Before heading into the weekend I thought about writing a small update about the KDecoration2 status. Since my last blog post I started integrating KDecoration2 into KWin. This was partially easier and partially more difficult than anticipated. Especially ripping out the old decoration code is rather complex. There are quite some design differences which make the transition complex and especially values inside KWin core are using enums defined in the decoration API – e.g. the maximized state is kept as a KDecorationDefines::MaximizedMode. This will need further work to move the enums and so at the moment the old decoration library is still compiled although the library is no longer in use.

Ah that means there is code? Yes, today I pushed the branch as “graesslin/kdecoration2” into kde:kwin git repository. To give it a proper try you also need the kde:kdecoration (master branch) and kde:breeze also on “graesslin/kdecoration2” branch. The new decoration API is working quite well and I’m rather satisfied. The memory usage of KWin dropped significantly. In a previous report I mentioned that KWin needs around 200 MB, right now my KWin only needs around 40 MB, the number of open windows is a little bit smaller, but still it shows in the right direction. And that’s without any optimisations. There is still some optimization potential in Breeze (check out our todos, all purple tasks are in Breeze) and in KWin (red tasks). Also a nice improvement is that the window decoration no longer flickers when resizing the window. This is a rather big annoyance of KWin 5.0. I expected that the new API would fix this issue, but seeing it confirmed is really nice 🙂

Last but not least the restart of KWin got faster which is a nice improvement for KWin developers, for users it’s not that important. The reason for this is that when we enabled/disabled compositing we recreated the window decorations. So when restarting KWin we first created all windows with their decoration before enabling compositing to just destroy them and create them again (yes it would have been possible to improve it, but it doesn’t hit users). Now with the new API there is no need to recreate the decoration. Only a Renderer is exchanged, but the rendering is delayed till it’s needed.

This screen shot does not only show the new Breeze decoration, but also some new features: when quick tiling a window the borders cornering the screen edges are removed. Also in the preview application one can see that the decoration scales which is nice for high-dpi screens. The decoration API follows the approach Plasma is using.

I have been running a KWin with the new decoration API since Monday, which means we are close to start the review process. But there’s of course still work to be done and I’d appreciate any help. The window tab API is not yet implemented, the configuration module needs adjustments to load and render the new deco and most important we have to port the existing decorations like Oxygen, Aurorae, deKorator and QtCurve. For the last three I want to improve the theme experience by allowing the plugin to say that it supports themes directly in the JSON meta data and point to where to find them. So the configuration module can just show all of them. The trick will be to pass the to be used theme to the factory method (we have a nice QVariantList there which can be used). Also the meta data will make it possible to point to GHNS configuration files so that we can not only download Aurorae themes from the configuration module, but also other themes.