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

Sound, brightness keys and the on-screen display

Press a volume key and a bar shows the level; press a brightness key and a bar shows that instead. Both come on with the profile: PipeWire with WirePlumber running underneath, the keymap’s volume, brightness and mic-mute binds routed through small scripts that step the control and poke the on-screen display, and a sink helper the Bluetooth picker calls.

configuration.nix and home.nix
programs.scoot.desktop = {
  enable = true;
  # No sound or OSD on this box (the binds run silent, as before):
  # audio.enable = false;
  # A longer on-screen hold (default 1.5 s):
  # audio.osd.timeoutMs = 2500;
};

What each press does: volume steps the default sink 5% (wpctl, fractions and percents both parsed, so 1.05 shows as 105), mute toggles it, mic-mute toggles the default source, brightness steps every backlight device the same relative amount, and the bar shows the rounded average. Past 100% (a 5%+ past full) the bar clamps into an urgent fill. Muted is the same bar washed out. Media keys stay silent, since play state already shows in the bar’s media module. Keyboard backlight LEDs are stepped by nothing (class leds, reserved and unbound; see the keymap below).

The OSD draws on the overlay layer with the look’s colors (background and text, accent fill, active-ring border, dim while muted, urgent past full), above fullscreen windows, so a fullscreen game never swallows the volume bar (music-desk paper and blue over a fullscreen terminal):

The volume OSD over a fullscreen terminal: the bar draws above the fullscreen window

It holds nothing when hidden: the daemon blocks until the next key press, keeps no surface, and wakes nothing (measured below). The bar’s volume, brightness, media and microphone modules stay the persistent display; the OSD is the transient one.

PipeWire runs with WirePlumber because wpctl is WirePlumber’s own CLI, and without a session manager there is no default-device memory. WirePlumber adds ~4.7 MiB (NAR bytes new over pipewire itself, measured at the pinned rev, aarch64-linux). The slot has no effects and no per-app routing UI.

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 RSS as VmRSS, wakeups as context-switch deltas over 62 s hidden:

Tool Version Full closure New over profile Idle RSS Wakeups hidden Why / why not
wob 0.16 57.5 MiB 225 KiB (2 paths: itself plus inih) ~2.2 MB 2 in 62 s the pick: no toolkit (wayland, inih, seccomp), overlay in its own source, hides itself after the timeout, per-output sections, one value [style] line per press
swayosd 0.3.1 1.06 GiB 228 MiB (49 paths) never runs here — a GTK4 stack (gtk4, layer-shell, pulse, ffmpeg, cups, avahi…) at ~19× the closure and ~1000× the marginal, and it replaces wpctl/brightnessctl/playerctl with its own backends instead of composing with them
a scootbar popup — 0 0 0 — rejected on complexity, not size: a key-driven transient OSD is a new surface role plus IPC plus an auto-dismiss timer in the bar’s Rust, and it forces the bar on for the OSD (the profile lets you turn the bar off); three wrapper scripts and no new protocol instead

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

Option Type Default Meaning
desktop.audio.enable bool true with the profile PipeWire with WirePlumber running, the OSD unit and scripts, the binds routed through them
desktop.audio.daemon enum ("wob") "wob" the program behind the OSD (a future scoot OSD widens this without renaming anything)
desktop.audio.osd.timeoutMs int (ms, at least 0) 1500 how long the OSD stays mapped after the last step
desktop.audio.osd.package / .dumpPackage package or null wob / pipewire (Linux-only: null off Linux) point at your own builds; null with the switch on fails evaluation naming it
desktop.theme.targets.osd.enable bool true theme the OSD from the look; false keeps wob’s own black-and-white (mute stays readable through a fixed gray style)

Switching sinks (speakers, headphones, a Bluetooth headset) from a terminal or a script (the Bluetooth picker’s Audio output… row runs the same helper; see WiFi and Bluetooth):

Terminal window
scoot-audio-sink list          # id plus name, one per line
scoot-audio-sink set 43        # by id, or by exact name
scoot-audio-sink cycle         # next after the current default, wrapping

set and cycle move the default and show its level on the OSD. One sink cycles onto itself with a message. Apple Silicon speakers keep their own tuning: the M2’s hand-wired speakers-heal unit stays yours to fold in (a user unit ordering after PipeWire). The profile runs the sound server and does not voice your hardware.

With no audio hardware at all (a headless box, a VM with no sound card) every bind fails per entry with the script’s own message on stderr and exit 1 (scoot-audio-sink list says no sinks, a volume step says no device), and the session carries on. A null tool beside audio.enable fails at evaluation instead, naming the option.

Troubleshooting, by symptom:

  • A volume or brightness key does nothing. Check the control first, not the bind: wpctl get-volume @DEFAULT_AUDIO_SINK@, brightnessctl -c backlight -m -l. Then the daemon: systemctl --user status scoot-osd; a dead unit means the fifo is missing and every step says “no OSD running”. Then check the bind reached the file ([binds] in ~/.config/scoot/config.toml).
  • The step lands but no bar shows. The OSD missed the fifo: same unit check as above. The step warns (“the step landed, the OSD did not show”) and exits 0; the control is fine, the display missed.
  • The bar never hides. Something keeps feeding the fifo, or the timeout is huge. Read ~/.config/wob/wob.ini (the generated file); the first content lines are the timeout.
  • scoot-audio-sink list is empty. No sinks: PipeWire runs with nothing behind it (a VM, or Bluetooth mid-reconnect). cycle with one sink stays put and says so.
  • Two bars stack. A second OSD runs beside this one (another wob, or swayosd): turn this one off (audio.enable = false) or uninstall the other.
  • The bar shows the wrong screen’s brightness. It shows the average across backlight devices, one bar for the whole desk.