Re: Question regarding tty special glyphs display defaults

[Eli Zaretskii]

> From: Gerd Möllmann <gerd.moellmann@gmail.com>
> Cc: emacs-devel@gnu.org
> Date: Wed, 09 Oct 2024 15:48:58 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Using Unicode (or non-ASCII in general) on text terminals is
> > problematic, because we need to establish whether a character is
> > supported before using it, and text terminals differ wildly in that
> > aspect.  We have char-displayable-p, but it is not 100% reliable
> > (except if you are on the Linux console, for which we have special
> > support), so using this by default is not reliable, either.
> 
> Ah thanks, that's what I was looking for and couldn't find. 
> 
> > Why cannot this be left to user customizations, leaving the ("ugly as
> > hell") ASCII characters as the default, since those are reliably
> > displayed?
> 
> I'm just wondering if one could do better. I think the Unicode box
> drawing characters like U+2502 '│' instead of '|' for example are quite
> commonly used in terminal programs.

I'm guessing you have terminal emulators in mind.  Those indeed use
GUI fonts, where these characters are usually available.  But I was
talking about real console devices, where that is not necessarily
true.  We don't default to U+2502 '│' in fill-column-indicator-mode
for that reason.

> And they produce a much nicer display. On my system I sometimes have
> to take a second look to see if I have a GUI version in front of me
> or not (it's the modeline that is slightly different).
> 
> Hm, don't know, if you don't want that, it's of course okay. I have my
> setup already as I like it.

I'm saying that doing that by default would be problematic.  We can
provide a defcustom or a minor mode which would replace these
characters, and let users who know their terminals can display those
use those opt-in features.