Yesterday during the Tokamak 6 sprint in Nuremberg we discussed the role of KWin in Plasma Workspaces 2. At the moment in Plasma Workspaces 1 KWin is of course the recommended window manager and compositor, but it’s also possible to use a different window manager. Back in the days there were quite a lot of users who run Plasma with Compiz. In theory that shouldn’t matter because everything is standardized with EWMH and ICCCM. Over the years we added more and more extensions to EWMH. It’s all open source so anyone can implement these extensions (Compiz used to do so), nevertheless right now there is probably no other window manager available to offer the full experience except KWin.

Plasma Workspaces 2 will be released at an interesting point of time. We don’t want to do the transition to Qt 5 and Wayland at the same time, so it will still be X based. But we all agree that our future will be on Wayland and even if we use X as the windowing system our primary focus is on Wayland. With Wayland quite a few things will change. KWin will play a more important role as it will be the Wayland compositor – we do not plan to use Weston.

Given that we know that the Wayland shell interface only covers part of what Plasma needs and some of our needs are extremely Plasma specific (for example Activities) it would be tempting to say that we tie KWin to Plasma. Let’s face it: which other compositor will be there to replace KWin? The reference compositor will probably never accept Plasma specific patches for things like Activities, Compiz won’t be ported to Wayland and GNOME Shell will probably never be a solution for Plasma. For the small window managers we do not know whether they will go to Wayland at all, but I expect rather not, though I expect that we will see Weston forks/extensions for substitutions of tiling window managers.

We decided to resist the temptation to go the easy road, but instead will develop all our integration bits in a way that one could replace KWin by a different Wayland compositor, even if that is just a theoretical option. Of course we will not do any fallback modes for the case that one is using e.g. Weston without Plasma integration bits. So the features which we need might then just be disabled. Adding fallback modes would most likely just result in bit rotting code as nobody would use it.

Of course to make it possible that others can provide compatibility features we need to properly document our extensions and additional interfaces. Luckily Wayland implicitly forces us to do so. The general plan is to publish our extensions and also try to standardize what makes sense to be standardized and we hope that this would also benefit other projects. What we especially had in mind is of course Razor-Qt which already supports using KWin. By properly documenting all our Plasma-KWin communication channel, they can also use what is useful to them and it ensures that we don’t break KWin in a way that it gets unusable for Razor-Qt.