Function TriggerRoadStopRandomisation

src/newgrf_roadstop.cpp:418–486

* Trigger road stop randomisation * * @param st the station being triggered * @param tile the exact tile of the station that should be triggered * @param trigger trigger type * @param cargo_type cargo type causing the trigger */

 * @param cargo_type cargo type causing the trigger
 */
void TriggerRoadStopRandomisation(BaseStation *st, TileIndex tile, StationRandomTrigger trigger, CargoType cargo_type)
{
	assert(st != nullptr);

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

	st->waiting_random_triggers.Set(trigger);

	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));
	}

	StationRandomTriggers used_random_triggers;
	auto process_tile = [&](TileIndex cur_tile) {
		const RoadStopSpec *ss = GetRoadStopSpec(cur_tile);
		if (ss == nullptr) return;

		/* 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) return;
		}

		if (!IsValidCargoType(cargo_type) || HasBit(ss->cargo_triggers, cargo_type)) {
			RoadStopResolverObject object(ss, st, cur_tile, INVALID_ROADTYPE, GetStationType(cur_tile), GetStationGfx(cur_tile));
			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 = st->GetRoadStopRandomBits(cur_tile);
				random_bits &= ~reseed;
				random_bits |= Random() & reseed;
				st->SetRoadStopRandomBits(cur_tile, random_bits);

				MarkTileDirtyByTile(cur_tile);
			}
		}
	};
	if (trigger == StationRandomTrigger::NewCargo || trigger == StationRandomTrigger::CargoTaken) {
		for (const RoadStopTileData &tile_data : st->custom_roadstop_tile_data) {
			process_tile(tile_data.tile);
		}