Re: Optional support for GDI+ on Windows (emacs-28)

[Stefan Monnier]

>> >> > we should provide variables to control whether GDI+ is used for each
>> >> > supported image format.  HAVE_GDIPLUS should guard code which uses
>> >> > GDI+, but it should NOT decide whether that code is actually used.
>> >> Why bother?
>> > Because I requested it.
>> 
>> I understand this part, but really there's a good chance this is
>> wasted effort.  The NS port didn't have to jump through those hoops to
>> get its code accepted.
>
> I didn't request anything that could be qualified as jumping through
> hoops.  This is our standard implementation paradigm for optional
> features on MS-Windows, you can see it all over the place in w32*.c
> files.  Convenience macros are available to make coding this
> more-or-less copy-pasting from some other similar feature.

I don't think "variables to control whether <foo> is used for each
supported <bar>" is comparable to what we do for other
"optional" features on MS-Windows.

Also, for "optional features on MS-Windows", the usual behavior if the
lib is not available at run-time is just not to provide the
corresponding functionality, rather than to fallback on some alternative
C implementation.

IOW, I think what would be comparable is: build with support for GDI+
images only (i.e. without support for images via libpng and friends),
and make sure Emacs does run even if GDI+ is not available (simply with
the limitation that it can't display those images, just like what we
have now if libpng is not available at run time).


        Stefan