; http://www.autohotkey.com/forum/viewtopic.php?t=55041
/*! TheGood
    Checks if a window is in fullscreen mode.
    ______________________________________________________________________________________________________________
    sWinTitle       - WinTitle of the window to check. Same syntax as the WinTitle parameter of, e.g., WinExist().
    bRefreshRes     - Forces a refresh of monitor data (necessary if resolution has changed)
    Return value    o If window is fullscreen, returns the index of the monitor on which the window is fullscreen.
                    o If window is not fullscreen, returns False.
    ErrorLevel      - Sets ErrorLevel to True if no window could match sWinTitle
   
        Based on the information found at http://support.microsoft.com/kb/179363/ which discusses under what
    circumstances does a program cover the taskbar. Even if the window passed to IsFullscreen is not the
    foreground application, IsFullscreen will check if, were it the foreground, it would cover the taskbar.
*/
IsFullscreen(sWinTitle = "A", bRefreshRes = False) {
    Static
    Local iWinX, iWinY, iWinW, iWinH, iCltX, iCltY, iCltW, iCltH, iMidX, iMidY, iMonitor, c, D, iBestD
   
    ErrorLevel := False
   
    If bRefreshRes Or Not Mon0 {
        SysGet, Mon0, MonitorCount
         SysGet, iPrimaryMon, MonitorPrimary
        Loop %Mon0% { ;Loop through each monitor
             SysGet, Mon%A_Index%, Monitor, %A_Index%
            Mon%A_Index%MidX := Mon%A_Index%Left + Ceil((Mon%A_Index%Right - Mon%A_Index%Left) / 2)
            Mon%A_Index%MidY := Mon%A_Index%Top + Ceil((Mon%A_Index%Top - Mon%A_Index%Bottom) / 2)
        }
    }
   
    ;Get the active window's dimension
    hWin := WinExist(sWinTitle)
    If Not hWin {
        ErrorLevel := True
        Return False
    }
   
    ;Make sure it's not desktop
    WinGetClass, c, ahk_id %hWin%
     If (hWin = DllCall("GetDesktopWindow") Or (c = "Progman") Or (c = "WorkerW"))
        Return False
   
    ;Get the window and client area, and style
    VarSetCapacity(iWinRect, 16), VarSetCapacity(iCltRect, 16)
    DllCall("GetWindowRect", UInt, hWin, UInt, &iWinRect)
    DllCall("GetClientRect", UInt, hWin, UInt, &iCltRect)
    WinGet, iStyle, Style, ahk_id %hWin%
   
     ;Extract coords and sizes
    iWinX := NumGet(iWinRect, 0), iWinY := NumGet(iWinRect, 4)
    iWinW := NumGet(iWinRect, 8) - NumGet(iWinRect, 0) ;Bottom-right coordinates are exclusive
    iWinH := NumGet(iWinRect, 12) - NumGet(iWinRect, 4) ;Bottom-right coordinates are exclusive
    iCltX := 0, iCltY := 0 ;Client upper-left always (0,0)
    iCltW := NumGet(iCltRect, 8), iCltH := NumGet(iCltRect, 12)
   
    ;Check in which monitor it lies
    iMidX := iWinX + Ceil(iWinW / 2)
    iMidY := iWinY + Ceil(iWinH / 2)
   
   ;Loop through every monitor and calculate the distance to each monitor
   iBestD := 0xFFFFFFFF
    Loop % Mon0 {
      D := Sqrt((iMidX - Mon%A_Index%MidX)**2 + (iMidY - Mon%A_Index%MidY)**2)
      If (D < iBestD) {
         iBestD := D
         iMonitor := A_Index
      }
   }
   
    ;Check if the client area covers the whole screen
    bCovers := (iCltX <= Mon%iMonitor%Left) And (iCltY <= Mon%iMonitor%Top) And (iCltW >= Mon%iMonitor%Right - Mon%iMonitor%Left) And (iCltH >= Mon%iMonitor%Bottom - Mon%iMonitor%Top)
    If bCovers
        Return True
   
    ;Check if the window area covers the whole screen and styles
    bCovers := (iWinX <= Mon%iMonitor%Left) And (iWinY <= Mon%iMonitor%Top) And (iWinW >= Mon%iMonitor%Right - Mon%iMonitor%Left) And (iWinH >= Mon%iMonitor%Bottom - Mon%iMonitor%Top)
    If bCovers { ;WS_THICKFRAME or WS_CAPTION
        bCovers := bCovers And (Not (iStyle & 0x00040000) Or Not (iStyle & 0x00C00000))
        Return bCovers ? iMonitor : False
    } Else Return False
}