In October last year, Microsoft announced the Surface Duo mobile device running Android with full support for Play Store apps. The Surface Duo comes with two 5.6” displays and it unfolds in to a 8.3” display. The 360-degree hinge will allow you to use this device in various modes. App developers can take advantage of the dual-screen and the hinge posture of the device. Microsoft recently published a blog post explaining how developers can make use of the hinge angle in their apps.
In this example, the app starts from the single screen and features a color picker and a clear button as the basic tools to use while drawing. You can do some random drawing on this screen to test it out. When you span the single screen to dual-screen mode, your drawing will be mirrored on the second screen.
You can learn more about the Hinge Angle Sensor API here. Also, you can find more details in the source link below.