Update vehicle image on demand when image is continuously updated by GRF

This is for trains/RVs only (to avoid issues with variable sprite bounds)

This largely fixes the performance issues of continuously updating
vehicle images

src/table/settings.ini

@@ -5033,7 +5033,7 @@ def      = false
 str      = STR_CONFIG_SETTING_DISABLE_VEHICLE_IMAGE_UPDATE
 strhelp  = STR_CONFIG_SETTING_DISABLE_VEHICLE_IMAGE_UPDATE_HELPTEXT
 proc     = InvalidateAllVehicleImageCaches
-cat      = SC_ADVANCED
+cat      = SC_EXPERT
 
 ; For the dedicated build we'll enable dates in logs by default.
 [SDTC_BOOL]

src/vehicle.cpp

@@ -1542,6 +1542,17 @@ static void DoDrawVehicle(const Vehicle *v)
 		if (to != TO_INVALID && (IsTransparencySet(to) || IsInvisibilitySet(to))) return;
 	}
 
+	{
+		Vehicle *v_mutable = const_cast<Vehicle *>(v);
+		if (HasBit(v_mutable->vcache.cached_veh_flags, VCF_IMAGE_REFRESH) && v_mutable->cur_image_valid_dir != INVALID_DIR) {
+			VehicleSpriteSeq seq;
+			v_mutable->GetImage(v_mutable->cur_image_valid_dir, EIT_ON_MAP, &seq);
+			v_mutable->sprite_seq = seq;
+			v_mutable->UpdateSpriteSeqBound();
+			ClrBit(v_mutable->vcache.cached_veh_flags, VCF_IMAGE_REFRESH);
+		}
+	}
+
 	StartSpriteCombine();
 	for (uint i = 0; i < v->sprite_seq.count; ++i) {
 		PaletteID pal2 = v->sprite_seq.seq[i].pal;
@@ -3787,6 +3798,8 @@ char *Vehicle::DumpVehicleFlags(char *b, const char *last, bool include_tile) co
 	dump('d', HasBit(this->vcache.cached_veh_flags, VCF_IS_DRAWN));
 	dump('t', HasBit(this->vcache.cached_veh_flags, VCF_REDRAW_ON_TRIGGER));
 	dump('s', HasBit(this->vcache.cached_veh_flags, VCF_REDRAW_ON_SPEED_CHANGE));
+	dump('R', HasBit(this->vcache.cached_veh_flags, VCF_IMAGE_REFRESH));
+	dump('N', HasBit(this->vcache.cached_veh_flags, VCF_IMAGE_REFRESH_NEXT));
 	if (this->IsGroundVehicle()) {
 		uint16 gv_flags = this->GetGroundVehicleFlags();
 		b += seprintf(b, last, ", gvf:");

src/vehicle_base.h

@@ -140,6 +140,8 @@ enum VehicleCacheFlags {
 	VCF_IS_DRAWN                = 2, ///< Vehicle is currently drawn
 	VCF_REDRAW_ON_TRIGGER       = 3, ///< Clear cur_image_valid_dir on changes to waiting_triggers (valid only for the first engine)
 	VCF_REDRAW_ON_SPEED_CHANGE  = 4, ///< Clear cur_image_valid_dir on changes to cur_speed (ground vehicles) or aircraft movement state (aircraft) (valid only for the first engine)
+	VCF_IMAGE_REFRESH           = 5, ///< Image should be refreshed before drawing
+	VCF_IMAGE_REFRESH_NEXT      = 6, ///< Set VCF_IMAGE_REFRESH in next UpdateViewport call, if the image is not updated there
 };
 
 /** Cached often queried values common to all vehicles. */
@@ -1280,17 +1282,28 @@ struct SpecializedVehicle : public Vehicle {
 			_sprite_group_resolve_check_veh_check = true;
 			VehicleSpriteSeq seq;
 			((T *)this)->T::GetImage(current_direction, EIT_ON_MAP, &seq);
+			if (EXPECTED_TYPE == VEH_TRAIN || EXPECTED_TYPE == VEH_ROAD) {
+				ClrBit(this->vcache.cached_veh_flags, VCF_IMAGE_REFRESH);
+				SB(this->vcache.cached_veh_flags, VCF_IMAGE_REFRESH_NEXT, 1, (_sprite_group_resolve_check_veh_check || _settings_client.gui.disable_vehicle_image_update) ? 0 : 1);
+				this->cur_image_valid_dir = current_direction;
+			} else {
 				this->cur_image_valid_dir = (_sprite_group_resolve_check_veh_check || _settings_client.gui.disable_vehicle_image_update) ? current_direction : INVALID_DIR;
+			}
 			_sprite_group_resolve_check_veh_check = false;
 			if (force_update || this->sprite_seq != seq) {
 				this->sprite_seq = seq;
 				this->UpdateSpriteSeqBound();
 				this->Vehicle::UpdateViewport(true);
 			}
-		} else if (force_update) {
+		} else {
+			if ((EXPECTED_TYPE == VEH_TRAIN || EXPECTED_TYPE == VEH_ROAD) && HasBit(this->vcache.cached_veh_flags, VCF_IMAGE_REFRESH_NEXT)) {
+				SetBit(this->vcache.cached_veh_flags, VCF_IMAGE_REFRESH);
+			}
+			if (force_update) {
 				this->Vehicle::UpdateViewport(true);
 			}
 		}
+	}
 
 	/**
 	 * Returns an iterable ensemble of all valid vehicles of type T