Archive for the ‘Plasma’ Category

wayland and libkscreen benchmarks

Thursday, November 12th, 2015

So, first of all, this is all very much work-in-progress and highly experimental. It’s related to the work on screen management which I’ve outlined in an earlier article.

libkscreen wayland benchmark data

I ran a few benchmarks across our wayland stack, especially measuring interprocess communication performance when switching from X11 (or, in fact XCB and XRandR) to wayland. I haven’t done a highly scientific setup, just ran the same code with different backends to see how long it takes to receive information about screens connected, their modes, etc..
I also ran the numbers when loading the libkscreen backend in-process, more on that later.


The spreadsheet shows three data columns, in vertical blocks per backend the results for 4-5 individual runs and their mean values. One column for the default out-of-process mode, one with loading the backend in process and one showing the speedup between in- and out-of-process of the same backend.
The lower part contains some cross referencing of the mean values to compare different setups.
All values are nano seconds.


My results show a speedup of between 2 and 2.5 times when querying screen information on X11 and on wayland, wayland being much faster here.
The qscreen and xrandr backends perform pretty similar, they’re both going through XCB. That checks out. The difference between wayland and xrandr/qscreen can then be attributed to either the wayland protocol or its implementation in KWayland being much faster than the corresponding XCB implementations.

But, here’s the kicker…

in- vs. out-of-process

The main overhead, as it turns out, is libkscreen loading the backend plugins out-of-process. That means that it starts a dbus-autolaunched backend process and then passes data over DBus between the libkscreen front-end API and the backend plugin. It’s done that way to shield the client API (for example the plasma shell process or systemsettings) from unsafe calls into X11, as it encapsulates some crash-prone code in the XRandR backend. When using the wayland backend, this is not necessary, as we’re using KWayland, which is much safer.
I went ahead and instrumented libkscreen in a way that these backends are being loaded in process, which avoids most of the overhead. This change has an even more dramatic influence on performance: on X11, the speedup is 1.6x – 2x, on wayland loading the backend in-process makes it run 10 times faster. Of course, these speedups are complementary, so combined, querying screen information on wayland can be done about 20 times faster.

While this change from out-of-process to in-process backends introduces a bit more complexity in the library, it has a couple of other advantages additional to the performance gains. In-process means that debugging is much easier. If there are crashes, we do not hide them anymore, but identify and fix them. It also makes development more worthwhile, since it’s much easier to debug and test the backends and frontend API together. It also means that we can load backend plugins at the same time.

I’ve uploaded the benchmark data here. Before merging this, I’ll have to iron out some more wrinkles and have the code reviewed, so it’s not quite ready for prime-time yet.

Screen management in Wayland

Friday, November 6th, 2015

One of the bigger things that is in the works in Plasma’s Wayland support is screen management. In most cases, that is reasonably easy, there’s one screen and it has a certain resolution and refresh rate set. For mobile devices, this is almost always good enough. Only once we starting thinking about convergence and using the same codebase on different devices, we need to be able to configure the screens used for rendering. Especially on desktops and laptops, where we often find multi-monitor setups or connected projectors is where the user should be able to decide a bunch of things, relative position of the screens, resolution (“mode”) for each, etc.. Another thing that we haven’t touched yet is scaling of the rendering per display, which becomes increasingly important with a wider range of displays connected, just imagine a 4K laptop running north of 300 pixels per inch (PPI) connected to a projector which throws 1024*768 pixels on a wall sized 4x3m.

The Wayland protocol currently does not provide a mechanism for setting up the screen, or tell us about displays that are not used for rendering, either because they’re disabled, or have just been connected, but not enabled “automatically” (yet). For most applications, that doesn’t matter, they’re just fine with knowing about the rendering screens and some details about those, which is provided by the wl_output interface. For screen management, this interface is insufficient, though, since it lacks a few things, EDID information, enabled/disabled flags and also ways to set the mode, scaling, rotation and position. This makes clearly recognizing display and setting them up harder than necessary, and thus error-prone. Let’s look at the background, first, however.

Setting up X11

On the hardware side, this has been a complete mess in the past. One problem is X11’s asynchronous nature. The XRandR extension that is used for this basically works by throwing a bunch of calls to the X server (“use this mode”, “position display there”) and then seeing what sticks to the wall. The problem is that we never really know what happened, there’s no well-defined “OK, this works” result, and we also don’t know when the whole procedure is done. The result is a flicker-fest and the desktop trying to catch up with what X11 made of the xrandr calls. It can also be an unpleasant experience, when a display gets connected, used for rendering, then the shell finds out about it, expanding the desktop to it, and then everything is resized again because there’s a predefined configuration for this. These kind of race conditions are very hard to fix due to the number of components involved in the process, and the lack of proper notification semantics around it.

X11 has the nasty habit of interacting with hardware directly, rather than through well-defined and modern kernel interfaces. On the kernel side, this has been fixed. We now have atomic mode setting, which allows us to check whether changes can be applied (through the DRM_MODE_ATOMIC_TEST_ONLY flag), and apply them all at once, or in portions that are known to not screw up, lock the user out, or are simply invalid in context with each other.
For the user, getting this right across the whole stack means quicker reconfiguration of the hardware and only minimal flickering when switching screen setups. We won’t be able to completely prevent the flickering on most displays, as that is simply how the hardware works, but we will be able to make it a lot less jarring. The compositor now being the one that calls the DRM subsystem on the user side, we can coordinate these things well with visual effects, so we’ll be able to make the user experience while re-configuring displays a bit smoother as well.

Atomic mode setting, DRM and kernel

From the kernel side, this needed quite radical changes, which have now landed throughout the DRM subsystem. The result is a kernel interface and helper library that allows interacting with the kernel using semantics that allow tighter control of the processes, better error prevention and handling and more modern power management semantics. Switching off the screen can now be done from the compositor, for example — this allows us to fix those cases where the display is black, but still has its backlight on, or where the display is off, but used for rendering (in which case you get huge blind spots in your user interface).
Daniel Vetter’s (part 1, part 2) provides an excellent overview over history, present and future of atomic mode setting on the kernel side. Pertaining is that a reasonably recent Linux kernel with working DRM drivers now provides all that we need to fix this problem on the user side. X11 is still in the way of a completely smooth solution, though.

Screen setup in Plasma

In Plasma, the screens can be set up using the Display configuration module in system settings. This module is internally called “KScreen”. KScreen provides a visual interface to position displays, set resolution, etc.. It’s backed by a daemon that can apply a configuration on login – useful stuff, but ultimately bound by the limits across the underlying software stack (X11, kernel, drivers, etc.).

KScreen is backed by libkscreen, a library that we ship with Plasma. libkscreen offers an API that allows to list displays, their properties, including disabled displays. libkscreen is driven by out-of-process running backends, commonly used is the “xrandr” backend, which talks to the X Server over the XRandR extension. libkscreen has other backends, notably a read-only QScreen backend a “fake” backend used for unit tests. A native Wayland backend is work in progress (you can find it in the libkscreen[sebas/wayland] branch.)

libkscreen been developed for the purpose of screen configuration, but we have also started using it for the Plasma shell. QScreen, the natural starting point of this was not up to the task yet, missing some functionality. In Qt 5.6, Aleix Pol has now landed the necessary missing functionality, so we can move the Plasma shell back onto QScreen entirely. QScreen is backed by the XCB Qt platform plugin (QPA). One problem in Plasma has been that we got acknowledged of changes through different code paths, which made it hard to set up the desktop, position panels, etc. In a Wayland session, this has to happen in a much more coordinated way, with clearly defined semantics when the screen setup changes, and as little of those changes as necessary.
KScreen should concentrate on doing what it’s good at: screen configuration. For X11 kscreen uses its xrandr backend, no changes there. In Plasma shell’s startup, we will be able to remove libkscreen and rely purely on QScreen directly as soon as we can depend on Qt 5.6, so that probably puts us into the time-frame of Q2 next year. For read-only access on wayland, we can use the libkscreen QScreen backend for now, it comes with some limitations around multi-screen, but these will be ironed by spring next year. The QScreen backend is actually used to start Plasma Mobile’s on kwin_wayland. For configuration, QScreen is not an option, however — it’s simply not its purpose and shouldn’t be.

In the Wayland protocol itself, there are no such semantics yet. Screen configuration has, so far, been outside of the scope of the agreed-upon wayland protocols. If we don’t run on top of an X server, who’s doing the actual hardware setup? Our answer is: KWin, the compositor.


KWin plays a more central role in a Wayland world. For rendering and compositing of windows, it interacts with the hardware. Since it already initializes hardware when it starts a Wayland server, it makes a lot of sense to put screen configuration also exactly there. This means that we will configure KWin at runtime through an interface that is designed around semantics of atomic mode setting, and KWin picks a suitable configuration for connected displays. KWin saves the configuration, applies it on startup or when a display gets switched off, connected or disconnected, and only then tells the workspace shell and the apps to use it. This design makes a lot of sense, since it is KWin that ultimately knows of all the constraints related to dynamic display configuration, and it can make concert how the hardware is used and how its changes are presented to the applications and workspace.

KWayland and unit testing

Much of Kwin/Wayland’s functionality is implemented in a library called KWayland. KWayland wraps the wayland protocol with a Qt-style API for wayland clients and servers, offers threaded connection and type-safety on top of the basic C implementation of libwayland.
KWayland provides a library that allows to run wayland servers, or just specific parts of it with very little code. The KWayland server classes allow us to test a great deal of the functionality in unittests, since we can run the unit tests on a “live” wayland server. Naturally, this is used a lot in kwayland’s own autotests. In the libkscreen wayland backend’s tests, we’re loading different configuration scenarios from json definitions, so we can not only test whether the library works in principle, but really test against live servers, so we cover a much larger part of the stack in our tests. This helps us a lot to make sure that the code works in the first place, but also helps us catch problems easily as soon as they arise. The good unit test coverage also allows much swifter development as a bonus.

Output management wayland interface design

The output management wayland protocol that we have implemented provides two things:

  • It lists connected output hardware and all of their properties, EDID, modes, physical size, and runtime information such as currently used mode, whether this output device is currently enabled for rendering, etc.
  • It provides an interface to change settings such as mode, rotation, scaling, position, for hardware and to apply them atomically

This works as follows:

  1. The server announces that the global interfaces for OutputManagement and a list of OutputDevices is available
  2. The configuration client (e.g. the Display Settings) requests the list of output devices and uses them to show the screen setup visually
  3. The user changes some settings and hits “apply”, the client requests an OutputConfiguration object from the OutputManagement global
  4. The configuration object is created on the server specifically for the client, it’s not exposed in the server API at this point.
  5. The client receives the config object and calls setters with new settings for position, mode, rotation, etc.
  6. The server buffers these changes in the per-client configuration object
  7. The client is done changing settings and asks the server to apply them
  8. The compositor now receives a sealed configuration object, tests and applies the new settings, for example through the DRM kernel interface
  9. The compositor updates the global list of OutputDevices and changes its setup, then it signals the client failure or success back through the configuration object

The output management protocol, client- and server-side library, unit tests and documentation are quite a hefty beast, combined they come in at ca. 4700 lines of code. The API impact, however, has been kept quite low and easy to understand. The atomic semantics are reflected in the API, and it encourages to do the right thing, both for the client configuring the screens, and the compositor, which is responsible for applying the setup.

Next steps

I am currently working on a libkscreen module for screen configuration under wayland, that implements atomic mode setting semantics in libkscreen. It uses a new wayland protocol which Martin Gräßlin and I have been working on in the past months. This protocol lands with the upcoming Plasma 5.5, the libkscreen module may or may not make the cut, this also depends on if we get the necessary bits finished in KWin and its DRM backend. That said, we’re getting really close to closing the last gaps in the stack.

On the compositor side, we can now connect the OutputManagement changes, for example in the DRM backend and implement the OutputDevices interface on top of real hardware.

Wall drawing

Friday, September 11th, 2015

Sol Lewitt's wall drawing at Stedelijk Museum Amsterdam

Sol Lewitt’s wall drawing at Stedelijk Museum Amsterdam

A few weeks ago, I visited the Stedelijk Museum in Amsterdam for an exhibition of Henry Matisse’s works. What stuck is not a painting or collage by Matisse, but a wall drawing by Sol Lewitt. I took a photo with my phone and have since then used it as wallpaper for it, and it works well, colors are nicely toned, everything provides enough contrast, and I like how it looks on a screen.

Yesterday, when I needed a break from hacking on Plasma’s Wayland integration, I remade the photo into vector art to use it as wallpaper. You can download the result here (the wallpaper package has versions for all resolutions, including phone and landscape versions, you can just unzip the package into /usr/share/wallpapers).

Embracing Mobile

Saturday, July 25th, 2015

At Blue Systems, we have been working on making Plasma shine for a while now. We’ve contributed much to the KDE Frameworks 5 and Plasma 5 projects, and helping with the transition to Qt5. Much of this work has been involving porting, stabilizing and improving existing code. With the new architecture in place, we’ve also worked on new topics, such as Plasma on non-desktop (and non-laptop) devices.

Plasma Mobile on an LG Nexus 5

Plasma Mobile on an LG Nexus 5

This work is coming to fruition now, and we feel that it has reached a point where we want to present it to a more general public. Today we unveil the Plasma Mobile project. Its aim is to offer a Free (as in Freedom), user-friendly, privacy-enabling and customizable platform for mobile devices. Plasma Mobile runs on top of Linux, uses Wayland for rendering graphics and offers a device-specific user interface using the KDE Frameworks and Plasma library and tooling. Plasma Mobile is under development, and not usable by end users now. Missing functionality and stability problems are normal in this phase of development and will be ironed out. Plasma Mobile provides basic functionality and an opportunity for developers to jump in now and shape the mobile platform, and how we use our mobile devices.

As is necessary with development on mobile devices, we’ve not stopped at providing source code that “can be made to work”, rather we’re doing a reference implementation of Plasma Mobile that can be used by those who would like to build a product based on Plasma Mobile on their platform. The reference implementation is based on Kubuntu, which we chose because there is a lot of expertise in our team with Kubuntu, and at Blue Systems we already have continuous builds and package creation in place. Much of the last year was spent getting the hardware to work, and getting our code to boot on a phone. With pride, we’re now announcing the general availability of this project for public contribution. In order to make clear that this is not an in-house project, we have moved the project assets to KDE infrastructure and put under Free software licenses (GPL and LGPL according to KDE’s licensing policies). Plasma Mobile’s reference implementation runs on an LG Nexus 5 smartphone, using an Android kernel, Ubuntu user space and provides an integrated Plasma user interface on top of all that. We also have an x86 version, running on an ExoPC, which can be useful for testing.

Plasma Mobile uses the Wayland display protocol to render the user interface. KWin, Plasma’s window manager and compositor plays a central role. For apps that do not support Wayland, we provide X11 support through the XWayland compatibility layer.

Plasma Mobile is a truly converged user interface. More than 90% of its code is shared with the traditional desktop user interface. The mobile workspace is implemented in the form of a shell or workspace suitable for mobile phones. The shell provides an app launcher, a quick settings panel and a task switcher. Other functionality, such as a dialer, settings, etc. is implemented using specialized components that can be mixed and matched to create a specific user experience or to provide additional functionality — some of them already known from Plasma Desktop.

Architecture diagram of Plasma Mobile

Architecture diagram of Plasma Mobile

Plasma Mobile is developed in a public and open development process. Contributions are welcome and encouraged throughout the process. We do not want to create another walled garden, but an inclusive platform for creation of mobile device user experiences. We do not want to create releases behind closed doors and throw them over the wall once in a while, but create a leveled playing field for contributors to work together and share their work. Plasma Mobile’s code is available on, and its development is discussed on the plasma-devel mailinglist. In the course of Akademy, we have a number of sessions planned to flesh out more and more detailed plans for further development.

With the basic workspace and OS integration work done, we have laid a good base for further development, and for others to get their code to run on Plasma Mobile. More work which is already in our pipeline includes support for running Android applications, which potentially brings a great number of mature apps to Plasma Mobile, better integration with other Plasma Devices, such as your desktop or laptop through KDE Connect, an improved SDK making it very easy to get a full-fledged development environment set up in minutes, and of course more applications.

thoughts on being merciful binary gods

Wednesday, July 15th, 2015

“Since when has the world of computer software design been about what people want? This is a simple question of evolution. The day is quickly coming when every knee will bow down to a silicon fist, and you will all beg your binary gods for mercy.” Bill Gates

For the sake of the users, let’s assume Bill was either wrong or (||) sarcastic.

Let’s say that we want to deliver Freedom and privacy to the users and that we want to be more effective at that. We plan to do that through quality software products and communication — that’s how we reach new users and keep them loving our software.

We can’t get away with half-assed software that more or less always shows clear signs of “in progress”, we need to think our software through from a users point of view and then build the software accordingly. We need to present our work at eye-level with commercial software vendors, it needs to be clear that we’re producing software fully reliable on a professional level. Our planning, implementation, quality and deployment processes need to be geared towards this same goal.

We need processes that allow us to deliver fixes to users within days, if not hours. Currently in most end-user scenario, it often takes months and perhaps even a dist-upgrade for a fix for a functional problem with our software.

The fun of all this lies in a more rewarding experience of making successful software, and learning to work together across the whole stack (including communication) to work together on this goal.

So, with these objectives in mind, where do we go from here? The answer is of course that we’re already underway, not at a very fast speed, but many of us have good understanding of many of the above structural goals and found solutions that work well.

Take tighter and more complete quality control, being at the heart of the implementation, as an example. We have adopted better review processes, more unit testing, more real-world testing and better feedback cycles with the community, especially the KDE Frameworks and Plasma stacks are well maintained and stabilized at high speeds. We can clearly say that the Frameworks idea worked very well technically but also from an organizational point of view, we have spread the maintainership over many more shoulders, and have been able to vastly simplify the deployment model (away from x.y.z releases). This works out because we test especially the Frameworks automatically and rather thoroughly through our CI systems. Within one year of Frameworks 5, our core software layer has settled into a nice pace of stable incremental development.

On the user interaction side, the past years have accompanied our interaction designers with visual artists. This is clearly visible when comparing Plasma 4 to Plasma 5. We have help from a very active group of visual designers now for about one and a half year, but have also adopted stricter visual guidelines in our development process and forward-thinking UI and user interaction design. These improvements in our processes have not just popped up, they are the result of a cultural shift towards opening the KDE also to non-coding contributors, and creating an atmosphere where designers feel welcome and where they can work productively in tandem with developers on a common goal. Again, this shows in many big and small usability, workflow and consistency improvements all over our software.

To strengthen the above processes and plug the missing holes in the big picture to make great products, we have to ask ourselves the right questions and then come up with solutions. Many of them will not be rocket science, some may take a lot of effort by many. This should not hold us back, as a commonly shared direction and goal is needed anyway, regardless of ability to move. We need to be more flexible, and we need to be able to move swiftly on different fronts. Long-standing communities such as KDE can sometimes feel to have the momentum of an ocean liner, which may be comfortable but takes ages to move, while it really should have the velocity, speed and navigational capabilities of a zodiak.

By design, Free Culture communities such as ours can operate more efficiently (through sharing and common ownership) than commercial players (who are restricted, but also boosted by market demands), so in principle, we should be able to offer competitive solutions promoting Freedom and privacy.

Our users need merciful binary source code gods and deserve top-notch silicon fists.

Convergence through Divergence

Thursday, July 2nd, 2015

It’s that time of the year again, it seems: I’m working on KPluginMetaData improvements.

In this article, I am describing a new feature that allows developers to filter applications and plugins depending on the target device they are used on. The article targets developers and device integrators and is of a very technical nature.

Different apps per device

This time around, I’m adding a mechanism that allows us to list plugins, applications (and the general “service”) specific for a given form factor. In normal-people-language, that means that I want to make it possible to specify whether an application or plugin should be shown in the user interface of a given device. Let’s look at an example: KMail. KMail has two user interfaces, the desktop version, a traditional fat client offering all the features that an email client could possibly have, and a touch-friendly version that works well on devices such as smart phones and tablets. If both are installed, which should be shown in the user interface, for example the launcher? The answer is, unfortunately: we can’t really tell as there currently is no scheme to derive this information from in a reliable way. With the current functionality that is offered by KDE Frameworks and Plasma, we’d simply list both applications, they’re both installed and there is no metadata that could possibly tell us the difference.

Now the same problem applies to not only applications, but also, for example to settings modules. A settings module (in Frameworks terms “KCM”) can be useful on the desktop, but ignored for a media center. There may also be modules which provide similar functionality, but for a different use case. We don’t want to create a mess of overlapping modules, however, so again, we need some kind of filtering.

Metadata to the rescue

Enter KPluginMetaData. KPluginMetaData gives information about an application, a plugin or something like this. It lists name, icon, author, license and a whole bunch of other things, and it lies at the base of things such as the Kickoff application launcher, KWin’s desktop effects listing, and basically everything that’s extensible or uses plugins.

I have just merged a change to KPluginMetaData that allows all these things to specify what form factor it’s relevant and useful for. This means that you can install for example KDevelop on a system that can be either a laptop or a mediacenter, and an application listing can be adapted to only show KDevelop when in desktop mode, and skipping it in media center mode. This is of great value when you want to unclutter the UI by filtering out irrelevant “stuff”. As this mechanism is implemented at the base level, KPluginMetaData, it’s available everywhere, using the exact same mechanism. When listing or loading “something”, you simply check if your current formfactor is among the suggested useful ones for an app or plugin, and based on that you make a decision whether to list it or skip it.

With increasing convergence between user interfaces, this mechanism allows us to adapt the user interface and its functionality in a fully dynamic way, and reduces clutter.

Getting down and dirty

So, how does this look exactly? Let’s take KMail as example, and assume for the sake of this example that we have two executables, kmail and kmail-touch. Two desktop files are installed, which I’ll list here in short form.

For the desktop fat client:

Comment=Fat-client for your email

For the touch-friendly version:

Comment=Touch-friendly email client

Note that that “FormFactors” key does not just take one fixed value, but allows specifying a list of values — an application may support more than one form-factor. This is reflected throughout the API with the plural form being used. Now the only thing the application launcher has to do is to check if the current form-factor is among the supplied ones, for example like this:

foreach (const KPluginMetaData &app, allApps) {
    if (app.formFactors().count() == 0 || app->formFactors().contains("desktop")) {

In this example, we check if the plugin metadata does specify the form-factor by counting the elements, and if it does, we check whether “desktop” is among them. For the above mentioned example files, it would mean that the fat client will be added to the list, and the touch-friendly one won’t. I’ll leave it as an exercise to the reader how one could filter only applications that are specifically suitable for example for a tablet device.

What devices are supported?

KPluginMetaData does not itself check if any of the values make sense. This is done by design because we want to allow for a wide range of form-factors, and we simply don’t know yet which devices this mechanism will be used on in the future. As such, the values are free-form and part of the contract between the “reader” (for example a launcher or a plugin listing) and the plugins themselves. There are a few commonly used values already (desktop, mediacenter, tablet, handset), but in principle, adding new form-factors (such as smartwatches, toasters, spaceships or frobulators) is possible, and part of its design.

For application developers

Application developers are encouraged to add this metadata to their .desktop files. Simply adding a line like the FormFactors one in the above examples will help to offer the application on different devices. If your application is desktop-only, this is not really urgent, as in the case of the desktop launchers (Kickoff, Kicker, KRunner and friends), we’ll likely use a mechanism like the above: No formfactors specified means: list it. For devices where most of the applications to be found will likely not work, marking your app with a specific FormFactor will increase the chances of it being found. As applications are being adopted to respect the form-factor’s metadata, its usefulness will increase. So if you know your app will work well with a remote control, add “mediacenter”, if you know it works well on touch devices with a reasonably sized display, add “tablet”, and so on.


We now have basic API, but nobody uses it (a chicken-and-egg situation, really). I expect that one of the first users of this will be Plasma Mediacenter. Bhushan is currently working on the integration of Plasma widgets into its user interface, and he has already expressed interest in using this exact mechanism. As KDE software moves onto a wider range of devices, this functionality will be one of the cornerstones of the device-adaptable user interface. If we want to use device UIs to their full potential, we do not just need converging code, we also need to add divergence features to allow benefiting from the difference of devices.

Say hi to cuttlefish!

Thursday, February 19th, 2015

Cuttlefish icon previewer

Cuttlefish icon previewer

One of the things I’ve been sorely missing when doing UI design and development was a good way to preview icons. The icon picker which is shipped with KDE Frameworks is quite nice, but for development purposes it lacks a couple of handy features that allow previewing and picking icons based on how they’re rendered.

Over the christmas downtime, I found some spare cycles to sit down and hammer out a basic tool which allows me to streamline that workflow. In the course of writing this little tool, I realised that it’s not only useful for a developer (like me), but also for artists and designers who often work on or with icons. I decided to target these two groups (UI developers and designers) and try to streamline this tool as good as possible for their usecases.

Cuttlefish is the result of that work. It’s a small tool to list, pick and preview icons. It tries to follow the way we render icons in Plasma UIs as close as possible, in order to make the previews as realistic as possible. I have just shown this little tool to a bunch of fellow Plasma hackers here at the sprint, and it was very well received. I’ve collected a few suggestions what to improve, and of course, cuttlefish being brand-new, it still has a few rough edges.

You can get the source code using the following command:

git clone kde:scratch/sebas/cuttlefish
git clone kde:plasmate

and build it with the cmake.

Enjoy cuttlefish!

[Edit] We moved cuttlefish to the Plasmate repository, it’s now part of Plasma’s SDK.

“Killing the Cashew” done right.

Wednesday, February 18th, 2015

Plasma Desktop's Toolbox

Plasma Desktop’s Toolbox

One of the important design cornerstones of Plasma is that we want to reduce the amount of “hidden features” as much as possible. We do not want to have to rely on the user knowing where to right-click in case she wants to find a certain, desktop-related option, say adding widgets, opening the desktop settings dialog, the activity switcher, etc.. For this, Plasma 4.0 introduced the toolbox, a small icon that when clicked opens a small dialog with actions related to the desktop. To many users, this is an important lifeline when they’re looking for a specific option.

In Plasma 4.x, there was a Plasmoid, provided by a third party, that used a pretty gross hack to remove the toolbox (which was depicted as the old Plasma logo, resembling a cashew a bit). We did not support this officially, but if people are deliberately risking to break their desktop, who are we to complain. They get to keep both pieces.

During the migration to QML (which begun during Plasma 4.x times), one of the parts I had been porting to QtQuick was this toolbox. Like so many other components in Plasma, this is actually a small plugin. That means it’s easy to replace the toolbox with something else. This feature has not really been documented as its more or less an internal thing, and we didn’t want to rob users of this important lifeline.

Some users want to reduce clutter on their desktop as much as possible, however. Since the options offered in the toolbox are also accessible elsewhere (if you know to find them). Replacing the toolbox is actually pretty easy. You can put a unicorn dancing on a rainbow around your desktop there, but you can also replace it with just an empty object, which means that you’re effectively hiding the toolbox.

For users who would rather like their toolbox to be gone, I’ve prepared a small package that overrides the installed toolbox with an empty one. Hiding the toolbox is as easy as installing this minimal package, which means the toolbox doesn’t get shown, or even get loaded.

I would not recommend doing this, especially not as default, but at the same time, I don’t want to limit what people do with their Plasma do what we as developers exactly envision, so there you go.

Download this file, then install it as follows:

plasmapkg2 -t package -i emptytoolbox.plasmoid

Now restart the Plasma Shell (either by stopping the plasmashell process, or by logging out and in again), and your toolbox should be gone.

If you want it back, run

plasmapkg2 -t package -r org.kde.desktoptoolbox

Then restart Plasma and it’s back again.

Even more than just removing the toolbox, I’d like to invite and encourage everybody to come up with nice, crazy and beautiful ideas how to display and interact with the toolbox. The toolbox being a QtQuick Plasmoid package, it’s easy to change and to share with others.

Diving into Plasma’s 2015

Wednesday, November 5th, 2014
Sea anemone with anemone fish

Sea anemone with anemone fish

TL;DR: The coming year is full of challenges, old and new, for the Plasma team. In this post, I’m highlighting end-user readiness, support for Wayland as display server and support for high-dpi displays.

Before you continue reading, have a gratuitous fish! (Photo taken by my fine scuba diving buddy Richard Huisman.)
Next year will be interesting for Plasma. Two things that are lined up are particularly interesting. In 2015, distributions will start shipping Plasma 5 as their default user interface. This is the point where more “oblivious” users will make their first contact with Plasma 5. As we’re navigating through the just-after-a-big-release phase, which I think we’re mastering quite nicely, we approach a state where a desktop that has so many things changed under its hood is becoming a really polished and complete working environment, that feels modern, supports traditional workflows well, and is built on top of a top-notch modern modularized set of libraries, KDE’s Frameworks.

In terms of user demographic, we’re almost certain to see one thing happening with the new Plasma 5 UI, as distros start to ship it by default, this is what these new users are going to see. Not everybody in this group of users is interested in how cool the technology stack lines up, they just want to get their work done and certainly not feel impeded in their daily workflows. This is the target group which we’ve been focusing our work on in months since summer, since the release of Plasma 5.0. Wider group of users sounds pretty abstract, so let’s take some numbers: While Plasma 5 is run by a group of people already, the number of users who get it via Linux distributions is much larger than the group of early adopters. This means by the end of next year, Plasma 5 will be in the hands of millions of users, probably around 10 million, and increasing. (This is interpolated from an estimation of Plasma users in the tens of millions, with the technology adaption lifecycle taken as base.)

The other day, I’ve read on a forum a not particularly well-informed, yet interesting opinion: “Plasma 5 is not for end users, its Wayland support is still not ready”. The Plasma 5 is not for end users, I do actually agree with, in a way. While I know that there is a very sizable group of people that have been having a blast running Plasma since 5.0, when talking about end-users, one needs to look at the cases where it isn’t suitable. For one, these give concrete suggestions what to improve, so they’re important for prioritization. This user feedback channel has been working very well so far, we’ve been receiving hundreds of bug reports, which we could address in one way or another, we have been refining our release and QA processes, and we’ve filled in many smaller and bigger gaps. There’s still much more work to do, but the tendency is exactly right. By ironing out many real-world problems, each of those fixes increases the group of users Plasma is ready for, and improve the base to build a more complete user experience upon.

What’s also true about the statement of the above “commenter on the Internet” is that our Wayland support isn’t ready. It is entirely orthogonal to the “is it ready for end users?” question. Support for Wayland is a feature we’re gradually introducing, very much in a release-early-release-often fashion. I expect our support for this new display server system to reach a point where one can run a full session on top of Wayland in the course of next year. I expect that long-term, most of our users will run the user interface on top of Wayland, effectively deprecating X11. Yet, X11 will stay around for a long time, there’s so much code written on top of X11 APIs that we simply can’t expect it to just vanish from one day to the other. Some Linux distros may switch relatively early, while for Enterprise distros, that switch might only happen in the far future, that doesn’t even count existing installations. That is not a problem, though, since Wayland and X11 support are well encapsulated, and supposed to not get in the way of each other — we do the same trick already on other operating systems, and it’s a proven and working solution.

Then, there’s the mission to finish high-dpi support. High DPI support means rendering a usable UI on displays with more than 200 DPI. That means that UI elements have to scale or be rendered with more detail and fidelity. One approach is to simply scale up everything in every direction by a fixed factor, but while it would get the sizing right, it would also negate any benefit of the increased amount of pixels. Plasma 5 already solves many issues around high-dpi, but not without fiddling, and going over different settings to get them right. Our goal is to support high-dpi displays out of the box, no fiddling, just sensible defaults in case a high dpi display gets connected. As there are 101 corner cases to this, it’s not easy to get right, and will take time and feedback cycles. Qt 5.4, which is around the corner, brings some tools to support these displays better, and we’ll be adjusting our solutions to make use of that.

It seems we are not quite yet running out of interesting topics that make Plasma development a lot of fun. :)

Plasma’s Road to Wayland

Friday, July 25th, 2014

Road to WaylandWith the Plasma 5.0 release out the door, we can lift our heads a bit and look forward, instead of just looking at what’s directly ahead of us, and make that work by fixing bug after bug. One of the important topics which we have (kind of) excluded from Plasma’s recent 5.0 release is support for Wayland. The reason is that much of the work that has gone into renovating our graphics stack was also needed in preparation for Wayland support in Plasma. In order to support Wayland systems properly, we needed to lift the software stack to Qt5, make X11 dependencies in our underlying libraries, Frameworks 5 optional. This part is pretty much done. We now need to ready support for non-X11 systems in our workspace components, the window manager and compositor, and the workspace shell.

Let’s dig a bit deeper and look at at aspects underlying to and resulting from this transition.

Why Wayland?

The short answer to this question, from a Plasma perspective, is:

  • Xorg lacks modern interfaces and protocols, instead it carries a lot of ballast from the past. This makes it complex and hard to work with.
  • Wayland offers much better graphics support than Xorg, especially in terms of rendering correctness. X11’s asynchronous rendering makes it impossible to be sure about correctness and timeliness of graphics that ends up on screen. Instead, Wayland provides the guarantee that every frame is perfect
  • Security considerations. It is almost impossible to shield applications properly from each other. X11 allows applications to wiretap each other’s input and output. This makes it a security nightmare.

I could go deeply into the history of Xorg, and add lots of technicalities to that story, but instead of giving you a huge swath of text, hop over to Youtube and watch Daniel Stone’s presentation “The Real Story Behind Wayland and X” from last year’s, which gives you all the information you need, in a much more entertaining way than I could present it. H-Online also has an interesting background story “Wayland — Beyond X”.

While Xorg is a huge beast that does everything, like input, printing, graphics (in many different flavours), Wayland is limited by design to the use-cases we currently need X for, without the ballast.
With all that in mind, we need to respect our elders and acknowledge Xorg for its important role in the history of graphical Linux, but we also need to look beyond it.

What is Wayland support?

KDE Frameworks 5 apps under Weston

KDE Frameworks 5 apps under Weston

Without communicating our goal, we might think of entirely different things when talking about Wayland support. Will Wayland retire X? I don’t think it will in the near future, the point where we can stop caring for X11-based setups is likely still a number of years away, and I would not be surprised if X11 was still a pretty common thing to find in enterprise setups ten years down the road from now. Can we stop caring about X11? Surely not, but what does this mean for Wayland? The answer to this question is that support for Wayland will be added, and that X11 will not be required anymore to run a Plasma desktop, but that it is possible to run Plasma (and apps) under both, X11 and Wayland systems. This, I believe, is the migration process that serves our users best, as the question “When can I run Plasma on Wayland?” can then be answered on an individual basis, and nobody is going to be thrown into the deep (at least not by us, your distro might still decide to not offer support for X11 anymore — that is not in our hands). To me, while a quick migration to Wayland (once ready) is something desirable, realistically, people will be running Plasma on X11 for years to come. Wayland can be offered as an alternative at first, and then promote to primary platform once the whole stack matures further.

Where at we now?

With the release of KDE Frameworks 5, most of the issues in our underlying libraries have been ironed out, that means X11-dependent codepaths have become optional. Today, it’s possible to run most applications built on top of Frameworks 5 under a Wayland compositor, independent from X11. This means that applications can run under both, X11 and Wayland with the same binary. This is already really cool, as without applications, having a workspace (which in a way is the glue between applications would be a pointless endeavour). This chicken-egg situation plays both ways, though: Without a workspace environment, just having apps run under Wayland is not all that useful. This video shows some of our apps under the Weston compositor. (This is not a pure Wayland session “on bare metal”, but one running in an X11 window in my Plasma 5 session for the purpose of the screen-recoding.)

For a full-blown workspace, the porting situation is a bit different, as the workspace interacts much more intimately with the underlying display server than applications do at this point. These interactions are well-hidden behind the Qt platform abstraction. The workspace provides the host for rendering graphics onto the screen (the compositor) and the machinery to start and switch between applications.

We are currently missing a number of important pieces of the full puzzle: Interfaces between the workspace shell, the compositor (KWin) and the display server are not yet well-defined or implemented, some pioneering work is ahead of us. There is also a number of workspace components that need bigger adjustments, global shortcut handling being a good example. Most importantly, KWin needs to take over the role of Wayland compositor. While some support for Wayland has already been added to KWin, the work is not yet complete. Besides KWin, we also need to add support for Wayland to various bits of our workspace. Information about attached screens and their layout has to be made accessible. Global keyboard shortcuts only support X11 right now. The screen locking mechanism needs to be implemented. Information about Windows for the task-manager has to be shared. Dialog positioning and rendering needs to be ported. There are also a few assumptions in startkde and klauncher that currently prevent them from being able to start a session under Wayland, and more bits and pieces which need additional work to offer a full workspace experience under Wayland.

Porting Strategy

The idea is to be able to run the same binaries under both, X11 and Wayland. This means that we (need to decide at runtime how to interact with the windowing system. The following strategy is useful (in descending order of preference):

  • Use abstract Qt and Frameworks (KF5) APIs
  • Use XCB when there are no suitable Qt and KF5 APIs
  • Decide at runtime whether to call X11-specific functions

In case we have to resort to functions specific to a display server, X11 should be optional both at build-time and at run-time:

  • The build of X11-dependent code optional. This can be done through plugins, which are optionally included by the build-system or (less desirably) by #ifdef’ing blocks of code.
  • Even with X11 support built into the binary, calls into X11-specific libraries should be guarded at runtime (QX11Info::isPlatformX11() can be used to check at runtime).

Get your Hands Dirty!

Computer graphics are an exciting thing, and many of us are longing for the day they can remove X11 from their systems. This day will eventually come, but it won’t come by itself. It’s a very exciting time to get involved, and make the migration happen. As you can see, we have a multitude of tasks that need work. An excellent first step is to build the thing on your system and try running, fix issues, and send us patches. Get in touch with us on Freenode’s #plasma IRC channel, or via our mailing list plasma-devel(at)