Re: [screen-devel] terminfo smacs feature, and screen "charset" command

[Micah Cowan]

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Alain Bench wrote:
> Hello Micah, and welcome on board,
> 
>  On Thursday, June 19, 2008 at 16:58:39 -0700, Micah Cowan wrote:
> 
>> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=144178
>>> screen only understands \E(0 and \E(B. It also emits these sequences
>>> to instruct the terminal its running in to move in/out of the ACS.
> 
>     Not exactly:
> 
>  - Screen understands ^N/^O once it has been correctly initialised by
> enacs=\E(B\E)0. Of course box drawing apps are expected to send enacs
> once, at the beginning, before any smacs/rmacs.

Ah. I did _not_ know about enacs. And, terminfo(5) does a terrible job
of making that clear. The XCurses spec is somewhat clearer (though not
by much).

>  - Screen then translates ^N/^O to the underlying terminal's
> smacs/rmacs, whatever they are, and sends this translation.
> 
> 
>>> with TERM=xterm, as infocmp shows that the correct sequences for this
>>> terminal type are ^N/^O.
> 
>     Bizare. In the latest terminfo from 2008-04-29:
> 
> | $ infocmp -1 xterm | grep acs=
> |     rmacs=\E(B,
> |     smacs=\E(0,
> 
> 
>> [Micah] My response:
>>> the fault is in the terminfo description for screen.
> 
>     Let's see:
> 
> | $ infocmp -1 screen | grep acs=
> |     enacs=\E(B\E)0,
> |     rmacs=^O,
> |     smacs=^N,
> 
>     This looks perfectly right to me, and should work. I don't
> understand the original problem, or rather the reported facts don't seem
> to be a problem.
> 
> 
>>> in UTF-8 mode, screen apparently uses the Unicode box characters,
>>> rather than the parent terminal's smacs feature.
> 
>     Some UTF-8 terminals don't accept mode changes, on the principle
> that UTF-8 is modeless. That's why all applications drawing boxes have
> to special case UTF-8... Screen does the job for the few poorly written
> apps not doing it themselves.

Right: I didn't mean to imply that's wrong behavior, it seems decidedly
right to me. I was just drawing the reporter's attention to that fact.

Okay, then, sounds like there's no reason to change either screen's
default setting for charset, or the terminfo description. I'll forward
that answer back downstream. Thanks!

- --
Micah J. Cowan
Programmer, musician, typesetting enthusiast, gamer,
and GNU Wget Project Maintainer.
http://micah.cowan.name/
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