How to get mass of all attached actors

Development World Creation
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1

I creating object from many actors for example, A,B,C,… means actors, and → means attached to. So I have:
A->B->C->D… ->Z and more attached actors, like a chain…
It is possible to get mass of all that actors or number of chained actors?

2

This is video showing my “actors chain”:


And the problem is how to calculate mass for a whole object?

Because when I call CalculateMass() on UPrimitiveComponent it allwayrs return 37 no matter how many blocks attached.

3

The mass of an actor depends on the masses of it’s UPrimitiveComponents. So to calculate the Mass of an actor which could feature a set of components like meshes or whatever you have to get all UPrimitiveComponents:

float ActorsMass = 0;
TArray<UPrimitiveComponent*> comps;
GetComponents(comps);
for (auto Iter = comps.CreateConstIterator(); Iter; ++Iter)
{
    UPrimitiveComponent* comp = Cast<UPrimitiveComponent>(*Iter)
    if (comp)
    {
        ActorsMass += comp->GetMass();
    }
}

Now if you go through your actor chain just compute the mass of all actors. You can also get the mass of a given bone by using UPrimitiveComponent::CalculateMass instead.

Cheers,
Moss

4

Each block is Acator deriver class (AVoxel) and it contais a UStaticMeshComponent as root component.
So each containt UPrimitiveComponent.

5

Is each a UPrimitiveComponent or are all blocks one big UPrimitiveComponent?

6

Yes but I dont know how many actors are connected, for example:
I attach actor B to A, so A have 1 child and B one paren, then I attach C do B, so B have 1 child and 1 parent, and C have 1 parent, in that case in all Actors CalculateMass() will return 37. But I dont know how to find number of connected actors ;]

7

So if you call CalculateMass() each time for each block an accumulate it you should get the mass you want I think. The value of 37 is the mass in KG of each component so if you have X you should get X*37.

8

I will test it tomorrow and give you answer if managed to make it :slight_smile:

9

Ah ok, to get the connected actor to a given actor. If you attache Actors using their components and a socket using AttachTo the new parent will hold a list of children AttachChildren, you then only have to go from the root actor and iterate all its AttachChildren and compute their masses. You can get the root using GetAttachmentRoot to get the root component of the attachment or GetAttachmentRootActor which gives the root. This method is working when using AttachRootComponentToActor which attaches components of different AActors.

If that is not working the AActor class has a list of Children which are the attached actors, if you are SetOwner of course.

10

Cool ^^ I wish you luck! I use ‘AttachRootComponentToActor’ to attach actors to sockets, that way I can just iterate the AttachChildren list recursively.

11

Propably I found solution but not implement it yet:
Can I use float pointer? For example float* TotalMass and share between all actors?

This is how look hierarchy of my actors.
When I attach actors to one branch it can be difficult to attach actors in another branch. So because of that I think about pointers. What you think about it?

http://i.imgur.com/pD3Mui7.png

12

I would rather hold a pointer to the root actor which holds the total-mass value, this way you can add more root-related data without modifying much code.

13

Yes but it is possible to detach root from the rest, so the rest will lost all data. I need to share pointer between all actors. The solution for more data is datastructure shared between actors.

For that should I use normal c++ pointer or UE4 shared pointer?

14

I think you can catch when a object is attached, detached, this way you have to maintain the hierarchy yourself. You can use a shared pointer or just a plain C++ one, but it totally depends on your implementation.

I would recommend holding a reference to the root and handling attaching/detaching.