Linux (Qt 6)

Tier 2 · Demi-supported

linux-qt renders Qt 6 Widgets through a small compiled C++ shim. It’s the toolkit beneath KDE Plasma, its QAccessible layer bridges to the native accessibility API on every OS (no other Day backend does that today), and it is portable enough to also be a development target on macOS and Windows.

Home

Controls

Canvas & shapes

Tabs

Getting started

Qt 6 development packages and pkg-config are the requirement; build.rs builds the shim without moc.

sudo apt install qt6-base-dev pkg-config      # Debian/Ubuntu
sudo dnf install qt6-qtbase-devel pkgconf     # Fedora
brew install qt pkg-config                    # macOS, for the macos-qt dev combo

cargo install day-cli
day new app my-app --toolkit linux-qt
cd my-app
day launch -p linux-qt

Two optional modules enable two pieces; without a module the build still succeeds and the piece degrades:

Module	Enables	Without it
`qt6-webengine-dev` (`Qt6WebEngineWidgets`)	`webview()`	a URL label; navigation calls become no-ops
`qt6-multimedia-dev` (`Qt6MultimediaWidgets`)	`media()`	a URL label; play/pause become no-ops

day doctor --toolkit qt probes Qt 6 Widgets, rcc, and the packaging tools (flatpak-builder, linuxdeploy, linuxdeploy-plugin-qt); it does not check WebEngine or Multimedia.

day pack -p linux-qt        # single-file .flatpak (org.kde.Platform runtime) AND a portable .appimage

day pack produces both formats by default: the flatpak resolves Qt from its runtime; the AppImage carries its own.

The webview crate declares a Qt WebEngine BaseApp requirement. If your binary links the engine, day pack includes that base (about 87 MB of Chromium), because no runtime ships it. Apps that don’t link it stay small; day pack inspects the built binary to decide.

Caveats

toggle is a QCheckBox, because Qt Widgets has no native switch control, so the same Day code shows a checkbox here and a switch elsewhere.
The list is emulated. Day drives a QScrollArea with its own recycling rather than QListView, so very large lists behave differently than a model/view Qt app would.
Forced light/dark needs Qt 6.8+. DAY_THEME uses QStyleHints::setColorScheme; on older Qt (Ubuntu 24.04 ships 6.4) Day falls back to the Fusion style with a hand-built dark palette.
No spell-check, because Qt ships none; Cap::TextSpellCheck reports unsupported and the patch is a no-op.
Lottie and map have no Qt arm; each renders its placeholder. cover() presents as a topmost window-sized child (no transition, programmatic dismissal only).
Qt on macOS and Windows (macos-qt, windows-qt) is a development combo, and stays at Tier 4, so day pack skips it. Windows builds against MSYS2’s Qt 6 with a GNU Rust toolchain (setup) and is marked experimental in CI. MSYS2 has no Qt 6 WebEngine, so the web view degrades to its URL label there. CI’s x86-64 MinGW ld additionally drops external piece renderer registrations, so those pieces draw placeholders on that build; a clang/lld MSYS2 environment keeps them.

What each piece becomes

The generated coverage matrix, checked in CI, covers every backend; this table adds links and notes.

Day piece	Qt class
`column` / `row` / `nav_stack` / `section`	`QWidget` (Day owns layout)
`label`	`QLabel`
`button`	`QPushButton`
`toggle`	`QCheckBox`; see the caveat above
`slider`	`QSlider`
`text_field`	`QLineEdit`
`text_area`	`QPlainTextEdit`
`picker().menu()`	`QComboBox`
`picker().segmented()`	checkable `QPushButton`s in an exclusive group
`picker().inline()`	`QRadioButton`s in an exclusive group
`progress(f)`	`QProgressBar`
`spinner()`	`QProgressBar` in busy mode (Qt has no spinner widget)
`divider`	`QFrame` (`HLine`)
`scroll`	`QScrollArea`
`list`	`QScrollArea` with Day-side recycling
`nav` (split)	`QSplitter`; the stack header adds a `QToolButton`
`nav_menu`	`QListWidget`
`tabs`	`QTabWidget`
`image`	`QLabel` subclass painting a scaled pixmap
`vector`	the same `QLabel` subclass painting the raster cache PNG (`.tint` has no Qt arm yet; glyphs draw as authored)
`canvas`	`QWidget` subclass painting with `QPainter`
dialogs / alerts	`QMessageBox`
prompts	`QInputDialog`
file dialogs	`QFileDialog`
menu bar / context menus	`QMenuBar` / `QMenu`
external `activity()`	`QProgressBar` (busy)
external `combobox()`	editable `QComboBox`
external `search_field()`	`QLineEdit` with a clear button and a find icon
external `date_picker()`	`QDateEdit` with a calendar popup, or `QCalendarWidget` inline
external `time_picker()`	`QTimeEdit`
external `webview()`	`QWebEngineView`
external `media()`	`QMediaPlayer` + `QVideoWidget`

Text measurement asks QLabel for its natural width with wrapping temporarily off, then heightForWidth at the granted width; the text area uses QTextDocument. Everything else uses sizeHint().