Event trigger with middle mouse button scrolling up/down(back/forward), how?

[freebsdx]

Greetings everyone. I am a newbie of this powerful wand.

My purpose, for simplicity, is to customize the event when I scroll the middle mouse button. 

For example, when I scroll the middle mouse button up (forward?), my script is expected to send "A" to the notepad, and when I scroll the middle mouse button down(backward?), my script is excepted to send "B" to the notepad. 

After googling for some time, I can't find the answer to my question. All tricks I got are the opposite things: pressing the key “A” to scroll the middle mouse button up and “B” to scroll the middle mouse button down.

Is any guru here willing to provide a hint? Your help is greatly appreciated. Thank you in advance. 

[mikell]

Scroll the middle mouse button, do you mean scroll the wheel ?

[freebsdx]

Scroll the middle mouse button, do you mean scroll the wheel ?

Exactly.

[mikell]

Ok, so here is an example which will be easy to arrange for your script

Hover the gui and scroll the mouse wheel

#include <GUIConstantsEx.au3>
#include <WindowsConstants.au3>

$gui = GUICreate("test", 120, 100)
GUISetBkColor(0x000000)
GuiSetFont(48, 600, 0, "Arial")
$label = GUICtrlCreateLabel("0", 10, 10, 85, 70, 2)
GUICtrlSetBkColor(-1, $GUI_BKCOLOR_TRANSPARENT)
GUICtrlSetColor(-1, 0xff0000)
GUISetState()  

GUIRegisterMsg($WM_MOUSEWHEEL, "WM_MOUSEWHEEL")
$n = 0

While 1
    $msg = GuiGetMsg()
    If $msg = $GUI_EVENT_CLOSE Then Exit
Wend

Func WM_MOUSEWHEEL($hWnd,$iMsg, $iwParam, $ilParam)
    #forceref $hwnd, $iMsg, $ilParam
    Local $a = GUIGetCursorInfo($gui)
    If $a[4] = $label Then 
        Local $iDelta = BitShift($iwParam, 16) 
        If $iDelta > 0 Then $n += 1
        If $iDelta < 0 Then $n -= 1
        GUICtrlSetData($label, $n)
    EndIf
  Return $GUI_RUNDEFMSG
EndFunc

[freebsdx]

My problem is solved. Thank you!!!