Re: [PATCH] Strange behavior of cmd.exe when hammered with clear screen operations from Cygwin program.

[Corinna Vinschen <corinna-cygwin at cygwin dot com>]

On Aug  2 23:19, Kaz Kylheku wrote:
> On 01.08.2016 01:51, Corinna Vinschen wrote:
> > On Jul 29 08:59, Kaz Kylheku wrote:
> > > On 29.07.2016 03:39, Corinna Vinschen wrote:
> > > > I applied a patch to perform this action.  It's in the latest
> > > > 2.6.0-0.5 test release I just announced.
> > > [...]
> > > I've done some interactive testing with this using
> > > the interpreter for a Lisp dialect. I would evaluate
> > > this expression to generate a 5 second delay and then
> > > a clear screen VT100 sequence:
> > > 
> > >   (progn (usleep 5000000) (put-string "\e[2J"))
> > > 
> > > during this time, I would scroll the buffer somewhere.
> > > 
> > > I also tested with a cursor position somewhere in the
> > > middle of the window, having issued:
> > > 
> > >   (put-string "\e[12H")
> > > 
> > > The programming language details don't matter; we
> > > could do this with bash echo $'\e...' and sleep 5.
> > > [...]
> > > With the third patch, I've run into behavior in which the
> > > display isn't cleared at all if the clear is issued
> > > in a scrolled-back state.
> > 
> > I can't reproduce this.  If I don't click wildly on the scroll bat at
> > the time the clear screen action takes place (so I move the window right
> > after clear screen), the cursor is positioned at the top of the screen,
> > at the end of the buffer.  So, how would I reproduce your observation so
> > that all window positioning is guaranteed to take place *before* the
> > clear screen action and still see the broken output?
> 
> Hi Corinna,
> 
> I have figured out how to reproduce it. There are two
> necessary conditions. No, three:
> 
> 1. You must scroll the display all the way to the top
>    as far as you can before the clear screen is issued.
> 
> 2. The scrollback history must be full. I.e., this
>    won't happen in a fresh cmd.exe window. First, print
>    thousands of lines of stuff to make the buffer "tall".
>    This is why  it only started happening to me after some
>    amount of testing; I had filled the buffer.
> 
> 3. It's probably a necessary condition that there is additional
>    output immediately after the clear screen (such as the
>    programming language prompt being printed), because
>    the console scrolls to bottom on any output.
> 
> I'm not sure if these are sufficient, but they seem to be
> on my end.

I could reproduce this now and I think I have fixed it.

There's still a problem with the position of the scrollbars in certain
scenarios where they are off by about one window size.  I added a FIXME
comment.

I have to admit I'm very puzzled that neither SetConsoleWindowInfo
nor the subsequent SetConsoleCursorPosition automatically set the
scrollbars correctly.  That's what I would expect, naively.

If anybody knows how to fix the scrollbar position in a Windows console
without moving the window contents around, please help.


Thanks,
Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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