//基本設定
var headerImgBoxName = "headerImgBox";//ヘッダーイメージボックス名
var headerImgName = "headerImg"; //ヘッダーイメージ名
var browsSeconds = 3;//イメージがステイしている時間（秒）
var opacityGrade = 10;//フェードの段階（100まで）
var imgOpacity = 100;
var randomImg = 0;
var photos = new Array(
	"http://tacten.net/images/header1.jpg",
	"http://tacten.net/images/header2.jpg",
	"http://tacten.net/images/header3.jpg",
	"http://tacten.net/images/header4.jpg",
	"http://tacten.net/images/header5.jpg",
	"http://tacten.net/images/header6.jpg",
	"http://tacten.net/images/header7.jpg",
	"http://tacten.net/images/header8.jpg",
	"http://tacten.net/images/header9.jpg",
	"http://tacten.net/images/header10.jpg"
);

//最初のイメージを決定
function headerRotate() {
	randomImg = Math.floor(Math.random() * photos.length);
	document.write('<a href="http://www.tacten.net"><img id="headerImg" width="750" height="98" alt="tacten" src="' +photos[randomImg] + '" /></a>');
}

//ヘッダーイメージアニメーション
function headerAnimation() {
	var imgObj = document.getElementById(headerImgName);
	document.getElementById(headerImgBoxName).style.backgroundImage = 'url(' + photos[randomImg] + ')';
	imgFade();
}

//フェード
function imgFade() {
	var imgObj = document.getElementById(headerImgName);
	if (imgOpacity <= opacityGrade) {//フェード外
		imgOpacity = 100;
		imgSelect();
		setTimeout("imgFade()",browsSeconds*1000);
	}else{//フェード中
		imgOpacity -= opacityGrade;
		setOpacity(imgObj,imgOpacity);
		setTimeout("imgFade()",50);
	}
}

//次イメージ選択
function imgSelect() {
	var divObj = document.getElementById(headerImgBoxName);
	var imgObj = document.getElementById(headerImgName);
	imgObj.src = photos[randomImg];
	setOpacity(imgObj,100);
	randomImg = Math.floor(Math.random() * photos.length);
	divObj.style.backgroundImage = 'url(' + photos[randomImg] + ')';
}

//不透明度設定
function setOpacity(obj, opacity) {
	opacity = (opacity == 100)?100:opacity;
	obj.style.filter = "alpha(opacity:"+opacity+")";	
	obj.style.KHTMLOpacity = opacity/100;
	obj.style.MozOpacity = opacity/100;
	obj.style.opacity = opacity/100;
}

window.onload = headerAnimation;