Integration of layer-shell in plasma

[Aleix Pol]

On Mon, Aug 24, 2020 at 4:20 PM Vlad Zahorodnii <vlad.zahorodnii at kde.org> wrote:
>
> Howdy,
>
> As you probably know, surfaces created by plasmashell need to be treated
> specially by the compositor. For example, notification windows must be
> always on top, panels may go above and below normal windows. That's why
> we use a proprietary protocol called plasma-shell for creating shell
> surfaces that provide the functionality required by plasmashell.
>
> Unfortunately, there are technical issues with the plasma-shell protocol
> that can be fixed only by rewriting the protocol from scratch. Luckily
> for us, the sway community came up with a protocol called layer-shell
> that a desktop environment could use in order to build components such
> as panels, notifications, etc. The layer-shell protocol doesn't suffer
> from the problems that we have with the plasma-shell protocol.
>
> The cool thing about is that with the layer-shell protocol it will be
> possible to make applications such as latte-dock run across desktop
> environments.
>
> Over the last a couple of weeks, I've been working on a layer-shell
> protocol implementation in kwin. With the compositor side being almost
> complete (it's still under code review), it's a good time to focus on
> the client side.
>
> The biggest difference between the layer-shell protocol and the
> plasma-shell protocol is that positioning is done in relative terms in
> the former protocol. For example, instead of saying "please place me at
> the specified position (x, y)," a client must say "please place me 10px
> away from the left screen edge." Which brings us to the first problem:
> we need to ditch specifying absolute window coordinates and transition
> to relative positioning. Unfortunately, we cannot do it all at once, so
> we need some way to smoothly transition between the two approaches. I
> see several options:
>
> * Mimic absolute positioning via relative positioning. It's good as a
> short-term solution, but imho, we need something better
> * Introduce a Plasma::Dialog with relative positioning and start
> gradually porting all plasma components to it
>
> The second problem is that we need to integrate the layer-shell protocol
> in Qt in some way. Since plasmashell creates both normal windows and
> special-purpose windows, we need to use **both** the xdg-shell and the
> layer-shell protocol. It's not really clear how it can be achieved.
>
> The most ideal case is where Qt provides native support for the
> layer-shell protocol out of the box. API-wise, plasmashell needs to set
> the layer, the namespace, the margins, etc. Alternatively, we could fork
> QtWayland QPA and extend it with features we need. Either way, we need
> some changes in Qt in order to be able to use several shell surface
> protocols simultaneously.
>
> Any ideas or thoughts on what the best way to integrate the layer-shell
> protocol in plasma and Qt is?
>
> Cheers,
> Vlad

I guess one way is by levarging QT_WAYLAND_SHELL_INTEGRATION plugin
system, like maliit does. I don't know how this could be done
per-window instead of per-process.

The shell integration plugin could be implemented in Qt together with
xdg-shell and ivi (see qtwayland/src/plugins/shellintegration).

HTH,
Aleix