Add interpolation to bitECS network transform.

[takahirox]

This PR adds easy linear interpolation to bitECS network transform.

Changes

• Add LinearTranslate/Rotate/Scale components
• Add linearTransform system to handle the added components
• network-transform sets the component when receiving data from remote
• Move millisecondsBetweenTicks from network-send-system to networking because it is referred from two places

[keianhzo]

We can probably remove the TODO at the end of this file

[takahirox]

Good catch, updated. Thanks

[keianhzo]

Mayeb it would be more consistent to name this targetX/Y/Z?

[takahirox]

No strong preference about it. Updated, thanks.

[keianhzo]

Feels a bit strange that we are removing the component inside it's own query. Wouldn't it make more sense to remove it in networked-transform.ts?

      tmpVec.fromArray(NetworkedTransform.position[eid]);
      if (!tmpVec.near(obj.position)) {
        addComponent(world, LinearTranslate, eid);
        LinearTranslate.duration[eid] = millisecondsBetweenTicks;
        LinearTranslate.destinationX[eid] = tmpVec.x;
        LinearTranslate.destinationY[eid] = tmpVec.y;
        LinearTranslate.destinationZ[eid] = tmpVec.z;
      } else {
        removeComponent(world, LinearTranslate, eid);
      }

and let this system do just what is responsible for, interpolating:

linearTranslateQuery(world).forEach(eid => {
    const duration = LinearTranslate.duration[eid];
    const destX = LinearTranslate.destinationX[eid];
    const destY = LinearTranslate.destinationY[eid];
    const destZ = LinearTranslate.destinationZ[eid];

    const deltaTime = world.time.delta;
    const obj = world.eid2obj.get(eid)!;

    obj.position.lerp(_vec3.set(destX, destY, destZ), deltaTime / duration);
    LinearTranslate.duration[eid] = duration - deltaTime;
    obj.matrixNeedsUpdate = true;
  });

[takahirox]

I don't think it is so strange to remove a component inside a query especially if it does operations across ticks and finishes at specified time or event. MediaLoader does it, too.

And LinearTranslate/Rotate/Scale and their system are designed as common components and systems that linearly (against time) update object's transform to target values using the specified duration time. I think removing component in that system is natural and makes them decoupled from other components and systems.

But if removing a component in its query can cause a bug in certain scenarios, we may need to revisit and write it in the internal design document. Would you please share if you have?