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Date: Tue, 15 Sep 2015 06:54:25 +0300
From: Andrey Repin <anrdaemon AT yandex DOT ru>
Reply-To: cygwin AT cygwin DOT com
Message-ID: <1548943127.20150915065425@yandex.ru>
To: Warren Young <wyml AT etr-usa DOT com>, cygwin AT cygwin DOT com
Subject: Re: Cygwin terminal weirdness
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References: <91152470 DOT 20150913213611 AT yandex DOT ru> <7AF4498C-6FE4-4541-9CAD-03EC3D867D72 AT etr-usa DOT com>
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Greetings, Warren Young!

>> Call "man" on a sufficiently long topic. man bash would be quite sufficient.
>> Or just `less` a long enough text.
>> Hold down "End" key.
>> The screen buffer will jump and tear repeatedly, until you release the key.

> That sounds like a video card performance issue, not a Cygwin, mintty, or less issue.

I can't believe it is a gfx performance issue, as I can't reproduce it with
PuTTY in the same situation.
I.e.
native console/local less = jumping and tearing.
mintty/local less = jumping and tearing.
native console/ssh+less = jumping and tearing.
mintty/ssh+less = jumping and tearing.
putty+less = no jumping, no tearing.

Let's try a different approach. The video id is ne3VmLZmD9g on a well-known
tube hosting service.

> I just tried it here on a VM hosted on a box with an NVIDIA GeForce GTX
> 680MX GPU, and all I saw was normal redrawing, with scarcely any tearing. 
> That chip is about 3 years old, which probably still outperforms any current CPU-integrated GPU.

> There are some small mitigations that might help.

> One would be to convince the maintainers of less to be smarter about
> repainting the whole screen when it isn’t necessary.  But given that they
> haven’t fixed the horizontal scrolling bug in the ~20 years I’ve been using
> it, I wouldn’t hold out hope on that front.

Well, let's say, this is unconvincing.

> Another would be to make mintty double-buffer its screen, if it doesn’t
> already.  That won’t help with the clear-screen call less is currently
> making, but it might reduce the tearing effect.

> The same thing is happening with something like “ls -lR /“.  The only
> difference is that you can easily see what’s going on in the “man bash”
> case, since the content remains static.

> Another way to see it is “vim /etc/sshd_config”, then hold down Ctrl-L.

I'm not familiar with vi/m, so I'll just trust you on the matter.


-- 
With best regards,
Andrey Repin
Tuesday, September 15, 2015 06:47:19

Sorry for my terrible english...