How does this AHK script work?

Question

The following AHK script automatically brings up the menu that you would normally get when you right-click on the uTorrent icon in the system task-bar tray:

DetectHiddenWindows, On
Process, Exist, utorrent.exe
WinGet, W, List, ahk_pid %ErrorLevel%
Loop %W%
 {
 WinGetClass, Class, % "ahk_id" W%A_Index%
 If InStr( Class, "µTorrent" ) {
   hWnd := W%A_Index%
   Break
 }}
PostMessage, 0x8001, 0,0x204,, ahk_id %hWnd% ; Right Click down
PostMessage, 0x8001, 0,0x205,, ahk_id %hWnd% ; Right Click Up

I understand most of it except the last two lines. 0x8001 is WM_APP+1. Why is a message in the WM_APP range used, and what exactly happens when these two messages are issued? Many thanks for the explanation.

Answer 1

According to MSDN (http://msdn.microsoft.com/en-us/library/windows/desktop/ms644927(v=vs.85).aspx#system_defined)

If your application is marked version 4.0, you can use message-identifier values in the range 0x8000 (WM_APP) through 0xBFFF for private messages.

So this would indicate that 0x8001 is an identifier that utorrent has chosen for a message. The 0x204 and 0x205 values are for the Right-Click Down and Up events respectively. My guess is that this code is intended to simulate a Right-Click on utorrent's icon in the Windows tray.

Also, if you're using Autohotkey_L the code can probably be simplified to three lines and perform the same:

DetectHiddenWindows, On
PostMessage, 0x8001, 0,0x204,, ahk_exe utorrent.exe ahk_class µTorrent ; Right Click down
PostMessage, 0x8001, 0,0x205,, ahk_exe utorrent.exe ahk_class µTorrent ; Right Click Up