Hi,
I upgrade KDE to 4.5.1 on Sabayon then kubuntu and I find out this pb on both OS.
Before upgrade I am running composing effect with opengl.
I use a transparent panel, desktop cube effect and some more effects.
After upgrade the transparent panel is an ugly grey with very very bad transparency. The overall is slow.
After checking this forum (link viewtopic.php?f=67&t=90494 or http://forum.kde.org/viewtopic.php?f=67&t=90494).
I decide to go for Xrender.
I had my transparency back but very slow.
I remove minimize window and a few more effects and now it is clean an very usable.
However, desktop cube is not able to start.
This are not big troubles but I am sad to have such regressions while upgrading.
Also I am not sure how I can improve that and the customization (xorg.conf ?) that I can try to have 100% of features on my KDE again.
I am running usually Sabayon linux last update on ASUS laptop with intel GPU (actually it is optimus nvidia/intel where nvidia is not usable on linux).
Did anybody have similar problems ? Any hint to fix ?

Try to disable Blur (in Desktop Effects) and see if it helps.

Blur is not working with xrender.
I moved back to opengl and disable blur and ....
Everything is working like a charm
Panel transparency, desktop cube etc ...
Thanks a lot.
Is it something due to 4.5.1 ?
It looks like that Xrender can't do some effects as opengl can do.
Does it means that xrender is not so performant ?
Any reason blur makes trouble with opengl ?
thanks again.

I'm not sure enough to answer those questions, so it's probably better to wait for someone else to give accurate answers. With that said, I don't think it's OpenGL that causes problem for Blur, but rather some graphic drivers. I use Blur on my netbook (Intel GMA 950) and it works fine, while my Nvidia card on my desktop computer doesn't support it at all.

On my openSUSE 11.3 system, running trunk ( also with an ASUS Optimus laptop as it turns out ) Blur performs fine... using OpenGL in "Texture From Pixmap" mode, with direct rendering enabled, and vsync disabled.

Some Intel driver versions report Blur being done in hardware, while instead it's done in software, causing extreme slowness when activated.