FTransform not moving the actor?

Development Programming & Scripting C++
1

Hi there,

I just started out using Unreal (coming from Unity), and i’m having troubles understanding the FTransform of an AActor (new class inherited from UActorComponent).

I tried to set the Translation/Rotation of the Object in the Scene like that:
GetOwner()->GetActorTransform().SetTranslation(FVector(0, 0, 0));

According to the documentation, this should set new values for the translation component, but for some reason, it doesnt change anything. Yet, calling this returns the correct values:
GetOwner()->GetActorTransform().GetTranslation();

This seems to work:
GetOwner()->SetActorLocation(FVector(0, 0, 0));

Why can’t i manipulate the Transform directly?

Thanks upfront!

2

Because it’s a const reference (FTransform const& or equivalently const FTransform &). I’m surprised that you said

because that code should result in a compilation error, since *FTransform::SetTranslation *is a non-const method.

From Actor.h:



class ENGINE_API AActor : public UObject
{

...

    /** Returns the transform of the RootComponent of this Actor*/
    FORCEINLINE const FTransform& GetActorTransform() const
    {
        return TemplateGetActorTransform(RootComponent);
    }
3

Hmm… thats interesting. Perhaps i should mention, that i’m using UE v4.21.2 of the editor. On my end, the function in Actor.h looks like this (not returning a const reference - thus probably no compiler error):


  
    /** Returns the transform of the RootComponent of this Actor*/
    FORCEINLINE FTransform GetActorTransform() const
    {
        return TemplateGetActorTransform(RootComponent);
    }

Perhaps this was changed in a recent update?
Either way, in my current version its returning a “struct FTransform”, that seems to hold the correct values…

I know i should probably update to the newest version, but i thought it would be odd, if something as fundamental as this function wasn’t working as intended up until recent updates…

I guess the only explanaition would be that the function returns a new FTransform instance (a clone of the searched FTransform), instead of the actual “ActorTransform”?

4

Yes, that would return the FTransform struct by value, so any change you make to it only affects the temporary copy, not the one the actor is using.

5

Yeah you can’t modify a transform in-place like that, you need to call SetActorTransform() and provide a new transform, which will set the transform of the root component and update all child components too.