xb-hands

name: xb-hands description: >- Add WebXR hand tracking to an XR Blocks app — enable hand joints, optional joint and mesh visualizations, pinch-to-select, and direct touch/grab of meshes. Use when you need the user's hands (index-finger touch, grab, wrist/joint positions) rather than just controller rays, or want to visualize hands in the simulator's pose mode. Covers enableHands(), the options.hands.* flags, xb.user.hands (getIndexTip, getWrist), and the object touch/grab lifecycle hooks. For named gestures (fist, point, spread…) use xb-gestures.

xb-hands: hand tracking

Setup

const options = new xb.Options();
options.enableReticles();
options.enableHands();

options.hands.enabled = true;
options.hands.visualization = true; // render hands
options.hands.visualizeJoints = true; // show joint spheres
options.hands.visualizeMeshes = true; // show hand meshes

// Develop hands on desktop: simulator pose mode.
options.simulator.defaultMode = xb.SimulatorMode.POSE;
xb.init(options);

Reacting to hands

xb.user drives direct interaction. Pinch maps to select, so onSelectStart/End already covers "pinch". For direct touch and grab of meshes in the scene, use the object-targeted hooks on your Script (return true to stop propagation):

class Grabbable extends xb.Script {
  init() {
    this.box = new THREE.Mesh(/* … */);
    this.add(this.box);
  }
  onObjectTouchStart(e) {
    // index fingertip entered a mesh's bounds
    // e.handIndex (0|1), e.touchPosition: THREE.Vector3
  }
  onObjectGrabStart(e) {
    // touching + pinching
    // e.handIndex, e.hand: THREE.Object3D (the wrist)
  }
  onObjectGrabbing(e) {}
  onObjectGrabEnd(e) {}
}

Reading joints directly

const hands = xb.user.hands; // present once enableHands() + tracking
if (hands) {
  const tip = hands.getIndexTip(0); // index fingertip of hand 0 (THREE.Object3D)
  const wrist = hands.getWrist(1);
  if (tip) tip.getWorldPosition(this._v3);
}
xb.user.isSelecting(0); // is hand 0 pinching?

Notes

• numHands is 2; hand index 0/1. xb.user.handedness (0 left, 1 right, 2 both).
• Joint name constants are exported (HandJointNames).
• Touch detection uses each mesh's bounding box vs. the index fingertip; grab = touch + pinch. See src/core/User.ts for exact semantics.
• See templates/2_hands for a complete example.