Subject: bug#38442: 27.0.50; segmentation fault switching to cairo

From: Juanma Barranquero <[email-masked]>
Date: Mon, 2 Dec 2019 18:28:32 +0100

On Mon, Dec 2, 2019 at 5:09 PM Eli Zaretskii <[email-masked]> wrote:

> We may be mis-communicating.

Entirely my fault.

> In most cases, the first (default) backend in the list finds a
> suitable font, but some fonts can only be used with specific backends,
> so they force Emacs to choose that backend.  An example is a the *.fon
> bitmapped fonts on MS-Windows, which will force the GDI backend.

But the font-backend's list on Windows defaults to (harfbuzz gdi), so that's
not surprising. Could Emacs automatically choose uniscribe, too, for some
font,
with the current default configuration, or would the user be forced to add
uniscribe to the frame's font-backend list?

I mean, if the answer is "yes, Emacs would use uniscribe"; then I agree with
you and just not saving/restoring font-backend is the best fix.

If the user has a font that needs uniscribe, and they *have* to add
uniscribe
to font-backend in default-frame-alist or via set-frame-parameter or
whatever,
then there's a (likely uncommon) use case and I think it makes at least a
bit
of sense to save font-backend with the frame and restore it afterwards.

I hope now my misunderstanding is a bit clearer.

Thanks,

    Juanma