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.opencode/skills/threejs/references/14-physics-vr.md

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+# Physics & VR/XR
+
+Integrate physics simulations and virtual reality.
+
+## Physics Integration
+
+Three.js doesn't include physics - use external libraries:
+
+### Rapier Physics (Recommended)
+
+Rust-based, high-performance:
+
+```javascript
+import { RapierPhysics } from 'three/addons/physics/RapierPhysics.js';
+
+// Initialize
+const physics = await RapierPhysics();
+
+// Create physics body
+const box = new THREE.Mesh(
+  new THREE.BoxGeometry(),
+  new THREE.MeshStandardMaterial()
+);
+scene.add(box);
+
+// Add physics (mass > 0 = dynamic)
+physics.addMesh(box, 1); // mass = 1
+
+// Static ground
+const ground = new THREE.Mesh(
+  new THREE.BoxGeometry(10, 0.5, 10),
+  new THREE.MeshStandardMaterial()
+);
+ground.position.y = -2;
+scene.add(ground);
+physics.addMesh(ground); // no mass = static
+
+// Update in animation loop
+function animate() {
+  physics.step();
+  renderer.render(scene, camera);
+  requestAnimationFrame(animate);
+}
+```
+
+### Ammo Physics
+
+Port of Bullet physics engine:
+
+```javascript
+import { AmmoPhysics } from 'three/addons/physics/AmmoPhysics.js';
+
+const physics = await AmmoPhysics();
+
+// Same API as Rapier
+physics.addMesh(mesh, mass);
+
+function animate() {
+  physics.step();
+  renderer.render(scene, camera);
+  requestAnimationFrame(animate);
+}
+```
+
+### Jolt Physics
+
+High-performance alternative:
+
+```javascript
+import { JoltPhysics } from 'three/addons/physics/JoltPhysics.js';
+
+const physics = await JoltPhysics();
+physics.addMesh(mesh, mass);
+```
+
+### Physics Constraints
+
+```javascript
+// After initialization
+const physics = await RapierPhysics();
+
+// Point-to-point constraint
+physics.addConstraint(meshA, meshB, 'fixed');
+physics.addConstraint(meshA, meshB, 'spring', { stiffness: 100 });
+
+// Remove constraint
+physics.removeConstraint(constraint);
+```
+
+## VR/XR Setup
+
+### Basic WebXR
+
+```javascript
+import { VRButton } from 'three/addons/webxr/VRButton.js';
+
+// Enable XR
+renderer.xr.enabled = true;
+
+// Add VR button to page
+document.body.appendChild(VRButton.createButton(renderer));
+
+// Animation loop for VR
+renderer.setAnimationLoop(() => {
+  renderer.render(scene, camera);
+});
+
+// Stop using requestAnimationFrame, use setAnimationLoop instead
+```
+
+### AR Mode
+
+```javascript
+import { ARButton } from 'three/addons/webxr/ARButton.js';
+
+renderer.xr.enabled = true;
+document.body.appendChild(ARButton.createButton(renderer));
+
+// AR-specific features
+const session = renderer.xr.getSession();
+session.requestHitTestSource({ space: viewerSpace }).then((hitTestSource) => {
+  // Use hit testing for placing objects
+});
+```
+
+### VR Controllers
+
+```javascript
+// Get controllers
+const controller1 = renderer.xr.getController(0);
+const controller2 = renderer.xr.getController(1);
+
+scene.add(controller1);
+scene.add(controller2);
+
+// Controller events
+controller1.addEventListener('selectstart', () => {
+  console.log('Trigger pressed');
+});
+
+controller1.addEventListener('selectend', () => {
+  console.log('Trigger released');
+});
+
+// Add visual controller models
+import { XRControllerModelFactory } from 'three/addons/webxr/XRControllerModelFactory.js';
+
+const controllerModelFactory = new XRControllerModelFactory();
+
+const grip1 = renderer.xr.getControllerGrip(0);
+grip1.add(controllerModelFactory.createControllerModel(grip1));
+scene.add(grip1);
+
+const grip2 = renderer.xr.getControllerGrip(1);
+grip2.add(controllerModelFactory.createControllerModel(grip2));
+scene.add(grip2);
+```
+
+### Hand Tracking
+
+```javascript
+import { OculusHandModel } from 'three/addons/webxr/OculusHandModel.js';
+
+const hand1 = renderer.xr.getHand(0);
+const handModel1 = new OculusHandModel(hand1);
+hand1.add(handModel1);
+scene.add(hand1);
+
+const hand2 = renderer.xr.getHand(1);
+const handModel2 = new OculusHandModel(hand2);
+hand2.add(handModel2);
+scene.add(hand2);
+```
+
+### Teleportation
+
+```javascript
+const raycaster = new THREE.Raycaster();
+const tempMatrix = new THREE.Matrix4();
+
+function handleController(controller) {
+  const intersections = getIntersections(controller);
+
+  if (intersections.length > 0) {
+    const intersection = intersections[0];
+
+    // Teleport on button release
+    controller.addEventListener('selectend', () => {
+      const offset = intersection.point.y;
+      camera.position.y += offset;
+    });
+  }
+}
+
+function getIntersections(controller) {
+  tempMatrix.identity().extractRotation(controller.matrixWorld);
+  raycaster.ray.origin.setFromMatrixPosition(controller.matrixWorld);
+  raycaster.ray.direction.set(0, 0, -1).applyMatrix4(tempMatrix);
+  return raycaster.intersectObjects(scene.children, true);
+}
+```
+
+### Spatial Audio for VR
+
+```javascript
+const listener = new THREE.AudioListener();
+camera.add(listener);
+
+const sound = new THREE.PositionalAudio(listener);
+const audioLoader = new THREE.AudioLoader();
+
+audioLoader.load('sound.ogg', (buffer) => {
+  sound.setBuffer(buffer);
+  sound.setRefDistance(1);
+  sound.setLoop(true);
+  sound.play();
+});
+
+// Attach to object
+object.add(sound);
+
+// Update listener in VR
+renderer.setAnimationLoop(() => {
+  // Listener automatically updates with camera in VR
+  renderer.render(scene, camera);
+});
+```
+
+### Room-Scale VR
+
+```javascript
+// Request room-scale experience
+navigator.xr.requestSession('immersive-vr', {
+  requiredFeatures: ['local-floor']
+}).then((session) => {
+  // Session setup
+});
+
+// Get play area bounds
+session.requestReferenceSpace('bounded-floor').then((space) => {
+  const bounds = space.boundsGeometry;
+  // Create visual boundary
+});
+```
+
+### Performance Tips for VR
+
+- Target 90 FPS (11.1ms per frame)
+- Use lower polygon counts
+- Reduce shadow quality
+- Limit post-processing
+- Use instancing for repeated objects
+- Enable foveated rendering if available
+- Test on actual VR hardware
+
+```javascript
+// Foveated rendering (Quest 2+)
+const gl = renderer.getContext();
+const ext = gl.getExtension('WEBGL_foveated_rendering');
+if (ext) {
+  ext.foveatedRenderingModeWEBGL(gl.FOVEATED_RENDERING_MODE_ENABLE_WEBGL);
+}
+```
+
+## Mixed Reality (MR)
+
+```javascript
+import { XRButton } from 'three/addons/webxr/XRButton.js';
+
+// Request MR features
+document.body.appendChild(
+  XRButton.createButton(renderer, {
+    requiredFeatures: ['hand-tracking', 'layers'],
+    optionalFeatures: ['local-floor', 'bounded-floor']
+  })
+);
+
+// Passthrough mode (Quest Pro, etc.)
+const session = renderer.xr.getSession();
+const baseLayer = session.renderState.baseLayer;
+baseLayer.compositionDisabled = true; // enable passthrough
+```
+
+## Common VR Patterns
+
+```javascript
+// Detect if in VR
+if (renderer.xr.isPresenting) {
+  // In VR mode
+}
+
+// Get VR camera (for raycasting)
+const vrCamera = renderer.xr.getCamera(camera);
+
+// Different behavior for VR vs desktop
+renderer.setAnimationLoop(() => {
+  if (renderer.xr.isPresenting) {
+    // VR rendering logic
+  } else {
+    // Desktop rendering logic
+  }
+  renderer.render(scene, camera);
+});
+```