Function GrowTownInTile

src/town_cmd.cpp:1535–1742

* Grows the given town. * There are at the moment 3 possible way's for * the town expansion: * @li Generate a random tile and check if there is a road allowed * @li TL_ORIGINAL * @li TL_BETTER_ROADS * @li Check if the town geometry allows a road and which one * @li TL_2X2_GRID * @li TL_3X3_GRID * @li Forbid roads, only build houses * * @param tile_ptr The current tile * @param c

 * @return Result so far.
 */
static TownGrowthResult GrowTownInTile(TileIndex *tile_ptr, RoadBits cur_rb, DiagDirection target_dir, Town *t1, TownExpandModes modes)
{
	RoadBits rcmd = ROAD_NONE;  // RoadBits for the road construction command
	TileIndex tile = *tile_ptr; // The main tile on which we base our growth

	assert(tile < Map::Size());

	if (cur_rb == ROAD_NONE) {
		/* Tile has no road.
		 * We will return TownGrowthResult::SearchStopped to say that this is the last iteration. */

		if (!TownAllowedToBuildRoads(modes)) return TownGrowthResult::SearchStopped;
		if (!_settings_game.economy.allow_town_level_crossings && IsTileType(tile, MP_RAILWAY)) return TownGrowthResult::SearchStopped;

		/* Remove hills etc */
		if (!_settings_game.construction.build_on_slopes || Chance16(1, 6)) LevelTownLand(tile);

		/* Is a road allowed here? */
		switch (t1->layout) {
			default: NOT_REACHED();

			case TL_3X3_GRID:
			case TL_2X2_GRID:
				rcmd = GetTownRoadGridElement(t1, tile, target_dir);
				if (rcmd == ROAD_NONE) return TownGrowthResult::SearchStopped;
				break;

			case TL_BETTER_ROADS:
			case TL_ORIGINAL:
				if (!IsRoadAllowedHere(t1, tile, target_dir)) return TownGrowthResult::SearchStopped;

				DiagDirection source_dir = ReverseDiagDir(target_dir);

				if (Chance16(1, 4)) {
					/* Randomize a new target dir */
					do target_dir = RandomDiagDir(); while (target_dir == source_dir);
				}

				if (!IsRoadAllowedHere(t1, TileAddByDiagDir(tile, target_dir), target_dir)) {
					/* A road is not allowed to continue the randomized road,
					 *  return if the road we're trying to build is curved. */
					if (target_dir != ReverseDiagDir(source_dir)) return TownGrowthResult::SearchStopped;

					/* Return if neither side of the new road is a house */
					if (!IsTileType(TileAddByDiagDir(tile, ChangeDiagDir(target_dir, DIAGDIRDIFF_90RIGHT)), MP_HOUSE) &&
							!IsTileType(TileAddByDiagDir(tile, ChangeDiagDir(target_dir, DIAGDIRDIFF_90LEFT)), MP_HOUSE)) {
						return TownGrowthResult::SearchStopped;
					}

					/* That means that the road is only allowed if there is a house
					 *  at any side of the new road. */
				}

				rcmd = DiagDirToRoadBits(target_dir) | DiagDirToRoadBits(source_dir);
				break;
		}

	} else if (target_dir < DIAGDIR_END && !(cur_rb & DiagDirToRoadBits(ReverseDiagDir(target_dir)))) {