bug#57962: 29.0.50; Odd font choices

[Lars Ingebrigtsen]

Eli Zaretskii <eliz@gnu.org> writes:

> Maybe with "fixed-*" fonts this is so.  But isn't True Type fonts
> scalable, so that we can request any size and get what we request?

We can request "size 12", but how big that is varies greatly by font,
unfortunately.  The font people haven't standarised this -- because of
the origins of font tech, and that "optical size" can vary even with the
same physical sizes.  So it's a mess, basically.

> Is that because ":spacing 'm" doesn't work (it seems to work for me)?
> If so, I think we should try fixing that instead of introducing new
> wizardry.

This:

(defface fixed-pitch
  `((t :font ,(font-spec :spacing 'M)))
  "The basic fixed-pitch face."
  :group 'basic-faces)

Made Emacs choose this font:

    ftcrhb:-GOOG-Noto Sans CJK 
KR-regular-normal-normal-*-45-*-*-*-*-0-iso10646-1 (#x24)

Which is not a monospace font (and is a different font family than the
`default' face uses:

    ftcrhb:-DAMA-Ubuntu Mono-regular-normal-normal-*-45-*-*-*-m-0-iso10646-1 
(#x47)

So that seems to be another bug in this area?

I also tried this in Emacs 28 and earlier, and it does nothing there, so
it's broken in a different way on master than in Emacs 28.