Re: *cause of* screen writing over restored buffer on detach/exit

[Thomas Dickey <dickey@his.com>]

----- Original Message -----
| From: "Thomas Dickey" <dickey@his.com>
| To: "Thomas Wolff" <towo@towo.net>
| Cc: "cygwin" <cygwin@cygwin.com>
| Sent: Thursday, April 11, 2019 7:06:22 PM
| Subject: Re: *cause of* screen writing over restored buffer on detach/exit

| ----- Original Message -----
|| From: "Thomas Wolff" <towo@towo.net>
|| To: "cygwin" <cygwin@cygwin.com>
|| Sent: Wednesday, April 10, 2019 5:51:34 PM
|| Subject: Re: *cause of* screen writing over restored buffer on detach/exit
| 
|| Hi Thomas,
|| 
|| Thomas Dickey wrote:
||> ----- Original Message -----
||> | From: "Shaddy Baddah" <lithium-cygwin@shaddybaddah.name>
||> | To: "cygwin" <cygwin@cygwin.com>
||> | Sent: Tuesday, April 9, 2019 11:18:19 PM
||> | Subject: Re: *cause of* screen writing over restored buffer on detach/exit
||>
||> | On 9/4/19 4:07 pm, Shaddy Baddah wrote:
||> |>
||> |> This helped with screen when using Putty to a Cygwin ssh session. For
||> |> some reason, it isn't helping for running screen locally in a mintty
||> |> session. And it's not mintty either, because I can ssh to a Debian
||> |> stretch server within mintty and I can use its screen without this
||> |> issue happening. Back to the drawing board for me.
||> |
||> | I understand the cause of the issue now, by capturing and comparing the
||> | escape characters used to control the terminal by screen on Cygwin and
||> | Debian.
||> |
||> | It is not so much the detach/exit is the issue, although the escape
||> | sequence for Cygwin includes a couple of extra xterm OSC Set Text
||> | Parameters -> Change Icon Name and Window Title outputs. I misdiagnosed
||> | this somehow. I can suppress the extra utmp error one of these OSC
||> | outputs, but it didn't/doesn't really make a difference.
||> |
||> | The issue is in the escape sequences sent to the terminal by Cygwin
||> | screen to switch to new windows buffer, as compared to Debian.
||> |
||> | Debian uses xterm sequence DECSET / ESC[?1049h in the switch to the new
||> | window. Cygwin uses the two sequences ESC7 / Save Cursor (DECSC) and
||> | ESC[?47l / DEC Private Mode Reset (DECRST) -> Use Normal Screen Buffer.
||> |
||> |
||> | The reason seems to be that the Debian screen package packages a custom
||> | /etc/screenrc that does not include this explicit term capability:
||> |
||> |
||> | #
||> | # Do not use xterms alternate window buffer.
||> | # This one would not add lines to the scrollback buffer.
||> | termcap xterm|xterms|xs ti=\E7\E[?47l
||> | terminfo xterm|xterms|xs ti=\E7\E[?47l
||> |
||> |
||> |
||> | If I comment these out, my screen issue is resolved.
||> |
||> | I'm not suggesting this is a problem with Cygwin screen... it is using
||> | the upstream settings. In fact, I am not confident to say where the
||> | fault lies. Perhaps screen is right to use these sequences, but the
||> | xterms used (putty and mintty) aren't doing the right thing?
||>
||> yes - that's one of a half-dozen cases where PuTTY has never matched xterm's
||> behavior.
|| I've tested the CSI?1049h and CSI?1049l pair on xterm, pterm, mintty and
|| see no difference. In what way would it not match? And what are the
| 
| I mentioned it here:
| 
| https://stackoverflow.com/questions/24613237/terminal-retains-bg-color-after-closing-vim-using-color-scheme-and-putty-256co/37869114#37869114
| 
|| cases, do you have a list?
| 
| no - I've a few notes which aren't incorporated into the terminal description
| 
| https://invisible-island.net/ncurses/terminfo.src.html#tic-putty
| 
| offhand, there's differences in wrapping, as well as how modifiers affect
| cursor-keys.

...though now that I'm reading it, that one deals with color.
(I do have a note about cursor-position problems with the interim 1047/1048,
but suppose PuttY doesn't do that).

-- 
Thomas E. Dickey <dickey@invisible-island.net>
http://invisible-island.net
ftp://ftp.invisible-island.net

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