Codechange: create MutableSpriteCache to remove the need to cast Vehicle to a mutable type in render methods

11 files changed, 74 insertions, 77 deletions

diff --git a/src/aircraft_cmd.cpp b/src/aircraft_cmd.cpp
index 447615e3b..c381fae97 100644
--- a/src/aircraft_cmd.cpp
+++ b/src/aircraft_cmd.cpp
@@ -341,8 +341,8 @@ CommandCost CmdBuildAircraft(TileIndex tile, DoCommandFlag flags, const Engine *
 		v->date_of_last_service = _date;
 		v->build_year = u->build_year = _cur_year;
 
-		v->sprite_seq.Set(SPR_IMG_QUERY);
-		u->sprite_seq.Set(SPR_IMG_QUERY);
+		v->sprite_cache.sprite_seq.Set(SPR_IMG_QUERY);
+		u->sprite_cache.sprite_seq.Set(SPR_IMG_QUERY);
 
 		v->random_bits = VehicleRandomBits();
 		u->random_bits = VehicleRandomBits();
@@ -374,7 +374,7 @@ CommandCost CmdBuildAircraft(TileIndex tile, DoCommandFlag flags, const Engine *
 			w->vehstatus = VS_HIDDEN | VS_UNCLICKABLE;
 			w->spritenum = 0xFF;
 			w->subtype = AIR_ROTOR;
-			w->sprite_seq.Set(SPR_ROTOR_STOPPED);
+			w->sprite_cache.sprite_seq.Set(SPR_ROTOR_STOPPED);
 			w->random_bits = VehicleRandomBits();
 			/* Use rotor's air.state to store the rotor animation frame */
 			w->state = HRS_ROTOR_STOPPED;
@@ -497,7 +497,7 @@ static void HelicopterTickHandler(Aircraft *v)
 	if (spd == 0) {
 		u->state = HRS_ROTOR_STOPPED;
 		GetRotorImage(v, EIT_ON_MAP, &seq);
-		if (u->sprite_seq == seq) return;
+		if (u->sprite_cache.sprite_seq == seq) return;
 	} else if (tick >= spd) {
 		u->tick_counter = 0;
 		u->state++;
@@ -507,7 +507,7 @@ static void HelicopterTickHandler(Aircraft *v)
 		return;
 	}
 
-	u->sprite_seq = seq;
+	u->sprite_cache.sprite_seq = seq;
 
 	u->UpdatePositionAndViewport();
 }
@@ -528,7 +528,7 @@ void SetAircraftPosition(Aircraft *v, int x, int y, int z)
 	v->UpdatePosition();
 	v->UpdateViewport(true, false);
 	if (v->subtype == AIR_HELICOPTER) {
-		GetRotorImage(v, EIT_ON_MAP, &v->Next()->Next()->sprite_seq);
+		GetRotorImage(v, EIT_ON_MAP, &v->Next()->Next()->sprite_cache.sprite_seq);
 	}
 
 	Aircraft *u = v->Next();
@@ -540,7 +540,7 @@ void SetAircraftPosition(Aircraft *v, int x, int y, int z)
 
 	safe_y = Clamp(u->y_pos, 0, MapMaxY() * TILE_SIZE);
 	u->z_pos = GetSlopePixelZ(safe_x, safe_y);
-	u->sprite_seq.CopyWithoutPalette(v->sprite_seq); // the shadow is never coloured
+	u->sprite_cache.sprite_seq.CopyWithoutPalette(v->sprite_cache.sprite_seq); // the shadow is never coloured
 
 	u->UpdatePositionAndViewport();
 
@@ -1278,7 +1278,7 @@ void Aircraft::MarkDirty()
 	this->colourmap = PAL_NONE;
 	this->UpdateViewport(true, false);
 	if (this->subtype == AIR_HELICOPTER) {
-		GetRotorImage(this, EIT_ON_MAP, &this->Next()->Next()->sprite_seq);
+		GetRotorImage(this, EIT_ON_MAP, &this->Next()->Next()->sprite_cache.sprite_seq);
 	}
 }
 
diff --git a/src/articulated_vehicles.cpp b/src/articulated_vehicles.cpp
index 4f42c6955..bdca9a507 100644
--- a/src/articulated_vehicles.cpp
+++ b/src/articulated_vehicles.cpp
@@ -439,7 +439,7 @@ void AddArticulatedParts(Vehicle *first)
 		v->max_age = 0;
 		v->engine_type = engine_type;
 		v->value = 0;
-		v->sprite_seq.Set(SPR_IMG_QUERY);
+		v->sprite_cache.sprite_seq.Set(SPR_IMG_QUERY);
 		v->random_bits = VehicleRandomBits();
 
 		if (flip_image) v->spritenum++;
diff --git a/src/disaster_vehicle.cpp b/src/disaster_vehicle.cpp
index 1244f99ab..a6059b244 100644
--- a/src/disaster_vehicle.cpp
+++ b/src/disaster_vehicle.cpp
@@ -110,7 +110,7 @@ void DisasterVehicle::UpdateImage()
 {
 	SpriteID img = this->image_override;
 	if (img == 0) img = _disaster_images[this->subtype][this->direction];
-	this->sprite_seq.Set(img);
+	this->sprite_cache.sprite_seq.Set(img);
 }
 
 /**
@@ -498,7 +498,7 @@ static bool DisasterTick_Helicopter_Rotors(DisasterVehicle *v)
 	v->tick_counter++;
 	if (HasBit(v->tick_counter, 0)) return true;
 
-	SpriteID &cur_image = v->sprite_seq.seq[0].sprite;
+	SpriteID &cur_image = v->sprite_cache.sprite_seq.seq[0].sprite;
 	if (++cur_image > SPR_ROTOR_MOVING_3) cur_image = SPR_ROTOR_MOVING_1;
 
 	v->UpdatePositionAndViewport();
diff --git a/src/effectvehicle.cpp b/src/effectvehicle.cpp
index 82054acc6..d92999a66 100644
--- a/src/effectvehicle.cpp
+++ b/src/effectvehicle.cpp
@@ -28,8 +28,8 @@
  */
 static bool IncrementSprite(EffectVehicle *v, SpriteID last)
 {
-	if (v->sprite_seq.seq[0].sprite != last) {
-		v->sprite_seq.seq[0].sprite++;
+	if (v->sprite_cache.sprite_seq.seq[0].sprite != last) {
+		v->sprite_cache.sprite_seq.seq[0].sprite++;
 		return true;
 	} else {
 		return false;
@@ -39,7 +39,7 @@ static bool IncrementSprite(EffectVehicle *v, SpriteID last)
 static void ChimneySmokeInit(EffectVehicle *v)
 {
 	uint32 r = Random();
-	v->sprite_seq.Set(SPR_CHIMNEY_SMOKE_0 + GB(r, 0, 3));
+	v->sprite_cache.sprite_seq.Set(SPR_CHIMNEY_SMOKE_0 + GB(r, 0, 3));
 	v->progress = GB(r, 16, 3);
 }
 
@@ -55,7 +55,7 @@ static bool ChimneySmokeTick(EffectVehicle *v)
 		}
 
 		if (!IncrementSprite(v, SPR_CHIMNEY_SMOKE_7)) {
-			v->sprite_seq.Set(SPR_CHIMNEY_SMOKE_0);
+			v->sprite_cache.sprite_seq.Set(SPR_CHIMNEY_SMOKE_0);
 		}
 		v->progress = 7;
 		v->UpdatePositionAndViewport();
@@ -66,7 +66,7 @@ static bool ChimneySmokeTick(EffectVehicle *v)
 
 static void SteamSmokeInit(EffectVehicle *v)
 {
-	v->sprite_seq.Set(SPR_STEAM_SMOKE_0);
+	v->sprite_cache.sprite_seq.Set(SPR_STEAM_SMOKE_0);
 	v->progress = 12;
 }
 
@@ -96,7 +96,7 @@ static bool SteamSmokeTick(EffectVehicle *v)
 
 static void DieselSmokeInit(EffectVehicle *v)
 {
-	v->sprite_seq.Set(SPR_DIESEL_SMOKE_0);
+	v->sprite_cache.sprite_seq.Set(SPR_DIESEL_SMOKE_0);
 	v->progress = 0;
 }
 
@@ -120,7 +120,7 @@ static bool DieselSmokeTick(EffectVehicle *v)
 
 static void ElectricSparkInit(EffectVehicle *v)
 {
-	v->sprite_seq.Set(SPR_ELECTRIC_SPARK_0);
+	v->sprite_cache.sprite_seq.Set(SPR_ELECTRIC_SPARK_0);
 	v->progress = 1;
 }
 
@@ -143,7 +143,7 @@ static bool ElectricSparkTick(EffectVehicle *v)
 
 static void SmokeInit(EffectVehicle *v)
 {
-	v->sprite_seq.Set(SPR_SMOKE_0);
+	v->sprite_cache.sprite_seq.Set(SPR_SMOKE_0);
 	v->progress = 12;
 }
 
@@ -173,7 +173,7 @@ static bool SmokeTick(EffectVehicle *v)
 
 static void ExplosionLargeInit(EffectVehicle *v)
 {
-	v->sprite_seq.Set(SPR_EXPLOSION_LARGE_0);
+	v->sprite_cache.sprite_seq.Set(SPR_EXPLOSION_LARGE_0);
 	v->progress = 0;
 }
 
@@ -193,7 +193,7 @@ static bool ExplosionLargeTick(EffectVehicle *v)
 
 static void BreakdownSmokeInit(EffectVehicle *v)
 {
-	v->sprite_seq.Set(SPR_BREAKDOWN_SMOKE_0);
+	v->sprite_cache.sprite_seq.Set(SPR_BREAKDOWN_SMOKE_0);
 	v->progress = 0;
 }
 
@@ -202,7 +202,7 @@ static bool BreakdownSmokeTick(EffectVehicle *v)
 	v->progress++;
 	if ((v->progress & 7) == 0) {
 		if (!IncrementSprite(v, SPR_BREAKDOWN_SMOKE_3)) {
-			v->sprite_seq.Set(SPR_BREAKDOWN_SMOKE_0);
+			v->sprite_cache.sprite_seq.Set(SPR_BREAKDOWN_SMOKE_0);
 		}
 		v->UpdatePositionAndViewport();
 	}
@@ -218,7 +218,7 @@ static bool BreakdownSmokeTick(EffectVehicle *v)
 
 static void ExplosionSmallInit(EffectVehicle *v)
 {
-	v->sprite_seq.Set(SPR_EXPLOSION_SMALL_0);
+	v->sprite_cache.sprite_seq.Set(SPR_EXPLOSION_SMALL_0);
 	v->progress = 0;
 }
 
@@ -238,7 +238,7 @@ static bool ExplosionSmallTick(EffectVehicle *v)
 
 static void BulldozerInit(EffectVehicle *v)
 {
-	v->sprite_seq.Set(SPR_BULLDOZER_NE);
+	v->sprite_cache.sprite_seq.Set(SPR_BULLDOZER_NE);
 	v->progress = 0;
 	v->animation_state = 0;
 	v->animation_substate = 0;
@@ -289,7 +289,7 @@ static bool BulldozerTick(EffectVehicle *v)
 	if ((v->progress & 7) == 0) {
 		const BulldozerMovement *b = &_bulldozer_movement[v->animation_state];
 
-		v->sprite_seq.Set(SPR_BULLDOZER_NE + b->image);
+		v->sprite_cache.sprite_seq.Set(SPR_BULLDOZER_NE + b->image);
 
 		v->x_pos += _inc_by_dir[b->direction].x;
 		v->y_pos += _inc_by_dir[b->direction].y;
@@ -311,7 +311,7 @@ static bool BulldozerTick(EffectVehicle *v)
 
 static void BubbleInit(EffectVehicle *v)
 {
-	v->sprite_seq.Set(SPR_BUBBLE_GENERATE_0);
+	v->sprite_cache.sprite_seq.Set(SPR_BUBBLE_GENERATE_0);
 	v->spritenum = 0;
 	v->progress = 0;
 }
@@ -474,8 +474,8 @@ static bool BubbleTick(EffectVehicle *v)
 	if ((v->progress & 3) != 0) return true;
 
 	if (v->spritenum == 0) {
-		v->sprite_seq.seq[0].sprite++;
-		if (v->sprite_seq.seq[0].sprite < SPR_BUBBLE_GENERATE_3) {
+		v->sprite_cache.sprite_seq.seq[0].sprite++;
+		if (v->sprite_cache.sprite_seq.seq[0].sprite < SPR_BUBBLE_GENERATE_3) {
 			v->UpdatePositionAndViewport();
 			return true;
 		}
@@ -520,7 +520,7 @@ static bool BubbleTick(EffectVehicle *v)
 	v->x_pos += b->x;
 	v->y_pos += b->y;
 	v->z_pos += b->z;
-	v->sprite_seq.Set(SPR_BUBBLE_0 + b->image);
+	v->sprite_cache.sprite_seq.Set(SPR_BUBBLE_0 + b->image);
 
 	v->UpdatePositionAndViewport();
 
diff --git a/src/roadveh_cmd.cpp b/src/roadveh_cmd.cpp
index 0e490fbc2..68b81ad0d 100644
--- a/src/roadveh_cmd.cpp
+++ b/src/roadveh_cmd.cpp
@@ -301,7 +301,7 @@ CommandCost CmdBuildRoadVehicle(TileIndex tile, DoCommandFlag flags, const Engin
 		v->date_of_last_service = _date;
 		v->build_year = _cur_year;
 
-		v->sprite_seq.Set(SPR_IMG_QUERY);
+		v->sprite_cache.sprite_seq.Set(SPR_IMG_QUERY);
 		v->random_bits = VehicleRandomBits();
 		v->SetFrontEngine();
 
diff --git a/src/saveload/oldloader_sl.cpp b/src/saveload/oldloader_sl.cpp
index fa7685731..ff4e6191e 100644
--- a/src/saveload/oldloader_sl.cpp
+++ b/src/saveload/oldloader_sl.cpp
@@ -1153,7 +1153,7 @@ static const OldChunks vehicle_chunk[] = {
 
 	OCL_SVAR(  OC_UINT8, Vehicle, owner ),
 	OCL_SVAR(   OC_TILE, Vehicle, tile ),
-	OCL_SVAR( OC_FILE_U16 | OC_VAR_U32, Vehicle, sprite_seq.seq[0].sprite ),
+	OCL_SVAR( OC_FILE_U16 | OC_VAR_U32, Vehicle, sprite_cache.sprite_seq.seq[0].sprite ),
 
 	OCL_NULL( 8 ),        ///< Vehicle sprite box, calculated automatically
 
@@ -1246,7 +1246,7 @@ bool LoadOldVehicle(LoadgameState *ls, int num)
 			if (v == nullptr) continue;
 			v->refit_cap = v->cargo_cap;
 
-			SpriteID sprite = v->sprite_seq.seq[0].sprite;
+			SpriteID sprite = v->sprite_cache.sprite_seq.seq[0].sprite;
 			/* no need to override other sprites */
 			if (IsInsideMM(sprite, 1460, 1465)) {
 				sprite += 580; // aircraft smoke puff
@@ -1257,7 +1257,7 @@ bool LoadOldVehicle(LoadgameState *ls, int num)
 			} else if (IsInsideMM(sprite, 2516, 2539)) {
 				sprite += 1385; // rotor or disaster-related vehicles
 			}
-			v->sprite_seq.seq[0].sprite = sprite;
+			v->sprite_cache.sprite_seq.seq[0].sprite = sprite;
 
 			switch (v->type) {
 				case VEH_TRAIN: {
diff --git a/src/saveload/vehicle_sl.cpp b/src/saveload/vehicle_sl.cpp
index 321ad53a6..6715eb97d 100644
--- a/src/saveload/vehicle_sl.cpp
+++ b/src/saveload/vehicle_sl.cpp
@@ -445,21 +445,21 @@ void AfterLoadVehicles(bool part_of_load)
 			case VEH_ROAD:
 			case VEH_TRAIN:
 			case VEH_SHIP:
-				v->GetImage(v->direction, EIT_ON_MAP, &v->sprite_seq);
+				v->GetImage(v->direction, EIT_ON_MAP, &v->sprite_cache.sprite_seq);
 				break;
 
 			case VEH_AIRCRAFT:
 				if (Aircraft::From(v)->IsNormalAircraft()) {
-					v->GetImage(v->direction, EIT_ON_MAP, &v->sprite_seq);
+					v->GetImage(v->direction, EIT_ON_MAP, &v->sprite_cache.sprite_seq);
 
 					/* The plane's shadow will have the same image as the plane, but no colour */
 					Vehicle *shadow = v->Next();
-					shadow->sprite_seq.CopyWithoutPalette(v->sprite_seq);
+					shadow->sprite_cache.sprite_seq.CopyWithoutPalette(v->sprite_cache.sprite_seq);
 
 					/* In the case of a helicopter we will update the rotor sprites */
 					if (v->subtype == AIR_HELICOPTER) {
 						Vehicle *rotor = shadow->Next();
-						GetRotorImage(Aircraft::From(v), EIT_ON_MAP, &rotor->sprite_seq);
+						GetRotorImage(Aircraft::From(v), EIT_ON_MAP, &rotor->sprite_cache.sprite_seq);
 					}
 
 					UpdateAircraftCache(Aircraft::From(v), true);
@@ -808,7 +808,7 @@ const SaveLoad *GetVehicleDescription(VehicleType vt)
 		 SLE_CONDVAR(Vehicle, z_pos,                 SLE_FILE_U8  | SLE_VAR_I32,   SL_MIN_VERSION, SLV_164),
 		 SLE_CONDVAR(Vehicle, z_pos,                 SLE_INT32,                  SLV_164, SL_MAX_VERSION),
 
-		     SLE_VAR(Vehicle, sprite_seq.seq[0].sprite, SLE_FILE_U16 | SLE_VAR_U32),
+		     SLE_VAR(Vehicle, sprite_cache.sprite_seq.seq[0].sprite, SLE_FILE_U16 | SLE_VAR_U32),
 		SLE_CONDNULL(5,                                                            SL_MIN_VERSION,  SLV_59),
 		     SLE_VAR(Vehicle, progress,              SLE_UINT8),
 		     SLE_VAR(Vehicle, vehstatus,             SLE_UINT8),
@@ -848,7 +848,7 @@ const SaveLoad *GetVehicleDescription(VehicleType vt)
 		 SLE_CONDVAR(Vehicle, current_order.dest,    SLE_FILE_U8 | SLE_VAR_U16,    SL_MIN_VERSION,   SLV_5),
 		 SLE_CONDVAR(Vehicle, current_order.dest,    SLE_UINT16,                   SLV_5, SL_MAX_VERSION),
 
-		     SLE_VAR(Vehicle, sprite_seq.seq[0].sprite, SLE_FILE_U16 | SLE_VAR_U32),
+		     SLE_VAR(Vehicle, sprite_cache.sprite_seq.seq[0].sprite, SLE_FILE_U16 | SLE_VAR_U32),
 		 SLE_CONDVAR(Vehicle, age,                   SLE_FILE_U16 | SLE_VAR_I32,   SL_MIN_VERSION,  SLV_31),
 		 SLE_CONDVAR(Vehicle, age,                   SLE_INT32,                   SLV_31, SL_MAX_VERSION),
 		     SLE_VAR(Vehicle, tick_counter,          SLE_UINT8),
diff --git a/src/ship_cmd.cpp b/src/ship_cmd.cpp
index 28e6be4f3..f50772470 100644
--- a/src/ship_cmd.cpp
+++ b/src/ship_cmd.cpp
@@ -864,7 +864,7 @@ CommandCost CmdBuildShip(TileIndex tile, DoCommandFlag flags, const Engine *e, u
 		v->SetServiceInterval(Company::Get(_current_company)->settings.vehicle.servint_ships);
 		v->date_of_last_service = _date;
 		v->build_year = _cur_year;
-		v->sprite_seq.Set(SPR_IMG_QUERY);
+		v->sprite_cache.sprite_seq.Set(SPR_IMG_QUERY);
 		v->random_bits = VehicleRandomBits();
 
 		v->UpdateCache();
diff --git a/src/train_cmd.cpp b/src/train_cmd.cpp
index 71fec8cfb..0c4a25eef 100644
--- a/src/train_cmd.cpp
+++ b/src/train_cmd.cpp
@@ -624,7 +624,7 @@ static CommandCost CmdBuildRailWagon(TileIndex tile, DoCommandFlag flags, const
 
 		v->date_of_last_service = _date;
 		v->build_year = _cur_year;
-		v->sprite_seq.Set(SPR_IMG_QUERY);
+		v->sprite_cache.sprite_seq.Set(SPR_IMG_QUERY);
 		v->random_bits = VehicleRandomBits();
 
 		v->group_id = DEFAULT_GROUP;
@@ -690,7 +690,7 @@ static void AddRearEngineToMultiheadedTrain(Train *v)
 	u->engine_type = v->engine_type;
 	u->date_of_last_service = v->date_of_last_service;
 	u->build_year = v->build_year;
-	u->sprite_seq.Set(SPR_IMG_QUERY);
+	u->sprite_cache.sprite_seq.Set(SPR_IMG_QUERY);
 	u->random_bits = VehicleRandomBits();
 	v->SetMultiheaded();
 	u->SetMultiheaded();
@@ -756,7 +756,7 @@ CommandCost CmdBuildRailVehicle(TileIndex tile, DoCommandFlag flags, const Engin
 		v->SetServiceInterval(Company::Get(_current_company)->settings.vehicle.servint_trains);
 		v->date_of_last_service = _date;
 		v->build_year = _cur_year;
-		v->sprite_seq.Set(SPR_IMG_QUERY);
+		v->sprite_cache.sprite_seq.Set(SPR_IMG_QUERY);
 		v->random_bits = VehicleRandomBits();
 
 		if (e->flags & ENGINE_EXCLUSIVE_PREVIEW) SetBit(v->vehicle_flags, VF_BUILT_AS_PROTOTYPE);
diff --git a/src/vehicle.cpp b/src/vehicle.cpp
index 8dead6cee..89cabe20d 100644
--- a/src/vehicle.cpp
+++ b/src/vehicle.cpp
@@ -1094,25 +1094,19 @@ static void DoDrawVehicle(const Vehicle *v)
 	/*
 	 * If the vehicle sprite was not updated despite further viewport changes, we need
 	 * to update it before drawing.
-	 *
-	 * I'm not keen on casting to mutable - it's the approach JGR uses in JGRPP but I
-	 * wonder if there's a cleaner option (even though we can only take the decision
-	 * whether to update once we already know the vehicle is going to appear in a
-	 * viewport)
 	 */
-	if (v->rstate.sprite_has_viewport_changes) {
-		Vehicle* v_mutable = const_cast<Vehicle*>(v);
+	if (v->sprite_cache.sprite_has_viewport_changes) {
 		VehicleSpriteSeq seq;
-		v_mutable->GetImage(v_mutable->direction, EIT_ON_MAP, &seq);
-		v_mutable->sprite_seq = seq;
-		v_mutable->rstate.sprite_has_viewport_changes = false;
+		v->GetImage(v->direction, EIT_ON_MAP, &seq);
+		v->sprite_cache.sprite_seq = seq;
+		v->sprite_cache.sprite_has_viewport_changes = false;
 	}
 
 	StartSpriteCombine();
-	for (uint i = 0; i < v->sprite_seq.count; ++i) {
-		PaletteID pal2 = v->sprite_seq.seq[i].pal;
+	for (uint i = 0; i < v->sprite_cache.sprite_seq.count; ++i) {
+		PaletteID pal2 = v->sprite_cache.sprite_seq.seq[i].pal;
 		if (!pal2 || (v->vehstatus & VS_CRASHED)) pal2 = pal;
-		AddSortableSpriteToDraw(v->sprite_seq.seq[i].sprite, pal2, v->x_pos + v->x_offs, v->y_pos + v->y_offs,
+		AddSortableSpriteToDraw(v->sprite_cache.sprite_seq.seq[i].sprite, pal2, v->x_pos + v->x_offs, v->y_pos + v->y_offs,
 			v->x_extent, v->y_extent, v->z_extent, v->z_pos, shadowed, v->x_bb_offs, v->y_bb_offs);
 	}
 	EndSpriteCombine();
@@ -1175,10 +1169,10 @@ void ViewportAddVehicles(DrawPixelInfo *dpi)
 					 * are part of a newgrf vehicle set which changes bounding boxes within a
 					 * single vehicle direction.
 					 *
-					 * TODO: is there a cleaner solution than casting to a mutable type?
+					 * TODO: this will consider too many false positives, use the bounding box
+					 * information or something which better narrows down the candidates.
 					 */
-					Vehicle* v_mutable = const_cast<Vehicle*>(v);
-					v_mutable->rstate.is_viewport_candidate = true;
+					v->sprite_cache.is_viewport_candidate = true;
 				}
 
 				v = v->hash_viewport_next;
@@ -1605,7 +1599,7 @@ void Vehicle::UpdatePosition()
 void Vehicle::UpdateViewport(bool dirty)
 {
 	Rect new_coord;
-	this->sprite_seq.GetBounds(&new_coord);
+	this->sprite_cache.sprite_seq.GetBounds(&new_coord);
 
 	Point pt = RemapCoords(this->x_pos + this->x_offs, this->y_pos + this->y_offs, this->z_pos);
 	new_coord.left   += pt.x;
diff --git a/src/vehicle_base.h b/src/vehicle_base.h
index 8ef316df1..d6a02cc0c 100644
--- a/src/vehicle_base.h
+++ b/src/vehicle_base.h
@@ -124,13 +124,6 @@ struct VehicleCache {
 	byte cached_vis_effect;  ///< Visual effect to show (see #VisualEffect)
 };
 
-/** Values for controlling how a vehicle's sprites are refreshed */
-struct VehicleSpriteRefreshState {
-	Direction last_direction;         ///< Last direction we obtained sprites for
-	bool is_viewport_candidate;       ///< The vehicle has been in the hash for a shown viewport recently
-	bool sprite_has_viewport_changes; ///< There have been viewport changes since the sprite was last updated
-};
-
 /** Sprite sequence for a vehicle part. */
 struct VehicleSpriteSeq {
 	PalSpriteID seq[4];
@@ -188,6 +181,17 @@ struct VehicleSpriteSeq {
 	void Draw(int x, int y, PaletteID default_pal, bool force_pal) const;
 };
 
+/**
+ * Cache for vehicle sprites and values relating to whether they should be updated before drawing,
+ * or calculating the viewport.
+ */
+struct MutableSpriteCache {
+	Direction last_direction;                 ///< Last direction we obtained sprites for
+	mutable bool is_viewport_candidate;       ///< The vehicle has been in the hash for a shown viewport recently
+	mutable bool sprite_has_viewport_changes; ///< There have been viewport changes since the sprite was last updated
+	mutable VehicleSpriteSeq sprite_seq;      ///< Vehicle appearance.
+};
+
 /** A vehicle pool for a little over 1 million vehicles. */
 typedef Pool<Vehicle, VehicleID, 512, 0xFF000> VehiclePool;
 extern VehiclePool _vehicle_pool;
@@ -282,7 +286,6 @@ public:
 	 * 0xff == reserved for another custom sprite
 	 */
 	byte spritenum;
-	VehicleSpriteSeq sprite_seq;        ///< Vehicle appearance.
 	byte x_extent;                      ///< x-extent of vehicle bounding box
 	byte y_extent;                      ///< y-extent of vehicle bounding box
 	byte z_extent;                      ///< z-extent of vehicle bounding box
@@ -334,7 +337,7 @@ public:
 	NewGRFCache grf_cache;              ///< Cache of often used calculated NewGRF values
 	VehicleCache vcache;                ///< Cache of often used vehicle values.
 
-	VehicleSpriteRefreshState rstate;   ///< Values relating to whether sprites should be refreshed, see #VehicleSpriteRefreshState
+	MutableSpriteCache sprite_cache;    ///< Cache of sprites and values related to recalculating them, see #MutableSpriteCache
 
 	Vehicle(VehicleType type = VEH_INVALID);
 
@@ -1044,7 +1047,7 @@ struct SpecializedVehicle : public Vehicle {
 	 */
 	inline SpecializedVehicle<T, Type>() : Vehicle(Type)
 	{
-		this->sprite_seq.count = 1;
+		this->sprite_cache.sprite_seq.count = 1;
 	}
 
 	/**
@@ -1193,24 +1196,24 @@ struct SpecializedVehicle : public Vehicle {
 		 * there won't be enough change in bounding box or offsets to need
 		 * to resolve a new sprite.
 		 */
-		if (this->direction != this->rstate.last_direction || this->rstate.is_viewport_candidate) {
+		if (this->direction != this->sprite_cache.last_direction || this->sprite_cache.is_viewport_candidate) {
 			VehicleSpriteSeq seq;
 
 			((T*)this)->T::GetImage(this->direction, EIT_ON_MAP, &seq);
-			if (this->sprite_seq != seq) {
+			if (this->sprite_cache.sprite_seq != seq) {
 				sprite_has_changed = true;
-				this->sprite_seq = seq;
+				this->sprite_cache.sprite_seq = seq;
 			}
 
-			this->rstate.last_direction = this->direction;
-			this->rstate.is_viewport_candidate = false;
-			this->rstate.sprite_has_viewport_changes = false;
+			this->sprite_cache.last_direction = this->direction;
+			this->sprite_cache.is_viewport_candidate = false;
+			this->sprite_cache.sprite_has_viewport_changes = false;
 		} else {
 			/*
 			 * Changes could still be relevant when we render the vehicle even if
 			 * they don't alter the bounding box
 			 */
-			this->rstate.sprite_has_viewport_changes = true;
+			this->sprite_cache.sprite_has_viewport_changes = true;
 		}
 
 		if (force_update || sprite_has_changed) {