Re: "Final" version of tty child frames

[Feng Shu]

Gerd Möllmann <gerd.moellmann@gmail.com> writes:

> 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.

The below adjust will show more issue:-)

1. Reduce terminal's width
2. let a long line auto wrap to many lines.

--