brightness

#!/usr/bin/env python

import os
import subprocess
import sys

value = sys.argv[1]

command = ["brightnessctl", "--exponent=4", "set", value]
for device in os.listdir("/sys/class/backlight/"):
    cmd = command + [f"--device={device}"]
    print(' '.join(cmd))
    subprocess.run(cmd)

# How it works:
# * /sys/class/backlight/ddcci1 is created when the ddcci_backlight module is loaded.
# * Same interface as the laptop backlight (/sys/class/backlight/intel_backlight).
# * The module is loaded by the windows manager when the user switches to a workspace that has an external monitor.

# Manually reload the modules:
# 1. sudo modprobe -r ddcci_backlight ddcci
# 2. sudo modprobe ddcci
# 3. lsmod | grep ddc

# pros and cons of alternatives:
# * ddcutil: too complicated to compute percent values and increases with exponent
# * ddcci-driver-linux-dkms: no hotplug detection, module must be reloaded

# ddcutil alternative:
# command = ["ddcutil", "setvcp", "10"]
# command.extend(value)
#  faster (measured with --stats) but might fail
# command += ["--sleep-multiplier", ".2"]
#  much faster to select by bus than display
# command += ["--bus"]
# for display in range(1, 4):
#     cmd = command + [str(display)]
#     print(' '.join(cmd))
#     #subprocess.run(cmd)