Why is this laggy in C++ but not in BP?

Development Programming & Scripting
1

Hi there,

I am wondering about the performance of a code snipped that I have in C++ vs BP. I use it to change the location of an actor when the mouse moves along the y axis.

In my Level BP this looks like the following:

26786-z_movement_bp.jpg
26786-z_movement_bp.jpg1669×285 54.3 KB

and in C++ the code in my PlayerController class is:

void AConfiguratorPlayerController::MouseY(float val)
{ 
	if (abs(val) > 0.f)
	{
		TArray<AActor*> OutActors;
		UGameplayStatics::GetAllActorsOfClass(this, ABodyActorModel::StaticClass(), OutActors);

		FVector currentLocation = OutActors[0]->GetActorLocation();
		FVector newLocation = currentLocation;
		newLocation.Z = FMath::Clamp((currentLocation.Z + val), 100.f, 140.f);
		OutActors[0]->SetActorLocation(newLocation);
	}
}

I know that the function GetAllActorsOfClass ([defined here][2]) is rather slow but besides that, the outcome is different in BP and C++.
When I use the BP implementation, setting the actor location is very smooth and the actor moves with the mouse up and down. When using the C++ implementation, changing the location is not smooth but lags a bit and sometimes stops.

Am I missing something here? I wanted to implement everything in C++ so that I do not have to expose variables and stuff.

2

Well the big difference between the two is that the C++ is looping over every actor returned by GetAllActorsOfClass and the BP version only does the first element. So perhaps there are more being returned on the C++ side than you think there should be. I’d change either the BP to have the same forloop or remove the loop from the C++ side and see if you don’t get the same behavior both places after that.

3

The function which is called on the BP node is defined here. Using exactly this code in C++ (updated my question) does not result in any improvements.

4

And what about the for loop? Did you take that out of the C++ version?

5

Updated my question/code again. Now I am completely using the same BP node code in C++ but still BP is smooth and C++ not.

In the previous version I did not take out the foor loop in C++ because the foor loop is present in the BP version.

6

Technically the abs() call in your C++ code should be fabs() but I can’t see that making any diff in performance. I would guess that perhaps you have some other differences between the two environments outside of this one particular function.