bug#57607: Feature request: Use the character cell on bottom-right corner of a terminal

[Akib Azmain Turja]

Eli Zaretskii <eliz@gnu.org> writes:

>> Cc: gerd.moellmann@gmail.com
>> Date: Mon, 03 Oct 2022 14:31:53 +0600
>> From:  Akib Azmain Turja via "Bug reports for GNU Emacs,
>>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
>> 
>> I have implemented it.  Implementing it was easier than I thought.  Here
>> is the patch:
>
> Thanks.  But could you please describe the idea of the patch in some
> comment?  It is hard to follow the code, especially since the diff has
> many pure whitespace changes.

The idea is that you write the string just like before (for example, you
want to write "hello" in a five columns width terminal, so you write
only "hell", so that the line shows "hell "), then move a character
backward and write the last glyph (write "o", so that the line shows
"helo "), move a character backward again and arrange that after writing
the next glyph, the character on the current position will be pushed
towards right and write the glyph before the last one (write "l", now
the line shows "hello").

Should I add the explanation to the function as comment?

>
> Also, this:
>
>> +      /* Go to the previous position. */
>> +      cmgoto (tty, curY (tty), curX (tty) - 1);
>> +      cmplus (tty, 1);
>
> Seem to assume the last character takes just one column?  What about
> characters whose width is 2 columns?

Yes, I assume that.  I don't think any multi-char width glyph reach this
function (I think they are converted to single column width glyphs, for
example "^L" is converted to "^" and "L").  The reason of the assumption
is the following code:

--8<---------------cut here---------------start------------->8---
  if (AutoWrap (tty)
      && curY (tty) + 1 == FRAME_TOTAL_LINES (f)
      && (curX (tty) + len) == FRAME_COLS (f))
    len --;
--8<---------------cut here---------------end--------------->8---

Which also assumes the same.

>
> And finally, it would be nice to avoid so much code duplication
> between tty_write_glyphs and tty_write_glyphs_with_face.  Is that
> feasible?

Yes, I think so.  I think it possible to just add a new argument
"face_id" to tty_write_glyphs would the trick.  tty_write_glyph will try
to use "face_id" if it is specified, otherwise fallback to the face_id
in the string.  But how to "not" specify a face_id?  Would a NULL work?

-- 
Akib Azmain Turja

Find me on Mastodon at @akib@hostux.social.

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