Re: XTerm char-width handling

[Markus Kuhn <Markus.Kuhn@cl.cam.ac.uk>]

GOTO Masanori wrote on 1999-10-09 16:20 UTC:
> > For reasons of simplicity, I think I'd prefer a strictly cell-based
> > cursor control concept. If half a double-cell character gets overwritten
> > by text that follows a cursor repositioning, then the other half can be
> > substituted with some default character such as space. This seems to me
> > to be both most easy to understand and most easy to implement.
> 
> In such a situation, other half character vanishes.
> If the other half is substituted with other characters,
> almost users are maybe embarassed.

With "vanishes", I assume you mean "substituted with a SPACE character".
I just wondered, because Unicode contains a single-cell character U+303F
IDEOGRAPHIC HALF FILL SPACE that looks like a box with diagonal lines,
and I understand that it was intended for representing the remaining
other half of a half-overwritten double-cell glyph. I have added this
glyph to those fixed fonts that might be used together with a
double-wide font, in case someone wants to make use of U+303F to
indicate brutally killed half-glyphs in a non-embarrasing way. ;-) I
don't know, from which CJK standard U+303F comes, but it does not seem
to originate in JIS X 0208. I guess, using a space would be just as
good.

> > When characters can now be either 1 or 2 cells wide, what would be the
> > preferred semantics for the cursor control sequences? Should they
> > position the cursor on the n-th cell or on the n-th character in a line?
> 
> I think, they should be the n-th character.

This would mean that there is no possibility to position the cursor onto
the second half of a double-cell character. It would probably also mean
that the cursor should double in size when it is positioned onto a
double-cell character.

It might be useful, if someone could give us a quick guided tour to

  - installing kterm
  - get a few EUC sample texts to play around with
  - get an EUC capable full-screen editor (vim?) that behaves nicely
    under kterm

such that people interested in double-cell character extensions of xterm
can get a bit of a feeling for existing practice.

Then we can better judge, whether the kterm way of doing cursor control
is also what we should do with UTF-8.

How does uxterm or 9term support double-cell characters?

Markus

-- 
Markus G. Kuhn, Computer Laboratory, University of Cambridge, UK
Email: mkuhn at acm.org,  WWW: <http://www.cl.cam.ac.uk/~mgk25/>

-
Linux-UTF8:   i18n of Linux on all levels
Archive:      http://mail.nl.linux.org/lists/