Re: No support for ImageMagick 7 in emacs-26

[Ulrich Mueller <ulm@gentoo.org>]

>>>>> On Sun, 25 Nov 2018, Eli Zaretskii wrote:

>> From: Ulrich Mueller <ulm@gentoo.org>
>> Date: Sun, 25 Nov 2018 09:26:56 +0100
>> 
>> Given that ImageMagick 7 was released in April 2016, wouldn't it make
>> sense to support that version in the upcoming Emacs 26.2?
>> 
>> AFAICS, commits 5729486951, bf1b147b55, 42ed35c68b, and 3cc42bb600
>> would have to be backported for that, which doesn't seem too
>> intrusive.
>> 
>> (In fact, Gentoo has a consolidated patch for 26.1:
>> https://gitweb.gentoo.org/proj/emacs-patches.git/tree/emacs/26.1/02_all_imagemagick-7.patch)

> 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;

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.