change_primary_display.py

import pywintypes
import win32api

#DISPLAY_DEVICE.StateFlags
DISPLAY_DEVICE_ACTIVE = 0x1
DISPLAY_DEVICE_MULTI_DRIVER = 0x2
DISPLAY_DEVICE_PRIMARY_DEVICE = 0x4
DISPLAY_DEVICE_MIRRORING_DRIVER = 0x8
DISPLAY_DEVICE_VGA_COMPATIBLE = 0x10
DISPLAY_DEVICE_REMOVABLE = 0x20
DISPLAY_DEVICE_DISCONNECT = 0x2000000
DISPLAY_DEVICE_REMOTE = 0x4000000
DISPLAY_DEVICE_MODESPRUNED = 0x8000000

#EnumDisplaySettingsEx.iModeNum
ENUM_CURRENT_SETTINGS = -1
ENUM_REGISTRY_SETTINGS = -2

#ChangeDisplaySettingsEx.dwflags
CDS_NONE                 = 0x00000000
CDS_UPDATEREGISTRY       = 0x00000001
CDS_TEST                 = 0x00000002
CDS_FULLSCREEN           = 0x00000004
CDS_GLOBAL               = 0x00000008
CDS_SET_PRIMARY          = 0x00000010
CDS_VIDEOPARAMETERS      = 0x00000020
CDS_ENABLE_UNSAFE_MODES  = 0x00000100
CDS_DISABLE_UNSAFE_MODES = 0x00000200
CDS_RESET                = 0x40000000
CDS_RESET_EX             = 0x20000000
CDS_NORESET              = 0x10000000

primary = r"\\.\DISPLAY5"
primary_device = None
primary_settings = None

# Find the settings of the new primary display
i = 0
while True:
    try:
        device = win32api.EnumDisplayDevices(None, i)
    except pywintypes.error:
        break

    if device.DeviceName == primary:
        primary_device = device
        primary_settings = win32api.EnumDisplaySettingsEx(device.DeviceName, ENUM_CURRENT_SETTINGS, 0)
        break
        
    i += 1
        
# Update all the positions of the displays relative to the new primary display
i = 0
while True:
    try:
        device = win32api.EnumDisplayDevices(None, i)
    except pywintypes.error:
        break

    if device.StateFlags & DISPLAY_DEVICE_ACTIVE != 0:
        print device.DeviceName
        settings = win32api.EnumDisplaySettingsEx(device.DeviceName, ENUM_CURRENT_SETTINGS, 0)
        print settings.PelsWidth, "x", settings.PelsHeight, "@", settings.Position_x, ",", settings.Position_y
        
        settings.Position_x -= primary_settings.Position_x
        settings.Position_y -= primary_settings.Position_y
        
        # CDS_UPDATEREGISTRY | CDS_NORESET = Don't make the changes yet until we've updated all the displays
        if device.DeviceName == primary:
            win32api.ChangeDisplaySettingsEx(device.DeviceName, settings, CDS_SET_PRIMARY | CDS_UPDATEREGISTRY | CDS_NORESET)
        else:
            win32api.ChangeDisplaySettingsEx(device.DeviceName, settings, CDS_UPDATEREGISTRY | CDS_NORESET)
        
    i += 1
        
# Update the displays with the registry settings
win32api.ChangeDisplaySettingsEx(None, None)