ambientd/ambientd.py

#!/usr/bin/python

# Simple daemon to change brightness based on luminance
# TODO: add a config
# TODO: add debug option
# TODO: add dry-run
# TODO automatically find the right brightness path and do not assume intel_backlight

import time

# Open the luminance sensor device file
try:
    luminance_file = open('/sys/bus/iio/devices/iio:device0/in_illuminance_raw', 'r')
except OSError as err:
    print(err)
    exit(1)

# max luminance of the screen - 100 (maybe)
max_luminance = 400

# get luminance value, on fail return the max
def get_luminance():
    try:
        l = int(luminance_file.read())
        luminance_file.seek(0)
    except:
        l = max_luminance
    return l

# Get the max brightness 
max_brightness = 100
with open('/sys/class/backlight/intel_backlight/max_brightness', 'r') as f:
    max_brightness = int(f.read())
min_brightness = int(max_brightness * 0.05)

# loop delay in seconds
delay = 3

lum = [get_luminance()]*4
user_offset = 0
brightness_target = min_brightness
brightness_old = min_brightness
while True:
    lum.append(lum.pop(0))
    lum[0] = get_luminance()
    
    luminance = sum(lum)/len(lum)
    luminance_percent = min(luminance/max_luminance, 1.0)
    brightness_old = brightness_target
    brightness_target = max(int(luminance_percent * max_brightness), min_brightness)
    brightness_delta = abs((brightness_target - brightness_old)/brightness_old)

    # if the brightness changes by more than 10% reduce the user offset, scaling
    # with the delta, this accounts for large changes in brightness no longer
    # corresponding to the adjustments that the user made to the brightness
    if brightness_delta > 0.1:
        user_offset = int(user_offset * max(min(1-(brightness_delta*1.2), 1), 0))

    brightness_adjusted = min(max(brightness_target + user_offset, min_brightness), max_brightness)
    b = open('/sys/class/backlight/intel_backlight/brightness', 'w')
    b.write(str(brightness_adjusted))
    b.close()

    time.sleep(delay)

    # if the value of the brightness changed then update the user offset
    a = open('/sys/class/backlight/intel_backlight/actual_brightness')
    x = int(a.read()) - brightness_target
    a.close()
    if brightness_target != max_brightness or x < 0:
        user_offset = x

    print("brightness target: ", brightness_target, "user offset: ", user_offset, "brightness adjusted: ", brightness_adjusted)