Colour temp theme switcher

auto-theme-switch.md

Colour temp theme switcher

A simple utility that listens for changes to the desired colour temperature and changes the light/dark mode OS theme accordingly.

auto-theme.webm

Installation

Use the install.sh script directly, or look at the contents to inspire a manual alternative...

curl -s "https://gist.githubusercontent.com/RobinKnipe/79c48673ce2c920d65e661d32df1eba9/raw/install.sh" | bash -s

The install script takes care of downloading the necessary files and registering a unit with systemd. This means everything is running in the background ready to switch themes. The utility should start immediately and make a switch if one is required. The script is run as part of the user session and will persist across restarts, until disabled or removed using systemctl.

Customisation

Set the desired light/dark theme names for your OS, and day/night colour temperatures, in the properties file. By default it should be installed into the unit's directory at ~/.config/systemd/user/col-temp-switch/ct-switch.properties. The script that detects and triggers the theme changes can also be found here (ct-switch.sh), and could be easily extended to trigger other actions.

The trigger is set at the midpoint between the day temp (6500, full white by default) and the "target" night temp, as set in your OS's Night Colour Control feature. The day/night temps should be picked up from your existing OS settings, but can be configured (overridden) in the unit's properties file.

NOTE: after making changes to the properties file systemd must be notified before they take affect:

systemctl --user daemon-reload
systemctl --user restart col-temp-switch.service

OS support

This has been tested with Kubuntu, but other KDE/Plasma varients should also work, and the core concept of listening for dbus changes (with dbus-monitor) should be easy enough to implement for other systems.

col-temp-switch.service

[Unit]
Description=Colour temp theme switcher
After=dbus.service

[Service]
Type=simple
ExecStart=%h/.config/systemd/user/col-temp-switch/ct-switch.sh
Restart=always
RestartSec=5
EnvironmentFile=%h/.config/systemd/user/col-temp-switch/ct-switch.properties

[Install]
WantedBy=default.target

ct-switch.properties

# use the following settings to override the default values (the current values are the default)
#DAY_THEME=BreezeLight
#NIGHT_THEME=BreezeDark
#DAY_TEMP=6500
#NIGHT_TEMP=3200

# NOTE: if commented out here, the NIGHT_TEMP will be derived from the "Night Colour Control" set via
#       the OS, by lookng in the `~/.config/kwinrc` file

ct-switch.sh

#!/bin/bash

light="${DAY_THEME:-BreezeLight}"
dark="${NIGHT_THEME:-BreezeDark}"
dayTemp=${DAY_TEMP:-6500}

# Function to change Plasma theme
setPlasmaTheme() {
  temp=$(qdbus org.kde.KWin /ColorCorrect org.kde.kwin.ColorCorrect.currentTemperature)
  # fail fast and hope dbus info is available next rerun when temp is empty
  if [ -z "$temp" ] ; then
    echo "WARNING: no screen temp info available from dbus, bailing..."
    exit 1
  fi
  
  # check if night temp has been set in properties file
  if [ -z "$NIGHT_TEMP" ] ; then
    # try to derive the OS setting
    if [ -f ~/.config/kwinrc ] ; then
      nightTemp=$(grep -iE 'NightTemperature=[[:digit:]]+' .config/kwinrc | cut -d'=' -f2)
      # fallback to using target temp (only works at night)
      if [ -z "$nightTemp" ] ; then
        nightTemp=$(qdbus org.kde.KWin /ColorCorrect org.kde.kwin.ColorCorrect.targetTemperature)
        # check the nightTemp makes sense, i.e. it is lower than dayTemp - otherwise use default
        [ $dayTemp -gt $nightTemp ] || unset nightTemp
      fi
    fi
  fi
  # NOTE: the above ensures the desired night temp is rechecked each colour temp change to pick-up
  #       any changes the user may have made to the desired night temp, i.e. via the OS

  # echo "night: ${nightTemp}, current: ${temp}, day: ${dayTemp}"
  # Check for a change-over point half way between assumed full day and desired night temperatures
  if [ $(($temp * 2)) -gt $(($dayTemp + ${nightTemp:-3200})) ]; then
    # echo "setting plasma night theme: '${light}'"
    plasma-apply-colorscheme "${light}" >/dev/null
  else
    # echo "setting plasma night theme: '${dark}'"
    plasma-apply-colorscheme "${dark}" >/dev/null
  fi
}

# ensure the theme is correctly set when the unit first runs
setPlasmaTheme

# D-Bus subscription to monitor blue light filter status changes
profile="interface='org.freedesktop.DBus.Properties',member='PropertiesChanged',path='/ColorCorrect'"
dbus-monitor --session --profile "${profile}" |
  while read -r line; do
    setPlasmaTheme
  done

install.sh

#!/bin/bash

# Install colour temp auto dark mode switcher

gist="https://gist.githubusercontent.com/RobinKnipe/79c48673ce2c920d65e661d32df1eba9/raw"
base_dir="${HOME}/.config/systemd/user/col-temp-switch"
props="${base_dir}/ct-switch.properties"
script="${base_dir}/ct-switch.sh"
unit="${HOME}/.config/systemd/user/col-temp-switch.service"

# download the necessary files
function install_files {
  # do not overwrite existing properties file
  if [ ! -e "${props}" ] ; then
    # ensure the unit directory exists
    mkdir -p "${base_dir}"
    curl -Lso "${props}" "${gist}/ct-switch.properties"
    curl -Lso "${script}" "${gist}/ct-switch.sh"
  fi
}

# download and activate the systemd unit
function install_unit {
  # stop the service if it is already installed
  if [ -f "${unit}" ] ; then
    # check if the unit is already running
    if systemctl --user status col-temp-switch.service 2> /dev/null ; then
      systemctl --user stop col-temp-switch.service 2> /dev/null
      systemctl --user disable col-temp-switch.service 2> /dev/null
    fi
    systemctl --user daemon-reload
  fi

  curl -Lso "${unit}" "${gist}/col-temp-switch.service"
  chmod u+x "${script}"
  systemctl --user daemon-reload
  systemctl --user start col-temp-switch.service
  systemctl --user enable col-temp-switch.service
}

install_files
install_unit