Hello,
I just looked into it; debian's libpng carries that same patch.
Specifically, libpng-1.6.37-apng.patch from
https://sourceforge.net/projects/libpng-apng/files/.
The request for upstream libpng to include the patch is at
https://sourceforge.net/p/libpng/feature-requests/16/, but upstream
libpng never merged it. Chromium bundles libpng without that patch, and
seems to have made APNGs work without needing to patch libpng. To fix
this bug, chromium should either use the bundled version of libpng, or
debian's libpng should drop libpng-1.6.37-apng.patch.
I'm curious what the libpng maintainers think?
its ok for me to drop the patch, but somebody says that firefox needs it, so
before dropping we should make sure
firefox for Debian and derivatives (also snap?) are using the bundled version
and it works correctly.
I'll try to drop it and see what happens.
G.
