When Google unveiled thePixel Foldback in May, one of the features it said wouldn’t be available at launch wasdual screen interpreter mode, a feature that utilizes the foldable’s inner and outer screens to display live translations. Dual screen interpreter mode rolled out with the Pixel Fold’sAndroid 14 update, and to date, it remains the only feature to make use of both screens on Google’s foldable. Fortunately, that might not be the case for much longer, since the Android 14 release quietly opened up the ability for third-party apps to make use of both screens on foldable phones.
Dual screen interpreter mode on the Pixel Fold. Source: Google.
To help app developers take advantage of features that are unique to foldables, Google created theJetpack WindowManagerlibrary, a support library that abstracts the lower-level WindowManager APIs in the framework. Developers add Jetpack WindowManager as an application dependency so they can make use of its APIs, such as the ones to manage split layouts and hinge angles. In the upcoming version 1.2.0 release of the library, new “experimental window APIs for accessing the rear screen” will be exposed to applications.
In order for Jetpack WindowManager to access things like the hinge angle sensor and rear screen, though, the OEM has to do some work to expose them to the library. This is done by implementing the relevantJetpack WindowManager Extensionsmodules, which are loaded into the application process at runtime. The activity embedding module is what enables applications to show “two activities simultaneously side-by-side in a multi-pane layout,” while the window layout information module makes the hinge position available to applications so they can “respond to and show optimized layouts in tabletop mode on foldables.”
The window area module gives applications “access to additional displays and display areas on some foldable and multi-display devices.” This module was first addedin Android 13 QPR3back in June, the OS version the Pixel Fold shipped with at launch. When implemented correctly by the OEM, the module enabled apps to make use of “rear display mode” so that they could show content on the outer display while the phone was unfolded. The Google Camera app made use of this forthe Pixel Fold’s Rear Camera Selfie feature, which lets you use the outer display as a viewfinder while taking photos from the rear cameras.
With Android 14, Google updated the window area module to let apps make use of “dual display mode” so that they can show content on both the inner and outer displays. This is why the Pixel Fold’s dual screen interpreter mode didn’t roll out until the phone received its Android 14 update, since it wasn’t possible for apps to make use of both screens on a foldable until now. And since the API that Google made is available to all applications, that means any app can now show content on the outer display only or on both the outer and inner displays if they want to, provided the OEM implements the window area module.
So far, both Google (obviously) and Samsung have implemented the window area module in their respective Android 14 releases for their flagship foldables. UsingGoogle’s Jetpack WindowManager sample app, my testers were able to get the rear and dual display modes working on the Pixel Fold and Galaxy Z Fold 5, as shown below.
Dual screen mode on the Galaxy Z Fold 5. Image credits: Andrew Myrick.
Dual screen mode on the Pixel Fold. Image credits: Anh.
Rear display mode on the Pixel Fold. Video credits: Anh.
Section 7.1.1.1 of the Android 14 Compatibility Definition Document (CDD)statesthat devices with one or more foldable displays (like the Pixel Fold or Galaxy Z Fold 5) or devices with a folding hinge between two or more displays (like the Surface Duo) are required to implement the “correct version of the Window Manager Extensions API level.” This means that foldables phones running Android 14 have to implement at least version 3 of WindowManager Extensions.
However, OEMs only have to implement features that their foldable actually has the hardware for. For example, OEMs are only required to implement rear display mode if their foldable includes an outer display that “aligns with the rear device cameras”. The CDD/WindowManager Extensions document doesn’t explicitly say that OEMs are required to implement dual display mode, so it’s possible some might disable it for thermal concerns, but I can’t say for sure. Hopefully this feature is supported on all foldables that receive Android 14, such as theOnePlus Open. I’m excited to see what developers do with this new capability, but what about you?
If you’re a developer looking to make use of both screens on a foldable, check out the API reference for theWindowArea classesunder Jetpack WindowManager or take a peek at Google’s sample code forrear display modeanddual display mode.
