Function UpdateLevelCrossing

src/train_cmd.cpp:1791–1816

* Update a level crossing to barred or open (crossing may include multiple adjacent tiles). * @param tile Tile which causes the update. * @param sound Should we play sound? * @param force_bar Should we force the crossing to be barred? */

 * @param force_bar Should we force the crossing to be barred?
 */
void UpdateLevelCrossing(TileIndex tile, bool sound, bool force_bar)
{
	if (!IsLevelCrossingTile(tile)) return;

	bool forced_state = force_bar;

	const Axis axis = GetCrossingRoadAxis(tile);
	const DiagDirection dir1 = AxisToDiagDir(axis);
	const DiagDirection dir2 = ReverseDiagDir(dir1);

	/* Check if an adjacent crossing is barred. */
	for (DiagDirection dir : { dir1, dir2 }) {
		for (TileIndex t = tile; !forced_state && t < Map::Size() && IsLevelCrossingTile(t) && GetCrossingRoadAxis(t) == axis; t = TileAddByDiagDir(t, dir)) {
			forced_state |= CheckLevelCrossing(t);
		}
	}

	/* Now that we know whether all tiles in this crossing should be barred or open,
	 * we need to update those tiles. We start with the tile itself, then look along the road axis. */
	UpdateLevelCrossingTile(tile, sound, forced_state);
	for (DiagDirection dir : { dir1, dir2 }) {
		for (TileIndex t = TileAddByDiagDir(tile, dir); t < Map::Size() && IsLevelCrossingTile(t) && GetCrossingRoadAxis(t) == axis; t = TileAddByDiagDir(t, dir)) {
			UpdateLevelCrossingTile(t, sound, forced_state);
		}
	}
}

/**
 * Find adjacent level crossing tiles in this multi-track crossing and mark them dirty.