NOTE2: This HowTo assumes you have basic Linux Terminal skills.
This week I found a way to fix QT/Xorg related video problems, resulting in a much more useful and much snappier KDE desktop. Multitasking is now faster on my machine and I am even amazed how light KDE can feel when this method is applied. This is mainly because Xorg is now consuming a much smaller percentage of my CPU. I thought it might be useful for others to create a tutorial on how to apply the Raster Engine Workaround.
Last week I have installed Debian Testing with KDE 4.6.5 on my desktop computer. I found Xorg to often use 25% CPU (1 full core of my quadcore 3200ghz CPU), causing a lot of sluggishness and repeated short system lock ups, being unable to interact with the system for about 5 seconds each time, making multitasking near to impossible. Even with desktop effects turned off. That's when I posted the following thread; http://forums.debian.net/viewtopic.php?f=6&t=73633. Vbrummond directed me to the Raster Engine Workaround on the Arch Linux Wiki; https://wiki.archlinux.org/index.php/KD ... workaround
From the Arch Linux Wiki;
So, if you have a quite powerful CPU, this method might also work for your machine. If you doubt about your CPU being powerful enough to use Raster rendering, it is worth the try and it will be easy to switch back to XRender. So, how do we go about configuring QT to use Raster rendering?The raster paint engine enables the CPU to do the majority of the painting, as opposed to the GPU. You may get better performance, depending on your system. This is basically a work-around for the terrible Linux driver stack, since the CPU should obviously not be doing graphical computations since it is designed for fewer threads of greater complexity, as opposed to the GPU which is many threads but lesser computational strength. So, only use Raster engine if you are having problems or your GPU is much slower than you CPU, otherwise is better to use XRender.
Installing KCM Qt Graphics System
We will install a package that enables us to configure the QT rendering method from the KDE System Settings menu. It enables us to configure QT to use system wide Raster rendering (or to reset the QT rendering to XRender afterwards). You can download it here from KDE-apps.org; http://kde-apps.org/content/show.php?co ... orumpage=0.
Before we install the package we have to install all dependencies. We will need cmake to compile the downloaded package. And for the package to work we'll need to install KDE/QT development libraries. Otherwise the package is going to complain about QT 4.7 not being available while compiling.
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apt-get install cmake kdelibs5-dev kdevelop
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cmake .. -DCMAKE_INSTALL_PREFIX=/usr
make
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make install
That's it! Please leave your reply if it works for you, but also if you encounter problems.
EDIT's: Typo's, grammar and additions.