// JavaScript Document
var arrImage1 = new Array();
arrImage1[0]="cmn_img/topbg1.jpg";
arrImage1[1]="cmn_img/topbg2.jpg";
arrImage1[2]="cmn_img/topbg3.jpg";
arrImage1[3]="cmn_img/topbg4.jpg";

function ChangePicture(){
	var H = screen.availHeight;
	var W = screen.availWidth;
	//
	document.getElementById("pic").style.height=H+"px";
	document.getElementById("pic").style.width=W+"px";
	//
	document.getElementById("navi_bg").style.height=H+"px";
	//
	var theNum=StartRandom();
	if(theNum==0){
		document.getElementById("pic").style.backgroundImage="url("+arrImage1[theNum]+")";
		document.getElementById("pic").style.backgroundPosition="right bottom";
	}else if(theNum==1){
		document.getElementById("pic").style.backgroundImage="url("+arrImage1[theNum]+")";
		document.getElementById("pic").style.backgroundPosition="-100px center";
	}else if(theNum==2){
		document.getElementById("pic").style.backgroundImage="url("+arrImage1[theNum]+")";
		document.getElementById("pic").style.backgroundPosition="0px center";
	}else{
		document.getElementById("pic").style.backgroundImage="url("+arrImage1[theNum]+")";
		document.getElementById("pic").style.backgroundPosition="200px center";
	}
		document.getElementById("pic").style.backgroundRepeat="no-repeat";
	//
}
function StartRandom(){
	return Math.round(Math.random()*(arrImage1.length-1));
}
window.onload=function(){
	ChangePicture();
}