code: public static MotionDirection getVerticalMotionDirection(MotionEvent e1, MotionEvent e2, float threshold) {
          float delta = getVerticalMotionRawDelta(e1, e2);
          return getVerticalMotionDirection(delta, threshold);
      }
docs: Calculate the vertical move motion direction.
  @param e1 start point of the motion.
  @param e2 end point of the motion.
  @param threshold threshold to detect the motion.
  @return the motion direction for the vertical axis.