NoSignal-OS/os updates/sddm-theme/README.md

sddm-theme — login screen matching the desktop (palette, wallpaper, font)

A small Qt6 QML SDDM greeter theme ("caelestia") that mirrors the desktop:

• Colours come from the caelestia Material scheme (~/.local/state/caelestia/scheme.json) — surface card, primary login button, error colour, all from the live palette.
• Background is the user's current wallpaper (copied into the theme — the greeter runs as the sddm user and cannot read the user's home).
• Font is the exact font the shell uses: Google Sans Flex, loaded by file path from the shell's bundled asset (/etc/xdg/quickshell/caelestia/assets/google-sans-flex/…ttf), falling back to Rubik (system-installed) if that file moves.

Layout: big clock + date, centered card with username/password, primary "Log in" button, a session cycler line ("Session: … ⟳", click to cycle), and Sleep/Restart/Shut down text buttons bottom-right (only shown when SDDM reports the action is allowed). Pure QtQuick — no QtQuick.Controls styles, no SddmComponents, so there are no style dependencies to break.

Gaming sessions are hidden from the greeter. Gaming Mode is entered from the desktop only (Super+Shift+S → DeckShift switch); logging into a gamescope session from the login screen would bypass that flow. The cycler filters out any session matching gaming|gamescope|steam|big picture (covers "Gaming Mode (ChimeraOS)" and both "Steam Big Picture" entries), and if SDDM's remembered last session is a gamescope one (it is, right after a reboot from Gaming Mode) the selection snaps to the first desktop session instead of preselecting it.

Files

caelestia/Main.qml          the theme (pure QtQuick, Qt6)
caelestia/metadata.desktop  theme metadata (QtVersion=6)
caelestia/theme.conf        default colours = foam-sea scheme
sddm-theme-sync             -> /usr/local/bin (root): regenerates theme.conf +
                            background from the live scheme/wallpaper
install-sddm-theme.sh       idempotent installer (needs sudo)

Theme installs to /usr/share/sddm/themes/caelestia; selected via the drop-in /etc/sddm.conf.d/20-sddm-theme.conf ([Theme] Current=caelestia). Remove that drop-in to fall back to SDDM's default greeter.

Install / test

sh install-sddm-theme.sh          # installs + runs the initial sync (sudo)
sddm-greeter-qt6 --test-mode --theme /usr/share/sddm/themes/caelestia   # preview, no logout
sudo sddm-theme-sync              # re-sync after changing wallpaper

Verified in test mode on the box (renders correctly, no QML errors).

Keeping it in sync with wallpaper changes

The greeter is a snapshot: it matches the scheme as of the last sddm-theme-sync. The installer runs one sync; after the user changes wallpaper the login screen keeps the old look until sudo sddm-theme-sync is run again. Good follow-up for the builder: hook the sync into the wallpaper-change path (e.g. a polkit-less systemd path unit watching the scheme state file, or a sudoers rule + caelestia hook) — left out here to keep the component simple and safe.

Builder notes — how to put this in the ISO

1. Integrate the standard way: component → layer (~/.local/share/nosignal/sddm-theme/), migration 1781398800-sddm-theme.sh → nosignal-update/migrations/, copy-list line:

   [ -d "$SRC/sddm-theme" ] && cp -a "$SRC/sddm-theme" "$DEST/"
   

2. Bake the theme into the image (this one IS applied at build time, unlike the opt-in Gaming Mode): theme dir to /usr/share/sddm/themes/caelestia, sync script to /usr/local/bin/, the 20-sddm-theme.conf drop-in to /etc/sddm.conf.d/.
3. Seed the background at build time: copy the default wallpaper (foam-sea.png) to /usr/share/sddm/themes/caelestia/backgrounds/wallpaper.png. The shipped theme.conf already carries the foam-sea palette, so the greeter matches the default desktop on first boot before any user sync has run.
4. The theme requires the caelestia shell's Google Sans Flex asset path; if the shell tree moves under the project rename, update fontFile= in theme.conf (sync script too) — Rubik fallback covers any breakage.
5. No package delta (qt6 QML comes with sddm; jq already in base).
6. Verify on a clean VM: first boot greeter = foam-sea background, Material card, Google Sans font; change wallpaper in the desktop → run sudo sddm-theme-sync → greeter follows.