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);

const loader = new GLTFLoader();
loader.setDRACOLoader(draco);              // share one DRACOLoader across loads
loader.load('assets/city-draco.glb', (gltf) => scene.add(gltf.scene));

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

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);
  });
});

Pitfalls

• Model loads but is invisible → it has lit (PBR) materials and the scene has no light or environment. Add a light or scene.environment (see threejs-materials-lighting), and check scale — glTF is in metres, so a 0.01-scaled asset is tiny.
• load is async → gltf only exists inside the callback; declare mixer/refs outside and assign them in the callback, or use await loader.loadAsync(url).
• Animation never moves → you didn't call mixer.update(delta) each frame, or you passed milliseconds instead of seconds (use timer.getDelta() after timer.update(time)), or you forgot action.play().
• DRACO/KTX2 model fails, or the network tab shows a 404 for draco_*/basis_* files → the decoder/transcoder files are not being served, or come from a different three.js version. Since r185 the loaders default to the copies inside three/examples/jsm/libs/; if your bundler or host doesn't serve those, copy the folders from the installed three and point setDecoderPath/setTranscoderPath at them.
• setKTX2Loader must be called before loading KTX2 textures or setMeshoptDecoder must be called before loading compressed files → the asset uses KHR_texture_basisu or meshopt compression (EXT_/KHR_meshopt_compression); attach the missing decoder (see the reference).
• Multiple mixers fighting → use one AnimationMixer per animated root and create all actions from it; don't make a new mixer per clip.
• Baked-in transforms surprise you → exporters sometimes bake scale/rotation onto child nodes. Dump the hierarchy (names + position/rotation/scale) before relying on a node's local transform; re-export from the source if the rig is unusable.
• Origins are off → re-parent a part under a fresh Object3D to give it a clean pivot rather than fighting baked offsets.

References

• For the full decode/transcode setup (DRACO + Meshopt + KTX2 together), loadAsync
  • a LoadingManager progress bar, reusing models with SkeletonUtils.clone, and exporter guidance (apply transforms, one clean root), read references/loaders-and-animation.md.

Related skills

• threejs-scene-setup — the renderer, camera, and loop this model renders into.
• threejs-materials-lighting — lighting/environment so PBR models look right.
• fps-shooter — a 3D genre that composes three.js skills.