Function TerraformTile_Track

src/rail_cmd.cpp:3043–3090

}

static CommandCost TerraformTile_Track(TileIndex tile, DoCommandFlags flags, int z_new, Slope tileh_new)
{
	auto [tileh_old, z_old] = GetTileSlopeZ(tile);
	if (IsPlainRail(tile)) {
		TrackBits rail_bits = GetTrackBits(tile);
		/* Is there flat water on the lower halftile that must be cleared expensively? */
		bool was_water = (GetRailGroundType(tile) == RailGroundType::HalfTileWater && IsSlopeWithOneCornerRaised(tileh_old));

		/* Allow clearing the water only if there is no ship */
		if (was_water && HasVehicleOnTile(tile, [](const Vehicle *v) {
				return v->type == VEH_SHIP;
			})) return CommandCost(STR_ERROR_SHIP_IN_THE_WAY);

		/* First test autoslope. However if it succeeds we still have to test the rest, because non-autoslope terraforming is cheaper. */
		CommandCost autoslope_result = TestAutoslopeOnRailTile(tile, flags, z_old, tileh_old, z_new, tileh_new, rail_bits);

		/* When there is only a single horizontal/vertical track, one corner can be terraformed. */
		Corner allowed_corner;
		switch (rail_bits) {
			case TRACK_BIT_RIGHT: allowed_corner = CORNER_W; break;
			case TRACK_BIT_UPPER: allowed_corner = CORNER_S; break;
			case TRACK_BIT_LEFT:  allowed_corner = CORNER_E; break;
			case TRACK_BIT_LOWER: allowed_corner = CORNER_N; break;
			default: return autoslope_result;
		}

		Foundation f_old = GetRailFoundation(tileh_old, rail_bits);

		/* Do not allow terraforming if allowed_corner is part of anti-zig-zag foundations */
		if (tileh_old != SLOPE_NS && tileh_old != SLOPE_EW && IsSpecialRailFoundation(f_old)) return autoslope_result;

		/* Everything is valid, which only changes allowed_corner */
		for (Corner corner = (Corner)0; corner < CORNER_END; corner = (Corner)(corner + 1)) {
			if (allowed_corner == corner) continue;
			if (z_old + GetSlopeZInCorner(tileh_old, corner) != z_new + GetSlopeZInCorner(tileh_new, corner)) return autoslope_result;
		}

		/* Make the ground dirty */
		if (flags.Test(DoCommandFlag::Execute)) SetRailGroundType(tile, RailGroundType::Barren);

		/* allow terraforming */
		return CommandCost(EXPENSES_CONSTRUCTION, was_water ? _price[PR_CLEAR_WATER] : (Money)0);
	} else if (_settings_game.construction.build_on_slopes && AutoslopeEnabled() &&
			AutoslopeCheckForEntranceEdge(tile, z_new, tileh_new, GetRailDepotDirection(tile))) {
		return CommandCost(EXPENSES_CONSTRUCTION, _price[PR_BUILD_FOUNDATION]);
	}
	return Command<CMD_LANDSCAPE_CLEAR>::Do(flags, tile);
}

static CommandCost CheckBuildAbove_Track(TileIndex tile, DoCommandFlags flags, Axis, int)
{