GTK handles the UI as well as UI events (click, key, scroll, drag, etc). It's very tightly integrated into GIMP itself (the 'G' in GTK use to stand for GIMP, in

GTK handles the UI as well as UI events (click, key, scroll, drag, etc). It's very tightly integrated into GIMP itself (the 'G' in GTK use to stand for GIMP, in fact), and has been for decades. GIMP is not new software. :) The challenge of new GTK versions is that they keep simplifying things, because it's aimed at software that's much less complex than GIMP. For instance, the tree views that GIMP relies on for so many things like layer docks are deprecated in GTK4. To deal with that, we'll have to do some redesigns of core features. There's no intermediate layer in-between GIMP and GTK. It wouldn't be impossible to code, but with the current number of volunteer developers, it would mean further delaying features that most users care more about.