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Wayland Display/Inputs driver

Overview

The Wayland driver offers support for simulating the LVGL display and keyboard/mouse inputs in a desktop window.
It is an alternative to X11 or SDL2

The main purpose for this driver is for testing/debugging the LVGL application, it can also be used to run applications in 'kiosk mode'

Dependencies

The wayland driver requires some dependencies.

On Ubuntu

sudo apt-get install libwayland-dev libxkbcommon-dev libwayland-bin wayland-protocols

On Fedora

sudo dnf install wayland-devel libxkbcommon-devel wayland-utils wayland-protocols-devel

Configuring the wayland driver

  1. Enable the wayland driver in lv_conf.h

#define LV_USE_WAYLAND  1

  1. Optional configuration options:

  • Enable window decorations, only required on GNOME because out of all the available wayland compositors only Mutter/GNOME enforces the use of client side decorations

#define LV_WAYLAND_WINDOW_DECORATIONS 1

  • Enable support for the deprecated 'wl_shell', Only useful when the BSP on the target has weston 9.x

#define LV_WAYLAND_WL_SHELL  1

Example

An example simulator is available in this repo

Usage

  1. In main.c #incude "lv_drivers/wayland/wayland.h"

  2. Enable the Wayland driver in lv_conf.h with LV_USE_WAYLAND 1

  3. LV_COLOR_DEPTH should be set either to 32 or 16 in lv_conf.h

  4. Add a display using lv_wayland_window_create(), possibly with a close callback to track the status of each display:

#define H_RES (800)
#define V_RES (480)

/* Create a display */
lv_disp_t * disp = lv_wayland_create_window(H_RES, V_RES, "Window Title", close_cb);

As part of the above call, the Wayland driver will register four input devices for each display:

  • a KEYPAD connected to Wayland keyboard events

  • a POINTER connected to Wayland touch events

  • a POINTER connected to Wayland pointer events

  • an ENCODER connected to Wayland pointer axis events

Handles for input devices of each display can be obtained using lv_wayland_get_indev_keyboard(), lv_wayland_get_indev_touchscreen(), lv_wayland_get_indev_pointer() and lv_wayland_get_indev_pointeraxis() respectively.

Fullscreen mode

To programmatically fullscreen the window, use the lv_wayland_window_set_fullscreen() function respectively with true or false for the fullscreen argument.

Maximized mode

To programmatically maximize the window, use the lv_wayland_window_set_maximized() function respectively with true or false for the maximized argument.

Custom timer handler

Always call lv_wayland_timer_handler() in your timer loop instead of the regular lv_timer_handler().

Note: lv_wayland_timer_handler() internally calls lv_timer_handler()

This allows the wayland client to work on well on weston, resizing shared memory buffers during a commit does not work well on weston.

Wrapping the call to lv_timer_hander() is a necessity to have more control over when the LVGL flush callback is called.

The custom timer handler returns false if the frame from previous cycle is not rendered. When this happens, it usually means that the application is minimized or hidden behind another window. Causing the driver to wait until the arrival of any message on the wayland socket, the process is in interruptible sleep.

Building the wayland driver

An example simulator is available in this repo

If there is a need to use driver with another build system. The source and header files for the XDG shell must be generated from the definitions for the XDG shell protocol.

In the example Cmake is used to perform the operation by invoking the wayland-scanner utility

To achieve this manually,

Make sure the dependencies listed at the start of the article are installed.

The wayland protocol is defined using XML files which are present in /usr/share/wayland-protocols

To generate the required files run the following commands:

wayland-scanner client-header </usr/share/wayland-protocols/stable/xdg-shell/xdg-shell.xml > wayland_xdg_shell.h
wayland-scanner private-code </usr/share/wayland-protocols/stable/xdg-shell/xdg-shell.xml > wayland_xdg_shell.c

The resulting files can then be integrated into the project, it's better to re-run wayland-scanner on each build to ensure that the correct versions are generated, they must match the version of the wayland-client dynamically linked library installed on the system.

Current state and objectives

  • Add direct rendering mode

  • Refactor the shell integrations to avoid excessive conditional compilation

  • Technically, the wayland driver allows to create multiple windows - but this feature is experimental.

  • Eventually add enhanced support for XDG shell to allow the creation of desktop apps on Unix-like platforms, similar to what the win32 driver does.

  • Add a support for Mesa, currently wl_shm is used and it's not the most effective technique.

Bug reports

The wayland driver is currently under construction, bug reports, contributions and feedback is always welcome.

It is however important to create detailed issues when a problem is encountered, logs and screenshots of the problem are of great help.

Please enable LV_USE_LOG and launch the simulator executable like so

WAYLAND_DEBUG=1 ./path/to/simulator_executable > /tmp/debug 2>&1

This will create a log file called debug in the /tmp directory, copy-paste the content of the file in the github issue. The log file contains LVGL logs and the wayland messages.

Be sure to replicate the problem quickly otherwise the logs become too big

lv_wayland.h