Maps edge index i (the edge between corner[i] and corner[i+1]) to the HEX_DIRECTIONS index for the neighbor across that edge. Derived by matching each edge's outward-normal angle to a direction vector.
Maps edge index i (the edge between corner[i] and corner[i+1]) to the HEX_DIRECTIONS index for the neighbor across that edge. Derived by matching each edge's outward-normal angle to a direction vector.