void SelectNewTile(Vector2 newPos)
 {
     if (selectedTile != null)
                     selectedTile.DeSelect ();
             if (newPos != -Vector2.one) {
                     selectedTile = tiles [(int)newPos.x, (int)newPos.y];
                     selectedTile.Select ();
             } else {
                     selectedTile = null;
             }
 }