Function GetClosestWaterDistance

src/map.cpp:263–310

* Finds the distance for the closest tile with water/land given a tile * @param tile the tile to find the distance too * @param water whether to find water or land * @return distance to nearest water (max 0x7F) / land (max 0x1FF; 0x200 if there is no land) */

 * @return distance to nearest water (max 0x7F) / land (max 0x1FF; 0x200 if there is no land)
 */
uint GetClosestWaterDistance(TileIndex tile, bool water)
{
	if (HasTileWaterGround(tile) == water) return 0;

	uint max_dist = water ? 0x7F : 0x200;

	int x = TileX(tile);
	int y = TileY(tile);

	uint max_x = Map::MaxX();
	uint max_y = Map::MaxY();
	uint min_xy = _settings_game.construction.freeform_edges ? 1 : 0;

	/* go in a 'spiral' with increasing manhattan distance in each iteration */
	for (uint dist = 1; dist < max_dist; dist++) {
		/* next 'diameter' */
		y--;

		/* going counter-clockwise around this square */
		for (DiagDirection dir = DIAGDIR_BEGIN; dir < DIAGDIR_END; dir++) {
			static const int8_t ddx[DIAGDIR_END] = { -1,  1,  1, -1};
			static const int8_t ddy[DIAGDIR_END] = {  1,  1, -1, -1};

			int dx = ddx[dir];
			int dy = ddy[dir];

			/* each side of this square has length 'dist' */
			for (uint a = 0; a < dist; a++) {
				/* MP_VOID tiles are not checked (interval is [min; max) for IsInsideMM())*/
				if (IsInsideMM(x, min_xy, max_x) && IsInsideMM(y, min_xy, max_y)) {
					TileIndex t = TileXY(x, y);
					if (HasTileWaterGround(t) == water) return dist;
				}
				x += dx;
				y += dy;
			}
		}
	}

	if (!water) {
		/* no land found - is this a water-only map? */
		for (const auto t : Map::Iterate()) {
			if (!IsTileType(t, MP_VOID) && !IsTileType(t, MP_WATER)) return 0x1FF;
		}
	}

	return max_dist;
}