窗口的高度 //
function pageHeight(){
			 return window.innerHeight != null? window.innerHeight : document.documentElement && document.documentElement.clientHeight ? document.documentElement.clientHeight : document.body != null? document.body.clientHeight : null;
}

// 计算当前窗口的上边滚动条//
function topPosition(){
			  return typeof window.pageYOffset != 'undefined' ? window.pageYOffset : document.documentElement && document.documentElement.scrollTop ? document.documentElement.scrollTop : document.body.scrollTop ? document.body.scrollTop : 0;
}

// 计算当前窗口的左边滚动条//
function leftPosition(){
			 return typeof window.pageXOffset != 'undefined' ? window.pageXOffset : document.documentElement && document.documentElement.scrollLeft ? document.documentElement.scrollLeft : document.body.scrollLeft ? document.body.scrollLeft : 0;
}

//解决外嵌样式style , 用js获取不到的问题。
function getStyle(elem, name){
			if(elem.style[name])
				return elem.style[name];
			else if(elem.currentStyle)	//ie
				return elem.currentStyle[name];
			else if(document.defaultView && document.defaultView.getComputedStyle){	//w3c
				name = name.replace(/([A-Z])/g,"-$1");
				name = name.toLowerCase();
				
				var s = document.defaultView.getComputedStyle(elem,"");
				return s && s.getPropertyValue(name);
			} else
				return null
}