Re: Weird font problem

[Eli Zaretskii <eliz@gnu.org>]

> From: Joost Kremers <joostkremers@fastmail.fm>
> Date: Wed, 05 Jun 2024 09:39:07 +0200
> 
> I'm running into a weird problem with displaying certain Unicode symbols. The
> relevant symbols are not displayed in a normal buffer, because Emacs cannot find
> a font set that has a glyph for them. However, when I try to insert such a
> character with 'C-x 8 RET', with vertico installed, I see the following (trying
> to insert DOCUMENT 0x01F5CE):
> 
> The DOCUMENT character is replaced with the missing glyph box, but the other
> characters *are* displayed. When I move the highlight down (M-n), the following
> happens:
> 
> Suddenly, DOCUMENT *is* displayed, and the character that is highlighted is not.
> Moving the highlight further down or back up gives the same effect for the other
> characters.
> 
> Things get even weirder, though: After taking a screen shot, suddenly *all*
> characters are gone:

Does Vertico display the character of the preview's current line in
some special face, like bold or italics?  If so, it could be that the
font used to show these symbols doesn't have the variant needed for
that display.

> This happens on two different computers, both running the same OS (Arch Linux;
> GNOME 46 on Wayland) and Emacs version (GNU Emacs 29.3 (build 1,
> x86_64-pc-linux-gnu, GTK+ Version 3.24.41, cairo version 1.18.0)).

Did you try to use a different font for this range of characters?
Like Symbola, for example?

> The fact that the symbols are displayed in the completion list suggests to me
> that Emacs seems to have a way to find glyphs for them. If that is correct, then
> why doesn't it find them when the characters are in a "normal" buffer?
> 
> Or is there something else that makes those characters appear, outside of Emacs'
> control? The fact that taking a screen shot has such an effect seems to indicate
> this...

Let's get out terminology right, to avoid confusion, okay?  These
characters do not "appear" and "disappear".  They are sometimes
displayed as their own glyphs and sometimes as boxes with hex
codepoints, which means Emacs cannot find a font to display them.

> And I'm also wondering what I can do to make Emacs find a glyph for these
> characters. Other applications, including GNOME Terminal, gedit and LibreOffice
> have to trouble displaying them.

Do "other applications" support Vertico?

Does Emacs have problem displaying these characters in situations
other than Vertico completion preview?