ECS Lifecycle

1. Constructs a World instance and registers core components/systems: Transform, Visibility, TransformSystem, VisibilitySystem.
2. Creates Three.js objects: Scene, PerspectiveCamera, WebGLRenderer; enables WebXR.
3. Wraps the Scene in an entity (world.sceneEntity) and initializes an activeLevel entity beneath it.
4. Sets up default lighting unless disabled (gradient environment + background).
5. Creates XRInputManager; wires player (XROrigin) and input into the world.
6. Registers core feature systems (always‑on UI, Audio; optional Locomotion/Grabbing) with explicit priorities.
7. Initializes AssetManager.
8. Starts the render loop (renderer.setAnimationLoop): each tick sets visibilityState, runs world.update(delta, time), then renders.
9. If options.xr.offer is ‘once’ or ‘always’, IWSDK offers an XR session after init (and re‑offers on end if ‘always’). Otherwise, call world.launchXR() manually when the user presses your XR button.
10. Preloads assets (if provided) and requests an initial level load via world.loadLevel(url?).

• Systems run on every animation frame in priority order before the scene is rendered.
• Default priorities (negative numbers run earlier): Locomotion (−5), Input (−4), Grabbing (−3). You can pass { priority: number } when registering a system.
• visibilityState is updated each frame from the XR session (or non-immersive).

• init()
  • Subscribe to query qualify/disqualify events.
  • Set up configs (this.config.foo.subscribe(...)).
  • Wire DOM/renderer listeners; enqueue cleanups into this.cleanupFuncs if you create disposables.
• update(delta, time)
  • Iterate your query sets. Use for (const e of this.queries.name.entities).
  • Use .peek() when reading config signals inside tight loops to avoid unnecessary reactivity.
  • Avoid allocations and nested loops in hot paths.
• destroy()
  • Dispose resources and undo listeners. IWSDK calls all cleanupFuncs for you.

• Adding/removing a component on an entity (addComponent / removeComponent) triggers query re‑evaluation for component presence.
• Changing a component value with setValue triggers re‑evaluation for queries whose where: predicates depend on that component.
• getVectorView returns a typed slice; mutating it does NOT trigger re‑evaluation on its own. If a query depends on that field, write back via setValue or mirror a scalar used in predicates.
• Subscribe to membership edges:

this.queries.panels.subscribe('qualify', (e) => {
  /* attach once */
});
this.queries.panels.subscribe('disqualify', (e) => {
  /* cleanup */
});

• createEntity() creates a bare entity (no object3D).
• createTransformEntity(object?, parentOrOptions?) creates an entity with an object3D, injects a Transform, and parents it under the level root or scene based on options.
• entity.destroy() marks the entity inactive, clears its bitmask, resets query membership, and detaches its object3D from the scene.

• If you pass { parent: Entity }, the resulting object3D is added under the parent’s object3D.
• { persistent: true } forces parenting under the scene (survives level swaps).
• Otherwise, entities created during a level load are parented under the active level root; persistent utilities under the scene.

set visibilityState → world.update(delta,time) → renderer.render(scene,camera)

requestAnimationFrame / XRAnimationFrame
  └─ compute delta,time
     ├─ world.visibilityState ← session.visibilityState
     ├─ world.update(delta,time)
     │   ├─ systems @ priority … -5, -4, -3, 0, 1 …
     │   └─ queries keep sets up to date (qualify/disqualify emitted)
     └─ renderer.render(scene,camera)