Redshift Delayed Dimming Hack

Tags: linux hardware

Redshift automatically winds down the color of my display as day turns to night. I don’t know if it helps me sleep as the experts say it will, but it cuts down on eye strain significantly. I only have one gripe: my display gets really red really early in the evening. That’s not even a fault of the application. My schedule and the sun share equal blame in the premature dimming of my screen.

I choose to toggle Redshift off if I’m editing images or styles since colors matter for those tasks, but I often forget to toggle it on once I’m done. I wanted a way to make sure that Redshift was enabled an hour before I go to bed on most nights so that I’d know to wind down.

D-Bus provides a great conduit for that sort of runtime inter-process communication and configuration, but Redshift doesn’t yet come with a D-Bus interface.

Three factors join forces that allow me to schedule Redshift display dimming in a less ideal way:

1. Redshift listens for USR1 signals and toggles dimming on receipt.

2. xrandr displays current gamma information (and Redshift dims the display by altering the gamma)

3. Cron scripts run by my user account have access to my XAuthority credentials.

#!/usr/bin/env bash
 
export DISPLAY=:0
current_gamma=`xrandr --current --verbose | grep -i gamma | awk '{print $2}' | head -1`
 
if [ $current_gamma != '1.0:1.0:1.0' ]
then
    echo "Redshift is enabled"
else
    if [ `ps -ef | grep /usr/bin/redshift | grep -v grep | wc -l` -eq 0 ]
    then
        echo "Redshift isn't running"
        nohup gtk-redshift 1>/dev/null 2>/dev/null &
    else
        echo "Redshift is running but toggled off"
        killall -s USR1 /usr/bin/redshift
    fi
fi

In an ideal world I’d add D-Bus support to Redshift for a more elegant solution and a fun bit of C programming. It’s on my “someday maybe” list for a time when I can afford to fumble with a language I last used around 2004. In the meantime, this inelegant shell script does the job and gets me back to work on more pressing projects. Maybe it’ll work for you, too.