弹跳的小球，小球从屏幕中心下落，触摸到上下边缘就改变方向，并且增大加速度，左右也有位移，触摸到边缘改变方向。-Bouncing ball, the ball falling from the center of the screen, touch the top and bottom edges to change direction, and increased acceleration, so there displacement touch to the edge change direc