In 4.5 RC 1 we hit several driver bugs again. We fixed a bug which caused blur not to work, but that fix intoduced different problems with some drivers.
It is possible that effects get suspended directy on startup. In that case try disabling the blur effect! If this does not solve the issue disable direct rendering in advanced effects tab.
There are also some problems with taskbar thumbnails and present windows. The previews might be upside down, too bright or the effect might be too slow. The same problem does not appear in desktop grid! This is caused by driver bugs already fixed upstream. So please update your drivers. You can disable the filter which is used for this in the global effects level, but this will also disable animations in Plasma.
We have bugreports for all those issues. If you want to comment on them please note driver and version.
Indeed I hit such a problem, KWin crashed and restarted without any effects. It’s good that you blogged about it and that you explained.
I’ll look at the existing bug reports and add any relevant info if I can.
Can you point the bug reports numbers please as I searched for KWin and could not spot them at first sight. thanks in advance!
Will do when I am back home and have access to my bugzilla account
I opened a new bug report to collect all the duplicates for all the issues caused by the Lanczos filter: https://bugs.kde.org/show_bug.cgi?id=243181
and for the performance problem disabling compositing directly we have https://bugs.kde.org/show_bug.cgi?id=242113