InputManager.cs

public void OnDrag(PointerEventData eventData)
{
    if (draggingStarted)
    {
        endPos = eventData.position;

        Vector2 difference = endPos - startPos; // difference vector between start and end positions.

        if (difference.magnitude > swipeThreshold)
        {
            if (Mathf.Abs(difference.x) > Mathf.Abs(difference.y)) // Do horizontal swipe
            {
                direction = difference.x > 0 ? Direction.Right : Direction.Left; // If greater than zero, then swipe to right.
            }
            else //Do vertical swipe
            {
                direction = difference.y > 0 ? Direction.Up : Direction.Down; // If greater than zero, then swipe to up.
            }
        }
        else
        {
            direction = Direction.None;
        }
    }
}