Re: No support for ImageMagick 7 in emacs-26

[Eli Zaretskii <eliz@gnu.org>]

> From: Ulrich Mueller <ulm@gentoo.org>
> Cc: emacs-devel@gnu.org
> Date: Mon, 26 Nov 2018 08:38:21 +0100
> 
> > It doesn't seem entirely trivial to me.  ImageMagick caused quitea few
> > problems to Emacs, so at this point I can only accept patches to
> > support v7 on the release branch if the code used by v6.x is
> > completely unchanged.
> 
> Sorry, but where do you see a change that could affect behaviour of
> v6.x? Effectively, the only code change in the consolidated patch is the
> following in image.c:
> 
> -      MagickRealType color_scale = 65535.0 / QuantumRange;
> +      double quantum_range = QuantumRange;
> +      MagickRealType color_scale = 65535.0 / quantum_range;

This is one part that I'd rather not do on the release branch (why is
it needed, anyway?).  The other one is that inclusion of a header file
was moved to a different place for some reason.  (Yes, I'm being
paranoid ;-)

> Also, I noticed that configure will silently disable imagemagick if v6
> is not found. This is o.k. for the default, but when I explicitly
> specify --with-imagemagick, then I would expect it to error out when it
> cannot enable the feature.

Patches to that effect are welcome, but that part should definitely
not go to the release branch.

Thanks.