Consider stricter lifecycle guarantees

Got bit recently with an unexpected issue writing a component, thought I'd write it up for ideas...

The nav-mesh component needs the mesh from the entity it's attached to, and needs to account for transformations on its parents. I'd imagined this would be simple enough:

AFRAME.registerComponent('nav-mesh', {
  init: function () {
    this.loadNavMesh();
    this.el.addEventListener('object3dset', () => this.loadNavMesh());
  },

  loadNavMesh: function () {
    const navMesh = this.el.getObject3D('mesh');

    if (!navMesh) return;

    const navMeshGeometry = navMesh.geometry.isBufferGeometry
      ? new THREE.Geometry().fromBufferGeometry(navMesh.geometry)
      : navMesh.geometry.clone();

    scene.updateMatrixWorld();
    navMeshGeometry.applyMatrix(navMesh.matrixWorld);
    this.system.setNavMeshGeometry(navMeshGeometry);
  }
});

Unfortunately this fails — when init runs, the entity's parents do not have their position/rotation/scale applied yet, so scene.updateMatrixWorld() does nothing, and the transformation isn't applied to the Geometry.

Next I assumed update() would be a safe place to put the loadNavMesh() call, but it too runs before parents are initialized. I don't want this code to run on play (it shouldn't reload when the scene pauses) so instead I ended up with:

tick: function (t) {
  if (t === 0) this.loadNavMesh();
}

Anyway, all of this was a little more complicated than I expected, and harder than component lifecycles in e.g. Angular. Saw this issue (or similar) called out as a pain point compared to Unity recently, too:

Have to wrestle with asynchronicity issues that you generally don’t run into with Unity (e.g. why is this model loading BEFORE something else it is dependent on …)

Anyway, I don't have a concrete proposal at the moment but wanted to think about tightening up component lifecycles in a future version and documenting clearly what component authors should expect.

Start by reviewing the init, update, play, and tick lifecycle entry points described in the issue, then reproduce the nav-mesh timing case with the shown object3dset listener and THREE geometry path. Done should be a concrete lifecycle guarantee or clearly documented expectation for component authors, supported by an agreed proposal.