Ids returned by BodyInterface.CreateAndAddBody appear to be overwritten

[GeorgePetri]

Hello,

I made a repo that reproduces the issue

const executeTest = () => {
  const id = createAndAddBody();
  console.log("id1", id.GetIndex());

  const id2 = createAndAddBody();
  console.log("id2", id2.GetIndex());

  //id 1 changed, it is now the same as id2
  console.log("id1", id.GetIndex());
};

It looks like later invocations of createAndAddBody update previous Ids, this makes it difficult do manage the body Ids in ecs.

Please take a look.

Thanks,
George

[jrouwe]

This is unfortunately a limitation of the way that these bindings are generated (through webidl_binder). Any object that is returned by [Value]:

JoltPhysics.js/JoltJS.idl

Line 1935 in 0a5d19c

[Value] BodyID CreateAndAddBody([Const, Ref] BodyCreationSettings inSettings, EActivation inActivationMode);

will not allocate a new JavaScript object on return but will store the value in a temporary that is valid until the next call to the same function.

You could change your createAndAddBody function to make a copy of id:

  ...

  const id = joltInterface
    .GetPhysicsSystem()
    .GetBodyInterface()
    .CreateAndAddBody(creationSettings, Jolt.EActivation_Activate);

  return new jolt.BodyID(id.GetIndexAndSequenceNumber());

[GeorgePetri]

Thanks for the quick reply.

It's good that this can be worked around, but I do find this unintuitive.

I don't need this anymore as I'm using a body pooling approach, but maybe it's possible to change the code in a way to make the js api more intuitive, so people won't waste time on this in the future.