Tag Archives: Wayland

Running frameworks powered applications on Wayland

After I got KWindowSystem to no longer require X11 on Linux I dared to start some of our applications which got ported to frameworks 5 with the magic “-platform wayland” command line switch. And look there: they started and were useable. But there were some obvious problems: e.g. our platform integration plugin was not loaded. But with a small change to Qt 5.3 this problem is solved. Now if you run a Wayland compositor in a KDE session you will get the KDE integration as one would expect. But this just openend a new set of problems: our default QStyle (Oxygen) was crashing any application on startup as it was still assuming that it’s on X11 if compiled with X11 support. Easy enough to fix and now Oxygen works as one would expect.

This experience highlighted an obvious problem: our applications will crash if they are compiled with X11 support and do not perform a runtime check. So I started to hunt down possible crashers in our libraries. In the perfect world there should not be any X11 specific code in the libraries (except KWindowSystems). And luckily our libraries supported non-X11 platforms for quite some time, so all the X specific code should be in HAVE_X11 blocks. So a small reminder for everybody who thinks that we should never have supported Windows in the first place: thanks to Windows support most of our applications just work on Wayland. Have a look at this nice collection of applications which are running just fine on Wayland:

Aus Weston

Right now we have reached a state where I am no longer able to crash applications at random and most applications which I give a try just work. We had a few problems in kde4support which prevented any applications which still used K(Unique)Application to start at all on Wayland and that framework had stronger usage of HAVE_X11 than I expected. Although the framework is deprecated I fixed all the issues I could find in it, to get applications to support Wayland faster. Basically if your application compiles on frameworks it will run on Wayland out of the box. Also thanks to that work our applications will just work on any proprietary windowing system (so no need to be upset that we put more work on e.g. Windows support than on your small pet project). My personal aim is to have Wayland support at least on par with Windows support in our first release of frameworks. Later on we will improve it to get it on the same level as X11 support.

Of course it’s possible that I haven’t spotten all crashes in the libraries yet. And I encourage our application developers to test their applications on Wayland. That’s quite simple in fact: just start Weston (can be nested in the X session) and prepare the setup:

source kf5_env.sh # your kf5 environment variables setup script
unset DISPLAY # to make sure that any XOpenDisplay call will fail
export WAYLAND_DISPLAY=wayland-0 # adjust to whatever you used in Weston

Now all you need is to pass “-platform wayland” to the command line args to start your application on Weston. In case you are using a KApplication and KCmdLineArgs you need to use “--platform wayland” instead. Update: as an alternative one can also export the environment variable “QT_QPA_PLATFORM” and set it to “wayland”. If you run into any problems with it, feel free to ping me on IRC. In case you get your application to crash in one of the frameworks and it’s a crash due to using X11, please report a bug and set me on CC. In case you hit a crash in your application there is a very easy pattern to solve the problem:

#if HAVE_X11
if (QX11Info::isPlatformX11()) {
    // do your X specific calls here
}
#endif

If you are not using QX11Info you can also do:

#if HAVE_X11
if (QGuiApplication::platformName() == QStringLiteral("xcb")) {
    // do your X specific calls here
}
#endif

As you can see it’s performing a string comparison so you don’t want to have that in a code path which gets called often. Recommendation: move it into a member variable which gets initialized only once in app life cycle and also ifdef the variable – no need to do these checks on e.g. Windows. If you have any questions with it, feel free to ask me.

In the workspace module I hit a few crashers in modules which make absolutely no sense on non-X11. The code is too X specific and most likely needs a complete rewrite if we want to have it on non-X11. Of course we don’t want to have modules which just crash in systemsettings. So I introduced a new method to KService to check whether the plugin makes sense on the current Qt platform. This is honored by ::noDisplay() so systemsettings (and also kcmshell5) won’t pick them. To specify one can use e.g.

X-KDE-OnlyShowOnQtPlatforms=xcb

in the plugin’s desktop file. There’s also a “X-KDE-NotShowOnQtPlatforms”.

KWindowSystem in Frameworks 5

KWindowSystem is a tier 1 framework which allows to interact with the windowing system. Historically it provided an implementation of NETWM on X11. It provides a NETRootInfo for accessing the global state (all that’s set on the root window) and NETWinInfo for all information about a specific window. The classes have a window manager and client perspective. This is the foundation which powers our window manager and various parts of the desktop shell such as the taskmanager.

On top of those X11-specific classes we have a convenient API KWindowInfo and KWindowSystem which provides a windowing system independent API for our applications. Thus we have different implementations depending of the platform it’s compiled on. On X11 the implementation depends on named NET* classes, on Windows and Mac what makes sense is implemented using the platform specific API.

In the good old days of Qt 4 this was a sufficient solution. If it’s build on unix-like systems we have X11 and we know it’s X11, on Windows it’s Windows and so on. With Qt 5 this no longer works. Just because we built with X11 support doesn’t mean the software will run on X11. Due to the introduction of the QPA it’s possible that another platform is used – most obvious Wayland. But there are more platforms for Linux like Android. With the solution from Qt 4 our applications would just crash as soon as they access KWindowSystem as that tries to interact with XLib/xcb unconditionally.

Over the last weeks I spent quite some time on making sure that KWindowSystem works as expected (that is doing nothing at the moment) when run on Wayland. Just adding a new implementation as in the Qt 4 days is no solution as we want our framework to support both X11 and Wayland at the same time. Otherwise our distributions would have a hard time packaging our software. The approach was to introduce an internal abstraction in KWindowInfo and KWindowSystem and have a platform implementation. This is now done for X11 together with a dummy implementation which is used as a fallback if we do not have an implementation for the currently used windowing system (e.g. Wayland). Unfortunately this has a side-effect: it broke the backend for Windows and MacOS. I don’t feel very happy about it as I don’t like to break the work of others, but I cannot fix it. Windows and MacOS are proprietary systems for which either a license or even specific hardware is required. I do hope that the specific teams will re-add the support till the release of frameworks 5. Please note: at the time of writing this blog post not all patches are merged yet.

A nice side-effect for this work was that I started to write unit tests for KWindowInfo on X11. This is far from trivial as it interacts with X11 and the running window manager. And the test kind of depends on the used window manager. Obviously given that it’s KDE it would make sense to write the test against KWin, but that’s not sufficient for our CI system as kwindowsystem is a dependency of KWin and thus kwindowsystem cannot depend on KWin (not even on runtime). Thus the tests are now performed against openbox on the CI system, but also succeed when running against KWin. They are quite a stress test for a window manager and found one very unlikely crash condition in KWin (of course already fixed).

The framework provides more functionality which is kind of X11 specific. For example there is the KSelectionOwner and KSelectionWatcher which implements a manager selection as described in ICCCM, section 2.8. Again a very important building block for our window manager. While it’s clearly X11 specific code which only gets built if X11 is available, there is no reason to crash if it’s not run on X11. So I went through all of our sources and tried to make sure that it correctly checks whether the runtime platform is xcb. Thus we don’t have to change all applications using it, but can rely on the library not to crash. Still if your application is using these X11 specific functionality I highly recommend to check for the platform as you might run into runtime errors. E.g. claiming a manager selection will fail, don’t rely on it.

As all of this is kind of a requirement to running frameworks based applications on Wayland, I have to do the obligatory screenshot of Kate on Weston:

Aus Weston

An unexpected journey

Since my last post quite some progress has been made in getting KWin working on top of a Wayland compositor. My main focus of work has been on the input stack. This is something I am not really familiar with as so far we did not have to care about it.

As some might know input handling in X11 is very insecure. Every application is able to listen to every key event. And in the KDE workspaces we obviously make use of these “features”. For example the global shortcut handling is implemented as a kded module listening to all key events and notifying the application via D-Bus that the shortcut got triggered. In a post-X11 world this will not work any more: applications are no longer able to listen to all key events.

One of the important tasks therefore is to not send all input events to the
X-Server but just to the window which should get it, or to handle the input events inside KWin and discard them without passing to the applications. My current branch already supports activating screen edges and using fullscreen effects like Present Windows completely without passing the input events through X. This means that some of the longstanding issues are automatically resolved. We no longer “steal” the screen edges from applications and starting the screen locker should be possible even if present windows is active (not tested and still needs some screen locker support in KWin).

But this also means that features like the global shortcut handling start to break. Mostly because kded is not listening on my virtual X but that’s just detail ;-) So I also had to start working on global shortcut support inside KWin – otherwise I would have had a hard time to use some of the important features like switching desktops or using Alt+Tab. At the moment the latest code only supports KWin’s internal shortcuts, but global support for kglobalacceld will have to follow. We had some ideas on how to improve global shortcut handling in general anyway.

When the infrastructure was in place I couldn’t resist the temptation to work on features which had been requested for a long time and were not really possible to do with X11 (or only with huge hacks): mouse shortcuts. Ctrl+Alt+left click activates desktop cube. But that’s not enough. While sitting in the Kubuntu Developer Summit I added also mouse wheel support which allows us to ctrl+alt+wheel to switch desktops and also to use the zoom effect. This work can be found in branch kwin/global-shortcuts on my personal workspace clone.

I hope that we will soon have a decision on the “what’s master” discussion and I can start merging the changes in. Once this is done I plan to switch focus to the Qt 5 port and concentrate on this for the next few weeks.

Nevertheless this should not be a reason to stop the work on the Wayland efforts. There are so many small things which can be done and lots of low hanging fruit. I will try to setup a trello board with a few tasks, so that interested developers could start picking up some easy tasks and get their hands dirty. Once something is in place I’ll write another post.

More Software Compositing

One of the most often repeated misconceptions about Wayland is that it requires hardware acceleration. I would have thought that this issues would have been resolved once the reference compositor, Weston, supported rendering through Pixman. The reason for this misconception is most likely that the earlier versions of Weston required hardware acceleration.

Now KWin in 4.11 introduces the same mistake. Our experimental Wayland support is only available in the OpenGL compositor – even OpenGL ES is not supported (something is broken on my system I cannot start it). I think this is a bad situation. One of the huge advantages of KWin is the exchangeable compositor allowing to switch to software based XRender in case there are no proper drivers available. In fact KWin switches automatically to XRender if it detects a driver which recommends the XRender backend (e.g. software rasterizer).

So last week I started to work on some new Wayland related features and extended the XRender compositor in a way that it renders to a Wayland surface. It’s a pretty simple setup. Our XRender compositor uses an off-screen pixmap for rendering. The adjusted backend uses a pixmap created through XShm, so we get the frame rendered into a shared memory segment. From there we just copy it into a shared memory Wayland buffer to share it with the Wayland compositor. It would be better if we could create the shared Wayland buffer directly from the XShm segment, but I did not see a solution on how to achieve this.

In the end it’s also not really relevant. After all we want to use Wayland and the last thing we want to do on Wayland is using an X11 rendering API for compositing. So we can consider this more as a proof-of-concept and as a task so that I can get more familiar with Wayland ;-) It helped me to improve the code, so it was worth the effort. Even if it is a more academic solution it serves a concrete use-case: KWin uses XRender as a fallback and we can expect that the backend works. Given that we have to enforce compositing in future, it’s good to know that all backends work. The current state of this work can be found in branch kwin/wayland-backend of my clone (note: the link might change in case I force push).

Video on YouTube

If XRender is an academic solution, we are still facing the problem that we lost our software compositor. So I thought I need to also do something about this problem and started to work on a new compositing backend based on QPainter. It’s a quite simple compositor which uses a QImage as the rendering target. The QImage is created directly from the Wayland buffer, so in opposite to the XRender backend we don’t have the needless memory copy from one to another buffer. This is a very interesting compositor as it’s the first part of KWin which has been written from scratch only with Wayland in mind. It doesn’t support X11 (at the moment). This is the first new compositor written in years, so I found some things to improve and which are already under review. And as it was much easier to write a new compositing backend than I expected, I decided to document it in our wiki. It would be totally awesome if someone could have a look at it and write a dedicated compositor for the RaspberryPi ;-) The new compositor can be found in branch kwin/qpainter-scene.

The switch to Wayland does not only affect our software compositors, but compositing in general. So far KWin has always had the possibility to not require compositing. This doesn’t make any sense in a Wayland world. So I needed to teach KWin that we might need to enforce compositing. Of course on X11 we still want to have the option to disable compositing, so the changes only affect the Wayland backend. When starting KWin with the Wayland display environment variable set, KWin will require compositing. Even if it is disabled in the config options it will be enabled. Even more it ignores the shortcut to suspend compositing and options like unredirection of fullscreen windows. But still the backend might fail and in this case KWin is just exiting. There is no need to continue execution if one cannot see the output. This work can be found in branch kwin/enforce-compositing (which also contains all the other mentioned branches).

Starting a full KDE Plasma session in Wayland

This week there will be the release of KDE SC 4.11 Beta 1 and this will come with an interesting new feature: an experimental Wayland backend inside KWin. This backend does not allow to manage Wayland clients, but uses another Wayland compositor as the rendering target. Instead of rendering to an X window, KWin renders to a Wayland surface. From an architecture point of view this means that there is a Wayland system compositor and KWin is running as a Wayland session compositor (although KWin is not yet a Wayland compositor).

Disclaimer: this is a highly experimental feature and not intended for productive usage. Please do not report any bug reports in the bug tracker. If you find an issue please open your editor, hack and submit a review request.

Now I expect that you are also excited about Wayland and that you want to run your KDE Plasma session on top of Wayland instead of X, right? So here are the instructions: First of all you need to change the “Tearing Prevention (VSync)” in KWin’s Advanced desktop effects settings to “Full scene repaints”. This is needed because KWin does not yet support the buffer-age extension needed to properly repaint in Wayland. Note: when using X11 you probably don’t want to use this option, it wastes quite some power.

The KDE Plasma session startup is controlled by a script called “startkde”. In order to start the KDE Plasma session with Wayland we also need this script, but need to have a few environment variables set to tell KWin that it should use Wayland. So best copy this script and call it” startkde-wayland”. Edit this file and add the following exports after the shebang:

export DISPLAY=:99
export WAYLAND_DISPLAY=wayland-system-0
export KWIN_OPENGL_INTERFACE=egl_wayland

Now all we need is another small shell script to start Wayland, Xvfb and the modified startkde script. Let’s call it kwayland:

#!/bin/sh
weston-launch -- --socket=wayland-system-0 &
Xvfb -screen 0 1366x768x24 :99 &
startkde-wayland &

Please change the screen resolution to the one used by your screen. KWin is not yet able to update the resolution of the X server to what Weston uses. This also means that you cannot change the resolution or add multiple screens (as I said: it’s an experimental feature).

Now log out of your running KDE session, switch to a tty and stop the still running X server. With X out of the way you can start the kwayland script. You should see Weston starting and shortly afterwards KWin should take over. If everything is configured correctly you should see the normal splash screen (seems like my system is not configured correctly).

Once the system is fully started you can just use it. If everything works fine, you should not even notice any difference, though there are still limitations, like only the three mouse buttons of my touchpad are supported ;-) I would post a screenshot but it’s fairly uninteresting as one cannot see a difference.

This blog post was written in a KDE Plasma session running in Wayland.

KWin running in Weston

This week I decided to do some research for the Wayland porting of the KDE Plasma workspaces. One of the features we will need in future is a Wayland session compositor which runs nested on a Wayland system compositor. Of course one could think of setups without a system compositor, but overall I think that a nested compositor simplifies the setup and allows to have all the low level technologies in one place without duplication in all the various compositors. +1 for working together.

After three days of work I already have something to demo (video on youtube):

Sorry for the bad audio. I’ll just explain what one can see. The video starts with the normal X-Server. After that it switches to a VT and we start Weston there. On Weston I’m starting KWin with some environment variables set to pick the correct libraries and force KWin into Wayland mode. KWin creates a connection to Wayland, creates a Wayland surface and uses it for OpenGL output. All the windows from the running X Server are rendered into this surface just as if it were a normal X11 output.

KWin also gets input from Wayland and passes it to the X Server. That’s the reason why we can see mouse interaction and working keyboard.

How it works

The OpenGL backend

KWin supports multiple backends for providing an OpenGL context and doing the texture from pixmap operation. At the moment we have an GLX and an EGL backend. Both create the OpenGL context on the XComposite overlay window and provide the texture from pixmap in the GLX case through the GLX_EXT_TEXTURE_FROM_PIXMAP extension and in the EGL case through the the EGL_KHR_image_pixmap extension.

A new backend is added which creates the OpenGL context on a Wayland surface. The backend started as a fork of the existing EGL backend with the X code stripped out. What’s a little bit tricky is getting the texture from pixmap working. The extension used in the normal EGL on X11 backend is not available. The proper solution would be a setup with XWayland, but that’s still too early as KWin does not yet support Wayland clients.

The solution I came up with is inspired by a fallback mechanism in KWin from the time when GLX_EXT_TEXTURE_FROM_PIXMAP was not guaranteed to be around: XShm to copy the pixmap content into an OpenGL texture. Not a nice solution but it works.

Input handling

Input is currently also a rather hackish solution until we have XWayland up and running. We just take all input events and forward them to the XServer with the XTest extension to inject fake events. It’s a huge hack and one can see how old X is there and how limited. I was rather surprised that it works at all. At the time of this writing the code supports keyboard events and the left, middle and right mouse button. Wheel events are tricky as X uses mouse buttons for them and for more mouse buttons I have problems with mapping them as I’m lacking a multi button mouse.

We are also not able to back sync the mouse position from X to Wayland. As far as I understood the Wayland protocol there is nothing like XWarpPointer, so if something in X warps the pointer we have a mismatch. I agree that warping is evil, but we use it in KWin for activating the screen edges :-(

Next Steps

Cursor

What is to do next is to get the changes to the cursor in X11 and set the cursor on the Wayland surface. That should not be really difficult as the XFixes extension provides everything one would need for that.

Thread

A rather huge limitation at the moment is that the connection to the Wayland display is hold in the main thread. We cannot block there, so we only get events when we actively check for them. This is currently during repainting the screen. So if you wondered why the ShowFPS effect in the video is turned on: it’s to force repaints and to keep the connection alive. This connection needs to go into a thread so that we can block there.

Buffer age

Currently the code forces as to do full-screen repaints. The two solutions we have for non-fullscreen repaints in the EGL backend do not work in the EGL on Wayland backend. The Wayland demo code shows that the EGL_EXT_buffer_age implementation could be used. We wanted to have support for that one anyway in KWin.

Giving it a try

Building from source

I just pushed the code into branch “kwin/wayland-egl-backend” on my clone kde:clones/kde-workspace/graesslin/kde-workspace. Be aware that I intend to force push to this branch.

To build you need to have the Wayland libraries around. The CMake module tries to find it through package kit. Watch the output of CMake, Wayland is only an optional dependency! If you build Wayland and Weston from source, please follow the instructions. You might also need to build Mesa from source.

How to start

Starting is rather simple. Just have an Xserver running somewhere, start Weston on a VT (don’t do nested on X, you would only get a black screen once KWin started) and open a terminal. Setup your environment variables to be able to start KWin and then start KWin in the following way:

DISPLAY=:0 KWIN_DIRECT_GL=1 KWIN_OPENGL_INTERFACE=egl_wayland kwin --replace &

KWIN_DIRECT_GL makes KWin skip the OpenGL Test application which is currently only supporting GLX and seems to fail if one is on a different VT. KWIN_OPENGL_INTERFACE tells KWin which backend to use. So by using “egl_wayland” one forces KWin to use the Wayland backend. In future we will probably detect whether the Wayland display environment variable is defined and just pick it directly (though that is dangerous in case of nested Weston on X).

When will it be available in a release

I want to get this work into 4.11 as an experimental feature for multiple reasons. I wanted to have a build dependency to Wayland in 4.11 for quite some time. So that’s a nice excuse. Unfortunately feature freeze is approaching.

Of course I want to give users something to play with. We have talked about Wayland for such a long time and there is nothing to really see that we are walking the way. Last but not least that might be a rather important solution for Plasma Active as that hopefully allows to run on hardware where we currently would not get OpenGL. With libhybris we should be able to get KWin working with OpenGL and being an X11 compositor even if the driver doesn’t support X11. Though I have not tested this case yet and have no devices to play with. But I know a few people in the community who might be interested to play with that.

Mir in Kubuntu

As you might have seen in Jonathan’s blog post we discussed Mir in Kubuntu at the “Mataro Sessions II”. It’s a topic I would have preferred to not have to discuss at all. But the dynamics in the free software world force us to discuss it and obviously our downstream needs to know why we as an upstream do not consider Mir adoption as a valid option.

This highlights a huge problem Canonical created with Mir. I cannot just say “Canonical sucks”[1] to discard Mir as an option, I have to provide proper technical arguments why we won’t integrate Mir. I have to invest time to investigate the differences, advantages and disadvantages. As I have those arguments, I thought it might be a good idea to share them in a blog post.

The discussion started during a presentation about X11 and Wayland to my fellow team mates at Blue Systems. I decided to first explain X11 as I think one cannot understand the needs for Wayland without understanding X11. I did not intend to discuss Mir at all, but somehow the discussion drifted into the direction and the valid questions were raised about what are the differences and advantages of Mir or Wayland. What followed was kind of a rant about Ubuntu and Canonical [2]. So later the week we discussed “Mir in Kubuntu” in more detail to try to find answers to the many questions this raises for our downstream.

Introduction

Frustration and lost Motivation

Before I go into more detail I want to make one thing clear: Canonical is totally allowed to develop whatever they want. I’m totally fine with this and don’t care whether they develop another display server, an own os kernel or yet another desktop shell. I couldn’t care less. It’s Canonical/Mark’s money and he can invest it in any way he considers as useful. I wouldn’t even care if it would be proprietary software, that’s all fine.

What is not fine is causing a major disruption in the free software ecosystem by giving false technical arguments and doing bold statements about software Canonical does not contribute to. This is not acceptable. This was very frustrating and destroyed lots of trust I had in Canonical. It will be difficult to rebuild this trust. Canonical can be glad that it is the free software world and not the normal corporate world. There were quite some statements which could have raised the legal department in the normal corporate world[3]. It also cost lots of motivation at least on my side and I even questioned whether it’s still worth to be a member of the free software ecosystem. Instead of working together we now have a situation where members of the ecosystem become a competitor and which badmouth part of the software stack. A very frustrating situation.

There certainly are valid reasons for developing Mir which also make sense. Unfortunately they have not been presented so far. I’m quite sure that I know the reasons and if they would have been said straight away it would have been for me and other projects probably much easier. It would have taken away the frustration which the announcement caused and we would not need to discuss it at all, because those question marks would not exist. But apparently Canonical decided to give false technical arguments over the real ones.

Not ready yet

At the moment Mir is not there yet, this is important to remember. With the announcement we basically had four options on how to handle the situation.

  1. Continue with the Wayland plan and ignore Mir
  2. Switch to Mir and ignore Wayland
  3. Support Mir and Wayland
  4. Delay decision until Mir is ready

If I map our time line for Plasma Workspaces 2 against the time line of Mir I see no overlap. We want to support Wayland before Mir is ready. So delaying the decision would be a rather bad idea. It would just throw us back. This also means that option 2 is not valid especially as we would need to delay until Mir is ready for this to happen. So the only valid options are supporting both Mir and Wayland or only Wayland. At the moment the code is not ready yet to properly decide whether supporting Mir in addition to Wayland is a valid approach or not. Last time I checked the source base I hit a few stubs and then obviously stopped looking at the code as it’s not worth the effort yet. So we have to evaluate on the knowledge we already have and that doesn’t look good on the Mir side.

Wayland vs Mir

Possible Advantages of Mir over Wayland

The differences between Mir and Wayland are rather minimal. One of the differences is that Mir uses server allocated buffers while Wayland uses client side buffer allocation. I cannot judge whether this is an advantage or disadvantage. But I trust Kristian and the Wayland team more on that topic.

Another difference is that Mir uses test-driven development. To me development methodology is not a technical argument. I rather use a working system without unit tests than a system with unit tests that doesn’t work [4]. Also KWin does not use TDD. If I would consider TDD superior I would have to question my own development methodology.

But that’s it. That are the differences I found so far which could count as an advantage for Mir. But of course there is the advantage that Mir is going to be awesome. For the disadvantages I will spend a complete section on each point.

Distro specific

So far Mir is a one-distribution solution. So far no other distribution has shown any interest in packaging Mir even if it would become a working solution. Unfortunately I don’t have the ability to see into the future, but I can use the past and the present to get ideas for the future. The past tells me that there are other Canonical specific solutions which are not available in other distributions. I do not know of any distribution which packages Unity and from all I have heard it’s even impossible to package Unity on non-Ubuntu distributions. Given that it is quite likely that Mir will go the same road. It’s designed as a solution for Unity and if distros don’t package Unity there is no need to package Mir.

This has quite some influence on a possible adoption. I do not know of any kde-workspace developer using (K)Ubuntu. I do not see how anyone would work on it or how we should be able to review code or even maintain code. It would mean all the adoption would have to go into ifdef sections nobody compiles and nobody runs. This is the best way to ensure that it starts to bit-rot. Even more our CI system runs on openSUSE so not even the CI would be able to detect breakage. Of course a downstream like Kubuntu could develop the adoption and carry it as a patch on top of upstream, but I would highly recommend them to not do this as KWin’s source code churn is too high. Also we all agree that downstream patches are evil and we would no longer be able to help in any way downstream’s user from a support perspective.

Architecture

Mir’s architecture is centered around Unity. It is difficult to really understand the architecture of Mir as the specification is so full of buzz-words that I don’t understand it [5]. From all I can see and understand Unity Next is a combination of window manager and desktop shell implemented on top of Mir. How exactly this is going to look like I do not know. Anyway it does not fit our design of having desktop shell and window manager separated and we do not know whether Mir would support that. We also do not know whether Mir would allow any other desktop shell except Unity Next, given that this is the main target. Wayland on the other hand is designed to have more than one compositor implementations. Using KWin as a session compositor is an example in the spec.

License

Wayland is licensed like X under the MIT license, which served us well for a display server. I think this is a very good choice and I am glad that the Wayland developers decided for this license. Mir is licensed under GPLv3-only with CLA. I think this is very unsuited for such a part of the stack and would render quite a risk for usage in KDE Plasma. KWin (and most KDE software) is GPLv2-or-later, this would no longer be possible, it would turn our code into GPLv3-only as KWin (or any other software which would depend on mir-server) would be a derived work of Mir. I do not consider GPLv3-only software as a possible dependency of any core part of our application stack. It renders a serious threat for the future in case of a GPLv4 which is not compatible with GPLv3. I also dislike the CLA [6]. So from a licensing perspective Mir is hardly acceptable.

Unity Specific/No Protocol

One of the most important aspects from Wayland for us is the ability to extend the protocol. This has already been a quite important feature in X and we are using our own extensions over ICCCM and EWMH to implement additional functionality. Of course our workspace has own ideas and it is important for us to be able to “standardize” those and also make them available to others if they are interested. This is possible thanks to protocol extensions.
Mir doesn’t have a real protocol. The “inner core” is described as “protocol-agnostic”. This renders a problem to us if we would want to use it. Our architecture is different (as described above) and we need a protocol between the desktop shell and the compositor. If Mir doesn’t provide that we would need to use our own protocol. And that already exists, it is called “Wayland”. So even if we would support Mir, we would need the Wayland protocol?!? That doesn’t make any sense to me. If we need to run Wayland on top of Mir just to get the features we need, why should we run Mir at all?

But it gets worse, the protocol between Mir server and Mir clients is defined as not being stable. In fact it’s promised that it will break. That’s a huge problem, I would even call it a showstopper. For Canonical that’s fine – they control the complete stack and can just adjust all bits using the protocol like QMir.

For us this looks quite different. Given that the protocol may change any time and given that the whole thing is developed for the needs of Unity we have to expect that the server libraries are not binary compatible or that old version of the server libraries cannot talk with the latest client libraries. We would constantly have to develop against an unstable and breaking base. I know that this sounds overly pessimistic but I know of one case where a change got introduced in a Canonical protocol late in the release cycle completely breaking an application in Kubuntu which wanted to use the protocol. Given this experience I would not trust that the protocol doesn’t change one day before the release meaning that Kubuntu cannot ship.

This is not awesome, it’s awful. It means KWin will not work just fine on Mir.

I hope this shows that using Mir inside the KDE Plasma workspaces is not an option. There are no advantages which would turn Mir into a better solution than Wayland and at the same time there are several showstoppers which mean that we cannot integrate Mir – not even optionally in addition to Wayland. The unstable protocol and the licensing choice are clearly not acceptable.

What this means to Kubuntu

Question marks

For Kubuntu the Mir switch by Canonical created quite some questions. One of those questions is answered: Upstream has no interest in supporting it and would most likely not accept patches for support. With upstream not using Mir the question is how the graphics stack for Kubuntu will look like once Ubuntu switched to Mir? The questions cannot be answered right now but it doesn’t look good.

Patches to the stack

Ubuntu has always had one of the worst graphics stack in the free software world. I can see this in the bug tracker. The quality of the Mesa stack in Ubuntu is really bad. For Mir Ubuntu will have to patch the Mesa stack even further. This is nothing which I would like to see. Also Mesa needs to be packaged with Wayland support. But will Canonical continue to do this? If not, would Kubuntu (and other Ubuntu flavors) need to ship their own Mesa stack? What if the changes by Canonical are so large that a standard Mesa stack doesn’t run on top of the Ubuntu stack?

Switching Sessions

One of the advantages of free software is that one can select the desktop environment in the login manager. This looks like no longer be possible in a Mir world. Unity will run with a Mir system compositor with LightDM nested underneath. We will need either the X Server or a Wayland system compositor. So from the login manager it will not be possible to start directly into a session using a different system compositor. How will it continue to be possible to use both Unity and KDE Plasma on the same system? Running a Unity and a KDE Plasma (or GNOME or XFCE or anything) session at the same time seems to no longer be possible.

System Compositor

How deep into the system is the system compositor going to be? Will it be possible to disable the Mir system compositor and replace it with X or Wayland? What if the packages start to conflict? Will it still be possible to install Kubuntu and Ubuntu on the same system? Will Canonical care about it? Will the system compositor mean that one has to decide in Grub whether to boot Ubuntu or Kubuntu?

Packages from Where

So far X, Wayland and Mesa have been packaged by Canonical. But what about the future? Will there still be packages for X, will there be packages for Wayland? If not, where to take them from? Debian unstable, most likely. But Debian might be frozen. Will it be possible at all to use the Debian packages for X and Wayland in the Ubuntu stack? Will they meet the requirements for KDE Plasma[7]? If Canonical doesn’t provide Wayland packages, they would drop to universe, so Mesa in main cannot depend on them. How to get then Mesa with Wayland support?

Only Future can tell

Those questions cannot be answered right now. It will have to wait until Mir is integrated into the Ubuntu stack. Then Kubuntu developers will see how far the stack broke. I’m not really optimistic that it will still be possible to provide the Ubuntu flavors once the transition to Mir is done. I don’t think that Canonical has any interest in the community provided distributions on top of Ubuntu any more. There are many small changes in the direction which indicate that. But we will see, maybe I’m too pessimistic.

[1] Given how Canonical introduced Mir with incorrect information about Wayland I consider this as a valid approach to dismiss the technology.

[2] I was very fed up with Ubuntu at the time anyway because our bug tracker once again exploded after the Ubuntu release.

[3] I do admit that I thought about asking KDE e.V. to send an Abmahnung after the statement that KWin would just work fine on Mir.

[4] In fact I consider TDD as utter non-sense and as a useless methodology though some aspects are useful.

[5] “with our protocol- and platform-agnostic approach, we can make sure that we reach our goal of a consistent and beautiful user experience across platforms and device form factors”

[6] Yes I know that Qt also has a CLA, which I have signed. But for Qt there is also the KDE Free Qt Foundation agreement.

[7]Last week a feature hit KWin which I cannot test/use because the X-Server is too old in Debian testing.

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.

War is Peace

Today I got many questions about KWin and Mir, how it affects us, what it means for our Wayland plans and so on. I did not want to write anything about it because I think there is nothing to write about, but before answering the same question again and again I think it’s better to put down a few lines here. Wiki will be updated once Wayland wiki is updated so that we have something to link to.

First question: Does Mir affect us? Yes, obviously. Because of Mir I have to write this blog post, Wayland developers have to get the FUD out of the Mir documentation, it’s creating tension and it harms the development. We will have to face again and again the question whether Wayland is better or not. So yes it affects us and I’m not happy about it.

Second question: Does it affect our plans for Wayland? I think it would be very unprofessional if we would change our plans just because Canonical did an announcement that they want to do an own display server for Unity (we didn’t throw away Plasma because of Unity either). Whether Mir provides technical advantages or not cannot be judged right now, we will have to wait and see, then we can make a decision whether it’s worth to change our plans. So far I have not seen anything in the documentation that would look like an advantage over Wayland. Given the incorrect statements about Wayland I’m very skeptical whether there can be any advantages. I don’t want to go into detail, just look on the Internet there’s already enough information about that. Also one should consider that Canonical changes plans for their distribution every other day. Just consider the number of toolkits which have been used for Unity – given that I would not bet on Mir will be used next year and that means of course that we should not consider it for our planning.

Third question: Will KWin support Mir? No! Mir is currently a one distribution only solution and any adjustments would be distro specific. We do not accept patches to support one downstream. If there are downstream specific patches they should be applied downstream. This means at the current time there is no way to add support and even if someone would implement support for KWin on Ubuntu I would veto the patches as we don’t accept distro-specific code. If Mir becomes available on more distributions one can consider the second question. Given the extreme success of Unity on non-Ubuntu distributions I’m positively optimistic that we will never have to do the evaluation of the second question.