# LinuxKMS Backend The LinuxKMS backend runs only on Linux and eliminates the need for a windowing system such as Wayland or X11. Instead it uses the following libraries and interface to render directly to the screen and react to touch, mouse, and keyboard input. - OpenGL via KSM/DRI. - Vulkan via the Vulkan KHR Display Extension. - libinput for input event handling from mice, touch screens, or keyboards. - libseat for GPU and input device access without requiring root access. The LinuxKMS backend supports different renderers. They can be explicitly selected for use through the `SLINT_BACKEND` environment variable. | Renderer name | Required Graphics APIs | `SLINT_BACKEND` value to select renderer | |---------------|------------------------|--------------------------------------------------| | FemtoVG | OpenGL ES 2.0 | `linuxkms-femtovg` | | Skia | OpenGL ES 2.0, Vulkan | `linuxkms-skia-opengl` or `linuxkms-skia-vulkan` | :::{note} This backend is still experimental. The backend has not undergone a great variety of testing on different devices and there are [known issues](https://github.com/slint-ui/slint/labels/a%3Abackend-linuxkms). ::: ## Display Selection with OpenGL FemtoVG uses OpenGL, and Skia - unless Vulkan is enabled - uses OpenGL, too. Linux's direct rendering manager (DRM) subsystem is used to configure display outputs. Slint defaults to selecting the first connected display and configures it at either its preferred resolution (if available) or its highest. Set the `SLINT_DRM_OUTPUT` environment variable to select a specific display. To get a list of available outputs, set `SLINT_DRM_OUTPUT` to `list`. For example, the output may look like this on a laptop with a built-in screen (eDP-1) and an externally connected monitor (DP-3): ``` DRM Output List Requested: eDP-1 (connected: true) DP-1 (connected: false) DP-2 (connected: false) DP-3 (connected: true) DP-4 (connected: false) ``` Setting `SLINT_DRM_OUTPUT` to `DP-3` will render on the second monitor. ## Display Selection with Vulkan When Skia's Vulkan feature is enabled, Skia will attempt use Vulkan's KHR Display extension to render directly to a connected screen. Slint defaults to selecting the first connected display and configures it at its highest available resolution and refresh rate. Set the `SLINT_VULKAN_DISPLAY` environment variable to select a specific display. To get a list of available outputs, set `SLINT_VULKAN_DISPLAY` to `list`. For example, the output may look like this on a laptop with a built-in screen (index 0) and an externally connected monitor (index 1): ``` Vulkan Display List Requested: Index: 0 Name: monitor Index: 1 Name: monitor ``` Setting `SLINT_VULKAN_DISPLAY` to `1` will render on the second monitor. To select a specific resolution and refresh rate (mode), set the `SLINT_VULKAN_MODE` variable. Set it to `list` to get a list of available modes. For example the output could look like this: ``` Vulkan Mode List Requested: Index: 0 Width: 3840 Height: 2160 Refresh Rate: 60 Index: 1 Width: 3840 Height: 2160 Refresh Rate: 59 Index: 2 Width: 3840 Height: 2160 Refresh Rate: 50 Index: 3 Width: 3840 Height: 2160 Refresh Rate: 30 Index: 4 Width: 3840 Height: 2160 Refresh Rate: 29 Index: 5 Width: 2560 Height: 1440 Refresh Rate: 59 Index: 6 Width: 1920 Height: 1080 Refresh Rate: 60 Index: 7 Width: 1920 Height: 1080 Refresh Rate: 59 Index: 8 Width: 1920 Height: 1080 Refresh Rate: 50 Index: 9 Width: 1680 Height: 1050 Refresh Rate: 59 ... ``` Set `SLINT_VULKAN_MODE` to `6` to select 1920x1080@60. ## Configuring the Keyboard By default the keyboard layout and model is assumed to be a US model and layout. Set the following environment variables to configure support for different keyboards: * `XKB_DEFAULT_LAYOUT`: A comma separated list of layouts (languages) to include in the keymap. See the layouts section in [xkeyboard-config(7)](https://manpages.debian.org/testing/xkb-data/xkeyboard-config.7.en.html) for a list of accepted language codes. for a list of supported layouts. * `XKB_DEFAULT_MODEL`: The keyboard model by which to interpreter keys. See the models section in [xkeyboard-config(7)](https://manpages.debian.org/testing/xkb-data/xkeyboard-config.7.en.html) for a list of accepted model codes. * `XKB_DEFAULT_VARIANT`: A comma separated list of variants, one per layout, which configures layout specific variants. See the values in parentheses in the layouts section in [xkeyboard-config(7)](https://manpages.debian.org/testing/xkb-data/xkeyboard-config.7.en.html) for a list of accepted variant codes. * `XKB_DEFAULT_OPTIONS`: A comma separated list of options to configure layout-independent key combinations. See the options section in [xkeyboard-config(7)](https://manpages.debian.org/testing/xkb-data/xkeyboard-config.7.en.html) for a list of accepted option codes.