Hi!
I have installed kde 4.9 and have a problem:
In kde 4.8 I could stretch fullscreen window on several monitors through System Setting -> Display and Monitor here was check box "Enable multiple monitor window fullscreen support", but I can't find this on new version of kde.
How can I enable this?

Have a look at the video wall script, for some background information read http://blog.martin-graesslin.com/blog/tag/scripting/

If your mediaplayer (or other application) is not supported yet, the code looks easy enough to be extented. On my system it is in "/usr/share/kde4/apps/kwin/scripts/videowall/contents/main.js".

I would be interested in knowing the usecase for this feature.

Just started Video on Demand via Silverlight on a Triple Head 3600 x 1920 setup (3x 24" 1920x1200 vertical).
Switched to Fullscreen.

Guess what!
Video has width 1200 and height 1200 * 9 / 16.
This gives a pretty small video (approx. 10% of all 3 monitors).

I tried to use xprop and wmctrl to maximize to 3600 x 1920.
Guess what!
It didn't change anything.

Sum it up: Where are the good old "stretch fullscreen window" settings from KDE 4.8 ??

I tried to use xprop and wmctrl to maximize to 3600 x 1920.
Guess what!
It didn't change anything.

Insanity: doing the same thing over and over again and expecting different results.
--- Einstein

If maximizing via the maximize button does not what you want, why do you think maximizing via the commandline should do??
You'd rather explicitly set the geometry - however...

Sum it up: Where are the good old "stretch fullscreen window" settings

Guess what!
Read the second post...