小球的抛物线轨迹。将轨迹分解成x坐标和y坐标，计算出每一个时刻的x和y值，然后对x和y进行成像就可以得到轨迹了-Parabolic trajectory of the ball. The track is decomposed into x and y coordinates, x and y values calculated each time, then x and y can be imaged on a trajectory