bug#34024: Segfault when resizing SVG images

[Alan Third <alan@idiocy.org>]

On Fri, Jan 11, 2019 at 09:35:02AM +0200, Eli Zaretskii wrote:
> > Cc: 34024@debbugs.gnu.org
> > From: Clément Pit-Claudel <cpitclaudel@gmail.com>
> > Date: Thu, 10 Jan 2019 18:27:53 -0500
> > 
> > > And we hope we will soon
> > > have on master image resize capability that doesn't need ImageMagick,
> > > courtesy of Alan Third.
> > 
> > This sounds very exciting.  I tried the latest master, which IIUC contains (some of?) Alan's changes, but it doesn't fix the issue yet.
> 
> Please read the thread discussing Alan's code.  I think you are
> supposed to disable ImageMagick to see the native resizing in action.
> Alan, please correct me if I'm wrong.

Yes, at the moment image-mode still defaults to ImageMagick, and
resizing any image will fallback to ImageMagick if available. More
work needs to be done in image.el (and possibly image-mode.el, I only
realised this second file exists last week) to stop it using
ImageMagick when it doesn’t need to.

One thing to note about SVG images is that the native resizing only
handles bitmaps, so the SVG is converted to a bitmap, then resized.
librsvg and the like don’t allow you to resize SVG files when you
convert them to bitmaps, we’d have to use Cairo or something similar
for lossless resizing.
-- 
Alan Third