In the future, if someone asks which desktop environment you use, and you say "KDE5," you might receive a look of surprise. That's because in the future, the KDE project will develop Plasma 5, KDE Frameworks 5, and KDE Applications 5 independently, and the results will not appear as a single package. In other words, you won't see a combined release date and a standalone component with the name KDE followed by a version number. Of course, that doesn't stop individual Linux projects from putting the pieces together. Various projects and distributions have been releasing next-generation KDE test images for some time now.

The KaOS project [1] has boldly pushed forward in an attempt to keep pace, and it has a reputation for faithfully following the latest KDE developments. KaOS has taken this loyalty a step further than any other distribution and has already migrated more than 150 applications from the KDE applications pool to Qt5, completing the rebuild before most of these applications have announced their own official Qt5 versions. The familiar apps updated for Qt5 include Dolphin, digiKam, Kipi-Plugins, Kdenlive, Marble, Ark, kMix, KDE Telepathy, KGet, Quassel, and Kompare. The underpinnings come courtesy of Plasma 5.7, Frameworks 5.2.1, and other components of the KDE environment.

Inside KaOS

KaOS is designed as a rolling release with basic components that include the 3.18.7 kernel, systemd 218, Xorg server 1.16.4, Mesa 10.4.5, Glibc 2.20, GCC 4.9.2, and Python 3.4.2. Deviating from the default Breeze theme, KaOS relies on the Midna theme in light and dark variants. If needed, you can change back to Breeze in the system settings (Figure 1). KaOS is only available for the 64-bit platform; although it borrows components from Arch, such as the Pacman package manager, it is otherwise a new development.

Figure 1: In addition to the default Midna theme, KaOS also offers Breeze and Oxygen.

Plasma 5

Plasma 5, the successor to KDE Plasma Workspaces 4, which has been under development since 2011, has now reached 5.2.1; this is the fifth generation desktop by the KDE project. Although the new version retains the control concept from KDE SC 4, the look and underpinnings have changed drastically. Qt5 now draws the desktop's graphical elements, freshening up the desktop's look with the new Breeze theme. Restrained pastel hues and an unobtrusive flat widget design are now the order of the day.

To harness the capabilities of state-of-the-art graphics chips in a better way, the KWin window manager relies on Qt5's Qt Quick 2 for OpenGL-based hardware acceleration. The technology also offers superior support for HiDPI displays [2] and produces a sharp image even when scaling the desktop content at very high resolutions. Plasma 5 is already ready for the next-generation Wayland display manager and for Wayland's Libinput library.

Systemd features appear at various points in KaOS – in particular, with login and session management (Figure 2). Logind ensures that Plasma knows about the type and number of active sessions at all times. The logind domain also includes handling device input. KWin uses keyboard and mouse input in a way that makes it impossible for other applications to manipulate these events. Setting and monitoring dates and times and changing timezones will be the responsibility of systemd-timedated in the future, thus deprecating the KDE module previously used for this purpose.

Figure 2: Systemd plays a central role in the Live distribution. KaOS delivers the matching configuration interface.

All told, systemd means less code and improved maintainability. The converged workspace shell is another improvement; it automatically switches between individual workplace environments for laptops, tablets, or desktops (e.g., when you connect a mouse or keyboard to a tablet). Its fourth-generation predecessor still used shells that needed to be installed separately.

The desktop controls are pretty much where you would expect them to be in Plasma 5. The bar that sits at the bottom of the screen by default offers the typical layout, although the designers have changed the icons grouped there to match the overall look. The application menu at bottom left can be toggled between two variants by right-clicking in the familiar way (Figure 3).

Figure 3: As in KDE4, the new version also offers the alternative kicker menu.

The "Cashew" control at the bottom right, which is mirrored at the top left on the screen, offers options for the desktop and the panel. The newly designed object is a stylized arrow that now points in the direction of the underlying options.

The Plasma 5 release cycle aims for a major version with new features every three months. Only monthly bugfixes occur between major releases.

Control Center

As the successor to the KDE Platform 4, KDE Frameworks 5 (KF5) has a far leaner look than its predecessor. This is where the most far-reaching changes in the new generation took place. The libraries form the major part of the frameworks (previously, Kdelibs). They are used to build Plasma and the applications; KDE SC 4 still had more than 60 libraries and frameworks in a large, impracticable package.

In the past three years, the developers have unraveled this bundle and created a modular offering. Some functions were adopted directly into Qt 5.2; the remainder comprises individual, often cross-platform packages that have virtually no dependencies and are thus available for all Qt programs. For example, the latest 0.9 version of the Qt-based LXQt desktop uses several of these libraries at the same time. The Hawaii desktop environment from the Maui project also makes use of this option. Other projects can even use the KWin window manager without Kdelibs.

These slimming measures have also meant that the fifth-generation KDE desktop is easier on resources than its predecessor. KDE Frameworks 5 is currently at version 5.7 and is updated on a monthly basis.