Function FollowReservation

src/pbs.cpp:191–253

Follow a reservation starting from a specific tile to the end. */

/** Follow a reservation starting from a specific tile to the end. */
static PBSTileInfo FollowReservation(Owner o, RailTypes rts, TileIndex tile, Trackdir trackdir, bool ignore_oneway = false)
{
	TileIndex start_tile = tile;
	Trackdir  start_trackdir = trackdir;
	bool      first_loop = true;

	/* Start track not reserved? This can happen if two trains
	 * are on the same tile. The reservation on the next tile
	 * is not ours in this case, so exit. */
	if (!HasReservedTracks(tile, TrackToTrackBits(TrackdirToTrack(trackdir)))) return PBSTileInfo(tile, trackdir, false);

	/* Do not disallow 90 deg turns as the setting might have changed between reserving and now. */
	CFollowTrackRail ft(o, rts);
	while (ft.Follow(tile, trackdir)) {
		TrackdirBits reserved = ft.new_td_bits & TrackBitsToTrackdirBits(GetReservedTrackbits(ft.new_tile));

		/* No reservation --> path end found */
		if (reserved == TRACKDIR_BIT_NONE) {
			if (ft.is_station) {
				/* Check skipped station tiles as well, maybe our reservation ends inside the station. */
				TileIndexDiff diff = TileOffsByDiagDir(ft.exitdir);
				while (ft.tiles_skipped-- > 0) {
					ft.new_tile -= diff;
					if (HasStationReservation(ft.new_tile)) {
						tile = ft.new_tile;
						trackdir = DiagDirToDiagTrackdir(ft.exitdir);
						break;
					}
				}
			}
			break;
		}

		/* Can't have more than one reserved trackdir */
		Trackdir new_trackdir = FindFirstTrackdir(reserved);

		/* One-way signal against us. The reservation can't be ours as it is not
		 * a safe position from our direction and we can never pass the signal. */
		if (!ignore_oneway && HasOnewaySignalBlockingTrackdir(ft.new_tile, new_trackdir)) break;

		tile = ft.new_tile;
		trackdir = new_trackdir;

		if (first_loop) {
			/* Update the start tile after we followed the track the first
			 * time. This is necessary because the track follower can skip
			 * tiles (in stations for example) which means that we might
			 * never visit our original starting tile again. */
			start_tile = tile;
			start_trackdir = trackdir;
			first_loop = false;
		} else {
			/* Loop encountered? */
			if (tile == start_tile && trackdir == start_trackdir) break;
		}
		/* Depot tile? Can't continue. */
		if (IsRailDepotTile(tile)) break;
		/* Non-pbs signal? Reservation can't continue. */