bug#66128: 28.2; visible-bell breaks setterm --inversescreen on

bug#66128: 28.2; visible-bell breaks setterm --inversescreen on

[tom]

in black linux console:

   $ setterm --inversescreen on

after that, in white linux console:

   $ emacs -Q --eval '(setq visible-bell t)'

all looks fine, emacs background is white
now press page-up key to trigger visual bell
and suddenly emacs background is black
visual bell should preserve terminal colors

the same problem is in a X based terminals but with the command:

   $ emacs -nw -Q --eval '(setq visible-bell t)'



In GNU Emacs 28.2 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo version 1.16.0, Xaw3d scroll bars)
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bug#66128: 28.2; visible-bell breaks setterm --inversescreen on

[Eli Zaretskii]

> From: tom@logand.com
> Date: Wed, 20 Sep 2023 22:14:49 +0200
> 
> 
> 
> in black linux console:
> 
>    $ setterm --inversescreen on
> 
> after that, in white linux console:
> 
>    $ emacs -Q --eval '(setq visible-bell t)'
> 
> all looks fine, emacs background is white
> now press page-up key to trigger visual bell
> and suddenly emacs background is black
> visual bell should preserve terminal colors

Emacs just sends to the terminal the sequence defined by the "vb"
termcap capability.  Is that not correct when the screen colors are
inverted?  Is this perhaps the problem of the terminal?

Btw, we always use the termcap's "vb", even when terminfo is
available; should we use the terminfo's "flash" instead?

bug#66128: 28.2; visible-bell breaks setterm --inversescreen on

[Tomas Hlavaty]

Hi Eli,

thanks for the quick reply.

On Thu 21 Sep 2023 at 08:00, Eli Zaretskii <eliz@gnu.org> wrote:
> Emacs just sends to the terminal the sequence defined by the "vb"
> termcap capability.  Is that not correct when the screen colors are
> inverted?

I do not know.

> Is this perhaps the problem of the terminal?

No, I get the same behaviour in xfce4-terminal and kitty, so this does
not seem to be specific problem with the linux console.

I think I wrote it in the bug report too, under an X based terminal:

   $ emacs -nw -Q --eval '(setq visible-bell t)'

then press PgUp.

> Btw, we always use the termcap's "vb", even when terminfo is
> available; should we use the terminfo's "flash" instead?

I do not know.

Regards,

Tomas

bug#66128: 28.2; visible-bell breaks setterm --inversescreen on

[Eli Zaretskii]

> From: Tomas Hlavaty <tom@logand.com>
> Cc: 66128@debbugs.gnu.org
> Date: Fri, 22 Sep 2023 22:18:14 +0200
> 
> On Thu 21 Sep 2023 at 08:00, Eli Zaretskii <eliz@gnu.org> wrote:
> > Emacs just sends to the terminal the sequence defined by the "vb"
> > termcap capability.  Is that not correct when the screen colors are
> > inverted?
> 
> I do not know.
> 
> > Is this perhaps the problem of the terminal?
> 
> No, I get the same behaviour in xfce4-terminal and kitty, so this does
> not seem to be specific problem with the linux console.
> 
> I think I wrote it in the bug report too, under an X based terminal:
> 
>    $ emacs -nw -Q --eval '(setq visible-bell t)'
> 
> then press PgUp.
> 
> > Btw, we always use the termcap's "vb", even when terminfo is
> > available; should we use the terminfo's "flash" instead?
> 
> I do not know.

Thomas, could you perhaps help us out here?  This is about sending the
"visible bell" sequence to a terminal after "setterm --inversescreen on".
The original report is:

    $ setterm --inversescreen on
    $ emacs -Q --eval '(setq visible-bell t)'

  Then in Emacs do something that causes a bell, like try moving beyond
  the buffer's end.  This causes the Emacs background to become white,
  i.e. the visible-bell somehow countermands the inversescreen state.

Can you think of any reason for this behavior?  Do terminals honor
inversescreen when they perform the visible-bell function?  Emacs just
sends the sequence reported by the "vb" termcap capability of the
terminal when the visible-bell is triggered.

Thanks.

bug#66128: 28.2; visible-bell breaks setterm --inversescreen on

[Thomas Dickey]

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On Sat, Sep 23, 2023 at 08:38:53AM +0300, Eli Zaretskii wrote:
> > From: Tomas Hlavaty <tom@logand.com>
> > Cc: 66128@debbugs.gnu.org
> > Date: Fri, 22 Sep 2023 22:18:14 +0200
> > 
> > On Thu 21 Sep 2023 at 08:00, Eli Zaretskii <eliz@gnu.org> wrote:
> > > Emacs just sends to the terminal the sequence defined by the "vb"
> > > termcap capability.  Is that not correct when the screen colors are
> > > inverted?
> > 
> > I do not know.
> > 
> > > Is this perhaps the problem of the terminal?
> > 
> > No, I get the same behaviour in xfce4-terminal and kitty, so this does
> > not seem to be specific problem with the linux console.
> > 
> > I think I wrote it in the bug report too, under an X based terminal:
> > 
> >    $ emacs -nw -Q --eval '(setq visible-bell t)'
> > 
> > then press PgUp.
> > 
> > > Btw, we always use the termcap's "vb", even when terminfo is
> > > available; should we use the terminfo's "flash" instead?
> > 
> > I do not know.
> 
> Thomas, could you perhaps help us out here?  This is about sending the
> "visible bell" sequence to a terminal after "setterm --inversescreen on".
> The original report is:
> 
>     $ setterm --inversescreen on

setterm doesn't have any special way of manipulating the terminal -
it uses the same escape sequences that emacs would

>     $ emacs -Q --eval '(setq visible-bell t)'
> 
>   Then in Emacs do something that causes a bell, like try moving beyond
>   the buffer's end.  This causes the Emacs background to become white,
>   i.e. the visible-bell somehow countermands the inversescreen state.
> 
> Can you think of any reason for this behavior?  Do terminals honor

https://github.com/util-linux/util-linux/blob/master/term-utils/setterm.c

https://github.com/util-linux/util-linux/blob/1e0ad14b3ac08d855cda6de346a65f9b834e00db/term-utils/setterm.c#L1005

	/* -inversescreen [on|off]. */
	if (ctl->opt_inversescreen)
		fputs(ctl->opt_invsc_on ? "\033[?5h" : "\033[?5l", stdout);

man console_codes

       ESC [ ? 5 h
              DECSCNM (default off): Set reverse-video mode.

but visual-bell can be the same thing

The "vb" termcap capability is found with "man 5 terminfo"

          flash_screen                flash     vb     visible bell (may
                                                       not move cursor)

to be "flash" in terminfo,
and "infocmp linux" shows

	flash=\E[?5h$<200/>\E[?5l,

which is to say,
	turn reverse-video on
	wait 200 milliseconds
	turn reverse-video off

> inversescreen when they perform the visible-bell function?  Emacs just
> sends the sequence reported by the "vb" termcap capability of the
> terminal when the visible-bell is triggered.
> 
> Thanks.

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

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bug#66128: 28.2; visible-bell breaks setterm --inversescreen on

[Eli Zaretskii]

> Date: Sun, 24 Sep 2023 20:07:03 -0400
> From: Thomas Dickey <dickey@his.com>
> Cc: Tomas Hlavaty <tom@logand.com>, Thomas Dickey <dickey@his.com>,
> 	66128@debbugs.gnu.org
> 
> setterm doesn't have any special way of manipulating the terminal -
> it uses the same escape sequences that emacs would
> 
> >     $ emacs -Q --eval '(setq visible-bell t)'
> > 
> >   Then in Emacs do something that causes a bell, like try moving beyond
> >   the buffer's end.  This causes the Emacs background to become white,
> >   i.e. the visible-bell somehow countermands the inversescreen state.
> > 
> > Can you think of any reason for this behavior?  Do terminals honor
> 
> https://github.com/util-linux/util-linux/blob/master/term-utils/setterm.c
> 
> https://github.com/util-linux/util-linux/blob/1e0ad14b3ac08d855cda6de346a65f9b834e00db/term-utils/setterm.c#L1005
> 
> 	/* -inversescreen [on|off]. */
> 	if (ctl->opt_inversescreen)
> 		fputs(ctl->opt_invsc_on ? "\033[?5h" : "\033[?5l", stdout);
> 
> man console_codes
> 
>        ESC [ ? 5 h
>               DECSCNM (default off): Set reverse-video mode.
> 
> but visual-bell can be the same thing
> 
> The "vb" termcap capability is found with "man 5 terminfo"
> 
>           flash_screen                flash     vb     visible bell (may
>                                                        not move cursor)
> 
> to be "flash" in terminfo,
> and "infocmp linux" shows
> 
> 	flash=\E[?5h$<200/>\E[?5l,
> 
> which is to say,
> 	turn reverse-video on
> 	wait 200 milliseconds
> 	turn reverse-video off

Thanks.  So Emacs should ideally reverse the sequence when the
terminal is in the reverse-video mode, or at least send the "\033[?5h"
sequence after sending "flash"?  But can Emacs know that the terminal
is in this mode at startup?

bug#66128: 28.2; visible-bell breaks setterm --inversescreen on

[Thomas Dickey]

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On Mon, Sep 25, 2023 at 08:03:38AM +0300, Eli Zaretskii wrote:
...
> Thanks.  So Emacs should ideally reverse the sequence when the
> terminal is in the reverse-video mode, or at least send the "\033[?5h"
> sequence after sending "flash"?  But can Emacs know that the terminal
> is in this mode at startup?

I don't see how - the usual way (an escape sequence which returns this
information) is not documented for Linux in console_codes.

Lacking that, you'd rely upon the user to tell Emacs what to do.

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

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bug#66128: 28.2; visible-bell breaks setterm --inversescreen on

[Eli Zaretskii]

> Date: Mon, 25 Sep 2023 04:07:22 -0400
> From: Thomas Dickey <dickey@his.com>
> Cc: dickey@his.com, tom@logand.com, 66128@debbugs.gnu.org
> 
> On Mon, Sep 25, 2023 at 08:03:38AM +0300, Eli Zaretskii wrote:
> ...
> > Thanks.  So Emacs should ideally reverse the sequence when the
> > terminal is in the reverse-video mode, or at least send the "\033[?5h"
> > sequence after sending "flash"?  But can Emacs know that the terminal
> > is in this mode at startup?
> 
> I don't see how - the usual way (an escape sequence which returns this
> information) is not documented for Linux in console_codes.
> 
> Lacking that, you'd rely upon the user to tell Emacs what to do.

I see.  I guess we will need to ask such users to customize the
inverse-video variable to a non-nil value, and then change
tty_ring_bell accordingly.

Thanks.