Change brightness of internal Laptop display and external HDMI/VGA monitor

redshift-hook_brightness.sh

#!/bin/bash

# or use sh instead of bash?

# set to executable flag, chmod +x !

set -eu

# on error : do not resume, but cancel , see https://stackoverflow.com/questions/13468481/when-to-use-set-e/13478622

#debug
exec >> ~/.redshift-hooks.log 2>&1

echo ""
echo "begin"


# Set brightness via xbrightness when redshift status changes

# Set brightness values for each status.
# Range from 1 to 100 is valid
brightness_day=100 #85
brightness_transition=50
brightness_night=10
#0 #30
# Set fps for smoooooth transition
#fps=1000
# Adjust this grep to filter only the backlights you want to adjust
#backlights=($(xbacklight -list | grep ddcci*))

echo "started now"
# output date
date

maxbrightness=$(mate-power-backlight-helper --get-max-brightness)

echo "max Laptop brightness = ${maxbrightness}"

set_brightness() {
	echo "set brightness to $1"
	ddcutil setvcp 10 $1 --display 1
	echo "return value was: $?"
	#calculate https://www.shell-tips.com/bash/math-arithmetic-calculation/
	laptopbrightness=$(expr $maxbrightness \* $1 / 100)
	echo "set laptop brightness to ${laptopbrightness}"
	#bypass security https://ubuntu-mate.community/t/keyboard-shortcut-for-display-brightness/11912/8 using pkexec
	#https://askubuntu.com/questions/78352/when-to-use-pkexec-vs-gksu-gksudo
	# alternative using sudo : https://askubuntu.com/a/469040
	pkexec mate-power-backlight-helper --set-brightness $laptopbrightness
	echo "return value was: $?"
	#for backlight in "${backlights[@]}"
	#do
	#	xbacklight -set $1 -fps $fps -ctrl $backlight &
	#done
}

if [ "$1" = period-changed ]; then
	echo "period changed : \"$2\" to \"$3\""
	case $3 in
		night)
			set_brightness $brightness_night
			;;
		transition)
			set_brightness $brightness_transition
			;;
		daytime)
			set_brightness $brightness_day
			;;
	esac
fi

echo "end"

# apt install ddcutil
# add user to group i2c-tools
# https://github.com/jonls/redshift/pull/512#issuecomment-359946517
# https://github.com/jonls/redshift/issues/436
# https://askubuntu.com/questions/894465/changing-the-screen-brightness-of-the-external-screen
# https://github.com/qualiaa/redshift-hooks

## ----------------------------------
## Redshift hooks:
## http://jonls.dk/2015/01/redshift-1-10-released/#hooks