Function GrowTownWithBridge

src/town_cmd.cpp:1312–1389

* Grows the town with a bridge. * At first we check if a bridge is reasonable. * If so we check if we are able to build it. * * @param t The current town * @param tile The current tile * @param bridge_dir The valid direction in which to grow a bridge * @return true if a bridge has been build else false */

 * @return true if a bridge has been build else false
 */
static bool GrowTownWithBridge(const Town *t, const TileIndex tile, const DiagDirection bridge_dir)
{
	assert(bridge_dir < DIAGDIR_END);

	const Slope slope = GetTileSlope(tile);

	/* Make sure the direction is compatible with the slope.
	 * Well we check if the slope has an up bit set in the
	 * reverse direction. */
	if (slope != SLOPE_FLAT && slope & InclinedSlope(bridge_dir)) return false;

	/* Assure that the bridge is connectable to the start side */
	if (!(GetTownRoadBits(TileAddByDiagDir(tile, ReverseDiagDir(bridge_dir))) & DiagDirToRoadBits(bridge_dir))) return false;

	/* We are in the right direction */
	uint bridge_length = 0;       // This value stores the length of the possible bridge
	TileIndex bridge_tile = tile; // Used to store the other waterside

	const TileIndexDiff delta = TileOffsByDiagDir(bridge_dir);

	/* To prevent really small towns from building disproportionately
	 * long bridges, make the max a function of its population. */
	const uint TOWN_BRIDGE_LENGTH_CAP = 11;
	uint base_bridge_length = 5;
	uint max_bridge_length = std::min(t->cache.population / 1000 + base_bridge_length, TOWN_BRIDGE_LENGTH_CAP);

	if (slope == SLOPE_FLAT) {
		/* Bridges starting on flat tiles are only allowed when crossing rivers, rails or one-way roads. */
		do {
			if (bridge_length++ >= base_bridge_length) {
				/* Allow to cross rivers, not big lakes, nor large amounts of rails or one-way roads. */
				return false;
			}
			bridge_tile += delta;
		} while (IsValidTile(bridge_tile) && ((IsWaterTile(bridge_tile) && !IsSea(bridge_tile)) || IsPlainRailTile(bridge_tile) || (IsNormalRoadTile(bridge_tile) && GetDisallowedRoadDirections(bridge_tile) != DRD_NONE)));
	} else {
		do {
			if (bridge_length++ >= max_bridge_length) {
				/* Ensure the bridge is not longer than the max allowed length. */
				return false;
			}
			bridge_tile += delta;
		} while (IsValidTile(bridge_tile) && (IsWaterTile(bridge_tile) || IsPlainRailTile(bridge_tile) || (IsNormalRoadTile(bridge_tile) && GetDisallowedRoadDirections(bridge_tile) != DRD_NONE)));
	}

	/* Don't allow a bridge where the start and end tiles are adjacent with no span between. */
	if (bridge_length == 1) return false;

	/* Make sure the road can be continued past the bridge. At this point, bridge_tile holds the end tile of the bridge. */
	if (!CanRoadContinueIntoNextTile(t, bridge_tile, bridge_dir)) return false;

	/* If another parallel bridge exists nearby, this one would be redundant and shouldn't be built. We don't care about flat bridges. */
	if (slope != SLOPE_FLAT) {
		for (auto search : SpiralTileSequence(tile, bridge_length, 0, 0)) {
			/* Only consider bridge head tiles. */
			if (!IsBridgeTile(search)) continue;

			/* Only consider road bridges. */