Function pointerSelection

Controller pointer-selection as an opt-in XrFeatureSpec (Babylon.js POINTER_SELECTION). Pass it to enterXr({ features: [pointerSelection(...)] }) and the session creates the laser/cursor visuals, casts each tracked ray per frame, and disposes everything on exit — no manual onFrame/onEnd wiring.

Requires input tracking (do not pass input: false to enterXr); it needs no native WebXR session feature.