Peder Norrby is doing a very cool project with Unity, using 3d eye tracking on Apple’s latest phone.
Using the position of an eye and the device screen rectangle a non-symmetric camera frustum can be defined. The frustum defines an off-axis projection that when used for rendering on the device allows for objects appearing in front of, and behind the screen of the device.
If you are an experienced Unity + iOS developer you can download the source code and build the app to your iPhone X but if you just want to try the app you can grab it free from the AppStore [in review, coming soon].
I cannot give support on how to use Unity and build the app. Only get the source if you know what to do with it.
Full source code is available here: TheParallaxView on GitHub
(Unity and Unity’s ARKitPlugin required)
Implemented in Unity with UnityARKitPlugin. The technique should easily transfer to native iOS apps and other devices.
Although you are welcome to use the code (under MIT license, basically with attribution) the point of sharing the code is more to show the technique to other developers than to serve as actual code building blocks.