var in_opacity=0;
var out_opacity=100;
var last_on="a1";
var wait = 1;
var auto = setInterval(function(){autoPlay();},7000);
function standby(){
	preloadimg("img/demo/ban_1.png","a1");
	preloadimg("img/demo/ban_2.png","a2");
}
function autoPlay(){
	var no =  Number(last_on.substr(last_on.length-1,last_on.length));
	if(no == 2){no = 1;}
	else{no = 1+no;}
	no = "a"+no;	
	changePic(no);
}
function preloadimg(url,objName){
	var img=new Image();
	var obj = document.getElementById(objName);
	obj.innerHTML="<p>Loading...</p>";
	img.onload=function(){
		obj.style.backgroundImage="url('"+url+"')";
		obj.innerHTML="";
	};
	img.onerror=function(){
		obj.innerHTML="<p>Failed To Loading！</p>";
	};
	img.src=url;
}
function fadeIn(id){
var a = document.getElementById(id);
	in_opacity=in_opacity+10;
	a.style.filter="alpha(opacity="+in_opacity+")";
	a.style.opacity=in_opacity/100;
	if(in_opacity<100){
		setTimeout(function(){fadeIn(id);},70);
	}else{
		in_opacity=0;
	}
}
function fadeOut(id){
  	var a = document.getElementById(id);
  	out_opacity=out_opacity - 10;
  	a.style.filter="alpha(opacity="+out_opacity+")";
  	a.style.opacity=out_opacity/100;
  	if(out_opacity>0){
  		setTimeout(function(){fadeOut(id);},70);
  	}else{
  		out_opacity=100;
  	}
}
function changeBtnPic(id){
	var no1 =  Number(id.substr(id.length-1,id.length));
	var no2 =  Number(last_on.substr(last_on.length-1,last_on.length));
	var a = document.getElementById("btn"+ no1);
	var b = document.getElementById("btn"+ no2);
	document.getElementById('btn'+ no1).style.backgroundImage="url('images/btn"+no1+"_on.gif')";
	document.getElementById('btn'+ no2).style.backgroundImage="url('images/btn"+no2+"_off.gif')";
}
function changePic(id){
	if(wait==1){
		if(id!=last_on){
			fadeIn(id);
			fadeOut(last_on);
			changeBtnPic(id);
			last_on = id;
			wait = 0;
			setTimeout("wait=1;",800);
		}
	}
}
function clickpic(id){
	changePic(id);
	clearInterval(auto);
}