- iOS 11.0+
- Xcode 9.3+
This sample app presents a simple interface allowing you to choose between four augmented reality (AR) visualizations on devices with a TrueDepth front-facing camera (see iOS Device Compatibility Reference).
The camera view alone, without any AR content.
The face mesh provided by ARKit, with automatic estimation of the real-world directional lighting environment.
Virtual 3D content that appears to attach to (and be obscured by parts of) the user’s real face.
A simple robot character whose facial expression is animated to match that of the user.
Use the “+” button in the sample app to switch between these modes, as shown below.
Start a Face Tracking Session in a SceneKit View
Like other uses of ARKit, face tracking requires configuring and running a session (an
ARSession object) and rendering the camera image together with virtual content in a view. For more detailed explanations of session and view setup, see Understanding World Tracking in ARKit and Building Your First AR Experience. This sample uses SceneKit to display an AR experience, but you can also use SpriteKit or build your own renderer using Metal (see
ARSKView and Displaying an AR Experience with Metal).
Face tracking differs from other uses of ARKit in the class you use to configure the session. To enable face tracking, create an instance of
ARFace, configure its properties, and pass it to the
run method of the AR session associated with your view, as shown below.
Before offering your user features that require a face tracking AR session, check the
is property on the
ARFace class to determine whether the current device supports ARKit face tracking.
Track the Position and Orientation of a Face
When face tracking is active, ARKit automatically adds
ARFace objects to the running AR session, containing information about the user’s face, including its position and orientation.
In a SceneKit-based AR experience, you can add 3D content corresponding to a face anchor in the
renderer: method (from the
ARSCNView protocol). ARKit adds a SceneKit node for the anchor, and updates that node’s position and orientation on each frame, so any SceneKit content you add to that node automatically follows the position and orientation of the user’s face.
In this example, the
renderer: method calls the
setup method to add SceneKit content to the
face. For example, if you change the
shows variable in the sample code, the app adds a visualization of the x/y/z axes to the node, indicating the origin of the face anchor’s coordinate system.
Use Face Geometry to Model the User’s Face
ARKit provides a coarse 3D mesh geometry matching the size, shape, topology, and current facial expression of the user’s face. ARKit also provides the
ARSCNFace class, offering an easy way to visualize this mesh in SceneKit.
Your AR experience can use this mesh to place or draw content that appears to attach to the face. For example, by applying a semitransparent texture to this geometry you could paint virtual tattoos or makeup onto the user’s skin.
To create a SceneKit face geometry, initialize an
ARSCNFace object with the Metal device your SceneKit view uses for rendering:
The sample code’s
setup method (mentioned above) adds a node containing the face geometry to the scene. By making that node a child of the node provided by the face anchor, the face model automatically tracks the position and orientation of the user’s face.
To also make the face model onscreen conform to the shape of the user’s face, even as the user blinks, talks, and makes various facial expressions, you need to retrieve an updated face mesh in the
renderer: delegate callback.
Place 3D Content on the User’s Face
Another use of the face mesh that ARKit provides is to create occlusion geometry in your scene. An occlusion geometry is a 3D model that doesn’t render any visible content (allowing the camera image to show through), but obstructs the camera’s view of other virtual content in the scene.
This technique creates the illusion that the real face interacts with virtual objects, even though the face is a 2D camera image and the virtual content is a rendered 3D object. For example, if you place an occlusion geometry and virtual glasses on the user’s face, the face can obscure the frame of the glasses.
To create an occlusion geometry for the face, start by creating an
ARSCNFace object as in the previous example. However, instead of configuring that object’s SceneKit material with a visible appearance, set the material to render depth but not color during rendering:
Because the material renders depth, other objects rendered by SceneKit correctly appear in front of it or behind it. But because the material doesn’t render color, the camera image appears in its place. The sample app combines this technique with a SceneKit object positioned in front of the user’s eyes, creating an effect where the object is realistically obscured by the user’s nose.
Animate a Character with Blend Shapes
In addition to the face mesh shown in the above examples, ARKit also provides a more abstract model of the user’s facial expressions in the form of a
blend dictionary. You can use the named coefficient values in this dictionary to control the animation parameters of your own 2D or 3D assets, creating a character (such as an avatar or puppet) that follows the user’s real facial movements and expressions.
As a basic demonstration of blend shape animation, this sample includes a simple model of a robot character’s head, created using SceneKit primitive shapes. (See the
robot file in the source code.)
Then, examine the key-value pairs in that dictionary to calculate animation parameters for your model. There are 52 unique
ARBlend coefficients. Your app can use as few or as many of them as neccessary to create the artistic effect you want. In this sample, the
Robot class performs this calculation, mapping the
ARBlend parameters to one axis of the
scale factor of the robot’s eyes, and the
ARBlend parameter to offset the position of the robot’s jaw.