Function GetTileSlopeGivenHeight

src/tile_map.cpp:23–48

* Get a tile's slope given the height of its four corners. * @param hnorth The height at the northern corner in the same unit as TileHeight. * @param hwest The height at the western corner in the same unit as TileHeight. * @param heast The height at the eastern corner in the same unit as TileHeight. * @param hsouth The height at the southern corner in the same unit as TileHeight. * @return

 * @return The slope and the lowest height of the four corners.
 */
static std::tuple<Slope, int> GetTileSlopeGivenHeight(int hnorth, int hwest, int heast, int hsouth)
{
	/* Due to the fact that tiles must connect with each other without leaving gaps, the
	 * biggest difference in height between any corner and 'min' is between 0, 1, or 2.
	 *
	 * Also, there is at most 1 corner with height difference of 2.
	 */
	int hminnw = std::min(hnorth, hwest);
	int hmines = std::min(heast, hsouth);
	int hmin = std::min(hminnw, hmines);

	int hmaxnw = std::max(hnorth, hwest);
	int hmaxes = std::max(heast, hsouth);
	int hmax = std::max(hmaxnw, hmaxes);

	Slope r = SLOPE_FLAT;

	if (hnorth != hmin) r |= SLOPE_N;
	if (hwest  != hmin) r |= SLOPE_W;
	if (heast  != hmin) r |= SLOPE_E;
	if (hsouth != hmin) r |= SLOPE_S;

	if (hmax - hmin == 2) r |= SLOPE_STEEP;

	return {r, hmin};
}

/**
 * Return the slope of a given tile inside the map.