Function CheckNextTrainTile

src/train_cmd.cpp:2234–2289

* Check if the train is on the last reserved tile and try to extend the path then. * @param v %Train that needs its path extended. */

 * @param v %Train that needs its path extended.
 */
static void CheckNextTrainTile(Train *v)
{
	/* Don't do any look-ahead if path_backoff_interval is 255. */
	if (_settings_game.pf.path_backoff_interval == 255) return;

	/* Exit if we are inside a depot. */
	if (v->track == TRACK_BIT_DEPOT) return;

	switch (v->current_order.GetType()) {
		/* Exit if we reached our destination depot. */
		case OT_GOTO_DEPOT:
			if (v->tile == v->dest_tile) return;
			break;

		case OT_GOTO_WAYPOINT:
			/* If we reached our waypoint, make sure we see that. */
			if (IsRailWaypointTile(v->tile) && GetStationIndex(v->tile) == v->current_order.GetDestination()) ProcessOrders(v);
			break;

		case OT_NOTHING:
		case OT_LEAVESTATION:
		case OT_LOADING:
			/* Exit if the current order doesn't have a destination, but the train has orders. */
			if (v->GetNumOrders() > 0) return;
			break;

		default:
			break;
	}
	/* Exit if we are on a station tile and are going to stop. */
	if (IsRailStationTile(v->tile) && v->current_order.ShouldStopAtStation(v, GetStationIndex(v->tile))) return;

	Trackdir td = v->GetVehicleTrackdir();

	/* On a tile with a red non-pbs signal, don't look ahead. */
	if (IsTileType(v->tile, MP_RAILWAY) && HasSignalOnTrackdir(v->tile, td) &&
			!IsPbsSignal(GetSignalType(v->tile, TrackdirToTrack(td))) &&
			GetSignalStateByTrackdir(v->tile, td) == SIGNAL_STATE_RED) return;

	CFollowTrackRail ft(v);
	if (!ft.Follow(v->tile, td)) return;

	if (!HasReservedTracks(ft.new_tile, TrackdirBitsToTrackBits(ft.new_td_bits))) {
		/* Next tile is not reserved. */
		if (KillFirstBit(ft.new_td_bits) == TRACKDIR_BIT_NONE) {
			if (HasPbsSignalOnTrackdir(ft.new_tile, FindFirstTrackdir(ft.new_td_bits))) {
				/* If the next tile is a PBS signal, try to make a reservation. */
				TrackBits tracks = TrackdirBitsToTrackBits(ft.new_td_bits);
				if (Rail90DegTurnDisallowed(GetTileRailType(ft.old_tile), GetTileRailType(ft.new_tile))) {
					tracks &= ~TrackCrossesTracks(TrackdirToTrack(ft.old_td));
				}
				ChooseTrainTrack(v, ft.new_tile, ft.exitdir, tracks, false, nullptr, false);
			}
		}
	}
}

/**