Re: When and how to register various font backends

[Robert Pluim <rpluim@gmail.com>]

>>>>> On Sat, 15 Jun 2019 12:50:23 +0300, Eli Zaretskii <eliz@gnu.org> said:

    >> Date: Fri, 14 Jun 2019 17:47:07 +0300
    >> From: Eli Zaretskii <eliz@gnu.org>
    >> Cc: emacs-devel@gnu.org
    >> 
    >> > (add-to-list 'default-frame-alist '(font-backend xft x)) works already, no? And
    >> > presumably continues to work with your solution.
    >> 
    >> No, it doesn't work with my solution, at least not reliably, because I
    >> didn't intend it to work.

    Eli> But what about being able to specify the backend(s) via
    Eli> default-frame-alist in the init file, and expecting that to affect all
    Eli> the frames including the initial one?  Mitsuharu's proposal allows
    Eli> that, whereas mine doesn't.  That's because in my implementation the
    Eli> font backend is registered at frame creation time, and only the
    Eli> backends known to be requested at that time are registered.  So when
    Eli> we call modify-frame-parameters later, after processing the init file,
    Eli> to make default-frame-alist parameters take effect, you cannot request
    Eli> a backend that wasn't registered.

    Eli> By contrast, Mitsuharu's method registers all the backends, but only
    Eli> activates some of them.  So modify-frame-parameters can work, because
    Eli> it just needs to activate an already registered backend.

I see. I guess one potential fix would be to change the default value
of default-frame-alist, but that wouldnʼt help people who have already
customised it.

So it seems that Mitsuharu's proposal is the only one that fulfills
all your requirements.

Robert