Version: (using KDE KDE 3.4.1) Installed from: Compiled From Sources Compiler: gcc-3.4.3 OS: Linux OK, Guys, let me say this first: I did everything I could to verify that this was not a configuration problem, and that indeed this only happens in KDE applications. Last week I upgraded my nvidia geforce 3 to an nvidia geforce fx6600gt. Since I did this Antialiased font rendering in almost all KDE applications has slowed down tremendously. I know, it immediately smells like hardware or driver problems. And I've been troubleshooting this endlessly. Then I noticed something strange. Firefox, which also is using XFT font rendering did not slow down! The same is true for all other GTK-based applications. The slowdown is noticed when scrolling a windows with AA fonts, or when dragging another window across one with AA fonts. The redraw is quite slow. I notice this in konqueror more than other apps. I can drag the same window in front of Firefox, and it will be redrawn almost instantly (so fast I can barely tell it happened. This used to be the case with KDE as well). What's also interesting is that a Pure QT Application not part of KDE, such as the kernel configuration and QT designer do not suffer from the slowdown. KDE Apps that suffer badly: konqueror kate konsole KDE Apps that do not suffer: kedit Things I have tried to debug this: Tried multiple version of nvidia drivers. Recompiled QT and KDE from scratch, making sure xft and xrender support is turned on. Upgraded fontconfig. Various reconfigurations of xorg.conf. (tried turning off/on render acceleration). Tried MB bios upgrade. Added: fprintf(stderr, "########## qt_use_xrender=%d ##########\n",qt_use_xrender); and fprintf(stderr, "########## qt_has_xft=%d ##########\n",qt_has_xft); to qapplication_x11.cpp on QT to verify that it did indeed initialize both xrender and xft. I'm sort of lost at this point as to what to do. If there is anything I can do to provide more useful info for this report please let me know. I am not afraid of throwing in a few test/debug patches and recompiling part of KDE if needed.
Apparantly I'm not the only one experiencing this with KDE and this card. See this thread at nvnews forums: http://www.nvnews.net/vbulletin/showthread.php?t=44317
This turned out to be a problem with X11 and this card. xorg-6.9-rc2 fixes it.
It turns out this is not an Xorg bug. Another problem in X ws masking it by switching subpixel color rendering to grey rendering. It appears subpixel rendering is broken on this nvidia card for QT/KDE only. Gtk apps work nice and fast.
you're using the nvidia driver, right? then complain to nvidia ;(
Yeah, this seems to be a KDE bug. Nvidia thinks so too, maybe both of you guys should look into it? :P I have this same problem, plain ol' AA fonts are slow in KDE, while GTK apps are fine, renderaccell is enabled in my driver. I'm on xorg 6.8.2, kde 3.5.1.
Upgraded to xorg 7.0, still have a problem...QT apps only.
I'm also on kde 3.5.1.
We (KDE) think it's a lack of optimisation in the NVidia driver for Xft antialiasing and subpixel hinting as used by Qt. It's not our bug though - the same cases are very quick under i915 and ATI.
Ok. Well, an update. I just stuck my old Geforce 4MX 440 back in my system. It was _MUCH_ faster, still, GTK apps were slightly faster. I think maybe KDE or QT is doing something else which might slow down font rendering compared to GTK apps, however, the bulk of the problem must lie in the nvidia driver.
Also, like the original post said, it doesn't affect some QT programs, like kedit is fine, kwrite is NOT.
Something else to add to this. I compiled qt-4.1 (from kde svn qt-copy) and svn versons of kdelibs and kdebase that uses qt-4.1 It appears that the newer stuff doesn't suffer from the problem. It appears the qtfontengine_x11.cpp has had massive changes so maybe the new implementation fixes this. Too bad kde4 is still a long way off.