Kate used to scroll just normally but after upgrade to version 4:4.8.1-0ubuntu1~oneiric1~ppa1 (and same KDE version), scrolling in kate became slow:

- if I rotate the wheel on mouse slowly, it scrolls normally
- if I rotate wheel on mouse quickly, it doesn't scroll as fast as it should scroll (and as it scrolls in libreoffice, firefox, etc).

It seems it's skipping scrolls ("speed 5" rotation of wheel actually scrolls slower than "speed 2" rotation)...

..any ideas?

Can you reproduce this in other KDE applications, in particular KWrite with text files, and Konqueror with web pages?

i would like to confirm this kind of behaviour in kwrite. scrolling feels slow, sluggish and bumpy in textual files of any bytesize and with lines of any length. it worsens if certain lines or parts of lines are highlighted (for instance, while searching for strings). also, the same goes for what's happening right now while i'm trying to scroll this text input box in konqueror. here's some info on my system:

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infobash -v3
Host/Kernel/OS  "tehbox" running Linux 3.4-0.slh.4-aptosid-686 i686 [ aptosid 2011-01 Γῆρας - kde-lite - (201102051540) ]
CPU Info        2x Intel Pentium 4 1024 KB cache flags( sse3 ht lm ) clocked at [ 2813.642 MHz ]
Videocard       Advanced Micro Devices [AMD] nee ATI RV535 [Radeon X1650 Series]  X.Org 1.12.1.902  [ 1920x1080@60.0hz ]
Memory 745.1/2026.2MB | GLX Renderer Gallium 0.4 on ATI RV530 | GLX Version Yes | Client Shell | Infobash v3.45


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apt-cache policy kdebase-bin
kdebase-bin:
  Installed: 4:4.8.3-0r1
  Candidate: 4:4.8.3-0r1


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apt-cache policy kwrite
kwrite:
  Installed: 4:4.8.3-0r1
  Candidate: 4:4.8.3-0r1


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apt-cache policy konqueror
konqueror:
  Installed: 4:4.8.3-0r1
  Candidate: 4:4.8.3-0r1


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apt-cache policy libqtcore4
libqtcore4:
  Installed: 4:4.8.1-1
  Candidate: 4:4.8.1-1


if there's any additional info required in order to improve this issue, let me know.

best regards!

edit: i might've pinpointed the culprit. after doing some research on the web, changing style in application appearance from oxygen to, for instance, cleanlooks improves scrolling significantly. it's rather bizarre, but i hope it helps.

edit2: having picked raster as qt graphics system instead of xrender, i got the scrolling working they way it should work. which is weird, since raster should be slower than xrender...

This is likely caused by XRender's unusual behaviour - some drivers have things implemented well, while others have no implementation at all. As a result it is slow if it is not implemented - or if the rate of change is high requiring a large amount of traffic between the Qt application and the X server.