Change: Cache depth of tile ship is on for speed calculation and NewG…

…RF purposes

This is to avoid risks of desync if the depth changes while a ship is on a tile, and one client
considers the old depth and another client (which arrived just now) considers the new depth.

src/newgrf_engine.cpp

@@ -866,7 +866,7 @@ static uint32 VehicleGetVariable(Vehicle *v, const VehicleScopeResolver *object,
 			Ship *s = Ship::From(v);
 			switch (variable - 0x80) {
 				case 0x62: return s->state;
-				case 0x66: return GetEffectiveWaterDepth(s->tile);
+				case 0x66: return s->tile_depth;
 			}
 			break;
 		}

src/saveload/vehicle_sl.cpp

@@ -764,6 +764,7 @@ const SaveLoad *GetVehicleDescription(VehicleType vt)
 		      SLE_VAR(Ship, state,                     SLE_UINT8),
 		SLE_CONDDEQUE(Ship, path,                      SLE_UINT8,                  SLV_SHIP_PATH_CACHE, SL_MAX_VERSION),
 		  SLE_CONDVAR(Ship, rotation,                  SLE_UINT8,                  SLV_SHIP_ROTATION, SL_MAX_VERSION),
+		  SLE_CONDVAR(Ship, tile_depth,                SLE_UINT8,                  SLV_WATER_DEPTH, SL_MAX_VERSION),
 
 		SLE_CONDNULL(16, SLV_2, SLV_144), // old reserved space
 

src/ship.h

@@ -24,11 +24,12 @@ typedef std::deque<Trackdir> ShipPathCache;
  * All ships have this type.
  */
 struct Ship FINAL : public SpecializedVehicle<Ship, VEH_SHIP> {
-	TrackBits state;      ///< The "track" the ship is following.
-	ShipPathCache path;   ///< Cached path.
-	Direction rotation;   ///< Visible direction.
-	int16 rotation_x_pos; ///< NOSAVE: X Position before rotation.
-	int16 rotation_y_pos; ///< NOSAVE: Y Position before rotation.
+	TrackBits state;       ///< The "track" the ship is following.
+	ShipPathCache path;    ///< Cached path.
+	Direction rotation;    ///< Visible direction.
+	WaterDepth tile_depth; ///< Cached depth of current tile.
+	int16 rotation_x_pos;  ///< NOSAVE: X Position before rotation.
+	int16 rotation_y_pos;  ///< NOSAVE: Y Position before rotation.
 
 	/** We don't want GCC to zero our struct! It already is zeroed and has an index! */
 	Ship() : SpecializedVehicleBase() {}

src/ship_cmd.cpp

@@ -221,8 +221,11 @@ void Ship::UpdateCache()
 {
 	const ShipVehicleInfo *svi = ShipVehInfo(this->engine_type);
 
+	/* Update current water depth */
+	this->tile_depth = GetEffectiveWaterDepth(this->tile);
+
 	/* Get speed fraction for the current water type. Aqueducts are always canals. */
-	bool is_ocean = GetEffectiveWaterDepth(this->tile) >= WATER_DEPTH_DEEP;
+	bool is_ocean = this->tile_depth >= WATER_DEPTH_DEEP;
 	uint raw_speed = GetVehicleProperty(this, PROP_SHIP_SPEED, svi->max_speed);
 	this->vcache.cached_max_speed = svi->ApplyWaterClassSpeedFrac(raw_speed, is_ocean);
 
@@ -754,7 +757,7 @@ static void ShipController(Ship *v)
 				v->state = TrackToTrackBits(track);
 
 				/* Update ship cache when the water depth changes. */
-				WaterDepth old_depth = GetEffectiveWaterDepth(gp.old_tile);
+				WaterDepth old_depth = v->tile_depth;
 				WaterDepth new_depth = GetEffectiveWaterDepth(gp.new_tile);
 				if (old_depth != new_depth) v->UpdateCache();
 			}