Currently, when libpng is available, Emacs has support for PNG. But it
only searches for XBM, XPM, and PBM icons for its toolbar, even though
PNG icons are considerably more attractive. I've written a patch for the
tool-bar.el from Emacs CVS, which tests for PNG support before adding
the PNG format to the search, facilitating a prettier Emacs toolbar.

tool-bar-local-item-from-menu and tool-bar-local-item duplicated the
image finding code, which I have moved for simplicity into a new,
separate function tool-bar-find-best-icon.

When editing the source I noticed it doesn't currently check whether
support for the other image file types is present or not, but I didn't
change this in case it was desired.

ChangeLog, new tool-bar.el, and tool-bar.el.diff (vs. current CVS)
attached.

NB for testers. You must compile Emacs with the new tool-bar.el if you
wish it to use it to load the main Emacs toolbar, since it is dumped
into Emacs.

If you're running X11 and you'd like some PNG icons to try with your
Emacs, see:

http://www.benjaminhawkeslewis.com/www/svn/emacs/themes/icons/

which currently features a screen shot of the toolbar in its full PNG
glory and some Ubuntu-themed icons. I haven't gotten round to adding
icons for news modes and so on, but the toolbar will happily fall back
to uglier icons.

--
Benjamin Hawkes-Lewis