• nightlight
  • Usage
  • Configuration
  • Requirements
  • Local variables
  • Get times
  • Set dim value
  • Set display
  • Log
  • Main

nightlight

This is a shell script for automatically setting the screen colors and brightness, based on daytime.

The script is created via literate programming. You can find the code below.

Usage

1. Make sure the requirements are fulfilled
2. Obtain your location code from here and paste it into the script
3. Get the IDs of your displays with xrandr --listmonitors and paste them into the script
4. (Optionally) set the fading window which specifies the amount of minutes in which the screen is dimmed
5. Make sure the script is executable (chmod +x nightlight) and run it with ./nightlight

If you are unhappy with the display settings, you can revert them always by stopping the script and calling the following command manually. Please adjust your display ID and call for every display seperately.

  xrandr --output <DISPLAY_ID> --gamma 1:1:1 --brightness 1

Configuration

Configuration is currently done via editing the script directly or editing this file and then tangling it with Emacs (C-c C-v t).

  # SETTINGS
  # Edit from here -->

  location="GMXX0128"  # Location code (get it from https://weather.codes/search/)
  displays=("eDP-1-1") # Displays e.g. ("eDP-1-1" "eDP-1-2") (get displays with "xrandr --listmonitors")
  window=60            # Fading window in minutes

  # <-- to here

Requirements

Wget

Used for getting sunrise and sunset times

bc

Used for floating point calculations

xrandr

Used for setting screen colors and brightess, usually shipped with X.Org

To make sure that all requirements are fulfilled, we check them before doing anything else.

  if ! command -v wget &> /dev/null
  then
      echo -ne "\e[1mwget\e[0m was not found, please install it"
      exit 1
  elif ! command -v bc &> /dev/null
  then
      echo -ne "\e[1mbc\e[0m was not found, please install it"
      exit 1
  elif ! command -v xrandr &> /dev/null
  then
      echo -ne "\e[1mxrandr\e[0m was not found, are you running the X.Org Server?"
      exit 1
  fi

Local variables

The file containing the sunrise and sunset is stored in /tmp.

  file=/tmp/$location

To make calculations easier, we scale the fading window down to seconds (*60) and divide it in half (*0.5). This results in a multiplication with 30.

  window=$(( $window * 30 ))

The following variables are also used in the script, but not initialized. For the sake of completion they are described here.

sunrise

Time in seconds since the Unix epoch until sunrise

sunset

Time in seconds since the Unix epoch until sunset

now

Time in seconds since the Unix epoch until now

value

Dim value in range [0:1] (0 at day, 1 at night, values in between if in window around sunrise or sunset)

Get times

The times for sunrise and sunset are fetched from weather.com. To filter out the exact values from the response, the regular expressions from this blog post are used.

  function get_times {

      wget -q "https://weather.com/weather/today/l/$location" -O "$file"

      SUNR=$(grep SunriseSunset "$file" | grep -oE '((1[0-2]|0?[1-9]):([0-5][0-9]) ?([AaPp][Mm]))' | head -1)
      SUNS=$(grep SunriseSunset "$file" | grep -oE '((1[0-2]|0?[1-9]):([0-5][0-9]) ?([AaPp][Mm]))' | tail -1)

      sunrise=$(date --date="$SUNR" +%s)
      sunset=$(date --date="$SUNS" +%s)

  }

Set dim value

The dim value is based on the current time, the sunrise and sunset. This is a mess and should be done with arithmetics, but it works for now.

Finally the value is scaled into range [0,1].

  function set_dim_value {

      # Get current time
      now=$(date +%s)

      # Night - pre day
      if (( $now <= $sunrise - $window )); then
           value=$(( 2 * $window ))
      # Sun rising
      elif (( $now > $sunrise - $window )) && (( $now < $sunrise + $window )); then
           value=$(( (2 * $window) - ($now - ($sunrise - $window)) ))
      else
          # Day
          if (( $now <= $sunset - $window )); then
              value=0
          # Sun setting
          elif (( $now > $sunset - $window )) && (( $now < $sunset + $window )); then
              value=$(( $now - ($sunset - $window) ))
          # Night - after day
          else
              value=$(( 2 * $window ))
          fi
      fi

      # Scale dim value in [0:1]
      value=$(echo "$value / (2.0 * $window)" | bc -l)

  }

Set display

For setting the display values, we need to calculate the current RGB colors and brightness. Values for all displays are set according to the following table.

	Night (value 1)	Day (value 0)
Red	1.0	1.0
Green	0.9	1.0
Blue	0.8	1.0
Brightness	0.8	1.0

  function set_display {

      red=1.0
      green=$(echo "1.0 - (0.1 * $value)" | bc -l)
      blue=$(echo "1.0 - (0.2 * $value)" | bc -l)
      brightness=$(echo "1.0 - (0.2 * $value)" | bc -l)

      # Set nightlight for all displays
      for d in ${displays[@]}; do
          xrandr --output $d --gamma $red:$green:$blue --brightness $brightness
      done

  }

Log

To make it easier to follow the script, a timestamp is prefixed on every logging output.

  function log {
      log_time=$(date '+%H:%M')
      echo -ne "[\e[1m$log_time\e[0m] $1"
  }

Main

At first the times are updated. Then the current display values are applied every minute.

  echo -ne "\n..:: \e[1mnightlight\e[0m ::..\n\n"
  get_times
  log "got sunrise and sunset values\n"
  while true; do
      set_dim_value
      set_display
      log "applied display values\r"
      sleep 60
  done