Face Tracking

Face Tracking detects and tracks the user's face. With Zappars Face Tracking library you can attach 3D objects to the face itself, or render a 3D mesh that fits to, and deforms with, the face as the user moves and changes their expression. You could build face-filter experiences to allow users to try on different virtual sunglasses, for example, or to simulate face paint.

Before setting up face tracking, you must first add or replace any existing camera you have in your scene. Find out more here.

To place content on or around a user's face, create a new FaceTracker object when your page loads:

let faceTracker = new ZapparThree.FaceTracker();


Model File

The face tracking algorithm requires a model file of data in order to operate - you can call loadDefaultModel() to load the one that's included by default with the library. The function returns a promise that resolves when the model has been loaded successfully.

let faceTracker = new ZapparThree.FaceTracker();
faceTracker.loadDefaultModel().then(() => {
    // The model has been loaded successfully
});

Alternatively the library provides a THREE Loader for loading a tracker and model file:

let faceTracker = new ZapparThree.FaceTrackerLoader().load();

If you're using the included LoadingManager then make sure to pass it in to the FaceTrackerLoader:

let faceTracker = new ZapparThree.FaceTrackerLoader(manager).load();


Face Anchors

Each FaceTracker exposes anchors for faces detected and tracked in the camera view. By default a maximum of one face is tracked at a time, however you can change this using the maxFaces parameter:

faceTracker.maxFaces = 2;

Note that setting a value of two or more may impact the performance and framerate of the library, so we recommend sticking with one unless your use case requires tracking multiple faces.

Anchors have the following parameters:

  • id: a string that's unique for this anchor.
  • visible: a boolean indicating if this anchor is visible in the current camera frame.
  • identity and expression: Float32Arrays containing data used for rendering a face-fitting mesh (see below).
  • onVisible and onNotVisible: event handlers that emit when the anchor becomes visible, or disappears in the camera view. These events are emitted during your call to camera.updateFrame(renderer).

You can access the anchors of a tracker using its anchors parameter - it's a JavaScript Map keyed with the IDs of the anchors. Trackers will reuse existing non-visible anchors for new faces that appear and thus there are never more than maxFaces anchors handled by a given tracker. Each tracker also exposes a JavaScript Set of anchors visible in the current camera frame as its visible parameter.

To attach 3D content (e.g. ThreeJS objects or models) to a FaceTracker or a FaceAnchor, the library provides FaceAnchorGroup. It's a ThreeJS Group that will follow the supplied anchor (or, in the case of a supplied FaceTracker, the anchor most recently visible in that tracker) in the 3D view:

let faceAnchorGroup = new ZapparThee.FaceAnchorGroup(camera, faceTracker);
scene.add(faceAnchorGroup);

// Add in any 3D objects you'd like to track to this face
faceAnchorGroup.add(myModel);

The group provides a coordinate system that has its origin at the center of the head, with positive X axis to the right, the positive Y axis towards the top and the positive Z axis coming forward out of the user's head.

Note that users typically expect to see a mirrored view of any user-facing camera feed. Please see the camera article for more information on mirroring the camera.


Events

In addition to using the anchors and visible parameters, FaceTrackers expose event handlers that you can use to be notified of changes in the anchors or their visibility. The events are emitted during your call to camera.updateFrame(renderer).

  • onNewAnchor: emitted when a new anchor is created by the tracker.
  • onVisible: emitted when an anchor becomes visible in a camera frame.
  • onNotVisible: emitted when an anchor goes from being visible in the previous camera frame, to being not visible in the current frame.

Here's an example of using these events:

faceTracker.onNewAnchor.bind(anchor => {
    console.log("New anchor has appeared:", anchor.id);

    // You may like to create a new FaceAnchorGroup here for this anchor, and add it to your scene
});

faceTracker.onVisible.bind(anchor => {
    console.log("Anchor is visible:", anchor.id);
});

faceTracker.onNotVisible.bind(anchor => {
    console.log("Anchor is not visible:", anchor.id);
});


Face Mesh

In addition to tracking the center of the face using FaceTracker, the Zappar library provides a face mesh that will fit to the face and deform as the user's expression changes. This can be used to apply a texture to the user's skin, much like face paint, or to mask out the back of 3D models so the user's head is not occluded where it shouldn't be.

To use the face mesh, first construct a new FaceMesh object and load its data file. The loadDefaultFace function returns a promise that resolves when the data file has been loaded successfully. It's recommended to display a loading screen to the user while this is taking place.

let faceMesh = new ZapparThree.FaceMesh();
faceMesh.loadDefaultFace().then(() => {
    // Face mesh loaded
});

Alternatively the library provides a THREE Loader for loading face mesh and data file:

let faceMesh = new ZapparThree.FaceMeshLoader().loadFace();

If you're using the included LoadingManager then make sure to pass it into the FaceMeshLoader:

let faceMesh = new ZapparThree.FaceMeshLoader(manager).loadFace();

While the faceMesh object lets you access the raw vertex, UV, normal and indices data for the face mesh, you may wish to use the library's FaceBufferGeometry object which wraps the data as a ThreeJS BufferGeometry for use in a ThreeJS Mesh. This ThreeJS Mesh object must still be added to a FaceAnchorGroup to appear in the correct place on-screen:

let faceBufferGeometry = new ZapparThree.FaceBufferGeometry(faceMesh);

let faceMeshMesh = new THREE.Mesh(faceBufferGeometry, 
    new THREE.MeshStandardMaterial({
        map: myFaceTexture, transparent: true
}));

faceAnchorGroup.add(faceMeshMesh);

Each frame, after camera.updateFrame(renderer), call one of the following functions to update the face mesh to the most recent identity and expression output from a face anchor:

// Update directly from a FaceAnchorGroup
faceBufferGeometry.updateFromFaceAnchorGroup(faceAnchorGroup);

// Update from a face anchor
faceBufferGeometry.updateFromFaceAnchor(myFaceAnchor);

There are two meshes included with the ThreeJS library, detailed below.

Default Mesh: covers the user's face, from the chin at the bottom to the forehead, and from the sideburns on each side. There are optional parameters that determine if the mouth and eyes are filled or not:

loadDefaultFace(fillMouth?: boolean, fillEyeLeft?: boolean, fillEyeRight?: boolean)

Full Head Simplified Mesh: covers the whole of the user's head, including a portion of the neck. This mesh is ideal for drawing into the depth buffer in order to mask out the back of 3D models placed on the user's head (see the Head Masking section below). There are optional parameters that determine if the mouth, eyes and neck are filled or not:

loadDefaultFullHeadSimplified(fillMouth?: boolean, fillEyeLeft?: boolean, fillEyeRight?: boolean, fillNeck?: boolean)


Head Masking

When placing a 3D model around the user's head, such as a helmet, it's important to make sure the user's face is not obscured by the back of the model in the camera view. To this end, the library provides ZapparThree.HeadMaskMesh, a THREE.Mesh that fits the user's head and fills the depth buffer, ensuring that the camera image shows instead of any 3D elements behind it in the scene.

To use it, construct the object using a ZapparThree.HeadMaskMeshLoader and add it to your face anchor group:

let mask = new ZapparThree.HeadMaskMeshLoader().load();
faceAnchorGroup.add(mask);

If you're using the included LoadingManager then make sure to pass it in to the HeadMaskMeshLoader:

let mask = new ZapparThree.HeadMaskMeshLoader(manager).load();
faceAnchorGroup.add(mask);

Then, in each frame after camera.updateFrame(renderer), call one of the following functions to update the head mesh to the most recent identity and expression output from a face anchor:

// Update directly from a FaceAnchorGroup
mask.updateFromFaceAnchorGroup(faceAnchorGroup);

// Update from a face anchor
mask.updateFromFaceAnchor(myFaceAnchor);

Behind the scenes, the HeadMaskMesh works using a full-head ZapparThree.FaceMesh with the mouth, eyes, and neck filled in. Its renderOrder is set to Number.MIN_SAFE_INTEGER to ensure it is rendered before any other objects in the scene, and its material's colorWrite property is set to false so that it fills the depth buffer but not the color buffer.

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