public void OnPointerDown(PointerEventData eventData)
        {
            List <PointerEventData> pointers = eventData.IsTouchInput() ? touchPointers : mousePointers;

            for (int i = 0; i < pointers.Count; i++)
            {
                if (pointers[i].pointerId == eventData.pointerId)
                {
                    pointers[i] = eventData;
                    return;
                }
            }

            pointers.Add(eventData);
        }