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Tactility/.claude/rules/lvgl.md
Ken Van Hoeylandt 87215baf55 Fix for crash
2026-10-15 18:54:31 +02:00

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Architecture: LVGL

User interfaces should scale well for everything between very large (e.g. 1280x720) and small (e.g. 135x240) displays. Vertical and horizontal layouts are supported.

Two kernel modules cover LVGL:

  • lvgl-module (Modules/lvgl-module/, <lvgl/*.h>) owns LVGL's lifecycle: init/deinit, the LVGL task loop, and lvgl_lock()/lvgl_try_lock()/lvgl_unlock() mutex-based locking that any task must hold before touching LVGL objects. It bridges Tactility's device model to LVGL indevs (lvgl/devices/*.h: display, pointer, keyboard, trackball), and provides shared fonts (lvgl/fonts.h: Montserrat text sizes, Material Symbols icon sets for statusbar/launcher/shared use) and a few shared widgets (lvgl/widgets/*.h: toolbar, spinner, sliderbox).
  • lvgl-window-manager-module (Modules/lvgl-window-manager-module/, <lvgl_window_manager/*.h>) manages a single stacked window per app instance on top of lvgl-module. window_manager_start()/window_manager_stop() create/tear down the root widget (plus optional chrome from a configured WindowManagerScreenInitFn); window_manager_create()/window_manager_remove() push/pop an app's window and (re)populate it via a WindowCreateWidgetsFn. Only the topmost window ever has live widgets - burying and resurfacing a window deletes and rebuilds its widget tree rather than hiding/showing it. That rebuild-on-remove path can run create_widgets on a different app's thread (whichever app's window_manager_remove() call caused this window to resurface), so create_widgets must only rebuild already-committed state, never decide what happens next - state transitions belong in the app's own main() event loop, driven by real APP_EVENT_RESULTs. Widget pointers an app keeps become dangling once its window is buried (e.g. by a dialog it started). Use window_manager_create_ext() with a destroy_widgets callback that clears them, and skip widget updates from the app's own thread while they're cleared.

Keyboard navigation

  • Put groups of related focusable widgets (pills/chips, rows of buttons, toggle tiles) in a grid navigation container with lvgl_grid_navigation_add() (lvgl/grid_navigation.h). Only the container joins the input group: left/right moves within the group and up/down moves between groups.
  • Never make checkable widgets (switches, checkable buttons) direct input group members: LVGL toggles them on arrow keys. Grid navigation forwards only Enter to them.

Theming (LSS)

The themes in Modules/lvgl-module/source/themes/lv_theme_material*.c/.h are generated: never edit them directly. They're compiled from the LVGL Style Sheets in Modules/lvgl-module/themes/*.lss by the LSS tool, a git submodule at Modules/lvgl-module/lss/ (see its README.md for the syntax).

  • Styles are defined once and attached to widget types with apply(<widget>) { <style>: <state/part>; } rules. Custom widget classes of lvgl-module (e.g. lvgl_card_class) are declared with @widget <name>: <class>;.
  • Change material.lss and material_mono.lss together, then regenerate (requires pip install lark):
cd Modules/lvgl-module
python lss/compile.py themes/material.lss --output source/themes
python lss/compile.py themes/material_mono.lss --output source/themes