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aframe

hand-controls doesn't render children of children entities attached programmatically (AFRAME 1.6.0)

For context, I'm trying to simulate a player grabbing a virtual object with their VR hand controller by attaching the object's entity as a child of the entity with a hand-controls component.

I'm running into an issue with a hand-controls entity not rendering the children of its children entities in AFRAME version: 1.6.0

Several levels of <a-entities> declared directly in the DOM render properly. For example, this will write 'foo bar' on the back of the hand model:

<a-entity hand-controls="hand: left; ...">
  <a-text value="foo" position="-0.028 0.05 0" rotation="185 90 0">
    <a-text value="bar" position="0.03 0 0"></a-text>
  </a-text>
</a-entity>

Where things go pear-shaped is when I attempt to do this programmatically, by detaching a group of entities from the scene and reattaching them to the hand-controls entity:

index.html:
<a-box id="foo" color="red" position="1 2 -3" width...>
  <a-box id="bar" color="yellow" position="-0.5 0 -1"></a-box>
</a-box>
<a-entity hand-controls="hand: left; ..."></a-entity>

some system or component JS file:
  foo = document.querySelector('#foo');
  foo.removeFromParent();
  // foo had a world position, resetting it so it's local to the hand controller's origin (otherwise it will render far from the hand model rather than in its palm)
  foo.setAttribute('position', '0 0 0');
  document.querySelector('[hand-controls]').appendChild(foo);

This will put the #foo box in the hand model, but the nested #bar box isn't rendered at all.

I just don't understand why that is, or what transformation/step I'm missing to make all the hierarchy of nested children render. Any help/insights appreciated.

Solution

  • TL;DR: re-parenting is not supported in AFRAME (see https://github.com/aframevr/aframe/issues/2425)

    2 workarounds:

    • copy the hand controller's position and rotation to the grabbed entity (with caveat that hand model is artificially rotated 90deg downward by AFRAME, so the grabbed object need to be wrapped in an entity countering that extra rotation)
    • leave the grabbed entity where it is in the DOM, but add it as a child of the hand controller's THREEJS Object3D ( bypassing AFRAME and breaking the sync between AFRAME and THREE.JS object hierarchies, which could cause issues down the road)