bug#61974: 29.0.60; customize checkbox and radio widgets don't render on macOS

[Eli Zaretskii <eliz@gnu.org>]

> From: Po Lu <luangruo@yahoo.com>
> Cc: David Caldwell <david@porkrind.org>,  61974@debbugs.gnu.org
> Date: Sun, 05 Mar 2023 16:01:10 +0800
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> Date: Sat, 4 Mar 2023 17:35:16 -0800
> >> From: David Caldwell <david@porkrind.org>
> >> 
> >> Fails:
> >> 
> >>    (insert-image (find-image '((:file "checked.svg"))))
> >> 
> >> Works:
> >> 
> >>    (insert-image (find-image '((:file "splash.svg"))))
> >> 
> >> It appears to be because the checkbox and radio svgs in etc/images all
> >> use height="1em" and the mac native renderer doesn't like that.
> >> 
> >> It works with rsvg because the emacs code that interfaces with rsvg code
> >> passes some extra styling info to it so that it can render that properly
> >> (image.c:11226 in the emacs-29 branch for me today).
> >> 
> >> Unfortunately the native renderer in nsimage.m doesn't do this. I spent
> >> some time today trying to figure it out, but it appears that the cocoa
> >> apis just don't have this feature, so it would have to be done some
> >> other way.
> >> 
> >> I can confirm this is the issue by opening "etc/images/checked.svg",
> >> hitting "C-c C-c" to edit, changing the "1em" to "16" and "C-c C-c"ing
> >> again to re-render it. It will appear with a non-percentage height.
> >
> > Does it work to use the checked.xpm image instead?  If it does,
> > perhaps we should switch the macOS build to using the XPM images
> > (assuming the problem you report is common to all macOS builds, that
> > is).
> 
> Shouldn't we disable SVG display with native image APIs instead?
> In general, the native image API code we have at present cannot
> display SVG images as well as librsvg, because it cannot know the
> scale at which the image will be displayed.

My impression was that such a conclusion would be too drastic, as many
SVG images can undoubtedly be displayed.