bug#54564: 29.0.50; [PATCH] Use gsettings font rendering entries for pgtk builds

[Eli Zaretskii <eliz@gnu.org>]

> Cc: 54564@debbugs.gnu.org
> Date: Sat, 26 Mar 2022 09:16:03 +0800
> From:  Po Lu via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> > Note that this patch won't dynamically re-render when emacs is already
> > running (like it does when changing the system font).  I made an
> > attempt to hook into the gsettings change callback, but could not
> > force a re-creation of the font with the changed parameters,for
> > instance using a 'font-render' config changed event. Any pointers on
> > how to achieve this?
> 
> I'm not sure, but perhaps someone else around here knows.

Maybe I could help if I understood the difficulty well enough.  What
exactly is the problem here?  In particular, what is meant by "force a
re-creation of the font with the changed parameters"?  How can Emacs
"re-create" a font?

> The basic approach is good, thanks for working on this.

AFAIU, this uses gsettings to determine some Emacs font-related
functionality.  One aspect that bothers me is whether users will have
the means to tell Emacs to ignore those gsettings and use the usual
Emacs defaults instead?  I don't think it's a good idea to apply those
gsettings unconditionally without letting users override that.