Place a fullscreen surface across multiple physical outputs

As the creator and maintainer of the wpe-webkit-mir-kiosk snap, I got a user question about multi-display setup in conjunction with fullscreen applications. They have 2-3 displays hooked up to a single machine via DisplayPort and/or HDMI running Ubuntu Core with mir-kiosk. Now when they launch wpe-webkit-mir-kiosk, it is placed in fullscreen but only on one of the screens. The goal is to have a single fullscreen surface across all physical outputs.

Their miral-kiosk.display file:

    - card-id: 0
        orientation: normal
        position: [1920,0]
        position: [0, 0]
        orientation: normal
        state: disabled

This is supposed to extend the Wayland surface across two 1920x1080 screens.

I’d like to know if
a) Mir supports this kind of setup
b) if it does: does the configuration need to be adjusted
c) what applications might need to do, e.g. provide an xdg_shell hint?

Pinging @alan_g – apologies if this is better suited for the snapcraft forum :slight_smile:

Thanks in advance!

1 Like

This is a perfectly reasonable place to ask. And a reasonable question.

The answer is that the Mir default for fullscreen acts on a single output. (That is the common behaviour for window managers on desktops systems.)

It does make sense for mir-kiosk to support a “display wall” arrangement that treats multiple outputs as a single display area, but that would need code changes. The right repository to raise that request would be



Helps a lot, thank you! I’ll direct the original request to the MirServer repository then.