Looks pretty good. I made some comments on c56f807, just little things that seem like they may be leftovers?

Yes, those are leftover from my original trace through the code to get SDL_USEREVENT to launch the dialog.

I'd be happy to merge it after the cleanup.

I have updated my branch with the clean up items we discussed.

I have not yet pulled and looked at what you did, but maybe it's worth noting that I made a sdl-controls.xml [1] for Wesnoth, that makes it rather playable ...

I added touchkey areas around the main map for directions (=scrolling the main map) and an escape button at the top right. The latter I needed because once one opens a right-click menu by holding it cannot be closed by clicking somewhere else (I guess that's a bug somewhere?!).

I also made a script to create the sdl-controls.xml [2] so one can easily adjust the direction button width.

As a side note:
I'm not sure if removing the cursor is really good, before drag scrolling works. Anyway, if one turns on "Show Color Cursors" in the Display preferences, the strange-looking tearing of the b/w cursor is gone... It does look quite nice then.

[1] https://github.com/NichtJens/wnbbpb-helper/blob/master/sdl-controls.xml
[2] https://github.com/NichtJens/wnbbpb-helper/blob/master/sdlcontrolxml.sh

Interesting note about the color cursor.

I have some fixes that add in drag scrolling onto the play screen which works quite well and make it much more playable. I'm in the process of ironing out the bugs and play testing.