https://www.pygame.org/docs/ref/rect.html#pygame.Rect
https://blog.csdn.net/YZXnuaa/article/details/79011795
pygame.Rect.clip:
crops a rectangle inside another
Returns a new rectangle that is cropped to be completely inside the argument Rect. If the two rectangles do not overlap to begin with, a Rect with 0 size is returned.