XPS 7590 brightness control script

xbrightness.py

#!/bin/python3

"""Below is a script to watch for changes to the brightness device and change
   the display brightness using xrandr appropriately. This is useful for
   laptops with OLED screens, like the XPS 7590, as they don't have a physical
   backlight.

   Requires inotify to be installed (sudo pip install inotify).
   Made by Cameron Clough.
"""

import inotify.adapters
import subprocess
import time

output='eDP-1'
brightness_path='/sys/class/backlight/dell_backlight/brightness'

current_target = 1.0
last_target = 1.0

min_brightness = 0.01
max_brightness = 1.05
brightness_range = max_brightness - min_brightness

steps = 5     # number of animation steps
duration = 0.25 # animation duration in seconds

# apply the given screen brightness to the display using xrandr
def apply(brightness_pct):
    global output
    brightness = min_brightness + brightness_pct * brightness_range
    subprocess.run(['xrandr', '--output', output, '--brightness', str(brightness)])
    time.sleep(duration / steps)

# interpolate between two brightness values, start and end
def interpolate(start, end, step):
    global steps

    delta = end - start
    return (delta / steps) * step + start

# animate to a given brightness value
def animate(target):
    global steps
    global last_target

    if target == last_target:
        return

    for step in range(steps):
        brightness = interpolate(last_target, target, float(step) + 1.0)
        apply(brightness)

    last_target = target

# read the target brightness from the brightness device
def read_target():
    with open(brightness_path, 'r') as brightness_file:
        return float(next(brightness_file)) / 15.0

# read the historical target value from the brightness device and apply it
def initialise():
    global last_target
    last_target = read_target()
    apply(last_target)

def _main():
    global brightness_path

    # set screen brightness immediately, to match historical setting
    initialise()

    # watch for changes to the brightess device
    i = inotify.adapters.Inotify()
    i.add_watch(brightness_path)

    for event in i.event_gen(yield_nones=False):
        (_, type_names, path, filename) = event

        if 'IN_MODIFY' not in type_names:
            continue

        # animate any changes to the brightness value
        animate(read_target())

if __name__ == '__main__':
    _main()