Re: master bf0aeaa0d7a: Re-enable displaying `han' characters on Android

[Pip Cet <pipcet@protonmail.com>]

"Po Lu" <luangruo@yahoo.com> writes:

> pipcet@protonmail.com writes:
>
>> Thanks! So supporting these fonts on Android using the sfnt driver is
>> very hard, correct?
>
> Yes, it would amount to writing a new font driver.

Just so that we have that option, I've done the minimal work necessary
to build Emacs for Android with fontconfig and the ftcrhb and ftcr font
drivers. As far as I can tell, it works now (including, regrettably,
color emoji provided in font files). Harfbuzz shaping seems to work,
too. I still have to look at what the DRAW_CURSOR stuff does...

Of course there are good reasons not to want to do this: the
sfntfont-android driver is very fast, this is not.  It also requires an
additional file to configure fontconfig and a cache directory for
fontconfig's disk-based cache. Plus there are the extra dependencies...

Obviously, this would be and remain an optional feature, with the other
font drivers still available (that's not true for my test builds
including these and quite a few other changes, which currently disable
the android-specific drivers: https://codeberg.org/pipcet/emacs-android )

>> The androidfont.c fallback driver appears to support them, but I
>> understand that's not a good option either. (I tried
>> (set-frame-parameter nil 'font-backend "android") and the difference
>> in a C-h h buffer was quite noticeable).
>
> Correct.

Which devices in the androidfont.c driver currently used on?  Very old
ones with 15/16 bpp?

>> In any case, asking users to install an extra font only to see basic
>> CJK glyphs can't be a long-term solution, can it?
>
> Till someone implements the aforesaid new font driver, why not?  The
> font is installed once, and that is the end of the matter, and
> ultimately it is the same font that would ideally be loaded from
> /system/fonts, with no degredation in quality.

How do we know? I can't find this alleged source form for the Noto CJK
font anywhere, just binaries produced by Google.  Maybe they are editing
one of the versions directly, and generating the other one from it,
which would probably mean the secondary version is degraded in quality,
but even then Google would have to make available instructions for how
to build one from the other in order for the font to be considered
free (or, if I understand the OSI definition correctly, "open source")

> The source code must be the preferred form in which a programmer would
> modify the program. Deliberately obfuscated source code is not
> allowed. Intermediate forms such as the output of a preprocessor or
> translator are not allowed.

Anyway, here's the main part of the patch:



Pip