Function CmdBuildSingleSignal

src/rail_cmd.cpp:1049–1194

* Build signals, alternate between double/single, signal/semaphore, * pre/exit/combo-signals, and what-else not. If the rail piece does not * have any signals, signal cycling is ignored * @param flags operation to perform * @param tile tile where to build the signals * @param track track-orientation * @param sigtype type of the signal * @param sigvar variant of signal type (normal/semaphore

 * @todo p2 should be replaced by two bits for "along" and "against" the track.
 */
CommandCost CmdBuildSingleSignal(DoCommandFlags flags, TileIndex tile, Track track, SignalType sigtype, SignalVariant sigvar, bool convert_signal, bool skip_existing_signals, bool ctrl_pressed, SignalType cycle_start, SignalType cycle_stop, uint8_t num_dir_cycle, uint8_t signals_copy)
{
	if (sigtype > SIGTYPE_LAST || sigvar > SIG_SEMAPHORE) return CMD_ERROR;
	if (cycle_start > cycle_stop || cycle_stop > SIGTYPE_LAST) return CMD_ERROR;

	if (ctrl_pressed) sigvar = (SignalVariant)(sigvar ^ SIG_SEMAPHORE);

	/* You can only build signals on plain rail tiles, and the selected track must exist */
	if (!ValParamTrackOrientation(track) || !IsPlainRailTile(tile) ||
			!HasTrack(tile, track)) {
		return CommandCost(STR_ERROR_THERE_IS_NO_RAILROAD_TRACK);
	}
	/* Protect against invalid signal copying */
	if (signals_copy != 0 && (signals_copy & SignalOnTrack(track)) == 0) return CMD_ERROR;

	CommandCost ret = CheckTileOwnership(tile);
	if (ret.Failed()) return ret;

	/* See if this is a valid track combination for signals (no overlap) */
	if (TracksOverlap(GetTrackBits(tile))) return CommandCost(STR_ERROR_NO_SUITABLE_RAILROAD_TRACK);

	/* In case we don't want to change an existing signal, return without error. */
	if (skip_existing_signals && HasSignalOnTrack(tile, track)) return CommandCost();

	/* you can not convert a signal if no signal is on track */
	if (convert_signal && !HasSignalOnTrack(tile, track)) return CommandCost(STR_ERROR_THERE_ARE_NO_SIGNALS);

	CommandCost cost;
	if (!HasSignalOnTrack(tile, track)) {
		/* build new signals */
		cost = CommandCost(EXPENSES_CONSTRUCTION, _price[PR_BUILD_SIGNALS]);
	} else {
		if (signals_copy != 0 && sigvar != GetSignalVariant(tile, track)) {
			/* convert signals <-> semaphores */
			cost = CommandCost(EXPENSES_CONSTRUCTION, _price[PR_BUILD_SIGNALS] + _price[PR_CLEAR_SIGNALS]);

		} else if (convert_signal) {
			/* convert button pressed */
			if (ctrl_pressed || GetSignalVariant(tile, track) != sigvar) {
				/* it costs money to change signal variant (light or semaphore) */
				cost = CommandCost(EXPENSES_CONSTRUCTION, _price[PR_BUILD_SIGNALS] + _price[PR_CLEAR_SIGNALS]);
			} else {
				/* it is free to change signal type (block, exit, entry, combo, path, etc) */
				cost = CommandCost();
			}

		} else {
			/* it is free to change orientation or number of signals on the tile (for block/presignals which allow signals in both directions) */
			cost = CommandCost();
		}
	}

	if (flags.Test(DoCommandFlag::Execute)) {
		Train *v = nullptr;
		/* The new/changed signal could block our path. As this can lead to
		 * stale reservations, we clear the path reservation here and try
		 * to redo it later on. */
		if (HasReservedTracks(tile, TrackToTrackBits(track))) {