By Martin Gräßlin - 18 June 2013 (Martin’s Blog From the land of wobbly windows)
What we did in KWin 4.11
With the release of the 4.11 Beta 1 behind us it’s a good moment to look back on this last half year on development. KWin 4.11 is a very important release for us. As you might have heard at the last Plasma sprint we decided to make 4.11 the last release of the KDE workspaces based on Qt 4. Fear not: the KDE Software Compilation with all it’s great application will see a 4.12 release – at least I have not heard anything else, just the workspaces need some time to do the Qt 5 transition. In addition we want to provide extended bug fix releases for the 4.11 release of the workspaces. So 4.11 is a very important release – being the bridge towards Qt 5.This is clearly what dominated the development of this release cycle. While porting to Qt 5 is easy in 99 % of the cases, KWin hits the 1 remaining per cent. There are many non-portable X11 specific features in Qt 4 and sometimes I think we used them all and all of them got removed in Qt 5. That’s not a bad thing – in fact I think it’s a good thing. I don’t want to go into detail about the problems we hit and why we used these Qt features in the first place – if you are interested come to my Akademy talk.
In many cases the changes in Qt required to rethink the problem. A good example is that a QPixmap no longer references an XPixmap which we heavily used during rendering the window decorations. This was causing us quite some performance problems with the
combination of Qt graphics system raster and the XRender compositor. At the moment I’m running this combination without any noticeable performance difference thanks to the restructuring forced by preparing for Qt 5. Also in the OpenGL case the decoration rendering got quite improved thanks to Fredrik forcing me to improve the proposed changes and also doing some further changes.
Speaking on performance improvements: Fredrik reworked our OpenGL 2 compositor code base and also
introduced a new OpenGL 3.1 code path. By default we still use OpenGL 2 with the fallback to OpenGL 1, but one can easily switch. If the
hardware doesn’t support OpenGL 3.1 it automatically falls back to OpenGL 2 or OpenGL 1. When running kwin_gles we default to OpenGL ES 3.0 if present otherwise OpenGL ES 2.0 is used.
But that’s not the only change done to the OpenGL compositor. Thomas and Ralf worked on improving our v-sync behavior. There are now multiple strategies one can choose from – this should help to serve all use cases and setups in a better way. Buffer age support has not made it for 4.11 yet, but I’m quite confident that this will end up in the next release.
One of the tasks we continued from 4.10 is the porting to XCB. This also forced us to rethink some of our code. One of the areas which got rewritten because of this is the screen edge handling. It’s now finally multi-screen aware, but still only the four real corners can be configured, corners between screens don’t make much sense. And here with the screen edges we have one of the few user visible changes in KWin: a highlight when approaching the edge. So this hidden feature is finally no longer hidden.
Another small visual change is concerning the outline when using quick tiling/maximizing on screen edges. The outline should now better indicate what area will be covered by the window. Also based on common feedback the moved window is put above the outline. This used to cause problems with dark Plasma themes causing.
The last changes I want to mention are some
effects rewritten in JavaScript. This is mostly to improve the maintainability of the code. The JavaScript effect API is optimized for animating windows based on state changes. If I remember correctly the
rewritten effects are Dialog Parent, Login, ScaleIn and Translucency. Thanks to Kai Uwe for helping us with these tasks. There are still a lot of effects which would benefit from this work. So get your editor ready ;-)
Overall the effects have seen some changes.
BoxSwitch effect got finally the kick as the functionality is now completely available in the QML
Window Switching functionality. Explosion got the kick as it has been unmaintained and broken for a long time. The Outline is no longer implemented as an effect, but moved back into KWin core.
The
add/remove desktop button in Desktop Grid and the close window button in
Present Windows got reworked with QML and Plasma components – another nice improvement thanks to Qt 5. Present Windows has also an unpopular change: the mouse action for closing a window got removed. But also we have the code ready to rewrite Present Windows and Desktop Grid with QML (a task for next version).
The Maximize window effect got a nice improvement in the OpenGL compositor: it cross fades with the previous window texture which removes the up/down scaling which was not looking that nice. Thanks to Aurelien for writing software exposing bugs in KWin which require reworks allowing to implement this feature.
I’m quite sure that I have forgotten to mention many really important changes which we did over the last half year. It’s a long time and after all we
changed 666 files with 32516 insertions and 29217 deletions (git diff –shortstat v4.10.0..master — kwin (master being 4a172a9d)) including the changes by scripty.
http://blog.martin-graesslin.com/blog/2013/06/what-we-did-in-kwin-4-11/
