Function SaveOrLoad

src/saveload/saveload.cpp:3258–3342

* Main Save or Load function where the high-level saveload functions are * handled. It opens the savegame, selects format and checks versions * @param filename The name of the savegame being created/loaded * @param fop Save or load mode. Load can also be a TTD(Patch) game. * @param sb The sub directory to save the savegame in * @param threaded True when threaded saving is allowed * @return R

 * @return Return the result of the action. #SL_OK, #SL_ERROR, or #SL_REINIT ("unload" the game)
 */
SaveOrLoadResult SaveOrLoad(std::string_view filename, SaveLoadOperation fop, DetailedFileType dft, Subdirectory sb, bool threaded)
{
	/* An instance of saving is already active, so don't go saving again */
	if (_sl.saveinprogress && fop == SLO_SAVE && dft == DFT_GAME_FILE && threaded) {
		/* if not an autosave, but a user action, show error message */
		if (!_do_autosave) ShowErrorMessage(GetEncodedString(STR_ERROR_SAVE_STILL_IN_PROGRESS), {}, WL_ERROR);
		return SL_OK;
	}
	WaitTillSaved();

	try {
		/* Load a TTDLX or TTDPatch game */
		if (fop == SLO_LOAD && dft == DFT_OLD_GAME_FILE) {
			ResetSaveloadData();

			InitializeGame(256, 256, true, true); // set a mapsize of 256x256 for TTDPatch games or it might get confused

			/* TTD/TTO savegames have no NewGRFs, TTDP savegame have them
			 * and if so a new NewGRF list will be made in LoadOldSaveGame.
			 * Note: this is done here because AfterLoadGame is also called
			 * for OTTD savegames which have their own NewGRF logic. */
			ClearGRFConfigList(_grfconfig);
			_gamelog.Reset();
			if (!LoadOldSaveGame(filename)) return SL_REINIT;
			_sl_version = SL_MIN_VERSION;
			_sl_minor_version = 0;
			_gamelog.StartAction(GLAT_LOAD);
			if (!AfterLoadGame()) {
				_gamelog.StopAction();
				return SL_REINIT;
			}
			_gamelog.StopAction();
			return SL_OK;
		}

		assert(dft == DFT_GAME_FILE);
		switch (fop) {
			case SLO_CHECK:
				_sl.action = SLA_LOAD_CHECK;
				break;

			case SLO_LOAD:
				_sl.action = SLA_LOAD;
				break;

			case SLO_SAVE:
				_sl.action = SLA_SAVE;
				break;

			default: NOT_REACHED();
		}

		auto fh = (fop == SLO_SAVE) ? FioFOpenFile(filename, "wb", sb) : FioFOpenFile(filename, "rb", sb);

		/* Make it a little easier to load savegames from the console */
		if (!fh.has_value() && fop != SLO_SAVE) fh = FioFOpenFile(filename, "rb", SAVE_DIR);
		if (!fh.has_value() && fop != SLO_SAVE) fh = FioFOpenFile(filename, "rb", BASE_DIR);
		if (!fh.has_value() && fop != SLO_SAVE) fh = FioFOpenFile(filename, "rb", SCENARIO_DIR);