自己写的小球在一个矩形框内反弹程序：编写一个小游戏，让小圆球在画面移动，当小球碰到画面边框时，反射方向继续运动。-Write your own ball in a rectangle rally program: to write a small game, make a small ball moving on the screen when the ball hit the screen borders, reflecting the direction of continuing move