Can't save Level when using UsdAssetUserData

Development Pipeline & Plugins
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1

Hi there,

Unreal Editor version 5.6.1 can’t save the level when importing a USD with “Metadata Options -> Collect on Components” enabled, then converting an imported Actor to a Blueprint.

Please let us know whether this issue can be resolved and if there is a temporary workaround we can use in the meantime.

Thanks,

Yurii

2

Steps to Reproduce

  1. In a new UE project, use “File -> Import Into Level…” and select a USD document (e.g. Kitchen_set).
  2. When the USD Import Options window pops up, make sure that “Metadata Options -> Collect on Components” is ticked.
  3. Import the document into the level.
  4. Select any resulting Actor in the hierarchy that contains a component with a UsdAssetUserData object in the Asset User Data property.
  5. Convert the actor to a Blueprint (e.g. using the button “Convert this actor into a reusable Blueprint Class that can have script behaviour” in the Details panel).
  6. Try to save the level; it will fail. In the Output Log, you will see an error like:
Warning: Referencers of UsdAssetUserData /Game/Kitchen_1_Blueprint.Kitchen_1_Blueprint_C:Kitchen_0_GEN_VARIABLE.UsdAssetUserData:
LogSavePackage: Warning: StaticMeshComponent /Game/Kitchen_1_Blueprint.Kitchen_1_Blueprint_C:Kitchen_0_GEN_VARIABLE (1 refs)
LogSavePackage: Warning: 0) ObjectProperty /Script/Engine.ActorComponent: AssetUserData.AssetUserData
Warning: Can't save '../../../../../../TestUsdAssetUserData/Content/_ExternalActors_/NewMap1/3/GX/TV26G8O538EKHANW1V3BYG.uasset': Illegal reference to private object: 'UsdAssetUserData /Game/Kitchen_1_Blueprint.Kitchen_1_Blueprint_C:Kitchen_0_GEN_VARIABLE.UsdAssetUserData' referenced by 'Kitchen_0_GEN_VARIABLE' (at '/Game/Kitchen_1_Blueprint.Kitchen_1_Blueprint_C') in its 'AssetUserData' property.
3

I found a workaround for the issue, but I’m not sure if this would be a proper fix for the underlying issue. When, after converting actors to a Blueprint, I re-create `UUsdAssetUserData` in the components using the Blueprint object as an Outer, but not the component object, this fixes the level save error.

Below, I’m sharing a code snippet that fixes the issue. Please let me know if this approach looks valid for you.

void RefineComponents(
	USCS_Node* Node,
	UBlueprint* Blueprint,
	UBlueprintGeneratedClass* BPGC
)
{
	UActorComponent* TemplateComp = Node->GetActualComponentTemplate(BPGC);
	if (!TemplateComp)
	{
		return;
	}
 
	TemplateComp->Modify();
 
	if (TSubclassOf<UUsdAssetUserData> AssetUserDataClass =
		UsdUnreal::ObjectUtils::GetAssetUserDataClassForObject(TemplateComp->GetClass()))
	{
		if (UUsdAssetUserData* OldUserData =
			UsdUnreal::ObjectUtils::GetAssetUserData(TemplateComp, AssetUserDataClass))
		{
			// Clone the UserData to avoid update bugs on the original object
			TemplateComp->Modify();
 
			//UObject* Outer = TemplateComp; // NOTE: this will make the save level to fail
			Object* Outer = Blueprint;                  // NOTE: this will fix the issue
			UUsdAssetUserData* NewUserData = NewObject<UUsdAssetUserData>(
				Outer, AssetUserDataClass, NAME_None, RF_Transactional);
 
			// Copy content
			NewUserData->StageIdentifierToMetadata = OldUserData->StageIdentifierToMetadata;
 
			// Remove old data, add new one
			TemplateComp->RemoveUserDataOfClass(AssetUserDataClass);
			TemplateComp->AddAssetUserData(NewUserData);
 
			TemplateComp->MarkPackageDirty();
		}
	}
 
	for (const TObjectPtr<class USCS_Node>& Child : Node->ChildNodes)
	{
		RefineComponents(Child, Blueprint, BPGC);
	}
}
 
// ...
 
FString BlueprintPath = // TODO: specify
TArray<AActor*> SelectedActors; // TODO: populate
 
// ...
 
// Convert selected Actors to a Blueprint
FKismetEditorUtilities::FHarvestBlueprintFromActorsParams Params;
Params.bReplaceActors = true;
Params.bOpenBlueprint = false;
Params.ParentClass = AActor::StaticClass();
UBlueprint* Blueprint = FKismetEditorUtilities::HarvestBlueprintFromActors(BlueprintPath, SelectedActors, Params);
 
// Apply the bug workaround
UBlueprintGeneratedClass* BPGC = Cast<UBlueprintGeneratedClass>(Blueprint->GeneratedClass);
const TArray<USCS_Node*>& Roots = Blueprint->SimpleConstructionScript->GetRootNodes();
RefineComponents(Roots[0], Blueprint, BPGC);
 
// Mark as modified & compile
FBlueprintEditorUtils::MarkBlueprintAsModified(Blueprint);
FKismetEditorUtilities::CompileBlueprint(Blueprint);
UEditorAssetLibrary::SaveLoadedAsset(Blueprint, false);
4

Unfortunately, the proposed workaround doesn’t satisfy the workflow we are trying to implement. Apart from converting the imported USD Actors into a Blueprint, we also want to be able to duplicate the Blueprint. Currently, it creates a duplicate, but it can’t save it afterwards.

I attached a BlueprintFunctionLibrary that you can use to reproduce the duplication error. The steps will be the following:

  1. Create a new UE project.
  2. Enable plugins: USD Core, USD Importer.
  3. Add the attached Blueprint Library Function into the project. Compile and run it.
  4. In a fresh level, do “File -> Import Into Level…” and import a USD document (e.g. Kitchen_set)
  5. When imported, select any Actor in the Outliner containing a component with a `UsdAssetUserData` object.
  6. Run the `ConvertSelectedActorsToBlueprint()` utility function (e.g. by executing the Python command `unreal.MyBlueprintFunctionLibrary.convert_selected_actors_to_blueprint()`

Result:

The utility function will create a Blueprint out of the selected Actor. Also, it will create a Blueprint duplicate, but it will fail to save the duplicate. In the Output Log, I see the following error:

LogSavePackage: Warning: Referencers of UsdAssetUserData /Game/Test/MyBP.MyBP:UsdAssetUserData_0:
 LogSavePackage: Warning:   SceneComponent /Game/Test/MyBP_Duplicate.MyBP_Duplicate_C:Kitchen_set_0_GEN_VARIABLE (1 refs)
 LogSavePackage: Warning:     0) ObjectProperty /Script/Engine.ActorComponent:AssetUserData.AssetUserData
 Warning: Can't save '../../../../../../Sandbox/UsdAssetUserDataBug/Content/Test/MyBP_Duplicate.uasset': Illegal reference to private object: 'UsdAssetUserData /Game/Test/MyBP.MyBP:UsdAssetUserData_0' referenced by 'Kitchen_set_0_GEN_VARIABLE' (at '/Game/Test/MyBP_Duplicate.MyBP_Duplicate_C') in its 'AssetUserData' property.

If you face any difficulties reproducing the issue, please let me know.

Thanks,

Yurii

5

Thank YYurii,

We are looking into this and will get back with you on it as soon as possible.

6

Hi Yurii,

I think your code snippet is almost correct. When you create the NewUserData, if you pass RF_Transactional | RF_Public, you should be able to save your level as well as duplicate your Blueprint.

Thanks for reporting the issue. We’ll do a fix so you won’t need to do a workaround cloning the user data.

Regards,

Anousack

7

Hi Anousack,

I tested the `RF_Transactional | RF_Public` flag, and it worked. Many thanks for the help!

- Yurii