lvgl_sim_qt

Provides a small example of how to embed an lvgl application in both a Qt Widgets and Qt Quick C++ application. Mouse events are supported, and in widgets, basic keyboard is supported (but must be manually hooked into a group). Treating the mousewheel as an encoder is left as an exercise to the reader. Demos that require lv_drivers are not currently supported. 32, 16, 8, and 1-bit color are supported, though most examples do not work well with 1-bit color.

Building

This software requires:

• C++ >= 14
• CMake >= 3.10
• Qt >= 5.9

git clone https://github.com/JonTheBurger/lvgl_sim_qt.git --recursive
cd lvgl_sim_qt
cmake -Bbuild -S.

Executables will be placed in build/lvgl_qt_quick and build/lvgl_qt_widgets.

Modifying

Edits lvgl_sim_qt has made to lv_conf.h and lv_ex_conf.h can be found by searching for /** lvgl_sim_qt */, which precedes all edits. To change which demo is being run, replace the lv_example function call found after /// lvgl_sim_qt_example in the main.cpp files. To change the tick period, modify LvglRenderer::Tick_Period_Ms. The default value is 16. Double buffering can be disabled by providing lv_disp_buf_init with nullptr instead of display_frame2_.

This project is setup to use lvgl v7.4.0. When upgrading, be sure to bump both the lvgl and lv_examples submodules to matching versions.

Implementation Notes

• If attempting to port code, note that LvglGraphicsView is added in Qt Designer using promote widget.
• Some amount of care has been taken to make this repository Qt6 compatible and lvgl update friendly, but no stable releases exist at time of writing, so these remain untested.
• Qt5 does not support 8-bit 332 color, so a quick and dirty 8-bit color palette is generated in this case.
• Both applications render to a QImage, so this common functionality is extracted into lvgl_qt/LvglRenderer.
• Forward declarations of classes are used when possible to speed up preprocess time.
• All render callbacks are piped through the Qt event loop, so no additional multithreading considerations should be necessary for this example.
• mouseMoveEvent only registers movement on a mouse click by default, so a simpler position query is used instead.
• Blindly setting Qt Quick properties from C++ is not a great idea in a production application. In fact, don't use this as an example of QML best practices.
• Decrease Tick_Period_Ms to improve responsiveness.
• Resize is supported, and mouse input coordinates are properly scaled.

Future Work

• Maybe hack around lv_drivers to get Qt based keyboard globally registered.