Good bye Notifications

When I arrived at Tokamak 6 last week Alex was studying D-Bus communication between various applications. Before I had a chance to really sit down he complained about KWin talking to kded whenever for example a window got moved. This didn’t make much sense, so we had a look at it.

As it turned out that was KWin sending out notifications. Which immediately raised the question of why? Why would a user want a notification that he started/finished moving a window? After all it’s an action the user triggered. What should be done with the notification? Show a message? “You successfully moved a window!”, yes thank you I can see that on the screen. Play an annoying sound? Pling! Hopefully not.

Looking at what KNotify supports only logging to file or running a script make sense in response to the notifications emitted by KWin. But for logging to file it’s rather questionable why one would want that and why one would do that from inside a window manager. So what remains is running a script – fair enough that can be useful.

A closer look to the notifications emitted by KWin showed a few more things. None of them is configured to do something with the notification. By default KNotify just discards the notifications. This means we do a communication with kded via D-Bus for nothing. Two applications are getting woken up, context switches and so on for exactly nothing. Some notifications have a sound file connected to them, but are not configured to play that sound by default. We made a small quiz by me playing the sound file and letting the rest of the group guess what it’s for – I think nobody got one right. Nobody of the core workspace developers knew these sounds.

Looking at the code where the notifications are emitted highlighted another interesting fact. At all places we also emit a Qt signal which is mapped into the KWin scripting environment. And that’s actually quite awesome. Because unlike the notifications it has context. A KWin script does not only get informed about a window that gets moved, but about which window gets moved. Let’s say you are only interested in movements of Firefox windows – with KWin scripting that’s possible, with the notifications it isn’t. Given that we already identified that scripting (and maybe sound) is the only use case for the notifications emitted by KWin it’s getting more questionable why they are still around. Obviously they had been added long before we had KWin scripts. I was unable to really figure out when it got added, as git blame ends in one of the moving around code commits years ago (with more patience one can figure it out, but knowing that it’s old, was enough).

Of course we do not want to break our users’ workflow, so removing the feature is not easy. We have to properly judge whether the users’ workflow is valid enough to penalize all users by the additional overhead in code and in communication especially the context switches. Given that KWin scripting also allows to perform D-Bus calls, it should be possible to rework each of the previously existing notifications in KWin scripts.

That said: in case you were a user of one of those notifications and the removal breaks your workflow: please let me know. Please tell me how you used it and best provide your script. I will have a look at it and try to ensure that it’s still possible with KWin scripting (if it’s simple enough I will just port it).

The History on Wayland Support inside KWin

Ever since a certain free software company decided to no longer be part of the larger ecosystem, I have seen lots of strange news postings whenever one of the KDE workspace developers mentioned the word “Wayland”. Very often it goes in the direction of “KDE is now also going on Wayland”. Every time I read something like that, I’m really surprised.

For me Wayland support has been the primary goal I have been working on over the last two years. This doesn’t mean that there is actual code for supporting Wayland (there is – the first commit for Wayland support in our git repositories is from June 11, 2011 (!)).

The Wayland research projects two years ago had been extremely important for the further development of KWin since then. First of all it showed that adding support for Wayland surfaces inside KWin’s compositor is rather trivial. Especially our effect system did not care at all about X11 or Wayland windows. So this is not going to be a difficult issue.

The more important result from this research project was that it’s impossible to work against an always changing target. At that time Wayland had not yet seen the 1.0 release, so the API was changing. Our code broke and needed adjustments for the changing API. It also meant that we could not merge the work into our master branch (distributions would kill us), we needed to be on a different branch for development. Tracking one heavily changing project is difficult enough, but also KWin itself is changing a lot. So the work needed to be on top of two moving targets – it didn’t work and the branch ended in the to be expected state. Now with Wayland 1.0 and 1.1 releases the situation changed completely.

The next lesson we learned from that research project was that the window manager part is not up to the task of becoming a Wayland compositor. It was designed as an X11 window manager and the possibility that there would not be X11 had never been considered. We started to split out functionality from the core window manager interface to have smaller units and to be able to add abstractions, where needed, to support in future more than just X11. That had been a huge task and is still ongoing and it comes with quite some nice side-effects like the rewrite of KWin scripting (helped to identify the interface of a managed Client inside KWin), the possibility to run KWin with OpenGL on EGL since 4.10, the new screen edge system in 4.11 and many many more. All these changes were implemented either directly or indirectly with Wayland in mind. That means we have been working on it for quite some time even if it is not visible in the code.

My initial plannings for adding Wayland support around October/November last year was to start hacking on it in January. I was so confident about it that I considered to submit a talk for FOSDEM which would demo KWin running on Wayland. In the end I decided against it as it would have meant working on some of our very important foundations under time pressure, which I don’t think is good for maintainability of the code base.

In December though I decided to adjust my plans and focus first on the Qt 5 port as that would allow us to use the Qt Wayland bindings which are a little bit more convenient for usage in a Qt based application than the native C library. This is not something I just come up with, I discussed this small adjustment with a few people (for example Aaron Seigo) at the Qt dev days last year.

On January, 22nd 2013 sebas outlined the time line for the transition to Qt 5 and Wayland of the KDE Plasma Workspaces. It clearly states that KWin will become a Wayland compositor and that this is a target we are working on with a clearly defined time line.

Given that I am really surprised to see media writing again and again that we started to work on Wayland because other projects deciding against or for Wayland. It’s not something we decided on recently and it is quite clear that our work does not depend on any decisions or announcements our competitors do. We are an independent project, which does it’s own decisions for long term planning. The fact that our work now shifts towards Wayland just at the time our competitors decide for or against Wayland is pure coincidence.

Last week we had a Plasma developer sprint in Nuremberg (thanks to SUSE) and of course Wayland was an important topic for discussion. We had many points on the agenda. After all it’s the first sprint for us since we work on Plasma Workspaces 2 and it is needed to define our direction for the next year. Given all that I wrote so far it’s rather obvious that we would have discussed Wayland even if a certain project would not have done a certain announcement. Some topics on the agenda were based on discussions we had on the mailing list before the certain announcement was made (I’m currently sitting in a train with not sufficient Internet connection so I cannot look up the reference). Which also shows that we had long term plans which were decided on long before the ecosystem shifted.

Summary: we had been working on Wayland for years and it is our long term strategy. Our strategy is of course not based on any announcements of our competitors. We of course need to evaluate new solutions available in the ecosystem when they come up. As I already pointed out in the past, this is not yet possible at the moment and all we can see so far is that Wayland is a better solution for our needs in the KDE Plasma Workspaces than other windowing systems which might be tailored towards the needs of our competitor’s desktop shell. One of the advantage of free software projects is that the development and discussions are open and that it’s quite easy to reach out to the developers and architects of the software.

The relationship between Plasma and KWin in Workspaces 2

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.

What makes a “lightweight” desktop environment lightweight?

Over the last few days I was wondering what is a “lightweight” desktop. And I must say I couldn’t come up with an answer to that question.

I was considering various things like “being memory efficient” which I discarded for obvious reasons. First of all it’s difficult to measure memory usage correctly (I haven’t seen anyone, who provides numbers, doing it correctly, this includes especially Phoronix). And then it’s comparing mostly apples to oranges. Loading a high-resolution wallpaper might make all the difference in the memory usage. Also if desktop environment Foo provides features which are not provided by Bar it’s obvious that Foo uses more memory. But still it’s apples vs oranges. It’s not a comparison on memory, it’s a comparison of features. And of course one might consider the Time-memory-tradeoff.

So is it all about features? Obviously not. If there is a feature a user needs and uses it cannot be bloat. The fact that a desktop environment has only few features cannot be the key to being lightweight. Being evil now: many people say GNOME is removing features, but nobody would say that GNOME is lightweight.

What about support for old systems? That’s not lightweight, that’s support for old hardware. And it’s something which doesn’t make any sense given Moore’s law. Which raises the first question: what is old hardware? One year, two years, ten years? Is it a moving target or is a Pentium III for all time the reference? Optimizing for old hardware means not making use of modern hardware capabilities. But does that make sense to not use modern hardware if it is available? Using the GPU for things the GPU can do better than the CPU is a good thing, isn’t it? Parallelize a computation on multi-core if possible is a good thing, isn’t it? But if you do so, you are optimizing for modern hardware and not for old hardware. So saying you are good for old hardware, implies you are bad on new hardware? Also I’m wondering how one can optimize for old hardware? Developers tend to have new hardware to not have problems like this. And how can one keep support for old hardware when the complete stack is moving towards new hardware? Who tests the kernel against old hardware? Who provides DRI drivers for obsoleted hardware which doesn’t fit into modern mainboards (who remembers AGP or PCI)? Who ensures that software is still working on 32 bit systems, who would notice such a breakage for example in the X-Server? So lightweight cannot be fit for old hardware. And remember: optimizing for old hardware is not the same as optimizing for modern low-end hardware. Even the Raspberry Pi has a stronger CPU (700 MHz) than the oldest Pentium III (450 MHz) – not to mention things like OpenGL…

What’s it then? Let’s ask Wikipedia. For Xfce it tells us, that “it aims to be fast and lightweight, while still being visually appealing and easy to use”. Unfortunately there’s no link on lightweight and also no reference. Let’s try again, LXDE: “The goal of the project is to provide a desktop environment that is fast and energy efficient”. Again no real definition and just stating a goal. But it goes on:

LXDE is designed to work well with computers on the low end of the performance spectrum such as older resource-constrained machines, new generation netbooks, and other small computers, especially those with low amounts of RAM.

I have no idea what a “new generation netbook” is, but it sounds like something modern half a decade ago. But we are down to the “being good on old hardware”, which we just discarded. Interestingly Wikipedia has references to prove that LXDE is good on RAM – unfortunately it’s references to Phoronix. Shame on you, Wikipedia, that’s a “benchmark” which has been considered seriously flawed by people understanding the topic.

Ok Phoronix aside, there is one more of the lightweight desktops to check. Razor-qt: “is a lightweight, Qt-based free software desktop environment for the X Window System. Unlike the KDE desktop environment which is also based on Qt, Razor-qt usually performs well even when used in computers with older hardware”. Damn, it again only claims and no reference for anything. Who says that KDE desktop environment (what’s that again?) is not performing well on older hardware? And what does the “usually” mean in that sentence?

So all Wikipedia gives us, is buzzword bingo and various claims without any proof (and not even a “reference missing”). Let’s try different and go to the projects directly.

Xfce tells us that it “is a lightweight desktop environment for UNIX-like operating systems. It aims to be fast and low on system resources, while still being visually appealing and user friendly.” Which sounds very similar to what Wikipedia wrote. Unfortunately nothing that tells us what lightweight means or what fast is or low on system resources. Fuzzy is fuzzy.

LXDE also has the same definition as shown in Wikipedia (maybe we should mark those wiki articles as advertisement?) but at least gives us a definition for what lightweight means to them: “It needs less CPU and performs extremely well with reasonable memory.” Fuzzy is fuzzy. What’s “reasonable memory” and “less CPU”? It goes on about various other things like “fast” and “energy saving” (which even are contradicting, e.g. fast is defined as working on hardware from 1999 and not require 3D – how that can be energy saving on new hardware one has to show me). The point energy saving is quite funny as it just says they are better than “other systems”. Oh well fuzzy is fuzzy.

Last but not least: Razor-qt. Razor doesn’t say it’s lightweight:

Razor-qt is an advanced, easy-to-use, and fast desktop environment based on Qt technologies. It has been tailored for users who value simplicity, speed, and an intuitive interface. Unlike most desktop environments, Razor-qt also works fine with weak machines.

Fuzzy is fuzzy. What’s a “weak machine”, what are the “most desktop environments”? Where’s the proof for other DEs not working well on those not-defined “weak machines”?

And here, poor fool! with all my lore I stand, no wiser than before. All what I could derive from studying what lightweight means is, that one just has to claim to be lightweight. Bonus points if you include it into your name. It seems like if you repeat it often enough people will repeat it and it will turn out into truth.

Hitting walls – a story of Present Windows 2

One of my favorite User Experience elements in KWin is the Present Windows/Desktop Grid combination. For me those are the most important elements to switch between windows and virtual desktops. Although Present Windows and Desktop Grid are two different “effects”, I consider them us one because of their very similar functionality. The primary use case for both is to change the active window, the main difference is that Desktop Grid sorts the windows by virtual desktops.

The effects are so similar that they even share the code to lay out the windows. Nevertheless there are quite some differences in the functionality. The following features are only available in Present Windows:

  • Filtering of windows
  • Icon and caption on each window
  • Closing windows through a button shown on hover
  • Enlarging windows on hover
  • Mouse Actions
  • External activation (used by Netbook Shell)

On the other hand there are features in Desktop Grid not available in Present Windows:

  • Drag windows from one screen to another
  • Add/remove virtual desktops

The difference in functionality cannot be explained – there is just no reason for it. This is clearly a problem for our users – the effects look identical, but they behave differently. From all I learned about usability this is pretty bad because it teaches users to not trust systems.

The obvious answer would be to merge those two effects. But here we have a problem. Present Windows has been implemented to be Present Windows – no matter how we tweak it, it will be Present Windows. And Desktop Grid has been implemented as a Desktop Grid – no matter how we tweak it, it will be Desktop Grid.

I know that people will tell me that nothing is impossible. Of course one could hack around and make the effects be the same. But we have been there and tried to bring non-Present Windows functionality into Present Windows. I once implemented an Alt+Tab mode in Present Windows – a huge mistake. All it did was adding lots and lots of special case handling to make it work. And it castrated the effect. It only supported one screen (needed of course special hacks), it didn’t support filtering (keyboard grab hold by Alt+Tab framework) and so on and on. It never made any sense and I am very glad that I realized this error and removed the Alt+Tab mode again.

But also with Desktop Grid we made the experience by adding the layout mode of Present Windows. It wasn’t good for the code base. Nowadays, after I implemented that addition, I compare the code base of Desktop Grid effect to a Jenga tower which is already shaking and I fear that if I touch it to change something it will completely collapse.

A merge would only be possible by removing features and that is always difficult. People were really upset when I removed the Alt+Tab mode of Present Windows. Arguments do not work, giving replacements does not help and trying to improve the workflow is of course not welcome.

What remains would be a complete rewrite from scratch. But that’s a task so large that I consider it as a possibility for a Google Summer of Code project. Together the two effects have more than 4000 lines of code. It’s nothing we could do in parallel to our normal work and rewriting as a KWin Effect does not really make sense. Yes one can use Effects for that but it’s rather limited.

One of the most clear disadvantages is that Effects require Compositing. While having always composited systems becomes more and more the reality, there is still no reason why there should be the break in the user workflow when turning off Compositing and I have had many discussions with users who did not understand that.

But the real problem is that we do not have a toolkit inside the Effects. We are down to key press/release events and mouse motion/press/release events. That’s rather limited. For the close button inside Present Windows we do quite some hacks to get the mouse events injected into the QWidget. It’s a hack and nothing that scales. Key events are not composed correctly – for example on my English keyboard I’m not able to write letters like “ä, ß” in Present Windows. But the real problem is the handling of things like the drag and drop of windows in Desktop Grid. The code is extremely nested (seven indentation levels) and has to cover many, many corner cases. It just shows how difficult it is to get that handled correctly with different modes.

But since recently we have a technology which solves many of these problems: QML. With QML we get a toolkit which we can use to properly interact with the windows and which is supported in both composited and non-composited setups. In combination with our KWin scripting framework we have capabilities which are quite similar to what our effects can do. As a nice side-effect QML forces us to separate logic from visualization which means that the logic of Present Windows/Desktop Grid could be reused and combined with new ideas of how to represent the data.

This week the logic part entered KWin’s source repository in form of a QAbstractItemModel which is exported to QML. The model is quite flexible and allows to sort the windows in multiple levels – currently it supports screens, virtual desktops and activities. In addition one can specify whether a window should be excluded. That’s for example important to have the different modes of Present Windows – there is one mode for only current desktop and one mode for only windows of the currently active application.

Having a model makes it rather easy to support filtering – we just need to connect it to a QSortFilterProxyModel and such a model is already provided and exported to KWin’s QML binding.

Implementing the logic for Desktop Grid inside QML becomes now as simple as:

ClientFilterModel {
    id: filterModel
    clientModel: ClientModelByScreenAndDesktop {
        exclusions: ClientModel.NotAcceptingFocusExclusion | ...
    }
    filter: filterItem.text
}

The idea is now to use this as a base for what I call “Present Windows 2″. It’s nothing I target for 4.11, because of the complexity of Present Windows and Desktop Grid. I hope that many things become easier once we are on Qt 5 and QtQuick 2. So it’s something I want to have for Plasma Workspaces 2. I’m still wondering whether to optionally include the current proof of concept QML script which renders a screen like this:

Aus KWin

One can already see the improvements like an always visible filter area. That’s one of the real disadvantages of the existing Present Windows effect: one doesn’t get any hint that it is possible to filter the shown windows. Also a clear improvement in this variant is the always visible close button for each of the windows.

The new models included in KWin might also get new tasks I haven’t thought about when I started to work on it. Our Plasma developers noticed that this would be a rather good base for the tasks applet. Whether that’s possible or not we do not yet know, but it would have clear advantages to have a shared code base for all the different ways of getting an overview of open windows.

(Sorry for having once again written such a long blog post)