Run water flooding at constant speed at day lengths >= 4

See: #482

src/landscape.cpp

@@ -827,14 +827,10 @@ CommandCost CmdClearArea(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32
 
 
 TileIndex _cur_tileloop_tile;
+TileIndex _aux_tileloop_tile;
 
-/**
- * Gradually iterate over all tiles on the map, calling their TileLoopProcs once every 256 ticks.
- */
-void RunTileLoop()
+static uint32 GetTileLoopFeedback()
 {
-	PerformanceAccumulator framerate(PFE_GL_LANDSCAPE);
-
 	/* The pseudorandom sequence of tiles is generated using a Galois linear feedback
 	 * shift register (LFSR). This allows a deterministic pseudorandom ordering, but
 	 * still with minimal state and fast iteration. */
@@ -846,7 +842,17 @@ void RunTileLoop()
 		0x4004B2, 0x800B87, 0x10004F3, 0x200072D, 0x40006AE, 0x80009E3,
 	};
 	static_assert(lengthof(feedbacks) == MAX_MAP_TILES_BITS - 2 * MIN_MAP_SIZE_BITS + 1);
-	const uint32 feedback = feedbacks[MapLogX() + MapLogY() - 2 * MIN_MAP_SIZE_BITS];
+	return feedbacks[MapLogX() + MapLogY() - 2 * MIN_MAP_SIZE_BITS];
+}
+
+/**
+ * Gradually iterate over all tiles on the map, calling their TileLoopProcs once every 256 ticks.
+ */
+void RunTileLoop()
+{
+	PerformanceAccumulator framerate(PFE_GL_LANDSCAPE);
+
+	const uint32 feedback = GetTileLoopFeedback();
 
 	/* We update every tile every 256 ticks, so divide the map size by 2^8 = 256 */
 	uint count = 1 << (MapLogX() + MapLogY() - 8);
@@ -873,6 +879,30 @@ void RunTileLoop()
 	_cur_tileloop_tile = tile;
 }
 
+void RunAuxiliaryTileLoop()
+{
+	/* At day lengths <= 4, flooding is handled by main tile loop */
+	if (_settings_game.economy.day_length_factor <= 4 || (_scaled_tick_counter % 4) != 0) return;
+
+	PerformanceAccumulator framerate(PFE_GL_LANDSCAPE);
+
+	const uint32 feedback = GetTileLoopFeedback();
+	uint count = 1 << (MapLogX() + MapLogY() - 8);
+	TileIndex tile = _aux_tileloop_tile;
+
+	while (count--) {
+		if (!IsNonFloodingWaterTile(tile)) {
+			FloodingBehaviour fb = GetFloodingBehaviour(tile);
+			if (fb != FLOOD_NONE) TileLoopWaterFlooding(fb, tile);
+		}
+
+		/* Get the next tile in sequence using a Galois LFSR. */
+		tile = (tile >> 1) ^ (-(int32)(tile & 1) & feedback);
+	}
+
+	_aux_tileloop_tile = tile;
+}
+
 void InitializeLandscape()
 {
 	for (uint y = _settings_game.construction.freeform_edges ? 1 : 0; y < MapMaxY(); y++) {

src/landscape.h

@@ -166,6 +166,7 @@ bool HasFoundationNE(TileIndex tile, Slope slope_here, uint z_here);
 
 void DoClearSquare(TileIndex tile);
 void RunTileLoop();
+void RunAuxiliaryTileLoop();
 
 void InitializeLandscape();
 void GenerateLandscape(byte mode);

src/misc.cpp

@@ -44,6 +44,7 @@
 
 
 extern TileIndex _cur_tileloop_tile;
+extern TileIndex _aux_tileloop_tile;
 extern void ClearAllSignalSpeedRestrictions();
 extern void MakeNewgameSettingsLive();
 
@@ -91,6 +92,7 @@ void InitializeGame(uint size_x, uint size_y, bool reset_date, bool reset_settin
 	_scaled_tick_counter = 0;
 	_scaled_date_ticks_offset = 0;
 	_cur_tileloop_tile = 1;
+	_aux_tileloop_tile = 1;
 	_thd.redsq = INVALID_TILE;
 	_road_layout_change_counter = 0;
 	_loaded_local_company = COMPANY_SPECTATOR;

src/openttd.cpp

@@ -1962,6 +1962,7 @@ void StateGameLoop()
 			SetWindowDirty(WC_STATUS_BAR, 0);
 		}
 
+		RunAuxiliaryTileLoop();
 		if (_tick_skip_counter < _settings_game.economy.day_length_factor) {
 			AnimateAnimatedTiles();
 			CallVehicleTicks();

src/saveload/afterload.cpp

@@ -646,6 +646,9 @@ bool AfterLoadGame()
 	/* The LFSR used in RunTileLoop iteration cannot have a zeroed state, make it non-zeroed. */
 	if (_cur_tileloop_tile == 0) _cur_tileloop_tile = 1;
 
+	extern TileIndex _aux_tileloop_tile;
+	if (_aux_tileloop_tile == 0) _aux_tileloop_tile = 1;
+
 	if (IsSavegameVersionBefore(SLV_98)) GamelogOldver();
 
 	GamelogTestRevision();

src/saveload/extended_ver_sl.cpp

@@ -177,6 +177,7 @@ const SlxiSubChunkInfo _sl_xv_sub_chunk_infos[] = {
 	{ XSLFI_NO_TREE_COUNTER,        XSCF_IGNORABLE_ALL,       1,   1, "no_tree_counter",           nullptr, nullptr, nullptr        },
 	{ XSLFI_TOWN_SETTING_OVERRIDE,  XSCF_NULL,                1,   1, "town_setting_override",     nullptr, nullptr, nullptr        },
 	{ XSLFI_LINKGRAPH_SPARSE_EDGES, XSCF_NULL,                1,   1, "linkgraph_sparse_edges",    nullptr, nullptr, nullptr        },
+	{ XSLFI_AUX_TILE_LOOP,          XSCF_NULL,                1,   1, "aux_tile_loop",             nullptr, nullptr, nullptr        },
 	{ XSLFI_SCRIPT_INT64,           XSCF_NULL,                1,   1, "script_int64",              nullptr, nullptr, nullptr        },
 	{ XSLFI_U64_TICK_COUNTER,       XSCF_NULL,                1,   1, "u64_tick_counter",          nullptr, nullptr, nullptr        },
 	{ XSLFI_LINKGRAPH_TRAVEL_TIME,  XSCF_NULL,                1,   1, "linkgraph_travel_time",     nullptr, nullptr, nullptr        },

src/saveload/extended_ver_sl.h

@@ -130,6 +130,7 @@ enum SlXvFeatureIndex {
 	XSLFI_NO_TREE_COUNTER,                        ///< No tree counter
 	XSLFI_TOWN_SETTING_OVERRIDE,                  ///< Town setting overrides
 	XSLFI_LINKGRAPH_SPARSE_EDGES,                 ///< Link graph edge matrix is stored in sparse format, and saved in order
+	XSLFI_AUX_TILE_LOOP,                          ///< Auxiliary tile loop
 
 	XSLFI_SCRIPT_INT64,                           ///< See: SLV_SCRIPT_INT64
 	XSLFI_U64_TICK_COUNTER,                       ///< See: SLV_U64_TICK_COUNTER

src/saveload/misc_sl.cpp

@@ -25,6 +25,7 @@
 #include "../safeguards.h"
 
 extern TileIndex _cur_tileloop_tile;
+extern TileIndex _aux_tileloop_tile;
 extern uint16 _disaster_delay;
 extern byte _trees_tick_ctr;
 extern uint64 _aspect_cfg_hash;
@@ -102,6 +103,7 @@ static const SaveLoad _date_desc[] = {
 	SLEG_CONDVAR_X(_road_layout_change_counter, SLE_UINT32,   SL_MIN_VERSION, SL_MAX_VERSION, SlXvFeatureTest(XSLFTO_AND, XSLFI_ROAD_LAYOUT_CHANGE_CTR)),
 	SLE_CONDNULL_X(1, SL_MIN_VERSION, SL_MAX_VERSION, SlXvFeatureTest(XSLFTO_AND, XSLFI_REALISTIC_TRAIN_BRAKING, 4, 6)), // _extra_aspects
 	SLEG_CONDVAR_X(_aspect_cfg_hash,      SLE_UINT64,         SL_MIN_VERSION, SL_MAX_VERSION, SlXvFeatureTest(XSLFTO_AND, XSLFI_REALISTIC_TRAIN_BRAKING, 7)),
+	SLEG_CONDVAR_X(_aux_tileloop_tile,    SLE_UINT32,         SL_MIN_VERSION, SL_MAX_VERSION, SlXvFeatureTest(XSLFTO_AND, XSLFI_AUX_TILE_LOOP)),
 	SLE_CONDNULL(4, SLV_11, SLV_120),
 };
 

src/saveload/upstream/misc_sl.cpp

@@ -24,6 +24,7 @@
 #include "../../safeguards.h"
 
 extern TileIndex _cur_tileloop_tile;
+extern TileIndex _aux_tileloop_tile;
 extern uint16 _disaster_delay;
 extern byte _trees_tick_ctr;
 

src/water.h

@@ -27,6 +27,7 @@ FloodingBehaviour GetFloodingBehaviour(TileIndex tile);
 void ClearNeighbourNonFloodingStates(TileIndex tile);
 
 void TileLoop_Water(TileIndex tile);
+void TileLoopWaterFlooding(FloodingBehaviour flooding_behaviour, TileIndex tile);
 bool FloodHalftile(TileIndex t);
 void DoFloodTile(TileIndex target);
 

src/water_cmd.cpp

@@ -1324,9 +1324,17 @@ void TileLoop_Water(TileIndex tile)
 {
 	if (IsTileType(tile, MP_WATER)) AmbientSoundEffect(tile);
 
+	/* At day lengths > 4, handle flooding in auxiliary tile loop */
+	if (_settings_game.economy.day_length_factor > 4) return;
+
 	if (IsNonFloodingWaterTile(tile)) return;
 
-	switch (GetFloodingBehaviour(tile)) {
+	TileLoopWaterFlooding(GetFloodingBehaviour(tile), tile);
+}
+
+void TileLoopWaterFlooding(FloodingBehaviour flooding_behaviour, TileIndex tile)
+{
+	switch (flooding_behaviour) {
 		case FLOOD_ACTIVE: {
 			int non_water_neighbours = 0;
 			for (Direction dir = DIR_BEGIN; dir < DIR_END; dir++) {