Function ChooseTrainTrack

src/train_cmd.cpp:2727–2889

choose a track */

/* choose a track */
static Track ChooseTrainTrack(Train *v, TileIndex tile, DiagDirection enterdir, TrackBits tracks, bool force_res, bool *got_reservation, bool mark_stuck)
{
	Track best_track = INVALID_TRACK;
	bool do_track_reservation = _settings_game.pf.reserve_paths || force_res;
	bool changed_signal = false;
	TileIndex final_dest = INVALID_TILE;

	assert((tracks & ~TRACK_BIT_MASK) == 0);

	if (got_reservation != nullptr) *got_reservation = false;

	/* Don't use tracks here as the setting to forbid 90 deg turns might have been switched between reservation and now. */
	TrackBits res_tracks = (TrackBits)(GetReservedTrackbits(tile) & DiagdirReachesTracks(enterdir));
	/* Do we have a suitable reserved track? */
	if (res_tracks != TRACK_BIT_NONE) return FindFirstTrack(res_tracks);

	/* Quick return in case only one possible track is available */
	if (KillFirstBit(tracks) == TRACK_BIT_NONE) {
		Track track = FindFirstTrack(tracks);
		/* We need to check for signals only here, as a junction tile can't have signals. */
		if (track != INVALID_TRACK && HasPbsSignalOnTrackdir(tile, TrackEnterdirToTrackdir(track, enterdir))) {
			do_track_reservation = true;
			changed_signal = true;
			SetSignalStateByTrackdir(tile, TrackEnterdirToTrackdir(track, enterdir), SIGNAL_STATE_GREEN);
		} else if (!do_track_reservation) {
			return track;
		}
		best_track = track;
	}

	PBSTileInfo   res_dest(tile, INVALID_TRACKDIR, false);
	DiagDirection dest_enterdir = enterdir;
	if (do_track_reservation) {
		res_dest = ExtendTrainReservation(v, &tracks, &dest_enterdir);
		if (res_dest.tile == INVALID_TILE) {
			/* Reservation failed? */
			if (mark_stuck) MarkTrainAsStuck(v);
			if (changed_signal) SetSignalStateByTrackdir(tile, TrackEnterdirToTrackdir(best_track, enterdir), SIGNAL_STATE_RED);
			return FindFirstTrack(tracks);
		}
		if (res_dest.okay) {
			/* Got a valid reservation that ends at a safe target, quick exit. */
			if (got_reservation != nullptr) *got_reservation = true;
			if (changed_signal) MarkTileDirtyByTile(tile);
			TryReserveRailTrack(v->tile, TrackdirToTrack(v->GetVehicleTrackdir()));
			return best_track;
		}

		/* Check if the train needs service here, so it has a chance to always find a depot.
		 * Also check if the current order is a service order so we don't reserve a path to
		 * the destination but instead to the next one if service isn't needed. */
		CheckIfTrainNeedsService(v);
		if (v->current_order.IsType(OT_DUMMY) || v->current_order.IsType(OT_CONDITIONAL) || v->current_order.IsType(OT_GOTO_DEPOT)) ProcessOrders(v);
	}

	/* Save the current train order. The destructor will restore the old order on function exit. */
	VehicleOrderSaver orders(v);