Syncs laptop backligh to LG HDMI monitor

sync_backlight.sh

#!/usr/bin/env bash

# Listen for changes in backlight and applies to external screen
MAX_BACKLIGHT=$(</sys/class/backlight/intel_backlight/max_brightness)
last_backlight=$(</sys/class/backlight/intel_backlight/brightness)

acpi_listen | while IFS='/' read -ra line; do
    if [ "$line" = "video" ]; then
        # Read laptop backlight
        sleep 0.2
        backlight=$(</sys/class/backlight/intel_backlight/brightness)
        
        if [ $last_backlight != $backlight ]; then
            # Only when values are different to not overload ddcutil (works on i2c and is slow)
            brightness=$(( 120 * backlight / MAX_BACKLIGHT ))
            brightness=$(( brightness > 100 ? 100 : brightness ))
            contrast=$(( 150 * backlight / MAX_BACKLIGHT ))
            contrast=$(( contrast > 60 ? 60 : contrast ))

            echo -e "B:$brightness\tC:$contrast"

            ddcutil setvcp 10 $brightness
            ddcutil setvcp 12 $contrast

            last_backlight=$backlight
        fi
    fi
done