Function TryPathReserve

src/train_cmd.cpp:2899–2963

* Try to reserve a path to a safe position. * * @param v The vehicle * @param mark_as_stuck Should the train be marked as stuck on a failed reservation? * @param first_tile_okay True if no path should be reserved if the current tile is a safe position. * @return True if a path could be reserved. */

 * @return True if a path could be reserved.
 */
bool TryPathReserve(Train *v, bool mark_as_stuck, bool first_tile_okay)
{
	assert(v->IsFrontEngine());

	/* We have to handle depots specially as the track follower won't look
	 * at the depot tile itself but starts from the next tile. If we are still
	 * inside the depot, a depot reservation can never be ours. */
	if (v->track == TRACK_BIT_DEPOT) {
		if (HasDepotReservation(v->tile)) {
			if (mark_as_stuck) MarkTrainAsStuck(v);
			return false;
		} else {
			/* Depot not reserved, but the next tile might be. */
			TileIndex next_tile = TileAddByDiagDir(v->tile, GetRailDepotDirection(v->tile));
			if (HasReservedTracks(next_tile, DiagdirReachesTracks(GetRailDepotDirection(v->tile)))) return false;
		}
	}

	Vehicle *other_train = nullptr;
	PBSTileInfo origin = FollowTrainReservation(v, &other_train);
	/* The path we are driving on is already blocked by some other train.
	 * This can only happen in certain situations when mixing path and
	 * block signals or when changing tracks and/or signals.
	 * Exit here as doing any further reservations will probably just
	 * make matters worse. */
	if (other_train != nullptr && other_train->index != v->index) {
		if (mark_as_stuck) MarkTrainAsStuck(v);
		return false;
	}
	/* If we have a reserved path and the path ends at a safe tile, we are finished already. */
	if (origin.okay && (v->tile != origin.tile || first_tile_okay)) {
		/* Can't be stuck then. */
		if (v->flags.Test(VehicleRailFlag::Stuck)) SetWindowWidgetDirty(WC_VEHICLE_VIEW, v->index, WID_VV_START_STOP);
		v->flags.Reset(VehicleRailFlag::Stuck);
		return true;
	}

	/* If we are in a depot, tentatively reserve the depot. */
	if (v->track == TRACK_BIT_DEPOT) {
		SetDepotReservation(v->tile, true);
		if (_settings_client.gui.show_track_reservation) MarkTileDirtyByTile(v->tile);
	}

	DiagDirection exitdir = TrackdirToExitdir(origin.trackdir);
	TileIndex     new_tile = TileAddByDiagDir(origin.tile, exitdir);
	TrackBits     reachable = TrackdirBitsToTrackBits(TrackStatusToTrackdirBits(GetTileTrackStatus(new_tile, TRANSPORT_RAIL, 0)) & DiagdirReachesTrackdirs(exitdir));

	if (Rail90DegTurnDisallowed(GetTileRailType(origin.tile), GetTileRailType(new_tile))) reachable &= ~TrackCrossesTracks(TrackdirToTrack(origin.trackdir));

	bool res_made = false;
	ChooseTrainTrack(v, new_tile, exitdir, reachable, true, &res_made, mark_as_stuck);

	if (!res_made) {
		/* Free the depot reservation as well. */
		if (v->track == TRACK_BIT_DEPOT) SetDepotReservation(v->tile, false);
		return false;
	}