Using the Linux FrameBuffer and libinput

Uno Platform supports the Linux FrameBuffer and libinput as a target, in the case where your target device does not provide a Window Manager.

There are some restrictions for the support for the FrameBuffer:

  • The mouse is supported through pointer events, but Uno Platform does not show the pointer for your app. You'll need to display one using the pointer events provided by Uno Platform (also in the CoreWindow class).
  • It is only supported on Linux where /dev/fbXX is available.

Get started with the FrameBuffer

Create a new app using:

dotnet new unoapp -o MyApp

In the Platforms/Desktop/Program.cs file, the SkiaHostBuilder can be configured to use the Framebuffer support, in case X11 support is detected first:

var host = SkiaHostBuilder.Create()
    .App(() => new App())

Each platform support is evaluated in order for availability and definition in builder. X11 is chosen when the DISPLAY variable is present.

Running the app

You can build and run this app by navigating to the MyApp and type the following:

dotnet run -f net8.0-desktop

The app will start and display on the first available framebuffer device. To change the active framebuffer, set the device name in the FRAMEBUFFER environment variable.

By default, the Debug configuration is used, which will show logging information in the current terminal and may overwrite the UI content.

To read the logging information, either:

  • Launch the application from a different terminal (through SSH, for instance)
  • Launch the app using dotnet run -f net8.0-desktop > logging.txt 2>&1, then launch tail -f logging.txt in another terminal.

Once the application is running, you can exit the application with:

  • Ctrl+C
  • F12, a key configuration found in the Program.cs file of your project which invokes Application.Current.Exit()

Creating a standalone app

You can create a standalone publication folder using the following:

dotnet publish -c Release -f net8.0-desktop -r linux-x64 --self-contained true

When using the Release configuration, logging is disabled for performance considerations. You can restore logging in the App.xaml.cs file.

Documentation on other hardware targets is available here.

DPI Scaling support

Whenever possible, the FrameBufferHost will try to detect the actual DPI scale to use when rendering the UI, based on the physical information provided by the FrameBuffer driver. If the value cannot be determined, a scale of 1.0 is used.

The automatic scaling can be overridden in two ways:

  • Set a value using FrameBufferHost.DisplayScale.
  • Set a value through the UNO_DISPLAY_SCALE_OVERRIDE environment variable. This value has precedence over the value specified in FrameBufferHost.DisplayScale.

Additional dependencies

If your device is significantly trimmed down for installed packages, you'll need to install:

  • libfontconfig
  • libfreetype
  • libinput