// JavaScript Document
function dispBg(){
	frame ++;
	if(frame == 1){
		d.getElementById('bg_img').src = bg_files[bg_number];
		setRatio();
	};
	
	if(frame <= 100){
		bg_opa += 1;
		d.getElementById('bg_img').style.filter = 'alpha(style=0, opacity='+bg_opa+')';
		d.getElementById('bg_img').style.opacity = bg_opa / 100;
		d.getElementById('bg_img').style.MozOpacity = bg_opa / 100;
		return;
	};
	
	if(frame <= 600){
		return;
	};
	
	if(frame <= 700){
		bg_opa -= 1;
		d.getElementById('bg_img').style.filter = 'alpha(style=0, opacity='+bg_opa+')';
		d.getElementById('bg_img').style.opacity = bg_opa / 100;
		d.getElementById('bg_img').style.MozOpacity = bg_opa / 100;	
	};
	
	if(frame == 700){
		frame = 0;
		bg_opa = 0;
		bg_number ++;
		if(bg_number >= bg_files.length){
			bg_number = 0;
		};
		return;		
	};	
};

function setRatio(){
	var bgW = d.getElementById('bg').offsetWidth;
	var bgH = d.getElementById('bg').offsetHeight;
	
	var bgRatio = bgW / bgH;
	var imgRatio = bg_size_x[bg_number] / bg_size_y[bg_number];
	
	if(bgRatio >= imgRatio){
		var imgW = bgW;
		var imgH = Math.floor(bg_size_y[bg_number] * bgW / bg_size_x[bg_number]);
		var posX = 0;
		var posY = Math.floor((bgH - imgH) / 2);
	}else{
		var imgW = Math.floor(bg_size_x[bg_number] * bgH / bg_size_y[bg_number]);
		var imgH = bgH;
		var posX = Math.floor((bgW - imgW) / 2);
		var posY = 0;
	}
	d.getElementById('bg_img').width = imgW;
	d.getElementById('bg_img').height = imgH;
	d.getElementById('bg_img').style.left = posX + 'px';
	d.getElementById('bg_img').style.top = posY + 'px';	
};