tinyworld-webxr - SKILL.md Agent Skill

name: tinyworld-webxr description: Use when adding or modifying WebXR, AR placement, VR immersion, headset controller input, or XR rendering modes in Tiny World Builder.

Tiny World WebXR

Tiny World uses a pinned global THREE r185 compatibility bundle (vendor/three/tinyworld-three.r185.min.js), not runtime module imports or ARButton/VRButton addons. Keep WebXR integration vanilla and single-file inside tiny-world-builder.html.

Platform split — WebXR covers "Google" AR (Android Chrome / Quest, via immersive-ar + hit-test), but Apple devices have no WebXR. iOS/iPadOS web AR is AR Quick Look only: an <a rel="ar"> pointing at a .usdz opens the system viewer, which finds a surface, places the model, and lets the user walk around it. So both paths must exist for full coverage.

Patterns:

For Apple AR, export the live world to USDZ on demand with THREE.USDZExporter from the r185 global bundle. USDZExporter only understands MeshStandardMaterial, so snapshot worldGroup into a fresh group, convert each Lambert/Basic/Shader material to a Standard equivalent (preserving colour/emissive/map), recentre on the origin with the base at y=0, and scale to a tabletop size. Wrap the resulting Uint8Array in a model/vnd.usdz+zip Blob → object URL, and launch via an <a rel="ar"> that contains a single <img> child (Safari's requirement) clicked programmatically.
Gate the Apple AR button on document.createElement('a').relList.supports('ar'); gate the WebXR buttons on navigator.xr support. Show the XR panel if either is available so iOS users see just the Apple AR button.
Enable WebXR with renderer.xr.enabled = true and drive the main loop with renderer.setAnimationLoop(animate) so desktop and headset frames share one path.
Keep headset transforms on xrWorldRoot, a scene-level parent for board/runtime meshes. Do not scale/move worldGroup alone; hover, selection, clouds, weather, smoke, crop duster, and previews must stay in the same local world space.
Keep controllers/reticles in scene, not xrWorldRoot; they are physical XR-space objects.
For AR desk mode, request immersive-ar with required hit-test, optional anchors, and a domOverlay root. Use the reticle pose to set xrWorldRoot and use anchors when available, but gracefully fall back to the last hit-test pose.
For floating mode, prefer immersive-ar, then fall back to immersive-vr; place the mini board in front of the current XR camera.
For inside mode, use immersive-vr with local-floor and leave xrWorldRoot at meter scale (scale = 1) so one tile is walkable room scale.
When picking tiles from controllers, raycast against worldGroup.children, then convert h.point through xrWorldRoot.worldToLocal() before deriving tile-local offsets. Desktop pointer picking can keep using screen-space raycasts.
Restore scene.background, xrWorldRoot transform/visibility, reticle state, and UI state on XR session end or failure.

Validation:

npm test and the inline script node --check must pass.
Real AR hit-test/VR entry requires HTTPS plus a headset/browser with WebXR support; browser smoke tests can only verify non-XR fallback UI and syntax.