Change brightness percentage that screen brightness keys increase/decrease

MozillaUser3172 · 03-23-2020, 04:45 PM

Hi,
I'd like to change percentage of brightness that the screen brightness keys increase/decrease the brightness.

On laptop A, which seems to have only 8 brightness levels. This laptop's 0 brightness level is actually 50%, which sucks. The keys increase/decrease by 1 unit (1/16 total brightness) from 100% down to 50%.

On laptop B, which has 1000 levels, the keys increase/decrease by seemingly 90 units (1/11 total brightness).

How, on laptop B at least, can I reduce the delta to 50?

Thanks.

Mill J · 03-23-2020, 05:19 PM

I use xrandr. It has a brightness option. It's also capable of adjusting gamma levels(red:green:blue).

It's not very user-friendly though. Its cli and unless you write a script or something it won't save changes over a reboot.

Edit: I think I misread the question so answer might not be relevant.

MozillaUser3172 · 03-23-2020, 05:47 PM

Quote:

Originally Posted by Mill J

I use xrandr. It has a brightness option.

This is ultimately a question of, when the user presses Brightness Up or Brightness Down keys, what happens behind the scenes to alter the brightness?

Mill J · 03-23-2020, 06:11 PM

Quote:

Originally Posted by MozillaUser3172

This is ultimately a question of, when the user presses Brightness Up or Brightness Down keys, what happens behind the scenes to alter the brightness?

Right I misread your first post. I'm guessing it's dependant on either the desktop or a kernel driver or both.

0XBF · 03-23-2020, 07:40 PM

I'm not sure on how you would go about redefining the increment amount for the brightness keys in the existing system. You could manage it with a script though. I had written a brightness script for an old MBP a while ago. I reworked the code so it could be called by a custom keyboard shortcut. In my system (KDE5) I just unbound the existing keyboard shortcut and then made a custom shortcut for the brightness keys, calling the script as follows:

Code:

sh <your script directory>/brightness_keys.sh up

or

Code:

sh <your script directory>/brightness_keys.sh down

brightness_keys.sh (note the comments)

Code:

#!/bin/sh
#
# brightness_keys.sh
#
# Adjusts the backlight in user specified increments
#

set -e

# Check what exists at your own /sys/class/backlight/* and
# adjust accordingly.
SYS_DIR="/sys/class/backlight/intel_backlight"

# Set your own desired increment here. E.g. 5% for 20 steps full scale
INCREMENT_PERCENT=5

MAX_BRIGHT=$(cat $SYS_DIR/max_brightness)
CUR_BRIGHT=$(cat $SYS_DIR/brightness)
INCREMENT_BRIGHT=$(( ($MAX_BRIGHT * $INCREMENT_PERCENT) / 100))

if ! [ -z "$1" ]; then
    case "$1" in
        "up")
                if [ $(($CUR_BRIGHT + $INCREMENT_BRIGHT)) -ge $MAX_BRIGHT ]; then
                        # Ensures we always get up to 100
                        echo "$MAX_BRIGHT" > $SYS_DIR/brightness 
                else
                        echo "$(( $CUR_BRIGHT + $INCREMENT_BRIGHT ))" > $SYS_DIR/brightness
                fi
            ;;
        "down")
                if [ $(($CUR_BRIGHT - $INCREMENT_BRIGHT)) -le 0 ]; then
                        # Ensures we always get down to 0
                        echo "0" > $SYS_DIR/brightness
                else
                        echo "$(( $CUR_BRIGHT - $INCREMENT_BRIGHT ))" > $SYS_DIR/brightness
                fi
            ;;
        *)
                echo "Proper usage: sh brightness_keys.sh (up|down)"
                exit 1
            ;;
    esac
else
        echo "Proper usage: sh brightness_keys.sh (up|down)"
        exit 1
fi

exit 0

Good luck!

I should note that this script is changing the value of /sys/class/backlight/<your_backlight_vendor>/brightness, while staying within its set limits. You could set it manually if you wish by echoing values into there.

MozillaUser3172 · 03-24-2020, 06:07 PM

Quote:

Originally Posted by Mill J

Right I misread your first post. I'm guessing it's dependant on either the desktop or a kernel driver or both.

It seems all Linuxes that run acpid can "see" the brightness up/down keypressed.

If you run acpi_watch it will print them.

However the shell script in /etc/acpi maybe doesn't get run for these events. I'm still investigating.