Re: HarfBuzz is available on MS-Windows

[Andy Moreton <andrewjmoreton@gmail.com>]

On Sat 08 Jun 2019, Eli Zaretskii wrote:
> There are 2 issues here: one is about the speed of finding fonts for
> certain characters, the other is about finding a suitable font at
> all.

Agreed.

> I was under the impression that your fontset customizations were
> meant to solve the speed issue, in which case I don't think it's an
> issue with the defaults, and in any case we shouldn't assume anything
> about the users' installation: they could have other fonts installed
> that they prefer, so it would be improper for Emacs to force them to
> use the built-in fonts.

The problem with incorrect character display is fixed by part of my
fontset customisation: the rest of it is to improve font lookup speed.
All of the mentioned fonts are installed by default on Windows 10.

Emacs should be capable of finding a font to display all of the 
characters in HELLO, as it can do so given some fontset customisation.
It should do so by default, so charatcers are displayed properly but
users can add further customisation to express a preference for
different fonts.

> In addition, quality of built-in fonts changes with time, so a font
> that comes with the system today might be less desirable to use
> tomorrow. Thus, including those fonts in our sources would mean we
> need to track the development of system fonts, update the fonts in our
> default fontsets, and perhaps make the fontset dependent on the OS
> version. This would be a maintenance burden.

It is more important to give users a working tool than to reduce
maintenance effort. The selection of fonts shipped with each platform
changes fairly slowly, so this should not present an undue burden.

> However, above you seem now to be talking about failure to find a font
> although some fonts do support the character.  That is a separate
> issue.  The question in this case is why doesn't Emacs find and select
> these fonts by itself, without any hints in the fontset in addition to
> what we already have there.

Yes, and this was the first part of what I wrote. This needs fixing.

> If you'd like to try debugging this, I can help by pointing to the
> code where this happens. In general, start with the fontset as defined
> in fontset.el, and then look in w32font.c:w32font_list_internal and
> its subroutines.

I can try debugging from there - any further hints are welcome.

    AndyM