As far as the GTK branch is concerned, anything in git is unfortunately out of date and since HGM changed a lot of things in master, it might almost be better to start new...
Well, this might be overly pessimistic. I am not sure when the last time was that gtk-xt was brought in sync with master, but don't think I changed much that required front-end support. Only after the GTK version was more or less moth-balled I did a major rewrite of the X11 front end, but this should not have any effect on the GTK version, as it is all in files that are not used in the GTK build. Of course it does mean that some of the impovements (like having a separate window for the second board in Dual Board mode) that could be done basically for free in the new X11 front end will not benefit the GTK branch. But it should still work in the old way, that the X11 front-end did before being ported to GTK. Thi is just cosmetics, and not a feature that would be entirely missing.
on the other hand as HGM pointed out now a lot less needs to be ported, since the graphic frontend is better separated from the rest of the code and most things can probably be copied from the gtk-xt branch.
This could be another approach. The GenericPopUp code was already ported by John, and the overhaul I did was basically remove all dedicated code for handling popup windows from xboard.c, and let GenericPopUp() handle them. To do this for some windows, the capabilities of GenericPopUp() had to be extended a bit, though. (E.g. to specify a 'graphics widget' for the Eval Graph and Board window, and a list-box widget for the Game List window.) This was quite straightforward, though: GenericPopUp() grew only slightly in size, and the code that was added was mostly taken from the dedicated routines that created these windows before (and were then deleted). The same strategy could be applied to the GTK version.
