>
> Before you modify display_line, you need to decide how will the
> vertical-layout display produce glyphs.


Can you please expand more on this?
How to produce glyphs in a column wise order?
I looked at gui_produce_glyphs and that led me to append_glyph, but I could
not figure out how the glyphs are produced.
There is also draw_glyphs but I think working with that will require
editing the low level *term files (if it even is the right function)

Thanks

On Sat, Sep 10, 2022 at 9:47 PM Eli Zaretskii <eliz@gnu.org> wrote:

> > From: समीर सिंह Sameer Singh <lumarzeli30@gmail.com>
> > Date: Sat, 10 Sep 2022 21:23:32 +0530
> > Cc: emacs-devel@gnu.org
> >
> > In order to find the "real meat" of the display_line function I started
> to slowly remove most of the lines of the
> > function as long as it does not break emacs and text can be typed.
> >
> > In the end I was left with this a 20-25 lines function (excluding
> comments and spaces):
> > (I have attached this function too)
> >
> > static bool
> > display_line (struct it *it, int cursor_vpos)
> > {
> >   struct glyph_row *row = it->glyph_row;
> >
> >   /* Clear the result glyph row and enable it.  */
> >   prepare_desired_row (it->w, row, false);
> >
> >   row->y = it->current_y;
> >
> >   /* Loop generating characters.  The loop is left with IT on the next
> >      character to display.  */
> >   while (true)
> >     {
> >
> >       /* Retrieve the next thing to display.  Value is false if end of
> > buffer reached.  */
> >       if (!get_next_display_element (it))
> > {
> >  break;
> > }
> >
> >       PRODUCE_GLYPHS (it);
> >
> >     at_end_of_line:
> >       /* Is this a line end?  If yes, we're also done, after making
> > sure that a non-default face is extended up to the right
> > margin of the window.  */
> >       if (ITERATOR_AT_END_OF_LINE_P (it))
> > {
> >  /* Consume the line end.  This skips over invisible lines.  */
> >  set_iterator_to_next (it, true);
> >  break;
> > }
> >
> >       set_iterator_to_next (it, true);
> >     }
> >
> >   /* Compute pixel dimensions of this line.  */
> >   compute_line_metrics (it);
> >
> >   /* Prepare for the next line.  This line starts horizontally at (X
> >      HPOS) = (0 0).  Vertical positions are incremented.  As a
> >      convenience for the caller, IT->glyph_row is set to the next
> >      row to be used.  */
> >
> >   it->current_y += row->height;
> >   ++it->glyph_row;
> >   return MATRIX_ROW_DISPLAYS_TEXT_P (row);
> > }
> >
> > Obviously most of the things do not work such as bidi, word wrapping,
> displaying cursor and line numbers but
> > still text is being shown
> > in rows one after the other and it can be scrolled, but now there are no
> lines mentioning the hpos, the
> > x-coordinate, first_visible_x or
> > last_visible_x, does that mean I do not understand the display_line
> function? I thought its function was to fill a
> > row with glyphs in the desired matrix
> > to display it on the glass but now I cannot find a line which fills the
> matrix.
>
> That hides behind the PRODUCE_GLYPHS macro.
>
> > You had advised to swap the x and y
> > coordinates, but here there
> > is no x coordinate present! How can the redisplay still work?
>
> display_line also makes the decisions when the screen line is full and
> the rest should be on the next screen line this is one of its most
> important roles.  But you have removed that code, so you don't see it
> in what's left.  The parts that deal with the X coordinate that
> exceeds last_visible_x are those which make that decision.
>