Re: HarfBuzz is available on MS-Windows

[Eli Zaretskii <eliz@gnu.org>]

> From: Andy Moreton <andrewjmoreton@gmail.com>
> Date: Fri, 07 Jun 2019 18:05:23 +0100
> 
> I've tested this with an MSYS2 64bit build on Windows 10.

Thanks, you can now just build the master branch.

> It appears to work ok, but is noticeably slower compared to the
> master branch.

I didn't see any tangible slowdown with HarfBuzz on my system.  Can
you post some benchmarks with timings?  (I assume both branches were
built using the same optimization switches.)

> a) On harfbuzz and master branches from "emacs -Q", a machine without
> the Symbola font does not display the emoji U+1F44B WAVING HAND SIGN (no
> font available). Babelmap shows that this character is available using
> the built-in "Segoe UI Symbol" or "Segoe UI Emoji" fonts (or by
> installing Symbola).
> 
> b) On the harfbuzz branch from "emacs -Q", the lao U+EC3 LAO VOWEL SIGN
> AY and U+EC3 LAO VOWEL SIGN O characters are not displayed (no font
> available). Babelmap shows that this character is available using the
> built-in "Leelawadee UI" font.

BabelMap just shows coverage, but Emacs also tests additional features
of the fonts (although I don't think we have any special requirements
for Emoji; Lao certainly does require some OTF features).

In any case, the font backend has nothing whatsoever to do with how
Emacs searches for a suitable font, at least on Windows.  What the
above means is that Leelawadee somehow doesn't fit the criteria for
the Lao script and/or the features bits these fonts exhibit don't
announce that they cover the respective codepoint ranges.  The way to
improve the font search is to customize the fontsets.

> I use the following to speed up finding built-in fonts on Windows 10:
> 
>   (pcase-dolist
>       (`(,font-spec . ,targets)
>        '(;; Unicode blocks ---------------------------------------
>          ("Segoe UI Emoji"
>           (#x1f900 . #x1f9ff)) ; Supplemental Symbols and Pictographs
>          ;; Unicode scripts --------------------------------------
>          ("Segoe UI Symbol"      braille mathematical symbol)
>          ("Leelawadee UI"        khmer thai lao)
>          ("Nirmala UI"           bengali devanagari gujarati kannada
>           malayalam oriya sinhala tamil telugu)
>          ("Microsoft Himalaya"   tibetan)
>          ("Myanmar Text"         burmese)
>          ("Ebrima"               ethiopic)
>          ("Gadugi"               canadian-aboriginal cherokee)))
>     (dolist (target targets)
>       (set-fontset-font "fontset-default" target font-spec nil 'prepend)))
> 
> Perhaps the built in fonts should be added to the default mappings for
> Windows 10.

I think the policy is not to mention non-free fonts in our fontsets.