Cache the result of GetImage() in Vehicle::UpdateViewport() where possible.

Sprite number is not cached if callback is made, or a variable access
outside a whitelist occurs.
Invalidate cached sprite number when direction or cargo changes,
or vehicle is marked dirty.

src/aircraft_cmd.cpp

@@ -1293,6 +1293,7 @@ TileIndex Aircraft::GetOrderStationLocation(StationID station)
 void Aircraft::MarkDirty()
 {
 	this->colourmap = PAL_NONE;
+	this->cur_image_valid_dir = INVALID_DIR;
 	this->UpdateViewport(true, false);
 	if (this->subtype == AIR_HELICOPTER) this->Next()->Next()->cur_image = GetRotorImage(this, EIT_ON_MAP);
 }

src/disaster_vehicle.cpp

@@ -186,6 +186,7 @@ void DisasterVehicle::UpdatePosition(int x, int y, int z)
 	this->z_pos = z;
 	this->tile = TileVirtXY(x, y);
 
+	this->cur_image_valid_dir = INVALID_DIR;
 	this->UpdateImage();
 	this->UpdatePositionAndViewport();
 
@@ -199,6 +200,7 @@ void DisasterVehicle::UpdatePosition(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->direction = this->direction;
+		u->cur_image_valid_dir = INVALID_DIR;
 
 		u->UpdateImage();
 		u->UpdatePositionAndViewport();

src/ground_vehicle.cpp

@@ -108,6 +108,7 @@ void GroundVehicle<T, Type>::CargoChanged()
 		weight += current_weight;
 		/* Slope steepness is in percent, result in N. */
 		u->gcache.cached_slope_resistance = current_weight * u->GetSlopeSteepness() * 100;
+		u->cur_image_valid_dir = INVALID_DIR;
 	}
 
 	/* Store consist weight in cache. */

src/newgrf_spritegroup.cpp

@@ -237,6 +237,8 @@ static U EvalAdjustT(const DeterministicSpriteGroupAdjust *adjust, ScopeResolver
 	}
 }
 
+bool _sprite_group_resolve_check_veh_enable = false;
+bool _sprite_group_resolve_check_veh_result = false;
 
 const SpriteGroup *DeterministicSpriteGroup::Resolve(ResolverObject &object) const
 {
@@ -252,6 +254,7 @@ const SpriteGroup *DeterministicSpriteGroup::Resolve(ResolverObject &object) con
 		/* Try to get the variable. We shall assume it is available, unless told otherwise. */
 		bool available = true;
 		if (adjust->variable == 0x7E) {
+			_sprite_group_resolve_check_veh_result = false;
 			const SpriteGroup *subgroup = SpriteGroup::Resolve(adjust->subroutine, object, false);
 			if (subgroup == NULL) {
 				value = CALLBACK_FAILED;
@@ -261,8 +264,49 @@ const SpriteGroup *DeterministicSpriteGroup::Resolve(ResolverObject &object) con
 
 			/* Note: 'last_value' and 'reseed' are shared between the main chain and the procedure */
 		} else if (adjust->variable == 0x7B) {
+			_sprite_group_resolve_check_veh_result = false;
 			value = GetVariable(object, scope, adjust->parameter, last_value, &available);
 		} else {
+			if (_sprite_group_resolve_check_veh_enable) {
+				switch (adjust->variable) {
+					// whitelist of variables which can be checked without requiring an immediate re-check on the next tick
+					case 0xC:
+					case 0x1A:
+					case 0x1C:
+					case 0x25:
+					case 0x40:
+					case 0x41:
+					case 0x42:
+					case 0x47:
+					case 0x49:
+					case 0x4B:
+					case 0x4D:
+					case 0x60:
+					case 0x7D:
+					case 0x7F:
+					case 0x80 + 0x0:
+					case 0x80 + 0x1:
+					case 0x80 + 0x4:
+					case 0x80 + 0x5:
+					case 0x80 + 0x39:
+					case 0x80 + 0x3A:
+					case 0x80 + 0x3B:
+					case 0x80 + 0x3C:
+					case 0x80 + 0x3D:
+					case 0x80 + 0x44:
+					case 0x80 + 0x45:
+					case 0x80 + 0x46:
+					case 0x80 + 0x47:
+					case 0x80 + 0x5A:
+					case 0x80 + 0x72:
+					case 0x80 + 0x7A:
+						break;
+
+					default:
+						_sprite_group_resolve_check_veh_result = false;
+						break;
+				}
+			}
 			value = GetVariable(object, scope, adjust->variable, adjust->parameter, &available);
 		}
 

src/roadveh_cmd.cpp

@@ -408,6 +408,7 @@ void RoadVehicle::MarkDirty()
 {
 	for (RoadVehicle *v = this; v != NULL; v = v->Next()) {
 		v->colourmap = PAL_NONE;
+		v->cur_image_valid_dir = INVALID_DIR;
 		v->UpdateViewport(true, false);
 	}
 	this->CargoChanged();

src/ship_cmd.cpp

@@ -259,6 +259,7 @@ Trackdir Ship::GetVehicleTrackdir() const
 void Ship::MarkDirty()
 {
 	this->colourmap = PAL_NONE;
+	this->cur_image_valid_dir = INVALID_DIR;
 	this->UpdateViewport(true, false);
 	this->UpdateCache();
 }

src/train_cmd.cpp

@@ -1638,6 +1638,8 @@ static void SwapTrainFlags(uint16 *swap_flag1, uint16 *swap_flag2)
  */
 static void UpdateStatusAfterSwap(Train *v)
 {
+	v->cur_image_valid_dir = INVALID_DIR;
+
 	/* Reverse the direction. */
 	if (v->track != TRACK_BIT_DEPOT) v->direction = ReverseDir(v->direction);
 
@@ -3052,6 +3054,7 @@ void Train::MarkDirty()
 	Train *v = this;
 	do {
 		v->colourmap = PAL_NONE;
+		v->cur_image_valid_dir = INVALID_DIR;
 		v->UpdateViewport(true, false);
 	} while ((v = v->Next()) != NULL);
 

src/vehicle.cpp

@@ -367,6 +367,7 @@ Vehicle::Vehicle(VehicleType type)
 	this->cargo_age_counter  = 1;
 	this->last_station_visited = INVALID_STATION;
 	this->last_loading_station = INVALID_STATION;
+	this->cur_image_valid_dir  = INVALID_DIR;
 }
 
 /**

src/vehicle_base.h

@@ -291,6 +291,7 @@ public:
 	uint16 load_unload_ticks;           ///< Ticks to wait before starting next cycle.
 	GroupID group_id;                   ///< Index of group Pool array
 	byte subtype;                       ///< subtype (Filled with values from #EffectVehicles/#TrainSubTypes/#AircraftSubTypes)
+	DirectionByte cur_image_valid_dir;  ///< NOSAVE: direction for which cur_image does not need to be regenerated on the next tick
 
 	NewGRFCache grf_cache;              ///< Cache of often used calculated NewGRF values
 	VehicleCache vcache;                ///< Cache of often used vehicle values.
@@ -1158,11 +1159,20 @@ struct SpecializedVehicle : public Vehicle {
 		/* Skip updating sprites on dedicated servers without screen */
 		if (_network_dedicated) return;
 
+		extern bool _sprite_group_resolve_check_veh_enable;
+		extern bool _sprite_group_resolve_check_veh_result;
+
 		/* Explicitly choose method to call to prevent vtable dereference -
 		 * it gives ~3% runtime improvements in games with many vehicles */
 		if (update_delta) ((T *)this)->T::UpdateDeltaXY(this->direction);
 		SpriteID old_image = this->cur_image;
-		this->cur_image = ((T *)this)->T::GetImage(this->direction, EIT_ON_MAP);
+		if (this->cur_image_valid_dir != this->direction) {
+			_sprite_group_resolve_check_veh_enable = true;
+			_sprite_group_resolve_check_veh_result = true;
+			this->cur_image = ((T *)this)->T::GetImage(this->direction, EIT_ON_MAP);
+			this->cur_image_valid_dir = _sprite_group_resolve_check_veh_result ? this->direction : INVALID_DIR;
+			_sprite_group_resolve_check_veh_enable = false;
+		}
 		if (force_update || this->cur_image != old_image) this->Vehicle::UpdateViewport(true);
 	}
 };