bug#53924: 26.1; fontification sometimes fails for some characters despite available glyphs

[Greg A. Woods]

At Thu, 10 Feb 2022 22:21:50 +0200, Eli Zaretskii <eliz@gnu.org> wrote:
Subject: Re: bug#53924: 26.1; fontification sometimes fails for some characters 
despite available glyphs
>
> > Date: Thu, 10 Feb 2022 11:02:19 -0800
> > From: "Greg A. Woods" <woods@robohack.ca>
> >
> > Emacs fails to display all available glyphs for some fonts, and in some
> > cases any available glyphs for some fonts.
>
> Thanks, but why do you consider that a problem?  You are trying to use
> arbitrary fonts available on your system, and Emacs sometimes finds
> them inappropriate for its purposes, or incapable of displaying some
> characters.  That's completely normal.  Not every font is good enough
> for Emacs.

Yes, indeed I do consider it a problem -- something is sometimes
swapping glyphs that should not be doing so, and doing so inconsistently
for some reason.

I don't consider all the fonts available to be "good enough for Emacs",
quite the contrary, but I do believe Emacs should be able to show me
text rendered with any and all available glyphs from these fonts upon
request.  If Xterm can, why can't Emacs?

The exception of course is if there's something actually wrong with the
font, or its encoding, or some such non-Emacs problem.  I would expect
such problems to show up in xfontsel though.

One more clue I've noticed -- the inconsistent results only occur for
proportional fonts -- not for mono-spaced fonts, and I have noticed that
I have one or two fonts which appear to be mono-spaced, and which have
the word "mono" in their family name, but which xfontsel and xlsfonts
insists are proportional fonts.

I'm no expert at font definitions and encodings -- I'm just trying to
get some consistent results that at least match what I can see with
xfontsel.

Note I'm working only with TTF fonts, primarily on a high-res display
(218dpi), and though I have the standard X11 fonts installed on the
machine running Emacs, all the fonts I am seeing problems with are
installed only on the X11 server machine, a desktop macOS with XQuartz
running in full-screen mode.

One more possibly relevant observation:  I don't see this problem with
Emacs built using the "nextstep" toolkit and running on native macOS.
There even when the font has a strange encoding (e.g. for symbol fonts),
or no ASCII glyphs at all, I see either the symbols in their place, or
empty boxes.

> Also, please try this in a newer Emacs.  v26 is very old and no longer
> developed; Emacs 28 is in pretest.

As soon as I can, but for now v26 is what is available in all my
production working environments.

--
                                        Greg A. Woods <gwoods@acm.org>

Kelowna, BC     +1 250 762-7675           RoboHack <woods@robohack.ca>
Planix, Inc. <woods@planix.com>     Avoncote Farms <woods@avoncote.ca>

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