Hi,

I'm coding an opensource cross-platform application (written in Qt), which leaves a trail of sprites after mouse cursor.It is implemented by creating a lot of transparent (Qt::WA_TranslucentBackground) top-level widgets, which are then moved/resized.It is supposed to be cross-platform, so I'd like to stay at this level of genericity.

Now, the sad fact is that either I'm doing something wrong, or KWin is not able to manage those widgets efficiently (it has other problems too, see below) :-( From all the desktop environments I've tried, it works worst, despite that Qt is native to KDE.

• Windows: runs flawlessly, full framerate with several tens of widgets
• MacOS X: runs Ok (as far as performance is concerned)
• metacity with enabled compositing (Gnome): jerky performance, halts for a second or two once more than 20 (rough estimate) widgets appear
• KWin: system becomes unresponsive starting with the first several widgets (FPS drops to levels that compositing is suspended). Additionaly, "Shadows" setting affects the widgets despite the fact that I set Qt::FramelessWindowHint and Qt::X11BypassWindowManagerHint among other flags...

I tested all that on a comparable hardware. KDE versions used: 4.2.x (under Gentoo Linux) and 4.3.0 (under FreeBSD), both using NVidia cards with vendor drivers. I'm curious what is going on - KDE's transparency effects for windows work with decent performance, am I doing something wrong?

There's little code and it is rather simple. Anyone who wants to try it him/herself can get it via

Code: Select all

svn co https://martostars.svn.sourceforge.net/svnroot/martostars/tags/whats_wrong
cd whats_wrong
qmake-qt4 && make


Best regards,
RCL

Here on my machine (Kubuntu Karmic Alpha (thus KDE 4.3), NVidia card with 185 series driver, *dis*abled desktop effects) it runs flawlessly despite the fact that the images have a black background (probably due to the disabled compositing).