Cosmic Shift

A redshift-style color temperature daemon for Pop!_OS / COSMIC — and any other Wayland compositor.

Classic redshift only speaks X11 gamma APIs, so it does nothing on a Wayland session. Cosmic Shift is a small, dependency-light C program that warms your screen at night the Wayland way.

How it works

Cosmic Shift has two backends and picks the best one automatically:

Backend	Mechanism	Where it's used
gamma	wlr-gamma-control-unstable-v1 hardware gamma tables (same as gammastep/wlsunset)	sway, Hyprland, river, niri — and COSMIC as soon as System76 ships gamma support
overlay	A full-screen, click-through, warm-tinted layer-shell surface on every output	COSMIC today, which doesn't implement any gamma protocol yet

The overlay color is derived from the same blackbody curve redshift uses. True gamma tables multiply each pixel per channel; an alpha-blended overlay mathematically cannot, so Cosmic Shift uses the least-squares affine approximation of the gamma result: mid-tones land on exactly the color hardware gamma would give, while the residual error is split between a slight lift of blacks and a slight dimming of whites. In practice the screen gets warmer and a little darker, like a real night light. The overlay is completely click-through and never takes focus. Because the backend is probed at startup, the moment your COSMIC update gains gamma support Cosmic Shift silently upgrades itself to the real thing.

Overlay tips:

• An overlay cannot subtract blue outright — blue is only reduced relative to red and green, either by painting warmth on (yellow cast) or by darkening the whole picture. -s picks the balance: try -s 0.25 if the yellow cast bothers you, -s 0 for pure dimming with no color at all.
• Very low temperatures amplify the trade-off. 3200–4500 K is the sweet spot; below ~3000 K expect dark content to look brownish.
• Add -b 0.85 if you want the screen dimmer still.

Wayland restores state when a client disconnects, so Cosmic Shift runs until stopped; Ctrl+C (or systemctl --user stop cosmic-shift) restores normal colors instantly.

Installing on Pop!_OS

sudo apt install build-essential pkg-config libwayland-dev
git clone https://github.com/sewalton/cosmic-shift.git
cd cosmic-shift
make
make install PREFIX=~/.local

That installs the cosmic-shift daemon, the cosmic-shift-gtk GUI and a "Cosmic Shift" entry in your app library — no sudo needed, everything lives in ~/.local. (System-wide instead: sudo make install.)

The GUI needs python3-gi and GTK 4, both preinstalled on Pop!_OS. All Wayland protocol XMLs are vendored in protocol/, so there are no other build dependencies. Works on any Wayland compositor: COSMIC uses the overlay backend (see below), while sway/Hyprland/river get true hardware gamma.

Uninstall with make uninstall PREFIX=~/.local.

GUI

cosmic-shift-gtk (installed alongside the daemon, and available as "Cosmic Shift" in your app library) is a redshift-gtk-style control panel: sliders for temperature, tint and brightness that update the screen live as you drag, an on/off switch, and a "Start at login" switch that manages the systemd user service for you. Settings persist in ~/.config/cosmic-shift.conf.

While running, the app shows an icon in the system tray (COSMIC's Status Area applet, or any StatusNotifierItem host). Closing the window minimizes to the tray — click the icon or pick "Open Cosmic Shift" from its menu to bring the window back, or "Quit" to exit the GUI. Neither turns off the color shift: quitting hands off to a background daemon. Without a tray host, closing the window hands off the same way. Requires python3-gi with GTK 4 (preinstalled on Pop!_OS).

Usage (command line)

cosmic-shift -t 3500              # constant warm screen (Kelvin)
cosmic-shift -l 40.7:-74.0        # follow the sun in New York
cosmic-shift -l 40.7:-74.0 -T 6500:3800   # custom day/night temps
cosmic-shift -t 4000 -b 0.9       # also dim slightly

Flag	Meaning	Default
-t TEMP	constant color temperature in Kelvin	4500
-l LAT:LON	location; enables automatic day/night mode	off
-T DAY:NIGHT	temperatures for automatic mode	6500:4000
-b BRIGHT	brightness multiplier, 0.1–1.0	1.0
-s TINT	overlay tint strength, 0.0–1.0; lower = less yellow cast, more dimming	0.5
-g GAMMA	gamma exponent, 0.5–2.0 (gamma backend only)	1.0
-m MODE	backend: auto, gamma, overlay	auto
-v	verbose output	off

In automatic mode the temperature is interpolated between night and day values while the sun is between −6° (civil dusk) and +3° elevation, the same thresholds redshift uses.

Run at login (systemd user service)

Edit the temperatures/location in cosmic-shift.service to taste, then:

mkdir -p ~/.config/systemd/user
cp cosmic-shift.service ~/.config/systemd/user/
systemctl --user daemon-reload
systemctl --user enable --now cosmic-shift

Stop or disable any time:

systemctl --user stop cosmic-shift      # colors restore instantly
systemctl --user disable cosmic-shift

Notes

• Multi-monitor and hotplug are handled: new or resized outputs get the current color automatically.
• Screenshots and screen recordings will include the tint while the overlay backend is active (hardware gamma, by contrast, is invisible to capture). Stop cosmic-shift briefly if you need color-accurate captures.
• -g (gamma exponent) has no effect in overlay mode.

Credits

Created by: Seth Walton

MIT licensed — see LICENSE.