index.html

<!doctype html>
<html>
<head>
  <meta charset="UTF-8">
  <meta name="viewport"
        content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
  <title>Hit to Place Demo</title>

  <!-- three.js -->
  <script src="https://unpkg.com/three@0.126.0/build/three.js"></script>

  <script src="https://unpkg.com/three@0.126.0/examples/js/loaders/GLTFLoader.js"></script>
</head>
<body>

<!-- Starting an immersive WebXR session requires user interaction.
    We start this one with a simple button. -->
<button onclick="activateXR()">Start Hit to Place Demo</button>
<script>
async function activateXR() {
  // Add a canvas element and initialize a WebGL context that is compatible with WebXR.
  const canvas = document.createElement("canvas");
  document.body.appendChild(canvas);
  const gl = canvas.getContext("webgl", {xrCompatible: true});

  const scene = new THREE.Scene();

  const directionalLight = new THREE.DirectionalLight(0xffffff, 1.0);
  directionalLight.position.set(10, 15, 10);
  scene.add(directionalLight);

// Set up the WebGLRenderer, which handles rendering to the session's base layer.
const renderer = new THREE.WebGLRenderer({
  alpha: true,
  preserveDrawingBuffer: true,
  canvas: canvas,
  context: gl
});
renderer.autoClear = false;

// The API directly updates the camera matrices.
// Disable matrix auto updates so three.js doesn't attempt
// to handle the matrices independently.
const camera = new THREE.PerspectiveCamera();
camera.matrixAutoUpdate = false;

// Initialize a WebXR session using "immersive-ar".
const session = await navigator.xr.requestSession("immersive-ar", {requiredFeatures: ['hit-test']});
session.updateRenderState({
  baseLayer: new XRWebGLLayer(session, gl)
});

// A 'local' reference space has a native origin that is located
// near the viewer's position at the time the session was created.
const referenceSpace = await session.requestReferenceSpace('local');

// Create another XRReferenceSpace that has the viewer as the origin.
const viewerSpace = await session.requestReferenceSpace('viewer');
// Perform hit testing using the viewer as origin.
const hitTestSource = await session.requestHitTestSource({ space: viewerSpace });


const loader = new THREE.GLTFLoader();
let reticle;
loader.load("https://immersive-web.github.io/webxr-samples/media/gltf/reticle/reticle.gltf", function(gltf) {
  reticle = gltf.scene;
  reticle.visible = false;
  scene.add(reticle);
})

let rabbit;
loader.load("https://immersive-web.github.io/webxr-samples/media/gltf/rabbit/scene.gltf", function(gltf) {
  rabbit = gltf.scene;
});

session.addEventListener("select", (event) => {
  if (rabbit) {
    const clone = rabbit.clone();
    clone.position.copy(reticle.position);
    scene.add(clone);
  }
});

// Create a render loop that allows us to draw on the AR view.
const onXRFrame = (time, frame) => {
  // Queue up the next draw request.
  session.requestAnimationFrame(onXRFrame);

  // Bind the graphics framebuffer to the baseLayer's framebuffer
  gl.bindFramebuffer(gl.FRAMEBUFFER, session.renderState.baseLayer.framebuffer)

  // Retrieve the pose of the device.
  // XRFrame.getViewerPose can return null while the session attempts to establish tracking.
  const pose = frame.getViewerPose(referenceSpace);
  if (pose) {
    // In mobile AR, we only have one view.
    const view = pose.views[0];

    const viewport = session.renderState.baseLayer.getViewport(view);
    renderer.setSize(viewport.width, viewport.height)

    // Use the view's transform matrix and projection matrix to configure the THREE.camera.
    camera.matrix.fromArray(view.transform.matrix)
    camera.projectionMatrix.fromArray(view.projectionMatrix);
    camera.updateMatrixWorld(true);

    const hitTestResults = frame.getHitTestResults(hitTestSource);
    if (hitTestResults.length > 0 && reticle) {
      const hitPose = hitTestResults[0].getPose(referenceSpace);
      reticle.visible = true;
      reticle.position.set(hitPose.transform.position.x, hitPose.transform.position.y, hitPose.transform.position.z)
      reticle.updateMatrixWorld(true);
    }