How to hold a modifier key so ahk sends keypresses to a different window - autohotkey

Question

I'm pretty new to ahk.
Say I have two separate vlc windows open and playing videos.
If one of the vlc windows is active, then I want to be able to hold a key to make all keypresses go to the other vlc window.
ie if I press Left, then it sends Left to the active vlc window, but if I hold ALT+Left, then it sends Left to the other vlc window.
If no vlc window is active, then I don't want autohotkey to do anything.
This is so I can control two vlc windows without having to click and choose which one is active.
I looked up GroupAdd hoping I could use a group that includes both vlc windows, but couldn't find a way to target specific vlc windows from the group to send keys to it.
edit: I got a very basic version working, but I feel it's pretty ugly. I would like a way to send any key that's pressed if you hold Shift to the other vlc window. Also this seems a bit unreliable in switching focus if you use it a few times quickly in succession.
GroupAdd, vlcgroup, ahk_exe vlc.exe
return
#IfWinActive ahk_exe vlc.exe
+Left:: ; shift-left
GroupActivate, vlcgroup, r
Send {Left}
GroupActivate, vlcgroup, r
return

Answer 1

A simple approach could be done like this:
#IfWinActive, ahk_exe vlc.exe
+Left::
WinGet, WindowList, List, ahk_exe vlc.exe
BottomMostVlcHwnd := WindowList%WindowList%
ControlSend, , {Left}, % "ahk_id " BottomMostVlcHwnd
return
^+Left::
WinGet, WindowList, List, ahk_exe vlc.exe
BottomMostVlcHwnd := WindowList%WindowList%
ControlSend, , ^{Left}, % "ahk_id " BottomMostVlcHwnd
return
...
#IfWinActive
You'd write out each hotkey.
WinGet, , List(docs) returns a legacy pseudo-array(docs) of hwnds to Vlc windows.
The last element in that array will be the bottom most window.
You can get the last element of a pseudo array via a dynamic variable trick WindowList%WindowList%.
Essentially you're accessing a variable named WindowListN, where N is the number for the last element in the pseudo-array.
Then ControlSend(docs) is used to send keys to the background window without the need to activate it.
And you refer to the background window by a window name like ahk_id 0x1234567(docs).
Of course writing out the hotkey for each key is pretty repetitive, so we can do something much better:
#IfWinActive, ahk_exe vlc.exe
+Left::
^+Left::
+Right::
^+Right::
+PgUp::
+PgDn::
WinGet, WindowList, List, ahk_exe vlc.exe
ControlSend, , % StrReplace(A_ThisHotkey, "+", "{") "}", % "ahk_id " WindowList%WindowList%
return
#IfWinActive
The hotkey definitions are just stacked on top of each other.
(If there were even more definitions, a loop with the Hotkey(docs) command could be nicer)
A_ThisHotkey(docs) will contain the hotkey that was used, and StrReplace(docs) is used to automatically replace the + with a {.
And finally the closing brace } is appended to the end.