Some are, some have a layer between them called CairoWidget so that they can just draw directly in Cairo. We also tend to use Gtkmm to derive, so that we don't

Some are, some have a layer between them called CairoWidget so that they can just draw directly in Cairo. We also tend to use Gtkmm to derive, so that we don't have to do a lot of C boiler-plate code (and you won't find a "full widget implementation" anywhere, because of this).