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Message-ID: <21f98e05-7de6-41b0-9470-375c840fcb5f@towo.net>
Date: Thu, 30 Jan 2025 21:59:14 +0100
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Subject: Re: [mintty] Problem of the control key on focus change
To: cygwin@cygwin.com
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In-Reply-To: <Z5ibxnnSFMYTrzVn@calimero.vinschen.de>
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Precedence: list
From: Thomas Wolff via Cygwin <cygwin@cygwin.com>
Reply-To: Thomas Wolff <towo@towo.net>
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Errors-To: cygwin-bounces~archive-cygwin=delorie.com@cygwin.com
Sender: "Cygwin" <cygwin-bounces~archive-cygwin=delorie.com@cygwin.com>


Am 28.01.2025 um 09:56 schrieb Corinna Vinschen via Cygwin:
> On Jan 28 00:50, Thomas Wolff via Cygwin wrote:
>> Am 27.01.2025 um 12:17 schrieb Takashi Yano via Cygwin:
>>> Hi Thomas,
>>>
>>> A few days ago, Corinna asked me to check a problem of TTY.
>>> The problem is as follows.
>>>
>>> Reproduce steps:
>>> (1) Open mintty.
>>> (2) Open another mintty.
>>> (3) Place the second mintty window over the first one.
>>> (4) Hold ctrl key down.
>>> (5) Press 'd' key while holding ctrl key. The second mintty
>>>       window will be closed. Keep ctrl key still hold down.
>>> (6) Now the first mintty window is focused. Then press 'd' key
>>>       while holding ctrl key down.
>>> (7) The first mintty window will not logout but displays 'd'.
>>>
>>> I checked the pty and found the pty in the first mintty
>>> receives just 'd' but not Ctrl-D from mintty. In other words,
>>> fhandler_pty_master::write() is called with 'd'. So I suspect it
>>> might be a problem of mintty. Therefore, I tried old version
>>> of mintty. The results are:
>>>
>>> ...
>>>
>> Hi Takashi,
>> sorry this was attributed to pty, it is an issue of mintty I was aware
>> of which appeared in 3.7.2.
>> More precisely, it slipped in with
>> be73970877a99548aeeab60a2572ffb04b695066 "revise AltGr handling to
>> support flexible right-Alt+left-Ctrl combinations (#1266)", as a
>> trade-off for what I meant to be a final fix for control modifier
>> handling. I guess I hadn't considered it serious enough to reopen the
>> issue for another workaround. To be reconsidered...
> I just had a look into that commit and saw the description of a hidden
> option OldAltGrDetection right at the start.  Looks like
> OldAltGrDetection=2 is a temporary workaround for the problem.  What's
> the drawback of using it?
I've uploaded a fix to the github repository and tried to find an answer
to your question but couldn't yet...
Some background information: root cause of the trouble is Windows'
insane handling of the AltGr modifier and its failure to assign a
distinct virtual keycode to it. Instead it provides left-Control and
right-Alt key events, both with the same timestamp. That alone is a bit
tricky to detect as both Control and Alt are modifiers on their own.
Worse, software handling of AltGr detection or (in the case of remote
desktop software) generation often deviates from this scheme and even
Windows' own onscreen keyboard is buggy about this. Mintty has a number
of workarounds to handle that. Also, basically in a terminal emulator
the expectation is to handle all of Control, Alt etc and also their
combinations properly. For a example, on a keyboard where AltGr+q is
'@', Control+AltGr+q should be ^@, Alt+AltGr+q should be ESC @, and
Control+Alt+AltGr+q should be ESC ^@. All this is accomplished by
mintty. Together with the workarounds mentioned above, this is a
delicate area and I hope the fix found now interworks well with all such
software.
Thomas

>
> Thanks,
> Corinna
>


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