Can Nested Struct Properties like FTransform be edited by ValuePtr?

Development Programming & Scripting C++
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1

Lets say I have an FTransform UProperty on a Uobject.

Let’s also say I want to be able to find the property by name and change just the X value of the Translation struct within the FTransform.

I already know it’s possible to change a struct such as an FVector that is a top level UProperty on a UObject like so

UObject* Target;  //Lets assume this is a valid UObject
FStructProperty* CurrentStruct = FindFProperty<FStructProperty>(Target->GetClass(), TEXT("X"));
	if (!CurrentStruct)
	{
		return false;
	}

	void* StructAddr = CurrentStruct->ContainerPtrToValuePtr<void>(Target);

	FProperty* NestedProp = CurrentStruct->Struct->FindPropertyByName(TEXT("X"));
	if(!NestedProp)
	{
		return false;
	}
	FFloatProperty* NestedFloatProp = CastField<FFloatProperty>(NestedProp);
	if(!NestedFloatProp)
	{
		return false;
	}
	void* ValueAddr = NestedFloatProp->ContainerPtrToValuePtr<void>(StructAddr);
	//void* ValueAddr = (uint8*)StructAddr + NestedFloatProp->GetOffset_ForInternal(); 
	NestedFloatProp->SetFloatingPointPropertyValue(ValueAddr, InValue);

This works because the outer of FVector is a Uobject*

In the case of FTransform - the outer is only a valid UObject* for the FTransform and not the struct within it called Translation.

Is it possible change a single property by name - that is nested within a struct, such that its Outer’s is not a UObject?

2

Using the Property system, you’d need to get the value, change it, and then set it again. This is similar to how Blueprint needs a “break structure” node to update a struct property.

That being said – you’re in C++. You can define an interface or object base class that has a property you can access as a C++ object, rather than through the property system. Get pointer to containing object, update field.X, done! It’ll also run a lot faster than going through properties.

1 Like
3

Thanks for the reply. I’m trying to leverage the property system so I can dynamically find the exposed values of a UClass - and link them to data coming from a network interface that isn’t compatible with Remote Control plugin from Epic.

As you said a static approach using just c++ ptr to a UObject is much faster but it doesn’t offer the flexibility I’m looking for. With the property system I can find all the exposed UProperties dynamically on any UObject. Is there a better way to dynamically link something like incoming network data to a UProperty?

To be clear - I’m creating a user defined linkage, which is why finding and settings the property by name needs to be dynamic in some way. I’ll have to be able to query a UObject for all it’s exposed properties.

All I’ve been able to find so far is leveraging the property system, but thats straying away from the original question.

4

If you’re doing something like receiving DIS PDU packets, and trying to render objects in the world, then there are several better options.

First, Actors have a known location/orientation. Instead of using UObject, you could say that anything driven by your incoming packets is an AActor, which lets you use direct pointers.

Second, you could implement a custom interface, and query for that interface, and then send whatever update you need through that interface. Something like IUpdateReceiver and have it have a ReceiveUpdatePacket method, if the structure of the packet is known.

That being said – if the abstraction penalty isn’t a big problem for you, that is indeed a very decoupled approach. In that case, get the struct value, update the value, and set the struct value again.

1 Like
5

Thanks for your insight. There might be some combination of an Interface and a known message structure that could work for all the knowns - but can always default on the property system if it has to. This was very fast very excellent information. I’ll mark it as resolved as soon as I can get it working.

Thank you!