ekklesiaandClaude Opus 5.5
aaa3f8d063
What Tiny Pebbles showed, what the lab measured (a new activity gives the same bare desktop; a file path as the fallback is ignored; live D-Bus is refused by the lockdown), the two parts of the fix, and the check with a real television switched on after a reboot — the one thing the lab cannot do, because KWin will not start with no screen. Co-Authored-By: Claude Opus 5.5 <[email protected]>
138 lines
7.5 KiB
Markdown
138 lines
7.5 KiB
Markdown
# Classroom display size (Plasma v2)
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Each room keeps its own `UI_SCALE` in `/etc/ekklesia-classroom/device.conf`.
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Package upgrades preserve the value. Plasma applies it at every classroom login.
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Native display resolution is unchanged.
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## Administrator setting
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On the classroom keyboard press **Meta+Ctrl+Alt+Shift+D** to open Display size.
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It is hidden from application lists and the teacher's panel. Saving requires
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administrator authentication through polkit; the keyboard shortcut grants no
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privilege. Choose a percentage and press Save and apply. Canceling the password
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prompt leaves the saved setting unchanged.
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Start at **200% for a 4K TV**, which gives 1920×1080 logical space while retaining
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3840×2160 output. The offered values are 100, 125, 150, 175, 200, 225, 250 and 300%.
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The choice applies to all connected, enabled displays on that classroom computer.
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For SSH administration, the fixed-purpose helper can also be run as root:
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```
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sudo /usr/local/bin/classroom-set-scale 2
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```
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It writes only UI_SCALE, preserving room configuration, broker credentials and
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file ownership and permissions. The new size takes effect at the next classroom
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login, or by running `classroom-scale` inside the classroom's graphical session.
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The hidden window saves and applies in one operation.
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## Implementation and validation limits
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`classroom-scale` uses `kscreen-doctor`; the login autostart runs only in KDE and
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the script applies only to the classroom account. Values read from older/manual
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configurations remain clamped to 0.8–3.0; invalid/nonfinite values become 1.0.
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The helper accepts only the window's predefined choices, takes no paths, and
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writes the root-owned settings file atomically. Polkit requires auth_admin for
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every save, with no retained authorization.
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Hardware checks required: shortcut registration, administrator authentication,
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200% at 4K, logout/reboot persistence, and Chrome/Parent Call/DVD sizing. XWayland
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applications may be softer than native Wayland applications when scaled.
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## Wallpaper in the v2 package
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The approved background source is `config/wallpapers/classroom-calm.png`. The
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package installs it at `/usr/share/backgrounds/ekklesia/classroom-calm.png`, the
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path used by the packaged Plasma layout. The layout is rebuilt at login, so
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upgraded classrooms receive the package wallpaper without per-room copying.
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### A desktop the layout never saw (0.2.6.6)
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Tiny Pebbles came through the 0.2.2 → 0.2.6.4 upgrade showing Plasma's own
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purple wallpaper. Its desktop was containment 10 with no `Wallpaper` group;
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River Kids' is containment 1 with one. The package and the picture were the
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same on both.
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The layout sets the wallpaper on the desktops that exist *while it runs*.
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Plasma makes a desktop for every screen or activity that appears later, and
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it makes those without the layout. 0.2.2's updater rebooted as soon as it
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had installed, at 03:00–03:30. A television switched off at the set is
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usually no screen at all, so the layout would have run with no desktop, and
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the desktop Plasma made when the television came on was bare. A panel built
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with no screen takes number 1 and its eight applets 2–9, which is exactly
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how a desktop ends up as 10. **The television is inferred, not observed**.
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See the hardware check in [testing.md](testing.md#the-television-switched-on-after-a-night-time-reboot).
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Measured in the lab (Plasma 6.3.6, Debian 13):
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| What was tried | What happened |
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| --- | --- |
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| Activity manager delayed 20 s at login | Plasma waited for it; desktop 1, wallpaper right. Not the cause |
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| A new activity created mid-session | Plasma made desktop 11 with no `Wallpaper` group, the same shape as Tiny Pebbles' 10. The screen showed Plasma's *Next*; the panel was untouched |
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| Look-and-feel default `Image=` set to a **file path** (0.2.2–0.2.6.5) | Ignored. `DefaultWallpaper` in libkworkspace6 looks the value up as a wallpaper **package** under `wallpapers/<name>`, the way Breeze says `Image=Next` |
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| The same default set to a **package name**, whose one image links to the file | Desktop 11, still with no `Image`, showed the classroom's picture after a shell restart |
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| Setting it live over D-Bus (`evaluateScript`, `plasma-apply-wallpaperimage`) | Refused: "Widgets are locked". The classroom's lockdown forbids the scripting console, and it stays forbidden |
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| Disabling the only screen to reproduce a screenless start | KWin refuses ("Disabling all outputs … is not allowed"), and the nested lab cannot hot-plug a screen |
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So there are two parts, and they do different jobs:
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* **The default is now a package**, `/usr/share/wallpapers/EkklesiaClassroom`.
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Its image is a link to the file above, and the look and feel names it.
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Any desktop Plasma makes without the layout shows the classroom's picture
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with nothing having to run. This is the fix for Tiny Pebbles.
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* **`classroom-desktop-wallpaper`** writes `wallpaperplugin=org.kde.image` and
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the classroom `Image` into every desktop containment already in the file,
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so the configuration says what the screen shows. It finds desktops by
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plugin (`org.kde.plasma.folder`, `org.kde.desktopcontainment`), never by
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number. It changes nothing else, and it does not write a file that is
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already right. It runs as plasmashell's `ExecStartPre`, the one moment
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the shell does not own the file: every login, every reboot, every restart
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after a crash. At a login it usually finds nothing, because
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`classroom-desktop-reset` has just removed the file for the layout to
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rebuild.
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To apply it in a running session without logging out, from the maintenance
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terminal:
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```
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classroom-desktop-wallpaper --check # read-only
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systemctl --user restart plasma-plasmashell.service # the panel blinks, windows stay
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```
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Run without `--check` while the shell is up, it refuses and prints that
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second line rather than edit the file underneath the shell.
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Tests: `tests/test-classroom-desktop-wallpaper.sh` (in the build) covers
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Tiny Pebbles' own file, a healthy River Kids file, differing numbers,
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idempotence and the guard. `tools/lab/wallpaper-check` covers real Plasma,
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reading the colour off the screen, and runs inside `tools/lab/dirty-upgrade`.
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`tools/validate-trixie-release.sh` covers the installed package when
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upgrading from a previous release.
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## What the one number reaches
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`classroom-ui-scale` prints it, clamped, and everything that cannot read
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the display scale for itself asks that command rather than the file:
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* **Plasma** — the panel, the clock, notifications, the volume display and
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every dialog, because `classroom-scale` sets it as the display's scale
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through `kscreen-doctor` at every login.
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* **Chrome** — `--force-device-scale-factor`, because Chrome on the sway
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session was measured not to follow the compositor's output scale on its
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own. **Under Plasma it does**, so this is now a second scaling: measured
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at 150%, Chrome's pages report `devicePixelRatio` 2.25, not 1.5. Left as
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it is in 0.2.6.1 because it is the size teachers know; see
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[wonder-ink.md](wonder-ink.md#how-large-a-lesson-is).
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* **Wonder Ink** — its window follows the compositor as every Qt
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application does, and its *pages* start at a zoom of `UI_SCALE`, so a
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lesson is the size the browser shows it.
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* **The disc player's own surfaces** — they are measured in the logical
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pixels the compositor is already scaling, so they follow without being
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told.
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The clock is the one thing that used to be left behind. It was pinned at
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15 points, which is the same 15 points at every scale, and on a 4K
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television it was a clock nobody at the back of the room could read. It
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is sized by the bar now.
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