VIVE HMD Lag When 'Lock To HMD' is Set to Off in 4.20.

[anonymous_user_98092ca1]

I had the same problem, btw it’s not exclusive to VIVE, starting from 4.20 unticking bLockToHmd disables LateUpdate which introduces a noticeable lag. The best workaround over this is to create a new class that inherits ‘UCameraComponent’ and override ‘GetCameraView’ function with this code:

void UCameraComponent::GetCameraView(float DeltaTime, FMinimalViewInfo& DesiredView)
{
	if (GEngine && GEngine->XRSystem.IsValid() && GetWorld() && GetWorld()->WorldType != EWorldType::Editor )
	{
		IXRTrackingSystem* XRSystem = GEngine->XRSystem.Get();
		auto XRCamera = XRSystem->GetXRCamera();

		if (XRCamera.IsValid())
		{
			if (XRSystem->IsHeadTrackingAllowed())
			{
				const FTransform ParentWorld = CalcNewComponentToWorld(FTransform());

				if (bLockToHmd)
				{
					XRCamera->SetupLateUpdate(ParentWorld, this, false);

					FQuat Orientation;
					FVector Position;
					if (XRCamera->UpdatePlayerCamera(Orientation, Position))
					{
						SetRelativeTransform(FTransform(Orientation, Position));
					}
					else
					{
						ResetRelativeTransform();
					}
				}

				XRCamera->OverrideFOV(this->FieldOfView);
			}
		}
	}

	if (bUsePawnControlRotation)
	{
		const APawn* OwningPawn = Cast<APawn>(GetOwner());
		const AController* OwningController = OwningPawn ? OwningPawn->GetController() : nullptr;
		if (OwningController && OwningController->IsLocalPlayerController())
		{
			const FRotator PawnViewRotation = OwningPawn->GetViewRotation();
			if (!PawnViewRotation.Equals(GetComponentRotation()))
			{
				SetWorldRotation(PawnViewRotation);
			}
		}
	}

	if (bUseAdditiveOffset)
	{
		FTransform OffsetCamToBaseCam = AdditiveOffset;
		FTransform BaseCamToWorld = GetComponentToWorld();
		FTransform OffsetCamToWorld = OffsetCamToBaseCam * BaseCamToWorld;

		DesiredView.Location = OffsetCamToWorld.GetLocation();
		DesiredView.Rotation = OffsetCamToWorld.Rotator();
	}
	else
	{
		DesiredView.Location = GetComponentLocation();
		DesiredView.Rotation = GetComponentRotation();
	}

	DesiredView.FOV = bUseAdditiveOffset ? (FieldOfView + AdditiveFOVOffset) : FieldOfView;
	DesiredView.AspectRatio = AspectRatio;
	DesiredView.bConstrainAspectRatio = bConstrainAspectRatio;
	DesiredView.bUseFieldOfViewForLOD = bUseFieldOfViewForLOD;
	DesiredView.ProjectionMode = ProjectionMode;
	DesiredView.OrthoWidth = OrthoWidth;
	DesiredView.OrthoNearClipPlane = OrthoNearClipPlane;
	DesiredView.OrthoFarClipPlane = OrthoFarClipPlane;

	// See if the CameraActor wants to override the PostProcess settings used.
	DesiredView.PostProcessBlendWeight = PostProcessBlendWeight;
	if (PostProcessBlendWeight > 0.0f)
	{
		DesiredView.PostProcessSettings = PostProcessSettings;
	}
}