bug#67810: 29.1; fonts use synthetic bold on Linux / pgtk

[Eli Zaretskii <eliz@gnu.org>]

> From: Po Lu <luangruo@yahoo.com>
> Cc: crypto@timruffing.de,  stefankangas@gmail.com,  67810@debbugs.gnu.org
> Date: Fri, 12 Jan 2024 17:59:29 +0800
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> From: Po Lu <luangruo@yahoo.com>
> >> Cc: Stefan Kangas <stefankangas@gmail.com>,  Eli Zaretskii <eliz@gnu.org>,
> >>   67810@debbugs.gnu.org
> >> Date: Fri, 12 Jan 2024 09:46:21 +0800
> >> 
> >> Tim Ruffing <crypto@timruffing.de> writes:
> >> 
> >> > @Po Lu:
> >> > Independent of icons, I still think that overstriking is a bit
> >> > unexpected. (I mean, even Eli didn't know about it.) I see that a font
> >> > regex is too much, but do you think a simple boolean option would be a
> >> > good idea? Or do you think the current behavior should simply be
> >> > documented more prominently?
> >> 
> >> I think this is a mechanism users should not understand in this much
> >> technical detail, because font backends might synthesize their bold or
> >> oblique variants by other means when one is requested from a font that
> >> doesn't provide them.  Rather, users should understand that Emacs will
> >> seek to display bold text when they specify it should, and that text
> >> which isn't meant to be bold text should not receive text properties
> >> labeling it as such.
> >
> > Would it make sense to introduce a variable that disables synthesizing
> > bold or oblique font variants?
> 
> I think it won't until someone informs us of how those features might be
> disabled in the font drivers that perform this.  The Mac driver is
> definitely one of them, and possibly the Fontconfig driver as well.

If we do introduce such a variable, wouldn't it prevent Emacs from
generating the missing variants?  And wouldn't avoiding to generate
them do what the OP wanted, i.e. have a default face's font where bold
looks like regular?