function updateBalls(){
	for(var i=0;i<balls.length;i++){
		balls[i].x+=balls[i].vx;
		balls[i].y+=balls[i].vy;
		balls[i].vy+=balls[i].g;
		if(balls[i].y>=WINDOW_HEIGHT-RANIUS){
			balls[i].y=WINDOW_HEIGHT-RANIUS;
			balls[i].vy=-balls[i].vy*0.75;
		}
		if(balls[i].x>WINDOW_WIDTH+RANIUS||balls[i].x<-RANIUS){
			balls.splice(i,1);
		}  // 从balls数组中移除跳出画布的小球
	}
	console.log(balls.length);
}