When using multiple monitors, and disconnecting and reconnecting them, I
noticed that Ubuntu 20.04 likes to set the external monitor's brightness
to 0.06, and the laptop's brightness to maximum. This is done without
changing the file at
(/sys/class/backlight/intel_backlight/actual_brightness).
I have modified the above script to work with multiple monitors, and to
change the brightness whenever a discrepancy between the desired and
actual brightnesses of all monitors is detected. The script assumes that
the internal laptop monitor's brightness is the only one to be changed
by brightness keys, and that the laptop's monitor is the first monitor
listed in the command `xrandr --listmonitors`.
Please reply if you have any issues with this script, as I do want to
improve this.
#!/bin/bash
#-----------------------------------------------------------------
# /usr/local/bin/brightness
# be sure this file is executable
#-----------------------------------------------------------------
# Define a function which finds luminance values in default Ubuntu
# location, converts into a factor of maximum brightness
# Get the max brightness for reference.
# Get it to 2 decimal places
backlight_path=/sys/class/backlight/intel_backlight
read -r max < "$backlight_path"/max_brightness
luminance() {
read -r level < "$backlight_path"/actual_brightness
printf "%.2f" $(bc <<< "scale=10;$level/$max")
}
# Set up infinite loop
while true
do
# Get the current brightness levels from xrandr. Store in array
mapfile \
-t xrandrbrightness \
< <(xrandr --verbose --current \
| grep Brightness \
| sed 's/.* //' \
| xargs printf "%.2f\n")
# Get list of monitors and store in array
mapfile \
-t monitors \
< <(xrandr --listmonitors --current \
| grep -v 'Monitors' \
| awk '{print $4}')
# If the current brightness for monitor 0 != the desired value +/-0.01
if (( $(echo "${xrandrbrightness[0]} != $(luminance)" | bc -l) ))
then
# Set the brightness of the laptop monitor to the desired value
echo "${monitors[0]} Current:${xrandrbrightness[0]}
Desired:$(luminance)"
xrandr --output "${monitors[0]}" --brightness "$(luminance)"
fi
# Go through the rest of the monitors in the list
for (( i=1; i<${#monitors[@]}; i++ ))
do
# Change the brightness of external monitors to 1 if they aren't
if (( $(echo "${xrandrbrightness[$i]} != 1.00" | bc -l) ))
then
echo "${monitors[$i]} Current:${xrandrbrightness[$i]}"
xrandr --output "${monitors[$i]}" --brightness 1
fi
done
# Check every 100ms
sleep 0.1
done
--
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Bugs, which is subscribed to Ubuntu.
https://bugs.launchpad.net/bugs/1831587
Title:
brightness control not work with OLED panel
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https://bugs.launchpad.net/hwe-next/+bug/1831587/+subscriptions
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