bug#73730: 31.0.50; Support for color fonts on MS-Windows

[Eli Zaretskii]

> Date: Sun, 20 Oct 2024 15:35:10 +0200
> From: Cecilio Pardo <cpardo@imayhem.com>
> Cc: 73730@debbugs.gnu.org, kbrown@cornell.edu
> 
> 
> On 17/10/2024 12:38, Cecilio Pardo wrote:
> 
> >>> 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.
> >>
> >> Is that really TRT?  What does it mean font_size = 0 in this case?
> > 
> > No, I was wrong, sorry. DirectDwrite is failing to create a font from 
> > certain GDI fonts. I need to then fall back to w32font. I'm on it.
> > 
> 
> The error is caused indeed by fonts with size == 0.
> 
>   - w32-find-non-USB-fonts calls open-font with size == nil.
>   - open-font gets the size from font-entity, that is also empty.
>   - It ends up calling CreateFontIndirect with a LOGFONT
>     with lfHeight == 0
>   - Then, w32-find-non-USB-fonts calls font-get-glyphs, which call
>     text_extents.
>   - text_extents on DirectWrite fails with a font of size 0, but
>     w32font_text_extents does return values that are not 0.
> 
> If the case of size <= 0, we are now falling back to
> w32font_text_extents.
> 
> Also, in the case of failures to get text size, draw, or encode char,
> now we will disable directwrite for the particular font.
> 
> I'll send a patch as soon as I can.

Great, thanks.