I have a fresh install of Ubuntu 20.04 and I've installed Gimp via Software Manager (so that it became a snap, located in /snap/gimp/252/). Now I want to install gimp-GAP. I see no other way than to use "gimp-gap-2.6.0.tar.bz2" from https://www.gimp.org/news/2009/06/05/gimp-animation-package-260-released/. However, after unpacking, when running ./configure it complains:

> No package 'gimp-2.0' found

> No package 'gimpui-2.0' found

> No package 'gimpthumb-2.0' found

>

> Consider adjusting the PKG_CONFIG_PATH environment variable if you

> installed software in a non-standard prefix.

Apparently, this gimp-GAP package assumes Gimp has been installed the classical way (not as a snap).
What should I do?

Edit:

echo $PKG_CONFIG_PATH gives the empty result and PKG_CONFIG_PATH (as one string) does not occur anywhere in the top-level files of the gimp-GAP installation files.

Searching for gimp-2.0 and gimpui-2.0 and gimpthumb-2.0 gives these locations:

/snap/gimp/252/usr/lib/libgimp-2.0.so

/snap/gimp/252/usr/lib/libgimp-2.0.so.0

/snap/gimp/252/usr/lib/libgimp-2.0.so.0.1000.18

/snap/gimp/252/usr/share/aclocal/gimp-2.0.m4

/snap/gimp/252/usr/lib/libgimpui-2.0.so

/snap/gimp/252/usr/lib/libgimpui-2.0.so.0

/snap/gimp/252/usr/lib/libgimpui-2.0.so.0.1000.18

/snap/gimp/252/usr/lib/libgimpthumb-2.0.so

/snap/gimp/252/usr/lib/libgimpthumb-2.0.so.0

/snap/gimp/252/usr/lib/libgimpthumb-2.0.so.0.1000.18

Should I set PKG_CONFIG_PATH to /snap/gimp/252/usr/lib/ and then again invoke configure?