private void bufferReset(){
		if( imageBuffer==null ){
			imageBuffer = this.createImage(SCREEN_WIDTH, SCREEN_HEIGHT);
			gBuffer = imageBuffer.getGraphics();
			System.out.println("ʼ");
		}
		gBuffer.setColor(bgColor);
		gBuffer.fillRect(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT);
//		gBuffer.drawImage(BackGround, 0, 0, null);
		if(firstTime){
			//ȥ˸
			gBuffer.drawImage(EnemyTank_Down, 2000, 2000, null);
			gBuffer.drawImage(EnemyTank_Left, 2000, 2000, null);
			gBuffer.drawImage(EnemyTank_Right, 2000, 2000, null);
			gBuffer.drawImage(EnemyTank_Up, 2000, 2000, null);
			
			gBuffer.drawImage(MyTank_Down, 2000, 2000, null);
			gBuffer.drawImage(MyTank_Left, 2000, 2000, null);
			gBuffer.drawImage(MyTank_Right, 2000, 2000, null);
			gBuffer.drawImage(MyTank_Up, 2000, 2000, null);
			
			gBuffer.drawImage(OzTank_Down, 2000, 2000, null);
			gBuffer.drawImage(OzTank_Left, 2000, 2000, null);
			gBuffer.drawImage(OzTank_Right, 2000, 2000, null);
			gBuffer.drawImage(OzTank_Up, 2000, 2000, null);
			
			gBuffer.drawImage(EnemyBullet, 2000, 2000, null);
			gBuffer.drawImage(BlackBullet, 2000, 2000, null);
			gBuffer.drawImage(MyBullet, 2000, 2000, null);
			
			firstTime = false;
		}
	}