code: private Collection<String> getNeighborGroups(Tile tile)
      {
          final Collection<String> neighborGroups = new ArrayList<>(TransitionType.BITS);
  
          addNeighborGroup(neighborGroups, tile, 1, -1);
          addNeighborGroup(neighborGroups, tile, -1, -1);
          addNeighborGroup(neighborGroups, tile, 1, 1);
          addNeighborGroup(neighborGroups, tile, -1, 1);
  
          return neighborGroups;
      }
docs: Get the direct neighbor angle groups.
  
  @param tile The current tile.
  @return The 4 neighbor groups.