GNU bug report logs - #80025
Margin columns

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Juri Linkov <juri <at> linkov.net>
To: bug-gnu-emacs <at> gnu.org
Subject: Margin columns
Date: Wed, 17 Dec 2025 20:28:17 +0200

[Message part 1 (text/plain, inline)]

[moved from emacs-devel]

>> I see that PRODUCE_GLYPHS calls either 'produce_glyphs' directly or
>> 'FRAME_RIF->produce_glyphs' ('gui_produce_glyphs').  Then both versions
>> have several calls to 'append_glyph'.  This means that the most suitable
>> place for filling with the SPC character glyph in the margins is
>> 'append_glyph'?
>
> Yes.  You need to modify this line:
>
>   glyph = it->glyph_row->glyphs[area] + it->glyph_row->used[area];
>
> It currently makes 'glyph' point to the next glyph-row slot, and then
> fills that slot with the information about the character.  Instead,
> the new code should (in case of margins only) find the slot whose
> index is the column number you want to use, and, if that slot is
> beyond the one identified by used[are] as above, fill the preceding
> columns with a space glyph.

Thanks for pointing to the right place.

So I tried to do exactly this, filling the columns with the space glyph,
and it works.

Currently the margin column is hard-coded for testing.
But since now the hardest part is done, it's trivial
to get the margin column from the display spec.

I see two ways of sending the value of the margin column
from 'handle_single_display_spec' to 'append_glyph':

1. using a static variable;
2. adding a new field to the struct 'it'.

What variant would be more preferable?

Here is the current state:

[margin_column.patch (text/x-diff, inline)]

diff --git a/src/xdisp.c b/src/xdisp.c
index 06d5481acd3..13f580e0e9d 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -31863,7 +31863,38 @@ append_glyph (struct it *it)
   eassert (it->glyph_row);
   eassert (it->char_to_display != '\n' && it->char_to_display != '\t');
 
-  glyph = it->glyph_row->glyphs[area] + it->glyph_row->used[area];
+  if (area == LEFT_MARGIN_AREA || area == RIGHT_MARGIN_AREA)
+    {
+      int margin_column = 2;
+      if (margin_column < (area == LEFT_MARGIN_AREA
+			   ? WINDOW_LEFT_MARGIN_WIDTH (it->w)
+			   : WINDOW_RIGHT_MARGIN_WIDTH (it->w)))
+	{
+	  int face_id = lookup_basic_face (it->w, it->f, DEFAULT_FACE_ID);
+	  while (it->glyph_row->used[area] < margin_column
+		 && it->glyph_row->glyphs[area] + it->glyph_row->used[area]
+		 < it->glyph_row->glyphs[area + 1])
+	    {
+	      struct glyph *fill_glyph =
+		it->glyph_row->glyphs[area] + it->glyph_row->used[area];
+	      *fill_glyph = space_glyph;
+	      fill_glyph->pixel_width = FRAME_COLUMN_WIDTH (it->f);
+	      fill_glyph->face_id = face_id;
+	      fill_glyph->frame = it->f;
+	      ++it->glyph_row->used[area];
+	    }
+
+	  glyph = it->glyph_row->glyphs[area] + margin_column;
+
+	  if (margin_column >= it->glyph_row->used[area])
+	    it->glyph_row->used[area] = margin_column + 1;
+	}
+      else
+	glyph = it->glyph_row->glyphs[area] + it->glyph_row->used[area];
+    }
+  else
+    glyph = it->glyph_row->glyphs[area] + it->glyph_row->used[area];
+
   if (glyph < it->glyph_row->glyphs[area + 1])
     {
       /* If the glyph row is reversed, we need to prepend the glyph
@@ -31928,7 +31959,8 @@ append_glyph (struct it *it)
 	  glyph->resolved_level = 0;
 	  glyph->bidi_type = UNKNOWN_BT;
 	}
-      ++it->glyph_row->used[area];
+      if (!(area == LEFT_MARGIN_AREA || area == RIGHT_MARGIN_AREA))
+	++it->glyph_row->used[area];
     }
   else
     IT_EXPAND_MATRIX_WIDTH (it, area);

Message #8 received at 80025 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Juri Linkov <juri <at> linkov.net>
Cc: 80025 <at> debbugs.gnu.org
Subject: Re: bug#80025: Margin columns
Date: Wed, 17 Dec 2025 20:41:53 +0200

> Cc: Eli Zaretskii <eliz <at> gnu.org>
> From: Juri Linkov <juri <at> linkov.net>
> Date: Wed, 17 Dec 2025 20:28:17 +0200
> 
> >> I see that PRODUCE_GLYPHS calls either 'produce_glyphs' directly or
> >> 'FRAME_RIF->produce_glyphs' ('gui_produce_glyphs').  Then both versions
> >> have several calls to 'append_glyph'.  This means that the most suitable
> >> place for filling with the SPC character glyph in the margins is
> >> 'append_glyph'?
> >
> > Yes.  You need to modify this line:
> >
> >   glyph = it->glyph_row->glyphs[area] + it->glyph_row->used[area];
> >
> > It currently makes 'glyph' point to the next glyph-row slot, and then
> > fills that slot with the information about the character.  Instead,
> > the new code should (in case of margins only) find the slot whose
> > index is the column number you want to use, and, if that slot is
> > beyond the one identified by used[are] as above, fill the preceding
> > columns with a space glyph.
> 
> Thanks for pointing to the right place.
> 
> So I tried to do exactly this, filling the columns with the space glyph,
> and it works.
> 
> Currently the margin column is hard-coded for testing.
> But since now the hardest part is done, it's trivial
> to get the margin column from the display spec.
> 
> I see two ways of sending the value of the margin column
> from 'handle_single_display_spec' to 'append_glyph':
> 
> 1. using a static variable;
> 2. adding a new field to the struct 'it'.
> 
> What variant would be more preferable?

The second one is cleaner.

> +	  glyph = it->glyph_row->glyphs[area] + margin_column;
> +
> +	  if (margin_column >= it->glyph_row->used[area])
> +	    it->glyph_row->used[area] = margin_column + 1;

I would omit the "+ 1" part in the last line, and then this:

> -      ++it->glyph_row->used[area];
> +      if (!(area == LEFT_MARGIN_AREA || area == RIGHT_MARGIN_AREA))
> +	++it->glyph_row->used[area];

could be left unchanged, AFAICT.

Thanks.

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