Change ship path cache to be optional and use a ring buffer

src/pathfinder/pathfinder_type.h

@@ -38,9 +38,6 @@ static const int YAPF_TILE_CORNER_LENGTH = 71;
  */
 static const int YAPF_INFINITE_PENALTY = 1000 * YAPF_TILE_LENGTH;
 
-/** Maximum length of ship path cache */
-static const int YAPF_SHIP_PATH_CACHE_LENGTH = 32;
-
 /** Distance from destination road stops to not cache any further */
 static const int YAPF_ROADVEH_PATH_CACHE_DESTINATION_LIMIT = 8;
 

src/pathfinder/yapf/yapf_ship.cpp

@@ -173,7 +173,7 @@ public:
 			uint steps = 0;
 			for (Node *n = pNode; n->m_parent != nullptr; n = n->m_parent) steps++;
 			uint skip = 0;
-			if (path_found) skip = YAPF_SHIP_PATH_CACHE_LENGTH / 2;
+			if (path_found) skip = SHIP_PATH_CACHE_LENGTH / 2;
 
 			/* walk through the path back to the origin */
 			Node *pPrevNode = nullptr;
@@ -181,7 +181,7 @@ public:
 				steps--;
 				/* Skip tiles at end of path near destination. */
 				if (skip > 0) skip--;
-				if (skip == 0 && steps > 0 && steps < YAPF_SHIP_PATH_CACHE_LENGTH) {
+				if (skip == 0 && steps > 0 && steps < SHIP_PATH_CACHE_LENGTH) {
 					path_cache.push_front(pNode->GetTrackdir());
 				}
 				pPrevNode = pNode;

src/saveload/vehicle_sl.cpp

@@ -293,7 +293,7 @@ public:
 	inline static const SaveLoad description[] = {
 		  SLEG_STRUCT("common", SlVehicleCommon),
 		      SLE_VAR(Ship, state,                     SLE_UINT8),
-		SLE_CONDDEQUE(Ship, path,                      SLE_UINT8,                  SLV_SHIP_PATH_CACHE, SL_MAX_VERSION),
+		SLEG_CONDVECTOR("path", _path_td,              SLE_UINT8,                  SLV_SHIP_PATH_CACHE, SL_MAX_VERSION),
 		  SLE_CONDVAR(Ship, rotation,                  SLE_UINT8,                  SLV_SHIP_ROTATION, SL_MAX_VERSION),
 	};
 	inline const static SaveLoadCompatTable compat_description = _vehicle_ship_sl_compat;
@@ -308,6 +308,16 @@ public:
 	{
 		if (v->type != VEH_SHIP) return;
 		SlObject(v, this->GetLoadDescription());
+
+		if (!_path_td.empty() && _path_td.size() <= SHIP_PATH_CACHE_LENGTH) {
+			Ship *s = Ship::From(v);
+			s->cached_path.reset(new ShipPathCache());
+			s->cached_path->count = _path_td.size();
+			for (size_t i = 0; i < _path_td.size(); i++) {
+				s->cached_path->td[i] = _path_td[i];
+			}
+		}
+		_path_td.clear();
 	}
 
 	void FixPointers(Vehicle *v) const override

src/settings.cpp

@@ -1709,7 +1709,7 @@ static void MaxVehiclesChanged(int32 new_value)
 static void InvalidateShipPathCache(int32 new_value)
 {
 	for (Ship *s : Ship::Iterate()) {
-		s->path.clear();
+		s->cached_path.reset();
 	}
 }
 

src/ship.h

@@ -10,7 +10,7 @@
 #ifndef SHIP_H
 #define SHIP_H
 
-#include <deque>
+#include <array>
 
 #include "vehicle_base.h"
 #include "water_map.h"
@@ -20,14 +20,55 @@ extern const DiagDirection _ship_search_directions[TRACK_END][DIAGDIR_END];
 void GetShipSpriteSize(EngineID engine, uint &width, uint &height, int &xoffs, int &yoffs, EngineImageType image_type);
 WaterClass GetEffectiveWaterClass(TileIndex tile);
 
-typedef std::deque<Trackdir> ShipPathCache;
+/** Maximum segments of ship path cache */
+static const uint8 SHIP_PATH_CACHE_LENGTH = 32;
+static const uint8 SHIP_PATH_CACHE_MASK = (SHIP_PATH_CACHE_LENGTH - 1);
+static_assert((SHIP_PATH_CACHE_LENGTH & SHIP_PATH_CACHE_MASK) == 0, ""); // Must be a power of 2
+
+struct ShipPathCache {
+	std::array<Trackdir, SHIP_PATH_CACHE_LENGTH> td;
+	uint8 start = 0;
+	uint8 count = 0;
+
+	inline bool empty() const { return this->count == 0; }
+	inline uint8 size() const { return this->count; }
+	inline bool full() const { return this->count >= SHIP_PATH_CACHE_LENGTH; }
+
+	inline void clear()
+	{
+		this->start = 0;
+		this->count = 0;
+	}
+
+	inline Trackdir front() const { return this->td[this->start]; }
+	inline Trackdir back() const { return this->td[(this->start + this->count - 1) & SHIP_PATH_CACHE_MASK]; }
+
+	/* push an item to the front of the ring, if the ring is already full, the back item is overwritten */
+	inline void push_front(Trackdir td)
+	{
+		this->start = (this->start - 1) & SHIP_PATH_CACHE_MASK;
+		if (!this->full()) this->count++;
+		this->td[this->start] = td;
+	}
+
+	inline void pop_front()
+	{
+		this->start = (this->start + 1) & SHIP_PATH_CACHE_MASK;
+		this->count--;
+	}
+
+	inline void pop_back()
+	{
+		this->count--;
+	}
+};
 
 /**
  * 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.
+	std::unique_ptr<ShipPathCache> cached_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.
@@ -61,6 +102,12 @@ struct Ship FINAL : public SpecializedVehicle<Ship, VEH_SHIP> {
 	ClosestDepot FindClosestDepot() override;
 	void UpdateCache();
 	void SetDestTile(TileIndex tile) override;
+
+	inline ShipPathCache &GetOrCreatePathCache()
+	{
+		if (!this->cached_path) this->cached_path.reset(new ShipPathCache());
+		return *this->cached_path;
+	}
 };
 
 bool IsShipDestinationTile(TileIndex tile, StationID station);

src/ship_cmd.cpp

@@ -567,22 +567,22 @@ static Track ChooseShipTrack(Ship *v, TileIndex tile, DiagDirection enterdir, Tr
 		path_found = false;
 	} else {
 		/* Attempt to follow cached path. */
-		if (!v->path.empty()) {
-			track = TrackdirToTrack(v->path.front());
+		if (v->cached_path != nullptr && !v->cached_path->empty()) {
+			track = TrackdirToTrack(v->cached_path->front());
 
 			if (HasBit(tracks, track)) {
-				v->path.pop_front();
+				v->cached_path->pop_front();
 				/* HandlePathfindResult() is not called here because this is not a new pathfinder result. */
 				return track;
 			}
 
 			/* Cached path is invalid so continue with pathfinder. */
-			v->path.clear();
+			v->cached_path->clear();
 		}
 
 		switch (_settings_game.pf.pathfinder_for_ships) {
 			case VPF_NPF: track = NPFShipChooseTrack(v, path_found); break;
-			case VPF_YAPF: track = YapfShipChooseTrack(v, tile, enterdir, tracks, path_found, v->path); break;
+			case VPF_YAPF: track = YapfShipChooseTrack(v, tile, enterdir, tracks, path_found, v->GetOrCreatePathCache()); break;
 			default: NOT_REACHED();
 		}
 	}
@@ -882,7 +882,7 @@ static void ReverseShipIntoTrackdir(Ship *v, Trackdir trackdir)
 	v->rotation_x_pos = v->x_pos;
 	v->rotation_y_pos = v->y_pos;
 	UpdateShipSpeed(v, 0);
-	v->path.clear();
+	if (v->cached_path != nullptr) v->cached_path->clear();
 
 	v->UpdatePosition();
 	v->UpdateViewport(true, true);
@@ -896,7 +896,7 @@ static void ReverseShip(Ship *v)
 	v->rotation_x_pos = v->x_pos;
 	v->rotation_y_pos = v->y_pos;
 	UpdateShipSpeed(v, 0);
-	v->path.clear();
+	if (v->cached_path != nullptr) v->cached_path->clear();
 
 	v->UpdatePosition();
 	v->UpdateViewport(true, true);
@@ -1081,7 +1081,7 @@ static void ShipController(Ship *v)
 
 			/* Ship is back on the bridge head, we need to consume its path
 			 * cache entry here as we didn't have to choose a ship track. */
-			if (!v->path.empty()) v->path.pop_front();
+			 if (v->cached_path != nullptr && !v->cached_path->empty()) v->cached_path->pop_front();
 		}
 
 		/* update image of ship, as well as delta XY */
@@ -1107,7 +1107,7 @@ bool Ship::Tick()
 void Ship::SetDestTile(TileIndex tile)
 {
 	if (tile == this->dest_tile) return;
-	this->path.clear();
+	if (this->cached_path != nullptr) this->cached_path->clear();
 	this->dest_tile = tile;
 }
 

src/sl/vehicle_sl.cpp

@@ -877,7 +877,7 @@ SaveLoadTable GetVehicleDescription(VehicleType vt)
 		SLE_WRITEBYTE(Vehicle, type),
 		SLE_VEH_INCLUDE(),
 		      SLE_VAR(Ship, state,                     SLE_UINT8),
-		SLE_CONDDEQUE(Ship, path,                      SLE_UINT8,                  SLV_SHIP_PATH_CACHE, SL_MAX_VERSION),
+		SLEG_CONDVARVEC(_path_td,                      SLE_UINT8,                  SLV_SHIP_PATH_CACHE, SL_MAX_VERSION),
 		  SLE_CONDVAR(Ship, rotation,                  SLE_UINT8,                  SLV_SHIP_ROTATION, SL_MAX_VERSION),
 		SLE_CONDVAR_X(Ship, lost_count,                SLE_UINT8,                     SL_MIN_VERSION, SL_MAX_VERSION, SlXvFeatureTest(XSLFTO_AND, XSLFI_SHIP_LOST_COUNTER)),
 		SLE_CONDVAR_X(Ship, critical_breakdown_count,  SLE_UINT8,                     SL_MIN_VERSION, SL_MAX_VERSION, SlXvFeatureTest(XSLFTO_AND, XSLFI_IMPROVED_BREAKDOWNS, 8)),
@@ -1043,6 +1043,17 @@ static void Save_VEHS()
 				}
 				_path_layout_ctr = rv->cached_path->layout_ctr;
 			}
+		} else if (v->type == VEH_SHIP) {
+			_path_td.clear();
+
+			Ship *s = Ship::From(v);
+			if (s->cached_path != nullptr && !s->cached_path->empty()) {
+				uint idx = s->cached_path->start;
+				for (uint i = 0; i < s->cached_path->size(); i++) {
+					_path_td.push_back(s->cached_path->td[idx]);
+					idx = (idx + 1) & SHIP_PATH_CACHE_MASK;
+				}
+			}
 		}
 		SlSetArrayIndex(v->index);
 		SlObjectSaveFiltered(v, GetVehicleDescriptionFiltered(v->type));
@@ -1123,6 +1134,13 @@ void Load_VEHS()
 				rv->cached_path->tile[i] = _path_tile[i];
 			}
 			rv->cached_path->layout_ctr = _path_layout_ctr;
+		} else if (vtype == VEH_SHIP && !_path_td.empty() && _path_td.size() <= SHIP_PATH_CACHE_LENGTH) {
+			Ship *s = Ship::From(v);
+			s->cached_path.reset(new ShipPathCache());
+			s->cached_path->count = _path_td.size();
+			for (size_t i = 0; i < _path_td.size(); i++) {
+				s->cached_path->td[i] = _path_td[i];
+			}
 		}
 	}
 }