Re: No support for ImageMagick 7 in emacs-26

[Eli Zaretskii <eliz@gnu.org>]

> Cc: emacs-devel@gnu.org
> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Mon, 26 Nov 2018 17:38:28 -0800
> 
> > -      MagickRealType color_scale = 65535.0 / QuantumRange;
> > +      double quantum_range = QuantumRange;
> > +      MagickRealType color_scale = 65535.0 / quantum_range;
> 
> We don't need to apply this to the emacs-26 branch, as it does not 
> affect behavior and is used only to pacify a GCC warning. I suppose 
> Gentoo enables warnings somehow, and doesn't want that warning. But in 
> general we no longer worry about --enable-gcc-warnings diagnostics in 
> the emacs-26 branch.

Agreed.

> So how about the attached patch for the emacs-26 branch?

Fine with me, except:

> --- a/src/image.c
> +++ b/src/image.c
> @@ -8272,11 +8272,20 @@ imagemagick_image_p (Lisp_Object object)
>  /* The GIF library also defines DrawRectangle, but its never used in Emacs.
>     Therefore rename the function so it doesn't collide with ImageMagick.  */
>  #define DrawRectangle DrawRectangleGif
> -#include <wand/MagickWand.h>
> +
> +#ifdef HAVE_IMAGEMAGICK7
> +# include <MagickWand/MagickWand.h>
> +# include <MagickCore/version.h>
> +/* ImageMagick 7 compatibility definitions.  */
> +# define PixelSetMagickColor PixelSetPixelColor
> +typedef PixelInfo MagickPixelPacket;
> +#else
> +# include <wand/MagickWand.h>
> +# include <magick/version.h>
> +#endif
>  
>  /* ImageMagick 6.5.3 through 6.6.5 hid PixelGetMagickColor for some reason.
>     Emacs seems to work fine with the hidden version, so unhide it.  */
> -#include <magick/version.h>
>  #if 0x653 <= MagickLibVersion && MagickLibVersion <= 0x665
>  extern WandExport void PixelGetMagickColor (const PixelWand *,
>  					    MagickPixelPacket *);

It makes little sense to me to move the inclusion of magick/version.h
into the v6 conditional, but leave the "#if 0x653" conditional
fragment and its comment outside that v6 conditional.  AFAIU, we are
including version.h _because_ we want that second #if, right?  So we
should keep them close together, and keep the comment explaining why
we do that before the code it explains.  (Which begs the question
whether we need to include MagickCore/version.h for v7, but I'm not
going to bother about that.)

Thanks.