It seems like this is a bit more difficult on MX4 (no space left in the respective filesystem) - but with a bit of persuading I was able to get the update installed following these steps:

1. sudo ubports-qa install xenial_-_edge_-_wayland (finished with error)
2. apt -o Dir::Cache::Archives=/home/phablet/Downloads full-upgrade (processing the updates using Downloads folder to save the packages to prior installing)

With the above modifications I can confirm the screen being black on startup :).
Unfortunately though I am still getting what(): SDL_Init failed: No available video device. And this could be an issue with my Wayland modifications in the code - which now seems more probable.

@dobey This one should be it: https://gitlab.com/zubozrout/sdl2-demo/tree/wayland

To build it it should hopefully be enough to follow these instructions: https://gitlab.com/zubozrout/sdl2-demo/tree/wayland#building-the-sdl2-demo-project

Ok, I am getting the same error even if I remove and install the app again or compile it with a higher version number.

@dobey Ha, good point. I'll try that when I can - and thank you very much for the info :).

I've tried this but it doesn't seem to be the way to go (It doesn't tell me more info):
WAYLAND_DEBUG=client ubuntu-app-launch zub.sdldemo_SDLDemo_0.2

And running just this doesn't tell me much more but I'd expect there would be something missing for the app to run without ubuntu-app-launch:

phablet@ubuntu-phablet:~$ WAYLAND_DEBUG=client /opt/click.ubuntu.com/zub.sdldemo/current/sdl_demo 
terminate called after throwing an instance of 'SDL2pp::Exception'
  what():  SDL_Init failed: No available video device
Aborted

@alan_g Seems ok to me:

phablet@ubuntu-phablet:~$ ls -al $XDG_RUNTIME_DIR/wayland-0
srwxrwxr-x 1 phablet phablet 0 srp 14 17:01 /run/user/32011/wayland

Thank you all for your reply :).

phablet@ubuntu-phablet:~$ echo $XDG_RUNTIME_DIR
/run/user/32011
phablet@ubuntu-phablet:~$ ls /run/user/32011/
confined      mir_socket          upstart-dbus-bridge.1685.pid
dbus-session  mir_socket_trusted  upstart-file-bridge.1685.pid
dconf         pulse               upstart-udev-bridge.1685.pid
keyring       signond             wayland-0
libertine     upstart             wayland-0.lock

$WAYLAND_DISPLAY - I don't thinks it is set at all but maybe I am looking wrong.

I've also tried to make the app unconfined and there is no difference in the error at all.
https://www.iubuntu.cz/apps/zub.sdldemo_0.2_armhf.click (unconfined click with some binaries with it - I've built it from the zub's source, it is hosted on my server, but you should never trust random packages like that so this is only for those very adventurous)

Hi,
I've tried to compile an SDL demo with Wayland instead of Mir which should be a way to go now on edge (at least as far as I know) but the compiled app seems not to be able to start at all:

terminate called after throwing an instance of 'SDL2pp::Exception'
  what():  SDL_Init failed: No available video device

Except for the Mir/Wayland SDL part everything is the same as in this project: https://gitlab.com/zub2/SDLDemo

Do I need to modify anything in the .desktop file for instance to get it running or is it more difficult than that?

@TotalSonic Unfortunately so far there are only additional issues with this:
https://github.com/ubports/ubuntu-touch/issues/1192
https://github.com/ubports/ubuntu-touch/issues/1193
https://github.com/ubports/ubuntu-touch/issues/1194

However, maybe with the new Mir we could have some of these apps compiled against Wayland and packaged as click packages. Unfortunately though so far I was unable to run such Wayland apps at all on edge. There is probably something I am missing required but until more people are using it I am hesitant to ask how to proceed with it.

I would not even try to think how much work would that mean. This is the Android source they have: https://github.com/mozilla-mobile/focus-android - It seems it could be easier to start from scratch, creating a custom UI that works with Mir/Wayland and is just using the FFox backend. And it doesn't have to be called Firefox - https://en.wikipedia.org/wiki/Mozilla_software_rebranded_by_Debian#Iceweasel - Sadly that's quite a lot of work and commitment since it would have to be maintained and updated regularly.

But it would "work" to just click-package the regular desktop Firefox with Wayland support enabled. With little tweaks here and there it could actually be ok, especially on tablets. For example there were plugins for touch interaction a few years back which could help. The UI could be scaled up and when running natively with the latest Mir the performance should also be better.