# Zappar for ThreeJS

This library allows you use Zappar's best-in-class AR technology with content built using the 3D rendering platform ThreeJS.

You may also be interested in:
 - [Zappar for A-Frame](https://www.npmjs.com/package/@zappar/zappar-aframe) (@zappar/zappar-aframe)
 - Zappar's library for Unity
 - [Zappar for JavaScript](https://www.npmjs.com/package/@zappar/zappar) (@zappar/zappar), if you'd like to build content with a different 3D rendering platform
 - ZapWorks Studio, a full 3D development environment built for AR, VR and MR

## Getting Started

### Bootstrap Projects

You can get started super-quickly using one of our bootstrap projects. They contain the basics of an AR experience for the different tracking types - no more, no less. 

Check out these repositories that contain `index.html` files to get you started:
https://github.com/zappar-xr/zappar-threejs-face-tracking-standalone-bootstrap
https://github.com/zappar-xr/zappar-threejs-instant-tracking-standalone-bootstrap
https://github.com/zappar-xr/zappar-threejs-image-tracking-standalone-bootstrap

Or these repositories that have `webpack` setups optimized for development and deployment:
https://github.com/zappar-xr/zappar-threejs-face-tracking-webpack-bootstrap
https://github.com/zappar-xr/zappar-threejs-instant-tracking-webpack-bootstrap
https://github.com/zappar-xr/zappar-threejs-image-tracking-webpack-bootstrap

### Example Projects

There's a repository of example projects for your delectation over here:

https://github.com/zappar-xr/zappar-threejs-examples

## Starting Development

You can use this library by downloading a standalone zip containing the necessary files, by linking to our CDN, or by installing from NPM for use in a webpack project.

#### Standalone Download

Download the bundle from this link:
https://libs.zappar.com/zappar-threejs/0.2.16/zappar-threejs.zip

Unzip into your web project and reference from your HTML like this:
```html
<script src="zappar-threejs.js"></script>
```

#### CDN

Reference the zappar.js library from your HTML like this:
```html
<script src="https://libs.zappar.com/zappar-threejs/0.2.16/zappar-threejs.js"></script>
```

#### NPM Webpack Package

Run the following NPM command inside your project directory:
```bash
npm install --save @zappar/zappar-threejs
```

Then import the library into your JavaScript or TypeScript files:
```ts
import * as ZapparThree from "@zappar/zappar-threejs";
```

The final step is to add this necessary entry to your webpack `rules`:
```ts
module.exports = {
  //...
  module: {
    rules: [
      //...
      {
        test: /zcv\.wasm$/,
        type: "javascript/auto",
        loader: "file-loader"
      }
      //...
    ]
  }
};
```

## Overview

You can integrate the Zappar library with the existing `requestAnimationFrame` loop of your ThreeJS project. A typical project may look like this. The remainder of this document goes into more detail about each of the component elements of this example.
```ts
// Set up ThreeJS in the usual way
let scene = new THREE.Scene();
let renderer = new THREE.WebGLRenderer();
document.body.appendChild(renderer.domElement);

// The Zappar library needs the WebGL context to process camera images
// Use this function to set your context
ZapparThree.glContextSet(renderer.getContext());

// Create a camera and set the scene background to the camera's backgroundTexture
let camera = new ZapparThree.Camera();
scene.background = camera.backgroundTexture;

// Request camera permissions and start the camera
ZapparThree.permissionRequestUI().then(granted => {
    if (granted) camera.start();
    else ZapparThree.permissionDeniedUI();
});

// Set up a tracker, in this case an image tracker
let imageTracker = new ZapparThree.ImageTrackerLoader().load(targetFile);
let trackerGroup = new ZapparThree.ImageAnchorGroup(camera, imageTracker);
scene.add(trackerGroup);

// Place any 3D content you'd like tracked from the image into the trackerGroup

function animate() {
    // Ask the browser to call this function again next frame
    requestAnimationFrame(animate);

    // The Zappar camera should have updateFrame called every frame
    camera.updateFrame(renderer);
    
    renderer.render(scene, camera);
}

// Start things off
animate();
```

## Local Preview and Testing

Due to browser restrictions surrounding use of the camera, you must use HTTPS to view or preview your site, even if doing so locally from your computer. If you're using `webpack`, consider using `webpack-dev-server` which has an `https` option to enable this.

Alternatively you can use the [ZapWorks command-line tool](https://www.npmjs.com/package/@zappar/zapworks-cli) to serve a folder over HTTPS for access on your local computer, like this:
```bash
$ zapworks serve .
```

The command also lets you serve the folder for access by other devices on your local network, like this:
```bash
$ zapworks serve . --lan
```

## Hosting and Publishing Content

Once you've built your site, you have a number of options for hosting your site:
 - Using ZapWork's integrated hosting
 - Self-hosting on servers and a domain that you manage

### Licensing

You need to maintain an activate subscription at ZapWorks in order to use this library.

If you are self-hosting your experience, you will have to register the full domain name with ZapWorks in order for the license check to complete successfully. Contact support@zappar.com to find out more.

You do **not** need to register if you're hosting your experience:
 - with ZapWorks (a `*.zappar.io` domain name); or,
 - locally for testing (with the one of following hostnames: `0.0.0.0`, `127.*`); or,
 - on your local network (with the one of following hostnames: `192.*`, `10.*`); or,
 - using [ngrok](https://ngrok.com/) (a `*.ngrok.io` domain name).

### ZapWorks Hosting

ZapWorks provides an easy-to-use and robust hosting solution for your AR experiences as part of your subscription. To get started, head over to [zap.works](https://zap.works).

Once you've logged in, you can create a new 'Universal AR' project using the + button.

Having created a 'Universal AR' project, head over to the "Experience" tab where you can either:
 - upload a ZIP of your website directly, or
 - find instructions for using the [ZapWorks command-line tool](https://www.npmjs.com/package/@zappar/zapworks-cli) to complete the upload.

For more information, head over to our [Publishing and Hosting](https://docs.zap.works/universal-ar/publishing-and-hosting/) docs article.

### Self-hosting

If you'd like to self-host your content, there are a number of recommendations we make to ensure the best experience for end-users:
 - You need to register your domain name with ZapWorks so that it passes the license check. For more information contact support@zappar.com
 - You must serve the content over HTTPS (due to browser restrictions surrounding the camera)
 - Files in the Zappar library ending with the `.wasm` file extension should be served with the `application/wasm` mime-type
 - Several files in this library (and likely others in your project too) compress well using `Content-Encoding: gzip`. In particular you should serve files with the following extensions with gzip content-encoding: `.wasm`, `.js`, `.zbin`, `.zpt`

## Loading UI

For your convenience, this package includes a three.js `LoadingManager` that you can use to display a progress bar while your experience loads (should you wish to). The `LoadingManager` is constructed like this:
```ts
let manager = new ZapparThree.LoadingManager();
```
Then make sure to pass the `manager` in to any three.js loaders you might use, e.g:
 - `THREE.TextureLoader`
 - `GLTFLoader`
 - `ZapparThree.ImageTrackerLoader` (see below)
 - `ZapparThree.FaceTrackerLoader` (see below)
 - `ZapparThree.FaceMeshLoader` (see below)
 - `ZapparThree.HeadMaskMeshLoader` (see below)

The `LoadingManager` will automatically handle the showing and hiding of the screen during the loading process.

## Initialization and Camera Processing

### Starting the GL Context

The ZapparThree library needs to use your WebGL context in order to process camera frames. You can set it when your page loads using the following function:
```ts
ZapparThree.glContextSet(renderer.getContext());
```

### Constructing the Camera

The library provides a camera object that you can use instead of a ThreeJS PerspectiveCamera. It's constructed like this:
```ts
let camera = new ZapparThree.Camera();
```

The camera object provides a THREE.Texture object containing the camera feed. You can use this texture however you wish but the easiest way to show the camera feed behind your content is to set it as your scene's background:
```ts
scene.background = camera.backgroundTexture;
```

### Permissions

The library needs to ask the user for permission to access the camera and motion sensors on the device.

To do this, you can use the following function to show a built-in UI informing the user of the need and providing a button to trigger the browser's permission prompts. The function returns a promise that lets you know if the user granted the permissions or not.
```ts
// Show Zappar's built-in UI to request camera permissions
ZapparThree.permissionRequestUI().then(granted => {
    if (granted) {
        // User granted the permissions so start the camera
        camera.start();
    } else {
        // User denied the permissions so show Zappar's built-in 'permission denied' UI
        ZapparThree.permissionDeniedUI();
    }
});
```

If you'd rather show your own permissions UI, you can use the following function to trigger the browser's permission prompts directly. The function returns a promise that resolves to `true` if the user granted all the necessary permissions, otherwise `false`. Please note - due to browser restrictions, this function must be called from within a user event, e.g. in the event handler of a button click.
```ts
ZapparThree.permissionRequest().then(granted => {
    if (granted) {
        // User granted the permissions so start the camera
    } else {
        // User denied the permissions
        // You can show your own 'permission denied' UI here or use Zappar's built-in one
        ZapparThree.permissionDeniedUI();
    }
});
```

### Starting the Camera

Once the user has granted the necessary permissions, you can start the rear-facing camera on the device with the following function on your camera object:
```ts
camera.start();
```

If you'd like to start the user-facing 'selfie' camera, pass `true`:
```ts
camera.start(true);
```

To switch between the front- and rear-facing cameras during your experience, just call `camera.start(...)` again passing either `true` or `false` as appropriate.

User-facing cameras are normally shown mirrored to users and so the camera object provides a number of modes to support this:

 - `ZapparThree.CameraMirrorMode.Poses`: this mode mirrors the background camera texture and ensures content still appears correctly tracked. In this mode your content itself isn't flipped, so any text in your tracked content doesn't appear mirrored. This is the default mode for the user-facing camera.
 - `ZapparThree.CameraMirrorMode.CSS`: in this mode, the Zappar camera applies a `scaleX(-1)` CSS transform to your whole canvas. This way both the camera and your content appear mirrored.
 - `ZapparThree.CameraMirrorMode.None`: no mirroring is performed. This is the default mode for the rear-facing camera.

 The `userCameraMirrorMode` and `rearCameraMirrorMode` parameters set which mode the camera object will use for each camera:
 ```ts
camera.userCameraMirrorMode = ZapparThree.CameraMirrorMode.CSS;
 ```


### Processing Camera Frames

Call the following function once an animation frame (e.g. during your `requestAnimationFrame` function) in order to process incoming camera frames:
```ts
camera.updateFrame(renderer);
```


### Camera Pose

The Zappar library provides multiple modes for the camera to move around in the ThreeJS scene. You can set this mode with the `poseMode` parameter of your camera object. There are the following options:
 - `ZapparThree.CameraPoseMode.Default`: in this mode the camera stays at the origin of the scene, pointing down the negative Z axis. Any tracked anchors will move around in your scene as the user moves the physical camera and real-world tracked objects.
 - `ZapparThree.CameraPoseMode.Attitude`: the camera stays at the origin of the scene, but rotates as the user rotates the physical device. When the Zappar library initializes, the negative Z axis of world space points forward in front of the user.
 - `ZapparThree.CameraPoseMode.AnchorOrigin`: the origin of the scene is the center of the anchor specified by the camera's `poseAnchorOrigin` parameter. In this case the camera moves and rotates in world space around the anchor at the origin.

 The correct choice of camera pose with depend on your given use case and content. Here are some examples you might like to consider when choosing which is best for you:
  - To have a light that always shines down from above the user, regardless of the angle of the device or anchors, use `ZapparThree.CameraPoseMode.Attitude` and place a light shining down the negative Y axis is world space.
  - In an application with a physics simulation of stacked blocks, and with gravity pointing down the negative Y axis of world space, using `ZapparThree.CameraPoseMode.AnchorOrigin` would allow the blocks to rest on a tracked image regardless of how the image is held by the user, while using `ZapparThree.CameraPoseMode.Attitude` would allow the user to tip the blocks off the image by tilting it.


## Tracking

The Zappar library offers three types of tracking for you to use to build augmented reality experiences:
 - *Image Tracking* can detect and track a flat image in 3D space. This is great for building content that's augmented onto business cards, posters, magazine pages, etc.
 - *Face Tracking* detects and tracks the user's face. You can attach 3D objects to the face itself, or render a 3D mesh that's fit 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.
 - *Instant World Tracking* lets you tracking 3D content to a point chosen by the user in the room or immediate environment around them. With this tracking type you could build a 3D model viewer that lets users walk around to view the model from different angles, or an experience that places an animated character in their room.

### Image Tracking

To track content from a flat image in the camera view, create a new `ImageTracker` object:
```ts
let imageTracker = new ZapparThree.ImageTracker();
```

#### Target File

`ImageTracker`s use a special 'target file' that's been generated from the source image you'd like to track. You can generate them using the ZapWorks command-line utility like this:
```bash
$ zapworks train myImage.png
```

The resulting file can be loaded into an image tracker object by passing it to the `loadTarget(...)` function as either a URL or an ArrayBuffer. The function returns a promise that resolves when the target file has been loaded successfully.

```ts
let imageTracker = new ZapparThree.ImageTracker();
imageTracker.loadTarget("myImage.zpt").then(() => {
    // Image target has been loaded
});
```

Alternatively the library provides a THREE Loader for loading a tracker and target file:
```ts
let imageTracker = new ZapparThree.ImageTrackerLoader().load("myImage.zpt");
```

If you're using the included `LoadingManager` then make sure to pass it in to the `ImageTrackerLoader`:
```ts
let imageTracker = new ZapparThree.ImageTrackerLoader(manager).load("myImage.zpt");
```

#### Image Anchors

Each `ImageTracker` exposes anchors for images detected and tracked in the camera view. At this time, `ImageTracker`s only track one image in view at a time.

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
 - `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 images that appear and thus, until `ImageTracker` supports tracking more than one image at a time, there is never more than one anchor managed by each `ImageTracker`. 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 an `ImageTracker` or an `ImageAnchor`, the library provides `ImageAnchorGroup`. It's a ThreeJS Group that will follow the supplied anchor (or, in the case of a supplied `ImageTracker`, the anchor most recently visible in that tracker) in the 3D view:
```ts
let imageAnchorGroup = new ZapparThree.ImageAnchorGroup(camera, imageTracker);
scene.add(imageAnchorGroup);

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

The group provides a coordinate system that has its origin at the center of the image, with positive X axis to the right, the positive Y axis towards the top and the positive Z axis coming up out of the plane of the image. The scale of the coordinate system is such that a Y value of +1 corresponds to the top of the image, and a Y value of -1 corresponds to the bottom of the image. The X axis positions of the left and right edges of the target image therefore depend on the aspect ratio of the image.

#### Events

In addition to using the `anchors` and `visible` parameters, `ImageTracker`s 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:
```ts
imageTracker.onNewAnchor.bind(anchor => {
    console.log("New anchor has appeared:", anchor.id);

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

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

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


### Face Tracking

To place content on or around a user's face, create a new `FaceTracker` object when your page loads:
```ts
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.
 
```ts
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:
```ts
let faceTracker = new ZapparThree.FaceTrackerLoader().load();
```

If you're using the included `LoadingManager` then make sure to pass it in to the `FaceTrackerLoader`:
```ts
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:
```ts
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`: `Float32Array`s 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:
```ts
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 section on mirroring the camera view earlier in this document.

#### Events

In addition to using the `anchors` and `visible` parameters, `FaceTracker`s 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:
```ts
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 number of meshes that will fit to the face/head and deform as the user's expression changes. These 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. You may wish to use to show a 'loading' screen to the user while this is taking place.
```ts
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:
```ts
let faceMesh = new ZapparThree.FaceMeshLoader().loadFace();
```

If you're using the included `LoadingManager` then make sure to pass it in to the `FaceMeshLoader`:
```ts
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:
```ts
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:
```ts
// Update directly from a FaceAnchorGroup
faceBufferGeometry.updateFromFaceAnchorGroup(faceAnchorGroup);

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

At this time there are two meshes included with the library. The 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:
```ts
loadDefaultFace(fillMouth?: boolean, fillEyeLeft?: boolean, fillEyeRight?: boolean)
```

The full head simplified mesh covers the whole of the user's head, including some neck. It's ideal for drawing into the depth buffer in order to mask out the back of 3D models placed on the user's head (see Head Masking below). There are optional parameters that determine if the mouth, eyes and neck are filled or not:
```ts
loadDefaultFullHeadSimplified(fillMouth?: boolean, fillEyeLeft?: boolean, fillEyeRight?: boolean, fillNeck?: boolean)
```

### Head Masking

If you're placing a 3D model around the user's head, such as a helmet, it's important to make sure the camera view of the user's real face is not hidden by the back of the model. To achieve this, the library provides `ZapparThree.HeadMaskMesh`. It's 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:
```ts
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`:
```ts
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:
```ts
// 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's rendered before any other objects in the scene, and its material has the `colorWrite` property set to `false` so it fills the depth buffer but not the color buffer.

### Instant World Tracking

To track content from a point on a surface in front of the user, create a new `InstantWorldTracker`:
```ts
let instantWorldTracker = new ZapparThree.InstantWorldTracker();
```

Each `InstantWorldTracker` exposes a single anchor from its `anchor` parameter.

To choose the point in the user's environment that the anchor tracks from, use the `setAnchorPoseFromCameraOffset(...)` function, like this:
```ts
instantWorldTracker.setAnchorPoseFromCameraOffset(0, 0, -5);
```
The parameters passed in to this function correspond to the X, Y and Z coordinates (in camera space) of the point to track. Choosing a position with X and Y coordinates of zero, and a negative Z coordinate, will select a point on a surface directly in front of the center of the screen.

To attach 3D content (e.g. ThreeJS objects or models) to an `InstantWorldTracker`, the library provides `InstantWorldAnchorGroup`. It's a ThreeJS Group that will follow the anchor in the supplied `InstantWorldTracker` in the 3D view:
```ts
let instantAnchorGroup = new ZapparThree.InstantWorldAnchorGroup(camera, instantWorldTracker);
scene.add(instantAnchorGroup);

// Add in any 3D objects you'd like to track to this point in space
instantAnchorGroup.add(myModel);
```

The group provides a coordinate system that has its origin at the point that's been set, with the positive Y coordinate pointing up out of the surface, and the X and Z coordinates in the plane of the surface. How far the chosen point is from the camera (i.e. how negative the Z coordinate provided to `setAnchorPoseFromCameraOffset` is) determines the scale of the coordinate system exposed by the anchor.

A typical application will call `setAnchorPoseFromCameraOffset` each frame until the user confirms their choice of placement by tapping a button, like this:
```ts
// Not shown - initialization, camera setup & permissions

let instantWorldTracker = new ZapparThree.InstantWorldTracker();
let instantWorldAnchorGroup = new ZapparThree.InstantWorldAnchorGroup(camera, instantWorldTracker);
scene.add(instantWorldAnchorGroup);

// Not shown - add content to the instantWorldAnchorGroup

let hasPlaced = false;

myConfirmButton.addEventListener("click", () => { hasPlaced = true });

function animate() {
    // Ask the browser to call this function again next frame
    requestAnimationFrame(animate);

    camera.updateFrame(renderer);

    if (!hasPlaced) instantWorldTracker.setAnchorPoseFromCameraOffset(0, 0, -5);

    // Render the ThreeJS scene as usual
    renderer.render(scene, camera);
}

// Start things off
animate();
```
