bug#26396: 25.1; char-displayable-p on a latin1 tty

[Paul Eggert]

On 04/13/2017 12:16 AM, Eli Zaretskii wrote:
> Yes, that would be better.  But it's probably a non-trivial project,
> since we'd need separate code to determine double-width glyphs,
> padding glyphs, and perhaps also something special for composed
> characters.  Does the Linux console allow us to figure out all of
> that?

This should not be a problem, as the Linux console has only single-width 
characters.

> And what does "display as-is" means in practice?  Should we send to
> the console the glyph codes corresponding to Unicode points, or should
> we send UTF-8 encoded characters?

It depends on whether the console is in UTF-8 mode. If so, send UTF-8; 
if not, send a byte that is transformed according to the current mapping 
table into a Unicode value. I hope we don't need to bother with the 
latter possibility.

> (Is there some document which
> describes these features in enough detail for us to figure out their
> implications on Emacs display code?)

Nothing definitive, but there is:

http://www.tldp.org/LDP/LG/issue91/loozzr.html
http://man7.org/linux/man-pages/man4/console_codes.4.html