WinSet, Transparent, 0

Gui, Add, GroupBox, x42 y39 w260 h170 , GroupBox
Gui, Show, w479 h379, Untitled GUI
FINF()
return

GuiClose:
FOUTF()
ExitApp

FINF() {
    WinGet, currentWindow, ID, A
    fade("in",currentWindow)
}

FOUTF() {
    WinGet, currentWindow, ID, A
    fade("out",currentWindow)
}

fade(direction,ID) {
    if (direction = "in")
        transparency := 0
    else
        transparency := 255
    loop
    {
        if (direction = "in")
            transparency += 5
        else
            transparency -= 5
        WinSet, Transparent, %transparency%, ahk_id %ID%
        sleep 10
        if ( transparency >= 255 ) or ( transparency <= 0 )
            break
    }
}