window.onload = function(){
	add_chimg("gmenu_top");
	add_chimg("gmenu_story");
	add_chimg("gmenu_chara");
	add_chimg("gmenu_sample");
	add_chimg("gmenu_download");
	add_chimg("gmenu_staff");
};

function add_chimg(id){
	if(document.getElementById(id)!=null){
		new RollOverImage(document.getElementById(id));
	}
}

function RollOverImage(img){
	this.img = img;
	this.originalPath = this.img.src;
	this.setMouseOverImage();
}
RollOverImage.prototype.setMouseOverImage = function(){
	var originalPath = this.originalPath;
	/* 第2の画像に置き換える場合 */
	this.mouseoverImg = new Image();
	this.mouseoverImg.src = originalPath.replace(".gif","_on.gif");
	this.img.onmouseover = RollOverImage.createHandler(this.img, this.mouseoverImg.src);
	/* 元の画像に戻す場合 */
	this.img.onmouseout = RollOverImage.createHandler(this.img, this.originalPath);
}
RollOverImage.createHandler = function(img, path){
	return function(){
		img.src = path;
	}
}