> On Thursday 19 September 2013 12:35:17 Aleksey Midenkov wrote: >> > Qt4 decided that they wanted to be a compositor instead of >> > passing compositing off to the native display server, and most of the >> > performance problems and drawing limitations stem from this decision. >> >> Hmm, interesting news. Ok, that's a good reason to stay with Qt3. I >> don't like how Qt4 performs either. > It's not interesting news, it's just wrong. Qt's internal rendering > doesn't > depend on whether compositing is used or not. Even more a compositor would > not > even be able to make use of any optimizations done inside Qt for the > composited case, because there is no way for the compositor to know that > the > app "supports" it. Compositing on X11 happens behind the scenes of the > window. > The window doesn't and doesn't need to know that it gets composited. > > Cheers > Martin > > Maintainer of the X11 Compositor of the KDE Plasma Workspaces My apologies; I was not referring to compositing in the window management sense, I was referring to the new painting system code in Qt4 (Arthur: http://www.trinitydesktop.org/docs/qt4/qt4-arthur.html), and even more specifically to things like the backing store introduced in Qt 4.1 (http://doc.qt.digia.com/qq/qq16-background.html). While I don't have a link to it handy, newer versions of Qt essentially are just blasting pre-rendered pixmaps to the X server on every change (graphics system raster). In fact, Qt is working hard on removing native bindings and replacing them with their software-only renderer (http://blog.qt.digia.com/blog/2009/12/18/qt-graphics-and-performance-the-raster-engine/) for performance reasons. I have to ask: If the XRender system worked so well in Qt3, even over the network, why is the XRender system working so badly in Qt4 that Nokia now needs to fall back on a software rasterizer? What changed? Even over a fast RDP connection (yes, RDP, not X11 native, though X11 native shows the same effect) I can tell the difference between Qt3 and Qt4 apps just from their redraw speed alone. Essentially, *as far as I can tell*, if your remote desktop is not blasting entire screens over the network on each update (e.g. some old versions of VNC), you will see a definite performance difference between Qt3 and Qt4 apps. My best *guess* is that the graphics server does not know what changed when a Qt4 app updates its visible contents, therefore it sends the entire contents of the window over the remote desktop connection, even if 99% of the pixels are the same. I probably got some of the Qt4 stuff above wrong as usual, but I don't really have the time or desire to keep up with the latest Qt4 information as I don't use Qt4 very often. :-) All I know is that there *is* a performance drop on many systems (unquantified, though this seems most severe on non-VNC remote desktops) that so far has eluded the teams at Nokia, the various KDE SC developers, the TDE developers, and various application developers such as Xilinx. Tim