Add z-order control into kiosk-shell?

Hoosier, Matt Matt.Hoosier at
Wed Oct 6 19:32:52 UTC 2021

To make this a little more concrete, I put together MR

From: Hoosier, Matt
Sent: Friday, October 1, 2021 2:32:04 PM
To: wayland-devel at
Subject: Add z-order control into kiosk-shell?

I've been very happy to see kiosk-shell get introduced in the past year or so. It seems to tick nearly every box that I frequently find myself wanting when trying to do embedded deployment of pre-existing Wayland apps which expect to use the customary desktop-centric shells:

  *   declarative control over which output gets which surface
  *   force the apps full-screen by default
  *   no new protocols needed

So this is really nice. Much lower barrier to entry than IVI Shell, and certainly a better re-use story for off-the-rack applications.

But there's a niche that doesn't have any obvious answer yet: controlling the stacking order of different toplevel apps. It's fairly common to construct an embedded system using distributed rendering from separate programs. This means you need a way to control which things go above or below each other to achieve the overall effect.

Would there be any interest in a contribution to enhance kiosk-shell to support configurable stacking orders? This might take the form of either relative specifications ("desktop surface XYZ always goes above desktop surface UWV") or absolute z-order specifications ("desktop surface XYZ's surfaces go into weston_layer #17").

I haven't thought deeply yet about how the syntax for setting the stacking-order configuration in weston.ini would look. Maybe some kind of subscript annotation following the surface ID?

    # app1 goes in weston_layer 0. app2 goes in weston_layer 1

Or maybe allow more than one "app-ids" line, keyed by a subscript?


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