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scoot — a grumpy ginger cat about to swat a window sidewaysscoot

Night light

Night light is on with the profile. The day’s blue fades to amber across the evening instead of snapping at sunset.

configuration.nix and home.nix
programs.scoot.desktop = {
  enable = true;
  # Warmer nights, or a fixed schedule of your own:
  # nightlight.nightTemp = 3000;
  # nightlight.sunrise = "06:30";
  # nightlight.sunset = "21:30";
  # No warming at all on this box:
  # nightlight.enable = false;
};

What runs: wlsunset as a user unit in scoot-session.target (so no other desktop starts it), driving every output’s gamma ramp through wlr-gamma-control-v1, one control per output. The schedule is manual by default (07:00/19:00, over 15 minutes), with no location, no geoclue and no network involved. Unlike home-manager’s services.wlsunset, which starts in the shared graphical-session.target, this unit starts in scoot’s own session scope, past the display import.

Measured at the pinned rev (8ce4ef6, aarch64-linux, on the M2): full closures by nix path-info --closure-size, marginals as new store paths over the profile’s own tools, idle wakeups as context-switch deltas over 60 s steady state under a headless scoot, RSS as VmRSS while running:

Tool Version Full closure New over profile Wakeups in 60 s steady RSS steady Schedule with no location
wlsunset 0.4.0 47.6 MiB (7 paths) 1 path, ~75 KiB (itself; glibc and wayland-client already ship with the profile) 0 ~2.3 MB yes (-S/-s)
gammastep 2.0.11 673.6 MiB (165 paths) 19 paths, ~33.7 MiB (geoclue, modemmanager, polkit, the ayatana indicator stack…) 16 ~6.1 MB no (always needs -l or geoclue)

Outside a transition wlsunset sleeps until the next boundary (zero wakeups), while gammastep polls about every few seconds. Only wlsunset warms on fixed times with nothing to locate it: gammastep without -l reaches for geoclue, which needs its system service and the network behind it, so the manual schedule is impossible there. gammastep stays as the location-based fallback (daemon = "gammastep" with latitude/longitude set): sunrise/sunset computed for where the box is, instead of fixed times.

The night temperature follows the look. Each look warms to its own default (its palette’s warmth: vinyl-sunset 3200, moonrise 3400, radial-burst 3500, music-desk 4000); a value you set in nightTemp wins per key, and theme.targets.nightlight.enable = false keeps the plain 3500 while the rest follows the look. Day stays 6500 everywhere (changes nothing).

Over the session lock the warming stays: gamma is output state, not pixels, so locking changes nothing about the ramp (protocols). A second output warming later is the same path: the daemon holds one control per output and re-pushes after a CRTC move, so hotplug needs no configuration. On --headless/--nested the ramp is accepted and changes nothing on screen, and raises no error.

scoot msg screenshot reads the framebuffer, which is pre-LUT and pre-CTM, so a capture shows the unmodified frame either way. See Screenshots. To see the ramp itself, read the CRTC color state back (drm_info or modetest on the --tty session).

Every value is an option, applied on rebuild/switch (the unit restarts into the new flags; no re-login):

Option Type Default Meaning
desktop.nightlight.enable bool true with the profile warm the screen (the daemon plus its unit)
desktop.nightlight.daemon enum ("wlsunset", "gammastep") "wlsunset" the program behind enable
desktop.nightlight.dayTemp int (Kelvin, 1000–10000) 6500 day color temperature (neutral: changes nothing)
desktop.nightlight.nightTemp int (Kelvin, 1000–10000, below dayTemp) 3500 (or the look’s, above) night color temperature (lower is warmer)
desktop.nightlight.sunrise / .sunset string (HH:MM) "07:00" / "19:00" manual schedule (read only without latitude/longitude)
desktop.nightlight.latitude / .longitude number or null null (manual schedule) where the box is, in decimal degrees (set both for location mode; gammastep needs both)
desktop.nightlight.duration int (seconds, 0–7200) 900 how long the day/night transition takes (manual schedule only; 0 snaps)
desktop.nightlight.gamma number (0.1–10) 1.0 extra gamma multiplier (neutral)
desktop.nightlight.package package or null the daemon’s tool (Linux-only: null off Linux) point at your own build of either daemon (its flags must agree with daemon); null with the switch on fails evaluation naming it
desktop.theme.targets.nightlight.enable bool true warm to the look’s own night temperature; false keeps the plain default (or your value)
configuration.nix and home.nix
programs.scoot.desktop = {
  enable = true;
  # Sunset where the box is, not fixed times:
  nightlight.daemon = "gammastep";
  nightlight.latitude = 37.33;
  nightlight.longitude = -121.89;
};

To switch the look itself at sunrise and sunset, run scoot look auto --sun. It takes its own --latitude and --longitude; it does not read desktop.nightlight.latitude, so type the same two numbers.

Force tonight now (wlsunset only): systemctl --user kill -s USR1 scoot-nightlight.service cycles forced-day, forced-night, then back to the schedule. There is no keybind for it, because the cycle has three modes while gammastep’s SIGUSR1 toggles it on and off, so a shared bind would do something different on each daemon.

Troubleshooting, by symptom:

  • The screen never warms. Check the unit: systemctl --user status scoot-nightlight, and that it started with the display (a hand-started session must reach scoot-session.target with WAYLAND_DISPLAY imported, on the desktop page). Then check the clock against the schedule: at noon with 07:00/19:00 nothing should be warm yet. Run the daemon by hand to hear its own cause (wlsunset -S 00:00 -s 23:59 warms at once in the evening state; kill it after, so two daemons do not fight over the outputs).
  • Two daemons fight over the outputs. Only one control holds an output at a time: the second get_gamma_control steals it and the first hears failed. Turn one off (this unit, or home-manager’s services.wlsunset, or a hand-started one); whichever stays owns every output.
  • A screenshot shows no warming. Expected: captures read pre-LUT/pre-CTM (above). Read the CRTC color state back instead (drm_info, modetest).
  • Warms nowhere, ever, on Apple silicon. The Apple display controller reports no gamma LUT (drm_info shows no GAMMA_LUT and gamma size 0 on both CRTCs), but it does expose a per-CRTC CTM color matrix, which scoot drives instead: the same unit warms normally, with the ramp’s white endpoints applied as a diagonal matrix (exact at the default gamma). If a push is still refused with failed, check drm_info for the CTM property; without it there is nothing to drive. The unit still runs with the right flags either way (check systemctl --user status scoot-nightlight).
  • gammastep exits at once. Without latitude/longitude it reaches for geoclue, which is not wired. Set both (or stay on wlsunset, whose manual schedule needs none). Evaluation refuses the missing pair before it ever runs.
  • A bad time or temperature fails the rebuild. The schedule reads 24-hour HH:MM, temperatures sit inside 1000–10000 with the night at or under the day, the transition inside 0–7200 seconds. Each refusal names the switch.
  • Headless or nested shows nothing. The ramp is accepted with no hardware LUT behind it, and no error. The unit still runs (and still sleeps between boundaries).