Function MaskWireBits

src/elrail.cpp:125–172

* Masks out track bits when neighbouring tiles are unelectrified. */

 * Masks out track bits when neighbouring tiles are unelectrified.
 */
static TrackBits MaskWireBits(TileIndex t, TrackBits tracks)
{
	/* Single track bits are never masked out. */
	if (HasAtMostOneBit(tracks)) [[likely]] return tracks;

	if (!IsPlainRailTile(t)) return tracks;

	TrackdirBits neighbour_tdb = TRACKDIR_BIT_NONE;
	for (DiagDirection d = DIAGDIR_BEGIN; d < DIAGDIR_END; d++) {
		/* If the neighbour tile is either not electrified or has no tracks that can be reached
		 * from this tile, mark all trackdirs that can be reached from the neighbour tile
		 * as needing no catenary. We make an exception for blocked station tiles with a matching
		 * axis that still display wires to preserve visual continuity. */
		TileIndex next_tile = TileAddByDiagDir(t, d);
		RailType rt = GetTileRailType(next_tile);
		if (rt == INVALID_RAILTYPE || !HasRailCatenary(rt) ||
				((TrackStatusToTrackBits(GetTileTrackStatus(next_tile, TRANSPORT_RAIL, 0)) & DiagdirReachesTracks(d)) == TRACK_BIT_NONE &&
				(!HasStationTileRail(next_tile) || GetRailStationAxis(next_tile) != DiagDirToAxis(d) || !CanStationTileHaveWires(next_tile)))) {
			neighbour_tdb |= DiagdirReachesTrackdirs(ReverseDiagDir(d));
		}
	}

	/* If the tracks from either a diagonal crossing or don't overlap, both
	 * trackdirs have to be marked to mask the corresponding track bit. Else
	 * one marked trackdir is enough the mask the track bit. */
	TrackBits mask;
	if (tracks == TRACK_BIT_CROSS || !TracksOverlap(tracks)) {
		/* If the tracks form either a diagonal crossing or don't overlap, both
		 * trackdirs have to be marked to mask the corresponding track bit. */
		mask = ~(TrackBits)((neighbour_tdb & (neighbour_tdb >> 8)) & TRACK_BIT_MASK);
		/* If that results in no masked tracks and it is not a diagonal crossing,
		 * require only one marked trackdir to mask. */
		if (tracks != TRACK_BIT_CROSS && (mask & TRACK_BIT_MASK) == TRACK_BIT_MASK) mask = ~TrackdirBitsToTrackBits(neighbour_tdb);
	} else {
		/* Require only one marked trackdir to mask the track. */
		mask = ~TrackdirBitsToTrackBits(neighbour_tdb);
		/* If that results in an empty set, require both trackdirs for diagonal track. */
		if ((tracks & mask) == TRACK_BIT_NONE) {
			if ((neighbour_tdb & TRACKDIR_BIT_X_NE) == 0 || (neighbour_tdb & TRACKDIR_BIT_X_SW) == 0) mask |= TRACK_BIT_X;
			if ((neighbour_tdb & TRACKDIR_BIT_Y_NW) == 0 || (neighbour_tdb & TRACKDIR_BIT_Y_SE) == 0) mask |= TRACK_BIT_Y;
			/* If that still is not enough, require both trackdirs for any track. */
			if ((tracks & mask) == TRACK_BIT_NONE) mask = ~(TrackBits)((neighbour_tdb & (neighbour_tdb >> 8)) & TRACK_BIT_MASK);
		}
	}

	/* Mask the tracks only if at least one track bit would remain. */
	return (tracks & mask) != TRACK_BIT_NONE ? tracks & mask : tracks;
}

/**
 * Get the base wire sprite to use.