GNU bug report logs - #73730
31.0.50; Support for color fonts on MS-Windows

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From: Cecilio Pardo <cpardo <at> imayhem.com>
To: Eli Zaretskii <eliz <at> gnu.org>, Ken Brown <kbrown <at> cornell.edu>
Cc: 73730 <at> debbugs.gnu.org
Subject: bug#73730: 31.0.50; Support for color fonts on MS-Windows
Date: Wed, 16 Oct 2024 23:35:34 +0200

[Message part 1 (text/plain, inline)]

Still not done with this, but I am sending a new patch to fix the bug 
with w32-find-non-USB-fonts.  It calls text_extents with a font of size 
0. Checking for that seems to solve the problem.

Also, most of the style changes are done.

- With MingGW64, use dwrite_3.h normally.
- renamed w32-inhibit-direct-write to w32-inhibit-dwrite, and some other 
things.

BTW, why does that variable show as undocumented with 
describe-variables? What am I doing wrong?

Pending:

- NEWS entry.
- Instead of aborting on failure, just disable DirectWrite and let emacs 
continue. This will take some work.
- mingw warnings.

>
>> +  glyph_run.bidiLevel = 0;
>                 ^^^^^^^^^^^^^
> Is this because otherwise DirectWrite will possibly reorder the
> glyphs or something?  Did you test this with R2L text, e.g. by
> displaying TUTORIAL.he?  I did try, and it looks OK, but are there any
> color fonts that cover the Hebrew block, so I could be sure everything
> works in that case?
>
> More generally, what color fonts can be used with this build on
> Windows for characters other than Emoji, in addition to Segoe UI
> Emoji?


The documentation describes this field as the "implicit resolved level 
of the glyph run". Odd levels indicate RTL, and the function asks for 
the right side position as origin, so I think they would be reordered.

As there is no reference to bidi in w32font.c, I assumed glyphs reach 
this layer prepared to be rendered ltr.

I think the only color font that Windows has is the emoji one. I'll try 
to find some other to test this.

>> +void *w32_font_get_dwrite_cache (struct font *font, float *font_size);
>> +void w32_font_set_dwrite_cache (struct font *font, void *cache, float font_size);
> 
> Why aren't these functions defined in w32dwrite.c?

They need to know about the uniscribe_font struct, which is defined there.

[0001-Implement-drawing-text-with-DirectWrite-on-MS-Window.patch (text/plain, attachment)]

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