Add map bit to suppress water flooding checks

Set if all neighbour tiles are also water
This reduces the overhead of flood checks on large maps

docs/landscape.html

@@ -1054,6 +1054,7 @@
      <li>m1 bits 6..5 : Water class (sea, canal or river)
      <li>m1 bits 4..0: <a href="#OwnershipInfo">owner</a> (for sea, rivers, and coasts normally <tt>11</tt>)</li>
      <li>m2: Depot index (for depots only)</li>
+     <li style="color: blue">m3 bit 0: No flooding state, set if all neighbouring tiles are also water</li>
      <li>m4: Random data for canal or river tiles</li>
      <li>m5: tile type:
       <table>

docs/landscape_grid.html

@@ -241,7 +241,7 @@ the array so you can quickly see what is used and what is not.
       <td class="caption">sea, shore</td>
       <td class="bits" rowspan=4><span class="used" title="Ship docking tile status">X</span> <span class="used" title="Water class">XX</span> <span class="used" title="Owner">XXXXX</span></td>
       <td class="bits" rowspan=3><span class="free">OOOO OOOO OOOO OOOO</span></td>
-      <td class="bits" rowspan=4><span class="free">OOOO OOOO</span></td>
+      <td class="bits" rowspan=4><span class="free">OOOO OOO</span><span class="patch" title="No flooding state">P</span></td>
       <td class="bits"><span class="free">OOOO OOOO</span></td>
       <td class="bits"><span class="used" title="Water tile type: coast, clear, lock, depot">O<span class="usable">OO</span>O</span> <span class="free">OOO</span><span class="used" title="Sea shore flag">X</span></td>
       <td class="bits" rowspan=4><span class="free">OOOO OOOO</span></td>

src/saveload/extended_ver_sl.cpp

@@ -146,6 +146,7 @@ const SlxiSubChunkInfo _sl_xv_sub_chunk_infos[] = {
 	{ XSLFI_INDUSTRY_CARGO_ADJ,     XSCF_IGNORABLE_UNKNOWN,   1,   1, "industry_cargo_adj",        nullptr, nullptr, nullptr        },
 	{ XSLFI_REALISTIC_TRAIN_BRAKING,XSCF_NULL,                1,   1, "realistic_train_braking",   nullptr, nullptr, "VLKA"         },
 	{ XSLFI_INFLATION_FIXED_DATES,  XSCF_IGNORABLE_ALL,       1,   1, "inflation_fixed_dates",     nullptr, nullptr, nullptr        },
+	{ XSLFI_WATER_FLOODING,         XSCF_NULL,                1,   1, "water_flooding",            nullptr, nullptr, nullptr        },
 	{ XSLFI_NULL, XSCF_NULL, 0, 0, nullptr, nullptr, nullptr, nullptr },// This is the end marker
 };
 

src/saveload/extended_ver_sl.h

@@ -100,6 +100,7 @@ enum SlXvFeatureIndex {
 	XSLFI_INDUSTRY_CARGO_ADJ,                     ///< Industry cargo adjustment patch
 	XSLFI_REALISTIC_TRAIN_BRAKING,                ///< Realistic train braking
 	XSLFI_INFLATION_FIXED_DATES,                  ///< Inflation is applied between fixed dates
+	XSLFI_WATER_FLOODING,                         ///< Water flooding map bit
 
 	XSLFI_RIFF_HEADER_60_BIT,                     ///< Size field in RIFF chunk header is 60 bit
 	XSLFI_HEIGHT_8_BIT,                           ///< Map tile height is 8 bit instead of 4 bit, but savegame version may be before this became true in trunk

src/water_cmd.cpp

@@ -88,6 +88,13 @@ static void MarkCanalsAndRiversAroundDirty(TileIndex tile)
 	}
 }
 
+static void ClearNeighbourNonFloodingStates(TileIndex tile)
+{
+	for (Direction dir = DIR_BEGIN; dir < DIR_END; dir++) {
+		TileIndex dest = tile + TileOffsByDir(dir);
+		if (IsValidTile(dest) && IsTileType(dest, MP_WATER)) SetNonFloodingWaterTile(dest, false);
+	}
+}
 
 /**
  * Build a ship depot.
@@ -400,6 +407,7 @@ static CommandCost RemoveLock(TileIndex tile, DoCommandFlag flags)
 			MakeRiver(tile, Random());
 		} else {
 			DoClearSquare(tile);
+			ClearNeighbourNonFloodingStates(tile);
 		}
 		MakeWaterKeepingClass(tile + delta, GetTileOwner(tile + delta));
 		MakeWaterKeepingClass(tile - delta, GetTileOwner(tile - delta));
@@ -570,6 +578,7 @@ static CommandCost ClearTile_Water(TileIndex tile, DoCommandFlag flags)
 				DoClearSquare(tile);
 				MarkCanalsAndRiversAroundDirty(tile);
 				if (remove) RemoveDockingTile(tile);
+				ClearNeighbourNonFloodingStates(tile);
 			}
 
 			return CommandCost(EXPENSES_CONSTRUCTION, base_cost);
@@ -593,6 +602,7 @@ static CommandCost ClearTile_Water(TileIndex tile, DoCommandFlag flags)
 				DoClearSquare(tile);
 				MarkCanalsAndRiversAroundDirty(tile);
 				if (remove) RemoveDockingTile(tile);
+				ClearNeighbourNonFloodingStates(tile);
 			}
 			return ret;
 		}
@@ -1248,14 +1258,19 @@ void TileLoop_Water(TileIndex tile)
 {
 	if (IsTileType(tile, MP_WATER)) AmbientSoundEffect(tile);
 
+	if (IsNonFloodingWaterTile(tile)) return;
+
 	switch (GetFloodingBehaviour(tile)) {
-		case FLOOD_ACTIVE:
+		case FLOOD_ACTIVE: {
+			int non_water_neighbours = 0;
 			for (Direction dir = DIR_BEGIN; dir < DIR_END; dir++) {
 				TileIndex dest = tile + TileOffsByDir(dir);
 				if (!IsValidTile(dest)) continue;
 				/* do not try to flood water tiles - increases performance a lot */
 				if (IsTileType(dest, MP_WATER)) continue;
 
+				non_water_neighbours++;
+
 				/* TREE_GROUND_SHORE is the sign of a previous flood. */
 				if (IsTileType(dest, MP_TREES) && GetTreeGround(dest) == TREE_GROUND_SHORE) continue;
 
@@ -1267,7 +1282,9 @@ void TileLoop_Water(TileIndex tile)
 
 				DoFloodTile(dest);
 			}
+			if (non_water_neighbours == 0 && IsTileType(tile, MP_WATER)) SetNonFloodingWaterTile(tile, true);
 			break;
+		}
 
 		case FLOOD_DRYUP: {
 			Slope slope_here = GetFoundationSlope(tile) & ~SLOPE_HALFTILE_MASK & ~SLOPE_STEEP;

src/water_map.h

@@ -504,4 +504,24 @@ static inline void MakeLock(TileIndex t, Owner o, DiagDirection d, WaterClass wc
 	MakeLockTile(t + delta, IsWaterTile(t + delta) ? GetTileOwner(t + delta) : o, LOCK_PART_UPPER, d, wc_upper);
 }
 
+
+/**
+ * Set the non-flooding water tile state of a tile.
+ * @param t the tile
+ * @param b the non-flooding water tile state
+ */
+static inline void SetNonFloodingWaterTile(TileIndex t, bool b)
+{
+	assert(IsTileType(t, MP_WATER));
+	SB(_m[t].m3, 0, 1, b ? 1 : 0);
+}
+/**
+ * Checks whether the tile is marked as a non-flooding water tile.
+ * @return true iff the tile is marked as a non-flooding water tile.
+ */
+static inline bool IsNonFloodingWaterTile(TileIndex t)
+{
+	return IsTileType(t, MP_WATER) && HasBit(_m[t].m3, 0);
+}
+
 #endif /* WATER_MAP_H */