Function TriggerStationRandomisation

src/newgrf_station.cpp:949–1019

* Trigger station randomisation * @param st station being triggered * @param trigger_tile specific tile of platform to trigger * @param trigger trigger type * @param cargo_type cargo type causing trigger */

 * @param cargo_type cargo type causing trigger
 */
void TriggerStationRandomisation(BaseStation *st, TileIndex trigger_tile, StationRandomTrigger trigger, CargoType cargo_type)
{
	/* List of coverage areas for each animation trigger */
	static const TriggerArea tas[] = {
		TA_WHOLE, TA_WHOLE, TA_PLATFORM, TA_PLATFORM, TA_PLATFORM, TA_PLATFORM
	};

	assert(st != nullptr);

	/* Check the cached cargo trigger bitmask to see if we need
	 * to bother with any further processing.
	 * Note: cached_cargo_triggers must be non-zero even for cargo-independent triggers. */
	if (st->cached_cargo_triggers == 0) return;
	if (IsValidCargoType(cargo_type) && !HasBit(st->cached_cargo_triggers, cargo_type)) return;

	uint32_t whole_reseed = 0;

	/* Bitmask of completely empty cargo types to be matched. */
	CargoTypes empty_mask{};
	if (trigger == StationRandomTrigger::CargoTaken) {
		empty_mask = GetEmptyMask(Station::From(st));
	}

	/* Store triggers now for var 5F */
	st->waiting_random_triggers.Set(trigger);
	StationRandomTriggers used_random_triggers;

	/* Check all tiles over the station to check if the specindex is still in use */
	for (TileIndex tile : GetRailTileArea(st, trigger_tile, tas[static_cast<size_t>(trigger)])) {
		if (st->TileBelongsToRailStation(tile)) {
			const StationSpec *ss = GetStationSpec(tile);
			if (ss == nullptr) continue;

			/* Cargo taken "will only be triggered if all of those
			 * cargo types have no more cargo waiting." */
			if (trigger == StationRandomTrigger::CargoTaken) {
				if ((ss->cargo_triggers & ~empty_mask) != 0) continue;
			}

			if (!IsValidCargoType(cargo_type) || HasBit(ss->cargo_triggers, cargo_type)) {
				StationResolverObject object(ss, st, tile, CBID_RANDOM_TRIGGER, 0);
				object.SetWaitingRandomTriggers(st->waiting_random_triggers);

				object.ResolveRerandomisation();

				used_random_triggers.Set(object.GetUsedRandomTriggers());

				uint32_t reseed = object.GetReseedSum();
				if (reseed != 0) {
					whole_reseed |= reseed;
					reseed >>= 16;

					/* Set individual tile random bits */
					uint8_t random_bits = GetStationTileRandomBits(tile);
					random_bits &= ~reseed;
					random_bits |= Random() & reseed;
					SetStationTileRandomBits(tile, random_bits);