SVG/PNG images in toolbars?

[Clément Pit-Claudel]

Hi all,

Do we support any form of scalable graphics for toolbar icons, or at least any 
format that supports anti-aliasing? All I can seem to get working is 
XPM/XBM/PBM, but I can't find a statement that we don't support anything better.

Additionally, I noticed that emacs -Q on my machine seems to ignore the 
find-image specs of toolbar-mode-map for the default tool bar (that is, running 
find-image with the specs found in tool-bar-map yields something like (image 
:type xpm :file "/usr/local/share/emacs/26.0.50/etc/images/refresh.xpm"), but 
that image looks nothing like the one actually displayed).  strace-ing Emacs 
suggests that this is because of `x-gtk-stock-map`.

Is there a way to use custom PNG or SVG icons in the toolbar, at least for GTK 
builds?  Or is x-gtk-stock-map the only option?

Thanks!
Clément.