three.js glTF Loading

Load .gltf/.glb models and play their animations in three.js, including compressed geometry (DRACO/Meshopt) and textures (KTX2). Patterns target r186; preserve an existing project's pinned release unless migration is requested.

When to use

• Use to import a 3D model, add it to the scene, inspect its node hierarchy, and play baked/skinned animation clips with an AnimationMixer.
• Use when files are .gltf/.glb, or code imports GLTFLoader / DRACOLoader / KTX2Loader from three/addons/loaders/....

When not to use: creating the renderer/camera/loop → threejs-scene-setup. Tuning surface look, lights, or shadows on the loaded model → threejs-materials-lighting. Authoring/exporting the model itself (Blender) is out of scope; prefer glTF over OBJ/FBX for runtime.

Core workflow

1. Why glTF. It's a transmission format: binary vertex data, PBR materials, and animations are ready to render with minimal parsing. Prefer it over OBJ (no scene graph, no animation) and FBX (heavy) for the web.
2. Load with GLTFLoader. loader.load(url, onLoad, onProgress, onError). The result gltf has gltf.scene (the Object3D root), gltf.animations (AnimationClip[]), gltf.cameras, and gltf.asset.
3. Add gltf.scene to your scene and frame it. Inspect the hierarchy with traverse / getObjectByName to find the parts you'll control.
4. Play animations with an AnimationMixer. One mixer per animated root; mixer.clipAction(clip).play(); advance with mixer.update(delta) every frame.
5. Decode compressed assets. Attach a DRACOLoader, a KTX2Loader, and/or the Meshopt decoder so DRACO meshes, KTX2 textures, and meshopt-compressed buffers load. Since r185 the DRACO and KTX2 loaders find their bundled decoder files on their own.
6. Validate changed glTF files when the project already has the tool. Run gltf-transform validate path/to/model.glb for each changed .gltf or .glb; fix reported errors before loading.
7. Verify what loaded — log the scene graph and gltf.animations, and confirm the model is visible (right scale, lit) and the clip actually plays.

Patterns

1. Load a model and frame it

import { GLTFLoader } from 'three/addons/loaders/GLTFLoader.js';

const loader = new GLTFLoader();
loader.load(
  'assets/robot.glb',
  (gltf) => {
    const root = gltf.scene;
    scene.add(root);
    // Inspect: gltf.animations is an array of AnimationClip.
    console.log('clips:', gltf.animations.map((c) => c.name));
  },
  (event) => {
    // total is 0 when the server sends no Content-Length (e.g. compressed responses)
    if (event.total) console.log(`${(event.loaded / event.total) * 100}% loaded`);
  },
  (error) => console.error('glTF load failed:', error)
);

2. Play a skinned animation with AnimationMixer

import * as THREE from 'three';
import { GLTFLoader } from 'three/addons/loaders/GLTFLoader.js';

let mixer;                                  // declare outside so the loop can see it
const timer = new THREE.Timer();            // THREE.Clock is deprecated since r183

new GLTFLoader().load('assets/character.glb', (gltf) => {
  scene.add(gltf.scene);
  mixer = new THREE.AnimationMixer(gltf.scene);          // one mixer per animated root
  const clip = THREE.AnimationClip.findByName(gltf.animations, 'Run')
            ?? gltf.animations[0];
  mixer.clipAction(clip).play();
});

renderer.setAnimationLoop((time) => {
  timer.update(time);
  const dt = timer.getDelta();
  if (mixer) mixer.update(dt);              // advance the animation by real seconds
  renderer.render(scene, camera);
});

3. Cross-fade between two clips

const actions = {};
mixer = new THREE.AnimationMixer(gltf.scene);
for (const clip of gltf.animations) {
  actions[clip.name] = mixer.clipAction(clip);
}
let current = actions['Idle'];
current.play();

function transitionTo(name, duration = 0.3) {
  const next = actions[name];
  if (!next || next === current) return;
  next.reset().play();                      // rewind and clear any old fade
  current.crossFadeTo(next, duration, false); // fade the old one out, new one in
  current = next;
}

4. DRACO-compressed geometry

import { GLTFLoader } from 'three/addons/loaders/GLTFLoader.js';
import { DRACOLoader, DRACO_GLTF_CONFIG } from 'three/addons/loaders/DRACOLoader.js';

// r185+: DRACOLoader finds the decoder that ships next to it in
// three/examples/jsm/libs/draco/, so no path is required. DRACO_GLTF_CONFIG
// (also r185+) selects the smaller glTF-only WASM build in libs/draco/gltf/.
const draco = new DRACOLoader().setDecoderPath(DRACO_GLTF_CONFIG);

On releases before r185, or when your host does not serve those files, pass a
folder instead: `draco.setDecoderPath('/decoders/draco/')` with the files copied
from the same `three` version.

### 5. Find and animate a named part

```js
const timer = new THREE.Timer();

new GLTFLoader().load('assets/car.glb', (gltf) => {
  scene.add(gltf.scene);
  const wheels = [];
  gltf.scene.traverse((node) => {
    if (node.name.startsWith('Wheel')) wheels.push(node);
  });
  renderer.setAnimationLoop((time) => {
    timer.update(time);
    const dt = timer.getDelta();
    for (const w of wheels) w.rotation.x += dt * 4;
    renderer.render(scene, camera);
  });
});