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Appearance: background image, window opacity, backdrop

App background image

Settings > Appearance > Background image works on Linux. Two things used to hide it:

  • MainPageViewModel built the image with new BitmapImage(Uri) from the stored plain path (/home/me/pic.png). Uno does not load a bare file path that way, so the image never decoded. The file is now read and decoded from a stream (as the app icon loader does), and reloaded when the setting changes.
  • The light theme file area was an opaque #FAFAFA in LinuxDesktopResources.xaml, covering the image. It is now #C0FCFCFC, the Windows value. Over the solid #F3F3F3 window fill it looks the same as before when no image is set.

Opacity, fit and alignment settings apply as before. Per-folder desktop.ini backgrounds are Windows-only.

Window opacity

Settings > Appearance > Window opacity (20% to 100%) sets _NET_WM_WINDOW_OPACITY on the top-level X11 window (X11WindowChrome.SetWindowOpacity); 100% removes the property.

  • It fades the whole window, text and icons included. It is not a translucent background.
  • Support is reported honestly (X11AppearanceSupport): the slider is enabled only on a compositor known to honour the property (KWin, Mutter, Xfwm, picom, compiz). Under xwayland-satellite (niri) the property is not forwarded, so the slider is disabled with an explanation; with no compositor or an unrecognised one the slider is disabled and says so ("unknown"). A successful property write is never treated as proof.
  • High contrast forces opaque surfaces.

Backdrop: Solid / Transparent / Blur

Settings > Appearance > Backdrop (BackdropMode) with Background opacity (BackgroundOpacity), separate from window opacity.

  • Uno 6.7.135's Skia X11 host does request a 32-bit TrueColor visual (24-bit fallback) and a premultiplied BGRA surface. Uno.UI.Xaml.WindowHelper.SetBackground(window, Transparent) clears to transparent, so per-pixel alpha is possible without an Uno patch. This supersedes the earlier claim that no alpha visual was available.
  • Transparent: the window clear colour is transparent and App.Theme.BackgroundBrush carries the single alpha plane; the other region fills become transparent so they do not compound.
  • Blur: on KWin (X11) the empty _KDE_NET_WM_BLUR_BEHIND_REGION hint is set; the hint blurs behind the alpha pixels only. If unsupported (other compositors, xwayland-satellite, no compositor) the mode falls back to Solid and the UI says why. niri 26.04+ blur needs compositor window rules or ext-background-effect, not reachable from this X11 host.
  • Requires an alpha-capable compositor; only recognised compositors are enabled, others fall back to Solid.

Colour source

ColourSource = Files | Adwaita | System (migrated from the old UseAdwaitaTheme; existing choices are preserved). System reads the XDG portal (color-scheme, accent-color, contrast) and a bounded GTK named-colour reader (ISystemAppearanceService), and maps roles onto the app resources. Manual custom colours still win.

Not offered

  • Native Wayland / org_kde_kwin_blur. The Skia host is X11 only.
  • Backdrop material (Mica/Acrylic). Not implemented on Linux; the Backdrop material card is hidden.

Display scale on niri

On niri with xwayland-satellite, Files can render at 1x when XWayland publishes no DPI, leaving text and icons soft after compositor scaling. Enable Detect display scale from the compositor (experimental) in Settings > Appearance to detect the output scale at startup as a last resort. The boolean DetectCompositorDisplayScale defaults to false and is read directly from the XDG user settings file before Uno/window creation, without DI. Missing, non-regular or malformed settings leave detection off. The saved preference is read only when niri detection is eligible and no environment override is set. Restart required; some setups may double-scale. Existing scale hints retain precedence: UNO_DISPLAY_SCALE_OVERRIDE, any Xft.dpi resource, GDK_SCALE/GDK_DPI_SCALE, or QT_SCALE_FACTOR/QT_SCREEN_SCALE_FACTORS take precedence, including an explicit 1x or malformed hint. Both NIRI_SOCKET and WAYLAND_DISPLAY must be set.

The fallback queries the Unix socket named by NIRI_SOCKET for Outputs and FocusedOutput. The niri IPC protocol encodes these unit requests as JSON strings ("Outputs" and "FocusedOutput"), each terminated by a newline. It reads logical.scale from the focused output, or the first output if focus is unavailable. If socket detection fails, it resolves niri through the existing absolute-directory PATH lookup and runs niri msg --json outputs (and focused-output) without a shell. Socket detection and the CLI fallback each have a 500 ms budget, with up to another 500 ms to reap a terminated CLI process; replies are capped at 256 KiB. Errors, timeouts and invalid output scales leave the existing detection unchanged. Valid scales are clamped to 1–4, and the selected IPC/CLI source is logged once to stderr as [display-scale].

After the display/toolkit hints, FILES_NIRI_SCALE=1 forces this fallback on and FILES_NIRI_SCALE=0 forces it off, overriding the saved setting. Unset or other values use the setting. Neither value overrides display/toolkit hints. To choose a scale manually, launch with e.g. UNO_DISPLAY_SCALE_OVERRIDE=1.25 files (use your output's scale). Detection runs once before Uno starts; moving the window between outputs does not update the scale. A sandbox that cannot access the niri socket or executable may still need the manual override.