Function IsWaitingPositionFree

src/pbs.cpp:427–450

* Check if a safe position is free. * * @param v the vehicle to test for * @param tile The tile * @param trackdir The trackdir to test * @param forbid_90deg Don't allow trains to make 90 degree turns * @return True if the position is free */

 * @return True if the position is free
 */
bool IsWaitingPositionFree(const Train *v, TileIndex tile, Trackdir trackdir, bool forbid_90deg)
{
	Track     track = TrackdirToTrack(trackdir);
	TrackBits reserved = GetReservedTrackbits(tile);

	/* Tile reserved? Can never be a free waiting position. */
	if (TrackOverlapsTracks(reserved, track)) return false;

	/* Not reserved and depot or not a pbs signal -> free. */
	if (IsRailDepotTile(tile)) return true;
	if (IsTileType(tile, MP_RAILWAY) && HasSignalOnTrackdir(tile, trackdir) && !IsPbsSignal(GetSignalType(tile, track))) return true;

	/* Check the next tile, it has to be free as well. Do not filter for compatible railtypes
	 * to make sure we never accidentally join up reservations. */
	CFollowTrackRail ft(v, RailTypes{});

	if (!ft.Follow(tile, trackdir)) return true;

	/* Check for reachable tracks. */
	ft.new_td_bits &= DiagdirReachesTrackdirs(ft.exitdir);
	if (Rail90DegTurnDisallowed(GetTileRailType(ft.old_tile), GetTileRailType(ft.new_tile), forbid_90deg)) ft.new_td_bits &= ~TrackdirCrossesTrackdirs(trackdir);

	return !HasReservedTracks(ft.new_tile, TrackdirBitsToTrackBits(ft.new_td_bits));
}