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Component has local offset when spawn (located at world 0,0,0)

Development Discussion C++ Gameplay Programming
#1

Hi!

I have created a simple actor in c++ with a scene component as root, a box component and a static mesh component.



        UPROPERTY(EditDefaultsOnly, Category = "Cell")
	USceneComponent* RootCmp;

	UPROPERTY(EditDefaultsOnly, Category = "Cell")
	UBoxComponent* DetectorCmp;

	UPROPERTY(EditDefaultsOnly, Category = "Cell")
	UStaticMeshComponent* CellMesh;

The constructor code is:



	RootCmp = CreateDefaultSubobject<USceneComponent>(TEXT("Root"));	
	SetRootComponent(RootCmp);

	DetectorCmp = CreateDefaultSubobject<UBoxComponent>(TEXT("Detector"));	
	DetectorCmp->AttachToComponent(RootCmp, FAttachmentTransformRules::KeepRelativeTransform);	
	
	CellMesh = CreateDefaultSubobject<UStaticMeshComponent>(TEXT("CellMesh"));
	CellMesh->AttachToComponent(RootCmp, FAttachmentTransformRules::KeepRelativeTransform);

it’s pretty simple but I have an issue… When I spawn my object into the world, the box and static mesh components are located at world 0,0,0 so they have a local offset relative to my root component.

I have tried to set the relative location at 0,0,0 after AttachToComponent line and I have used SetupAttachment instead of AttachToComponent with no success. What’s wrong??

Thanks!

#2

Use SetupAttachment instead of AttachToComponent, if you’re doing this in the constructor. Also, use the ObjectInitializer version of the Constructor. Not doing so nearly always causes headaches or random hard-to-track issues. e.g:



AMyClass::AMyClass(const FObjectInitializer& OI)
: Super(OI)
{
    	RootCmp = OI.CreateDefaultSubobject<USceneComponent>(this, TEXT("Root"));
	SetRootComponent(RootCmp);
}

Are you sure the Root Component isn’t also at world origin?

#3

Had a similar problem…
I would spawn a weapon Actor, and StaticMeshComponent’s relative location would go crazy. I couldn’t get it to reset to 0, and have a gun at socket location. I listened this advice, and it worked like it should. :slight_smile:

Here’s the code:
ExampleWeapon.h


//It is important to use ObjectInitializer version, since RootComponent attachment can get buggy when trying to set it up in the constructor.
    AUrathaWeapon(const FObjectInitializer& OI);

    UPROPERTY(EditDefaultsOnly, Category = "Weapon")
    UBoxComponent* WeaponRoot;

    UPROPERTY(EditDefaultsOnly, BlueprintReadWrite, Category = "Weapon")
    UStaticMeshComponent* WeaponMeshComponent;

ExampleWeapon.cpp


AUrathaWeapon::AUrathaWeapon(const FObjectInitializer& OI) : Super(OI)
{
     // Set this actor to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
    PrimaryActorTick.bCanEverTick = true;

    //This is a recommendable way to create sub object when attachment to RootComponent is buggy (e.g. relative location is screwed).
    WeaponRoot = OI.CreateDefaultSubobject<UBoxComponent>(this, FName("WeaponRoot"));
    SetRootComponent(WeaponRoot);

    WeaponMeshComponent = CreateDefaultSubobject<UStaticMeshComponent>(FName("WeaponMeshComponent"));
    //Use this instead of AttachToComponent when doing this in the constructor. Interestingly enough, AttachToComponent works as intended in Blueprint.
    WeaponMeshComponent->SetupAttachment(WeaponRoot);
}

ExampleCharacter.cpp


if (WeaponBlueprint)
    {
        //UE4 sometimes struggles with passing socket name as TEXT("SocketName"). Using this instead...
        FName SocketName("WeaponSocket");
        FActorSpawnParameters spawnParams;
        spawnParams.Owner = this;

        //Spawn weapon at 0,0,0 with 0,0,0 rotation. A precaution...
        Weapon = GetWorld()->SpawnActor<AUrathaWeapon>(WeaponBlueprint, FVector(0.f, 0.f, 0.f), FRotator(0.f, 0.f, 0.f), spawnParams);
        UE_LOG(LogTemp, Warning, TEXT("Weapon spawned!"));

        //Attach to player's hand. FINALLY WORKING!
        Weapon->AttachToComponent(GetMesh(), FAttachmentTransformRules::SnapToTargetIncludingScale, SocketName);
    }