Two years ago I started to re-implement the Window Switching capabilities of the KDE Plasma workspaces (also known as Alt+Tab or TabBox). The old implementation was based on a QWidget with custom painting which of course had some drawbacks. The new TabBox evolved into a framework around Qt’s Model-View concept to design your own window switcher.

Before I started to work on that area I did evaluate the existing Window Switching capabilities of the various desktop shells (both free software and proprietary solutions) and I noticed that all of them have drawbacks. None is the solution where I would say: that’s the perfect switcher.

The main issue is that depending on the user’s habits different work flows are required. A switcher optimized for users with few open windows fails for users with many open windows and vice versa. Especially thumbnails become useless for many open windows.

So I realized that we need something flexible enough to give users the possibility to use different layouts or to even define their own layout. This ended in a framework for window switching. The layout is described with an XML file and rendered through custom painting code in a Qt delegate.

When I implemented this framework I wanted to add a GUI to easily configure own layout. Unfortunately I never got around to implement this UI and I think there has never been any other layout except the default shipped once. It is a rather unknown feature and I’m quite unhappy that this great functionality never got implemented.

In the mean time the trolls did a great job to make UI development easier: QML. This makes it possible to do what I wanted to have for window switching: easy to design and exchangeable layouts. So this weekend I implemented the default (informative) layout in QML and plan to completely replace the existing View and Delegate code in 4.8. And this gives us the possibility to let users write their own layouts and to share and exchange them.

But this is only the beginning of usage of QML in KWin. I have many more ideas by making window thumbnails available to QML UIs in a limited way. This will allow us to even integrate the BoxSwitch effect into the normal window switching framework and replace the Window Strip in Plasma Active.

So great UI times ahead in KWin.