public void update(Graphics g)
	{
		if(null==bkImage) { bkImage=this.createImage(WIN_WIDTH,WIN_HEIGHT); }

		g.drawImage(bkImage,0,0,null);  //ͼƬݻǰ

		Graphics gBkImg=bkImage.getGraphics();
		gBkImg.clearRect(0,0,WIN_WIDTH,WIN_HEIGHT); //ͼƬ
		this.paint(gBkImg);  //ͼȻͼƬ
	}