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Old 03-13-06, 11:56 PM   #13
gtx260/8200M G/DIY Linux
Join Date: Aug 2004
Location: Austin, TX USA
Posts: 137
Default Re: Slow AA text rendering in KDE

Originally Posted by netllama
There's no need to send anything to, as the same people who respond to linux-bugs respond here (including me).

I don't see anything in this thread to suggest that this is an nvidia driver bug. This sounds like a KDE bug, especially if its not present anywhere but in KDE/qt based applications. If I run a konsole and gnome-terminal side by side, with the same font, and dmesg in an infinite while loop, there is noticable and significant lag only in the konsole window. If there was a driver bug, I'd expect both windows to exhibit the same latency.

Has anyone submitted a bug to the KDE developers?



The reason I suspect a driver bug is this doesn't seem to affect other nvidia cards. Just the 6600 series as far as I've been able to determine. I can put my old geforce 3, 4, and fx5200, and they all work perfectly in the same machine on the same installation. I put my FX6600GT back in, and it is slow again.

This is only when using color subpixel font antialiasing. If I turn off subpixel and use grey antialiasing, it runs fast. As far as the KDE/QT software is concerned, it doesn't know what it is sending the fonts to, it just passes the rendering down to the X libraries, and X down to the driver.

One thing to note is that a change made in the prerelease xorg fixed it temporarily, but broke binary compatibility. Aaron p. from nvidia then submitted a patch to restore binary compatability, which slowed it back down again. Come to find out though, before Aaron's patch, KDE/QT was rendering in grey instead of true color sub-pixel, so it just "appeared" fixed at first glance. Maybe this will point in the direction of the problem.

There has to be something wrong between QT/X/Nvidia driver communication for this specific card.

If you want to duplicate it yourself, use an AGP (don't know if PCIE is affected) version of the 6600gt, and in the KDE control panel under fonts/antialias configuration, click "use sub-pixel hinting". Log out of KDE and log back in after changing this setting. Then bring up a konqueror window on "", and watch konqueror render it slowly, and then drag a konqueror window across the web browser. It will be REALLY slow redrawing it.

If you can't duplicate it, I can shoot a video of it on my monitor with/without the subpixel rendering so you can see it.

BTW, I did post a KDE bug, but never got any response. I'm sure they took one look and blamed it on X or driver.

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