//ローテーション基本設定
var headerImgBoxName = "headerfotoBox";
var headerImgName = "headerfoto"; 
var browsSeconds = 5;
var opacityGrade = 5;
var imgOpacity = 100;
var randomImg = 0;
var photos = new Array(
"img/top_main/01.jpg",
"img/top_main/02.jpg",
"img/top_main/03.jpg"
);

//最初の写真を決定
function headerRotate() {
randomImg = Math.floor(Math.random() * photos.length);
document.write('<img id="headerfoto" width="940" height="381" alt="main photo" src="' +photos[randomImg] + '" />');
}

//ヘッダー写真アニメーション
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);
}
}

//次の写真を選択
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;