Window transparency changing affecting active windows - autohotkey

Question

I have a code for hiding a window with AutoHotKey:
NumpadEnter::
Trans:=255
Loop
{
WinSet, Transparent, %Trans%, A
Sleep, 20
Trans-=1
if(Trans <= 0)
Break
}
return
Works like a charm, but you can see that execution time of this function is about 4-5 seconds. I can't switch between other windows in these 4-5 seconds, because other windows will be affected with WinSet function.
I need to save window handle to variable before the loop. And use it on the line with WinSet function.
How can I do that?

Answer 1

One way is to use the winexist() function with the A option as the wintittle parameter, that will give you the ID of the active window so that you can use that.
Something like this
NumpadEnter::
hWnd := WinExist("A")
Trans:=255
Loop
{
WinSet, Transparent, %Trans%, Ahk_id %hWnd%
Sleep, 20
Trans-=1
if(Trans <= 0)
Break
}
return
Hope it helps

Answer 2

Edit:
The full documentation: http://www.autohotkey.com/board/topic/80577-how-to-animate-a-gui-window/
Edit 2:
You mentioned it didn't work for you. Here is a working example on Windows 8 machine using Ahk_L (aka. Autohotkey_L or Autohotkey_Lexiko):
DetectHiddenWindows, On ;//Allow hidden windows to be detectable
SetWinDelay, -1 ;//Make Window update very fast (smooth animation)
FADE := 524288
SHOW := 131072
HIDE := 65536
FADE_SHOW := FADE+SHOW
FADE_HIDE := FADE+HIDE
SetFormat, Integer, Hex
FADE_SHOW+=0 ;//Converts to 0xa0000
FADE_HIDE+=0 ;//Converts to 0x90000
SetFormat, Integer, d
Gui, Font, w500 s35 Center, Verdana
Gui, Add, Text, , Hello! This Window will hide in 5 Seconds.
Gui, Show, NA Hide, Test Window ; //Create the Window hidden
Gui, +LastFound
GUI_ID := WinExist() ;//Get Window ID
Duration := 3000 ;//Speed of Window showing/hiding
DllCall("AnimateWindow","UInt",GUI_ID,"Int",Duration,"UInt", FADE_SHOW) ;//Fade in Window
Sleep, 5000 ;//Pause for 5 seconds
DllCall("AnimateWindow","UInt",GUI_ID,"Int",Duration,"UInt", FADE_HIDE) ;//Fade out Window
Return