bug#10399: [PATCH] Document win32 font backends

[Daniel Colascione <dancol@dancol.org>]

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On 12/31/11 2:56 AM, Eli Zaretskii wrote:
>> Date: Thu, 29 Dec 2011 09:16:16 -0800
>> From: Daniel Colascione <dancol@dancol.org>
>> CC: Juanma Barranquero <lekktu@gmail.com>, 10399@debbugs.gnu.org
>>
>> Since we're on the subject of Windows font backends: is it worth
>> creating a DirectWrite backend? It does a better job of inter-character
>> spacing and rendering at small sizes than Uniscribe does.
>>
>> https://bugzilla.mozilla.org/show_bug.cgi?id=517642
>>
>> https://blog.mozilla.com/nattokirai/2009/10/22/better-postscript-cff-font-rendering-with-directwrite/
> 
> Looks like it has only C++ bindings?  One of the comments on MSDN
> says:
> 
>   DirectDraw header file is not compatible with C programming language
>   and can only be included in C++ code. However, C-style redeclaration
>   of contents in this header file alone (excluding other header files it
>   includes), will succeed in resolving the issue.

DirectWrite is COM, and all COM facilities can be used by plain C.

The C compatibility issue arises from a problem with the header for
the COM interface produced by the IDL compiler (probably, nobody tried
to actually use DirectWrite from C before shipping.)  This problem
doesn't prevent our using DirectWrite from C: as the MSDN comment
indicates, the declarations just need to be extracted and rephrased as
standard C.

> Also, I see no dwrite.h header in the MinGW runtime and w32api
> distributions, and no lib*.a import libraries for dwrite.dll.  Am I
> missing something?

No. Either these packages would need to be updated to include
DirectWrite or we'd need to just include declarations for the
appropriate functions and interfaces ourselves.


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