Re: "Final" version of tty child frames

[Gerd Möllmann]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Gerd Möllmann <gerd.moellmann@gmail.com>
>> Cc: Emacs Devel <emacs-devel@gnu.org>
>> Date: Wed, 23 Oct 2024 06:40:11 +0200
>> 
>> Gerd Möllmann <gerd.moellmann@gmail.com> writes:
>> 
>> > Feng Shu <tumashu@163.com> writes:
>> >
>> >> Gerd Möllmann <gerd.moellmann@gmail.com> writes:
>> >>
>> >>> Feng Shu <tumashu@163.com> writes:
>> >>>
>> >>>> border do not work well when current buffer is CJK, maybe because CJK
>> >>>> Char width is not 1
>> >>>
>> >>> Could you please send me a bit of CJK text so that I have something I
>> >>> can test this with?
>> >
>> > Thanks!
>> 
>> Hm, okay, but not sure how to fix that.
>> 
>> The problem comes indeed from the root frame displaying characters that
>> are more then 1 column wide, say N. When we output such a character to
>> the terminal, the cursor moves by N columns. Emacs represents that in
>> the glyph matrix by producing N glyphs for the character, all bu tthe
>> first have a padding flag set. So we have
>> 
>>   ... (C, 0) (C, 1) ...
>> 
>> in the glpyh matrix, where C is the character, and the number is the
>> padding flag.
>> 
>> Now assume, for example, that the child frame is posititoned so that its
>> left border where we want to display a '|' is in the column for the (C,
>> 1).
>> 
>> That can't work, because writing C to the terminal moves 2 columns and 
>> will skip over the column where we want the '|' to appear.
>
> I think the solution should be the same as what we do when a line
> needs to wrap (i.e. be continued) and we don't have enough columns to
> put all the N glyphs before the continuation glyph: we don't show the
> entire N-glyph group.  IOW, the border glyph should be shown instead
> of multi-column character, padded with enough spaces before it to make
> up for the M < N glyphs of C that could be shown before the border.
> In your example above, C will not be shown, and instead we will show
> one space glyph followed by the '|' glyph.

Yes, I came up with this (WIP):

/* If the glyph in ROW at position X is part of a wide character, change
   every glyph belonging to the wide character to a space glyph.  */

static void
neutralize_wide_char (struct frame *root, struct glyph_row *row, int x)
{
  eassert (x >= 0 && x < root->desired_matrix->matrix_w);
  struct glyph *glyph = row->glyphs[0] + x;
  if (glyph->type == CHAR_GLYPH && CHARACTER_WIDTH (glyph->u.ch) > 1)
    {
      struct glyph *row_start = row->glyphs[0];
      struct glyph *row_limit = row_start + row->used[0];

      /* Glyph is somewhere in a sequence of glyphs for a wide
         character, find the start.  */
      while (glyph > row_start && glyph->padding_p)
        --glyph;

      /* Make everything in the sequence a space glyph.  */
      eassert (!glyph->padding_p);
      make_glyph_space (glyph);
      for (++glyph; glyph < row_limit && glyph->padding_p; ++glyph)
        make_glyph_space (glyph);
    }
}

I have some problems reproducing the whole thing on my system with the
CJK file Feng Shu gave me. Hm.