Yesterday the KDE Community released the Beta for Plasma 5.12 LTS. With that release the feature freeze for 5.12 is in place and also an eternal feature freeze for KWin/X11. To quote the release announcement: “5.12 is the last release which sees feature development in KWin on X11. With 5.13 onwards only new features relevant to Wayland are going to be added.” This raised quite some questions, concerns and misunderstandings in the social networks. With this blog post I try to address those question and explain why this change in policy is done.
Is KWin/X11 still maintained?
Yes! We are just in the process of releasing an LTS. Of course KWin is fully maintained in the LTS life time. While in 5.8 only X11 was maintained, now we are able to offer maintenance for both X11 and Wayland. For the maintenance we do not differentiate between windowing systems.
Will X11 bugs still be fixed?
As X11 is under maintenance, I expect bugs to still get fixed.
Does this mean that in 5.13 X11 will be unmaintained?
We are going to forward port bug fixes from the 5.12 branch to master. Thus any release after 5.12 will get all bug fixes from 5.12. Given that I would say 5.13 will also be maintained on X11.
Does this mean that in the next LTS X11 will be unmaintained?
We will decide when the time comes. Currently I do not expect that we would drop maintenance.
Does this mean Plasma 5.13 will default to Wayland?
This is about feature freeze for X11. Whether Wayland will be the default or not is completely unrelated to this.
Will X11 users not get any new features in KWin?
Of course there will be new features! Most functionality in KWin is independent of the windowing system. Any improvement to those areas benefit Wayland and X11 users. Currently we have a few improvements in the pipeline, for example tooltips on decoration buttons, improved blur effect, a rework of slide desktop effect, improvements to the cube effect and a few more. All of them will be available to both X11 and Wayland users.
How do you decide whether it’s an X11 only feature?
In the case of KWin this is very simple. There are areas in our code structure which are only get pulled in if run on X11, other areas are marked in an if (x11) section. If the new feature touches this code, it’s probably not going to be added.
Does this feature freeze also apply to other KDE software?
No, but personally I would recommend any maintainer to apply a similar feature freeze. I personally will not help developing any X11 specific feature any more and resigned as maintainer of various X11 specific frameworks this week.
What are you going to do if someone present a feature for X11?
It won’t be merged.
This requires a little bit more explanation. I had a look at the most prominent issues we had over the last years. Where are our stability problems, where are our quality problems, what costs most development time? I observed that it was always in new features specific to X11. Very often even for features we added to Wayland without causing problems.
So I started to look into why that’s so. The obvious answer that we don’t get bugs for Wayland because nobody uses is, is not the case. We get many bug reports for Wayland and many users are nowadays running Wayland. So the reason must be somewhere else.
On Wayland we are able to test the code. Let’s take an example: we get input events through libinput. For this we have unit tests through mocking. Thus we can automate the testing of the lowest layer. From libinput events are sent into KWin core through an internal API and that we can also use in the integration tests. So we can simulate everything from the point where libinput events would hit KWin core. We can test this properly, we know that we get all events (because KWin is the display manager) and we can test every aspect. We can lock the screen and verify how it works, we can make applications grab the pointer or keyboard and test this. We can invoke global shortcuts, etc. etc. It’s all just as if we get the events through libinput. The quality of these new areas in KWin feels really good.
A few weeks ago some commits I did hit the Linux media about KWin/Wayland without X11 starting too fast and due to that causing bugs. These issues were found through our test suite, before any user would ever be exposed to them.
What we did in the past was taking these new features and bring them to X11. But there we cannot test. There is no way on X11 to e.g. fake a touch screen. On X11 we cannot test how this behaves if we lock the screen or used Alt+Tab. We can write the code and manually test it. Hey it works, awesome! But that was mostly not the case. There were corner cases which caused trouble. And to this comes that the main devs run Wayland instead of X11. If features break they are not exposed to the bugs.
Could you give some examples of things that broke?
Sure! The first feature we backported to X11 was “modifier only shortcut”. We spent months fixing the fallout because of X11 weirdness. Another feature backported was panels on shared screen edges. It worked great for Wayland, but on X11 some corner cases were overseen and caused issues, which affected our users and required time to fix. We backported the touch screen swipe gesture on X11 which was a mess. On X11 touch screens are also mouse events, that made it difficult and created many corner cases.
The problem is not adding the feature. The problem is fixing the bugs created by the new features.
But if a new foo requires adjustments?
KWin won’t be adjusted to any new requirements in the XServer, Mesa, input stack, proprietary drivers, etc. If something breaks it’s the fault of those components which broke it.