Last month our Wayland efforts made a huge step forward. In KWin we are now at a state where I think the big underlying work is finished, we entered the finishing line of the KWin Wayland porting. The whole system though still needs a little bit more work.
The big remaining task which I worked on last month was geometry handling. That is simplified: moving and resizing windows. Sounds relatively easy, but isn’t. Moving and resizing windows or in general the geometry handling is one of the core aspects of a window manager. It’s where our expertise is, the code which makes KWin such a good window manager. Naturally we don’t want to throw that code out and want to reuse it in a Wayland world.
And that meant: refactoring. The big problem here was that the code in question is also highly X11 specific. Examples are: the sync protocol for synced resizing, window gravity handling, various X11 specific quirks for moving X11 window moving smooth (e.g. only update at end of move if compositing is active, direct updates if not active).
The task was now to separate the X11 specific geometry handling from generic geometry handling so that it can support both Wayland and X11 windows. With this now in place all the geometry handling works also for Wayland windows. This includes move/resize through the alt+f3 menu, but also triggered from the window itself. During move/resize the quick tiling areas are of course triggered correctly, show the outline and snap to the area if released. Resizing is automatically synced to the speed the client supports and that also in a much better way than on X11 (yay for Wayland and double-buffered state!). During move/resize the windows snap to screen borders and other windows.
Unfortunately our checks to ensure that the window titlebar is not moved outside the visible area doesn’t work, because of client side decorations. Yay, everything is awesome! Have I mentioned that client side decorations are a stupid idea because it breaks useful stuff? No, cannot be. Related to that: QtWayland enters move mode if you click the title bar to activate the window. Of course there should be a delay which KWin implements for it’s decorations. After all we have more than 15 years of experience in doing window decorations. Yay, client side decos! Given control to the application! Let’s leave them in charge of window management, what could go wrong? Wohoo! Totally awesome! Broken window management! That’s the way to go! Of course that could be fixed in Qt, but well it doesn’t fix the problem. We have seen this in Chromium years ago, we even had to adjust our quick tiling/maximization behavior because of it. Another fun fact: QtWayland deco has a minimize button which does nothing because it’s not supported in wl_shell protocol. Have I mentioned that client side decos are awesome?
All right, all right, I’ll end the sarcasm mode now. Our geometry handling has a few more very handy features like window packing: you can configure a shortcut to move the window left (or other direction) and it will move to the next window or the screen border. Similar we support growing or shrinking the window to the next window. I was hardly aware of that feature before doing the refactoring, so I thought I should point it out. It can be used from scripting, so should be useful for ideas like poor man tiling or resizing multiple quick tiled windows at the same time. As a nice addition this code is now covered by auto tests.
So with geometry handling in place it’s possible to do real testing and one of my systems (my notebook) migrated from X11 to Wayland. Actually I have been using Wayland on that system already for watching videos since April as it gives tear-free rendering. A clear plus when watching videos.
And this gives us already the outlook for what we will see in the November update: I’ll focus on stabilizing the current state of Plasma/Wayland and fix bugs, fix bugs and fix bugs. My aim is to have a useable early-adopters version ready for the Plasma 5.5 release. It’s looking good, so I’m confident that we will reach that state.