I came across swaybg and wondered if it works with Mir. The short answer is “yes”.
Looking at the documentation, the longer answer is “yes, if you enable a couple of extensions: zwlr_layer_shell_v1 and zxdg_output_manager_v1”. And that just happens to be what egmde does for “shell-components”. (They are also enabled by default in the mir_demo_server from mir-test-tools.)
The only slight complication is that swaybg takes options on the command-line and egmde doesn’t (currently) support command-line options in it’s --shell-components configuration.
So I wrote a small wrapper script:
$ cat `which my-swaybg`
#!/bin/sh
exec swaybg -i '/home/alan/Pictures/wallpapers/IMG_1804.jpg'
And that allowed me to start egmde with a bespoke background:
sudo apt install swaybg
egmde --shell-components my-swaybg:waybar
I’m also using Waybar as described her: