Re: Identifying the face between STRETCH and right fringe.

[Robert Pluim <rpluim@gmail.com>]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Robert Pluim <rpluim@gmail.com>
>> Date: Fri, 23 Nov 2018 16:58:41 +0100
>> Cc: emacs-devel@gnu.org
>> 
>> > Ah, okay.  Then we agree: there's some bug on NS that causes the face
>> > to be extended.  The expected behavior is the one we see on X and on
>> > Windows (and also on TTY frames).
>> 
>> Any idea where the code that handles this is? I took a quick look at
>> HAVE_NS, but nothing jumped out at me.
>
> I didn't see something like that, either.  But it could be the other
> way around: that NS needs some code to prevent that from happening.
>
> I think the place to look is ns_maybe_dumpglyphs_background: what is
> the width of the rectangle that it clears with the background color of
> the face?

Itʼs ns_dumpglyphs_stretch, which is doing exactly as itʼs told:
drawing the background to the right edge of the frame. Thatʼs because
in xdisp.c:display_line we have:

		      /* Make sure that a non-default face is extended
			 up to the right margin of the window.  */
                      extend_face_to_end_of_line (it);

which later causes set_glyph_string_background_width to set the
background_width of the glyph to the full width (commenting out that
call makes NS work the same as X11 for this specific case).

What I donʼt understand is that under X11 Emacs takes exactly the same
code path, yet somehow it doesnʼt end up setting the background up to
the right edge.

Robert