Convergence, or the ability the serve different form factors from the same code base, is an often discussed concept. Convergence is at the heart of Plasma‘s design philosophy, but what does this actually mean to how apps are developed? What’s in it for the user? Let’s have a look!



First, let’s have a look at different angles of “Convergence”. It can actually mean different things, and there is overlap between these. Depending on who you ask, convergence could mean any of the following:

Being able to plug a monitor, keyboard and mouse into smartphone and use it as a full-fledged desktop replacement

Develop an application that works on a phone as well as on a desktop

Create different device user interfaces from the same code base

Convergence, in the broadest sense, has been one of the design goals of Plasma when we started creating it. When we work on Plasma, we ultimately expect components to run on a wide variety of target devices, we refer to that concept as the device spectrum.



Alex, one of Plasma’s designers has created a visual concept for a convergent user interface, that gives an impression how a fully convergent Plasma could look like to the user:

Input Methods and Screen Characteristics

Technically, there are a few aspects of convergence, the most important being: input methods, for example mouse, keyboard, touchscreens or combinations of those, and screen size (both physical dimensions, portrait vs. landscape layout and pixel density).

Touchscreen support is one aspect when it comes to run KDE software on a mobile device or within Plasma Mobile. Touchscreens are not specific to phones any more however, so making an app, or a Plasma component ready for touchscreen usage also benefits people who run Plasma on their convertible laptops, for example. Another big factor is that the app needs to work well on the screen of a smartphone, this means support for high dpi screens as well as a layout that presents the necessary controls in a way that is functional, attractive and user-friendly. With the Kirigami toolkit, which builds on top of QtQuick, we develop apps that work well on both target devices. From a more general point of view, KDE has always developed apps in a cross- platform way, so portability to other platforms is very much at the heart of our codebase.

The Kirigami toolkit, which offers a set of high-level application flow-controls for QtQuick applications achieves exactly that: it allows to built responsive apps that adapt to screen characteristics and input method.

(As an aside, there’s the case for Kirigami also supporting Android. Developing an app specifically for usage in Plasma may be easier, but it is also limiting its reach. Imagine an app running fine on your laptop, but also on your smartphone, be it Android or drive by Plasma Mobile (in the future). That would totally rock, and it would mean a target audience in the billions, not millions. Conversely, providing the technology to create such apps decreases the relative investment compared to the target audience, making technologies such as QtQuick and Kirigami an excellent choice for developers that want to maximize their target audience.)

Plasma Mobile vs. Plasma Desktop

Plasma Mobile is being developed in tandem with the popular Plasma desktop, in fact it shares more then 90% of the code with it. This means that work done on either of the two, mobile and desktop often benefits the other, and that there’s a large degree of compatibility between the two. The result is a system that feels the same across different devices, but makes use of the special capabilities of a given device, and supports different ways of using the software. On the development side, this means huge gains in terms of productivity and quality: A wider set of usage scenarios and having the code running on more machines means that it gets more real-world testing and bugs get shaken out quicker.

Who cares, anyway?

Whether or not convergence is something that users want, I think so. It takes a learning curve for users, and I think advancements in technology to bring this to the market, you need rather powerful hardware, the right connectors, and the right hardware components, so it’s not an easy end-goal. The path to convergence already bears huge benefits, as it means more efficient development, more consistency across different form factors and higher quality code.

Whether or not users care is only relevant to a certain point. Arguably, the biggest benefit of convergence lies in the efficiency of the development process, especially when multiple devices are involved. It doesn’t actually matter all that much if users are going to plug their mouse and keyboard into a phone and use it as a desktop device. Already today, users expect touchscreen to just work, even on laptops, users already expect the convertible being usable when the keyboard is flipped away or unplugged, users already expect to plug a 4K into their 1024×768 resolution laptop and the UI neither becoming unreadable or comically large.

In short: There really is no way around a large degree of convergence in Plasma (and similar products).