采用基于子画面动画的行星飞行程序，其中的三个行星在碰到屏幕边缘时分别采用停止、环绕、反弹三种不同的边界动作- Uses based on the sub- picture animation planet flight procedure, three planets are bumping into the screen edge time-sharing not to use stop, surrounding, the resilience three kind of differen