I have a certain number of points and there is a box move across these points.When there are some points behind the box,they have to move in front of the box.Therefore,there are always a certain number of points inside the box.
Then i make a gh for it.It almost works.The logic is-There is a smaller box in the right side of the big box.These two boxes always move in the same direction and same distance.Because there are always 3 points behind the big box,so i just need to creat the 3 new points everytime.