Today I cannot make such a nice announcement as Aaron yesterday, but I can at least try announce something I personally consider as awesome.

This weekend I tried to make it possible to write KWin effects in JavaScript. After about two hours of work the effect loader was adjusted to load a Qt script instead of the library written in C++. This is a quite important step for the future of effects in KWin. It finally makes it possible to share effects via Get Hot New Stuff, so that our users can download new effects directly from the control module.

For packaging effects we use the well established Plasma Package structure, so that our script developers only need to know this one common way. The API itself will share as much as possible with the KWin scripting API – of course with adjustments for effects. For animating the API is based on the AnimationEffect introduced in 4.8.

From a performance point of view using JavaScript does not change anything. Our effect system has two phases: one to react on changes in the window manager (e.g. a window got activated) and one to perform the rendering. The scripting API only interacts with the window manager, so all the rendering is still good old C++ code – a similar approach to QML.

Now I guess you want to know what you can do with it. So here I present for example a Fade like effect written in JavaScript (for comparison: C++ version is > 200 SLOC):

var duration = 250; effects.windowAdded.connect(function(w) { effect.animate(w, Effect.Opacity, duration, 1.0); }); effects.windowClosed.connect(function(w) { effect.animate(w, Effect.Opacity, duration, 0.0, 1.0); });

For us KWin core developers the scripted effects will be an important step as well. For quite some time we have been unhappy with the fact that there are too many effects which become difficult to maintain – especially if we have to adjust the API. With effects written in JavaScript this becomes much simpler. As we do not have to keep the ABI (API compatibility is enough) stable we can move effects written in JavaScript out of the source tree and make them available for download.

At the moment the JavaScript API is just at the beginning. But I expect it to evolve over the course of the current release cycle. For me the scripts are rather important as it also provides us an easy way to have device specific adjustments.

As I wrote currently the scripts do not operate during the rendering. Because of that we don’t have bindings for WebGL. This would at the moment not make any sense. Nevertheless it might be that we allow to upload custom shaders, but I won’t pursue such a task in the 4.9 cycle.