A Windows script written in Python 3.6+ to control brightness of connected monitors

bc.py

"""
A Windows script written in Python 3.6+ to control brightness of connected monitors.
Potentially this works only with Display Port connected monitors. 
Other type of cables could be supported as long as they use the DDC/CI protocol.

Author: Lorenzo Montanari
"""

from ctypes import windll, byref, Structure, WinError, POINTER, WINFUNCTYPE
from ctypes.wintypes import BOOL, HMONITOR, HDC, RECT, LPARAM, DWORD, BYTE, WCHAR, HANDLE
import sys
import getopt
from enum import IntFlag

_MONITORENUMPROC = WINFUNCTYPE(BOOL, HMONITOR, HDC, POINTER(RECT), LPARAM)


DEFAULT_PARAMETERS = {
    "brightness": 10
}


class Commands(IntFlag):
    """
    Short list of commonly used DDC commands. 
    Taken from: https://github.com/bhuvanchandra/ddcci
    """
    FACTORY_RESET = 0x04
    RESET_BRIGHTNESS_CONTRAST = 0x05
    FACTORY_RESET_GEOMETRY = 0x06
    FACTORY_RESET_COLOR = 0x08
    BRIGHTNESS = 0x10
    CONTRAST = 0x12
    INPUT_SOURCE_SELECT = 0x60
    AUDIO_SPEAKER_VOLUME = 0x62
    SETTINGS = 0xb0
    OSD = 0xca
    OSD_LANG = 0xcc
    COLOR_PRESET = 0xe0
    POWER_CONTROL = 0xe1


class PhysicalMonitor(Structure):
    _fields_ = [
        ('handle', HANDLE),
        ('description', WCHAR * 128)
    ]

    def __repr__(self) -> str:
        return self.description


def list_monitors():
    monitors = []

    def callback(hmonitor, hdc, lprect, lparam):
        monitors.append(HMONITOR(hmonitor))
        return True

    if not windll.user32.EnumDisplayMonitors(None, None, _MONITORENUMPROC(callback), None):
        raise WinError('EnumDisplayMonitors failed')

    physical_devices = []
    for monitor in monitors:
        # Get physical monitor count
        count = DWORD()
        if not windll.dxva2.GetNumberOfPhysicalMonitorsFromHMONITOR(monitor, byref(count)):
            raise WinError()

        # Get physical monitor handles
        physical_array = (PhysicalMonitor * count.value)()
        if not windll.dxva2.GetPhysicalMonitorsFromHMONITOR(monitor, count.value, physical_array):
            raise WinError()

        physical_devices.extend(physical_array)

    return physical_devices


def close_handle(handle):
    if not windll.dxva2.DestroyPhysicalMonitor(handle):
        raise WinError()


def set_vcp_feature(monitor, code, value):
    """Sends a DDC command to the specified monitor."""
    if not windll.dxva2.SetVCPFeature(HANDLE(monitor), BYTE(code), DWORD(value)):
        raise WinError()


def parse_args(argv):
    args_dict = {}

    def _print_help_and_exit(exit_code = 0):
        print("bc.py -b <brightness>")
        sys.exit(exit_code)

    try:
        opts, args = getopt.getopt(argv, "hb:", ["brightness="])
    except getopt.GetoptError:
        _print_help_and_exit(1)

    for opt, arg in opts:
        if opt == '-h':
            _print_help_and_exit()

        if opt in ("-b", "--brightness"):
            args_dict["brightness"] = int(arg)

    return args_dict


def main(argv):
    parsed = parse_args(argv)
    args = { **DEFAULT_PARAMETERS, **parsed }

    monitors = list_monitors()
    
    for monitor in monitors:
        handle = monitor.handle
        set_vcp_feature(handle, Commands.BRIGHTNESS, args["brightness"])        
        close_handle(handle)


if __name__ == '__main__':
    main(sys.argv[1:])