SetBackgroundPerMonitor

#NoEnv  ; Recommended for performance and compatibility with future AutoHotkey releases.
SendMode Input  ; Recommended for new scripts due to its superior speed and reliability.
SetWorkingDir %A_ScriptDir%  ; Ensures a consistent starting directory.

#SingleInstance Force

;check background on login
WM_DISPLAYCHANGE(0,0)

OnMessage(0x7E, "WM_DISPLAYCHANGE")
  return
  
WM_DISPLAYCHANGE(wParam, lParam)
  {
  ;WM_DISPLAYCHANGE is triggered any time a change is made to the display settings
  ;get the monitor count
  SysGet, mc, MonitorCount

  if mc = 1
    {
    ;if 1 monitor, use this background
    source = C:\*folder* ;do not include end forward-slash
    filesn = 
    files =
    filetopick = 
    file =
    background_file = 
    numberoffiles := 
    Loop,%source%\*.*,0,0
 	filesn.= A_LoopFileName . "`n"
    StringSplit, files, filesn, `n
    ;set tile and style accordingly
    Sleep, 600
    SetWallpaperStyle("Fill")
    ;set background file  
    Loop, %source%\*.*, 1, 1 
  	numberoffiles += 1  
    Random,filetopick,1,numberoffiles
    file .= files%filetopick% 
    background_file = %source%\%file%  
    DllCall("SystemParametersInfo", UInt, 0x14, UInt, 0, Str, background_file, UInt, 2) 
    SetTimer, Reset, 600000 ;reload every 10 minutes after new background is set
    }
  else if mc = 2
    {
    ;if 2 monitors, use this background
    source = C:\*folder* ;do not include end forward-slash
    filesn = 
    files =
    filetopick = 
    file =
    background_file = 
    numberoffiles :=
    Loop,%source%\*.*,0,0
 	filesn.= A_LoopFileName . "`n"
    StringSplit, files, filesn, `n
    ;set tile and style accordingly
    Sleep, 600
    SetWallpaperStyle("Tiled")
    ;set background file
    Loop, %source%\*.*, 1, 1 
  	numberoffiles += 1
    Random,filetopick,1,numberoffiles
    file .= files%filetopick%   
    background_file = %source%\%file%
    DllCall("SystemParametersInfo", UInt, 0x14, UInt, 0, Str, background_file, UInt, 2)
    SetTimer, Reset, 600000 ;reload every 10 minutes after new background is set
    } 
  }

#3::Reload

  Reset:
{
	Reload
}
  
  SetWallpaperStyle(style)
  {
    ;for tiled,    use TileWallpaper=1 WallpaperStyle=0
    ;for centered, use TileWallpaper=0 WallpaperStyle=0
    ;for strech,   use TileWallpaper=0 WallpaperStyle=2
    ;for fit,      use TileWallpaper=0 WallpaperStyle=6
    ;for fill, 	   use TileWallpaper=0 WallpaperStyle=10
    if style=Tiled
      {
      RegWrite, REG_SZ, HKEY_CURRENT_USER, Control Panel\Desktop, TileWallpaper, 1
      RegWrite, REG_SZ, HKEY_CURRENT_USER, Control Panel\Desktop, WallpaperStyle, 0
      }
  else if style=Centered
      {
      RegWrite, REG_SZ, HKEY_CURRENT_USER, Control Panel\Desktop, TileWallpaper, 0
      RegWrite, REG_SZ, HKEY_CURRENT_USER, Control Panel\Desktop, WallpaperStyle, 0
      }
  else if style=Streched
      {
      RegWrite, REG_SZ, HKEY_CURRENT_USER, Control Panel\Desktop, TileWallpaper, 0
      RegWrite, REG_SZ, HKEY_CURRENT_USER, Control Panel\Desktop, WallpaperStyle, 2
      }
  else if style=Fit
      {
      RegWrite, REG_SZ, HKEY_CURRENT_USER, Control Panel\Desktop, TileWallpaper, 0
      RegWrite, REG_SZ, HKEY_CURRENT_USER, Control Panel\Desktop, WallpaperStyle, 6
      }
  else if style=Fill
      {
      RegWrite, REG_SZ, HKEY_CURRENT_USER, Control Panel\Desktop, TileWallpaper, 0
      RegWrite, REG_SZ, HKEY_CURRENT_USER, Control Panel\Desktop, WallpaperStyle, 10
      }
  }