gtk3+ support

[weiguangcui]

Is it possible to compile gadgetviewer with gtk3+? I tried to point the program to the correct folder, but it seems only look for gtk+-2.0.pc

checking for GTK+ - version >= 2.0.0... Package gtk+-2.0 was not found in the pkg-config search path.
Perhaps you should add the directory containing `gtk+-2.0.pc'

Thank you for any suggestions.

[jchelly]

I believe the gtk2 and 3 APIs are incompatible. Gadgetviewer uses the gtk2 API so at the moment it's not possible to compile it with gtk3. Are you able to install packages on your system? It may be that you already have the gtk-2 libraries but not the 'dev' package (which contains the headers and the .pc files, amongst other things). On Ubuntu I think something like 'sudo apt install libgtk2.0-dev' would do it.

For my own reference, I'm going to leave a link to this migration guide I found here: https://developer.gnome.org/gtk3/3.0/migrating.html

[weiguangcui]

I thought they are compatible, at least downwards. But it seems they are not. I will install gtk2+ for gadgetviewer, but it would be good to have gtk3+ supported as well.
Thank you.

[jchelly]

Partially implemented in #23.