Re: When and how to register various font backends

[Robert Pluim]

>>>>> On Fri, 14 Jun 2019 15:19:14 +0300, Eli Zaretskii <address@hidden> said:

    >> From: Robert Pluim <address@hidden>
    >> Cc: address@hidden,  YAMAMOTO Mitsuharu <address@hidden>
    >> Date: Fri, 14 Jun 2019 11:14:17 +0200
    >> 
    >> Currently under X11 the font backends end up as
    >> 
    >> (xft xfthb x)
    >> 
    >> Reordering that to put xfthb first is a matter of reordering the
    >> register_font_driver calls in Fx_create_frame

    Eli> That's true, but we don't want to have 3 font backends in the list,
    Eli> because then looking for a font that isn't available on the system
    Eli> will take much longer (Emacs tries to find the font with each backend
    Eli> in turn).  We want to have only 2 backends by default.

That I think pleads for your solution, where xfthb is preferred to xft
unless xft is specifically requested.

    >> Since xfthb is strictly better than xft, as far as I can tell, and we
    >> want people to actually use it, we should just prefer it for emacs-27,
    >> and remove the xft and x backends in emacs-28.

    Eli> I'm not sure removing x (and gdi on Windows) is a good idea, even in
    Eli> Emacs 28.  I understand (more accurately, was told very recently) that
    Eli> HarfBuzz was designed to be able to work with any font, not just OTF,
    Eli> but I'm not sure our integration of HarfBuzz allows that.  We should
    Eli> actively test that with old fonts, like bitmapped fonts and BDF,
    Eli> before we make the decision.  For example, I suspect the methods we
    Eli> currently use for finding fonts suitable for HarfBuzz filter out
    Eli> non-OTF fonts (at least on Windows, this is definitely so).

OK. So itʼs just xft (and uniscribe) weʼd be removing, eventually.

    >> default-frame-alist and similar will still be available for people
    >> who absolutely want to turn it off

    Eli> The main issue at hand is how to allow users to specify the
    Eli> non-preferred backends when they want that.  See Yamamoto-san's
    Eli> message about that.

(add-to-list 'default-frame-alist '(font-backend xft x)) works already, no? And
presumably continues to work with your solution.

Robert