Originally Posted by relix
But if this is using the nvidia xinerama extension, how come it's not possible to get the same results (Compiz-able triple head) using 2 videocards instead of a DH2G? Is it just because Xinerama is buggy? Or is "Xinerama" not the same as "The nVidia Xinerama extension"?
Correct! From what i understand, the nvidia Xinerama extensions just
tells applications the desired screen attributes, but internally, the
X-Server only needs to handle a single card with a single frame buffer.
Similiar "fakes" do exist for libXinerama and the X-server but requires
When combining two cards with xinerama, then the X-Server needs to
split the graphical operations amongst these two cards. BTW.: When
"true" xinerama is enabled, then the nvidia xinerama extension is disabled
and the XineramaTwinViewOverride options doesn't work any more
(this is why you have to patch libXinerama or the X-Server in order to
get the correct screen report).
There are now two problems with Compiz: first, it makes use of Xrandr
(edit: which will be disabled when "true" xinerama is enabled) in
order to detect refresh frequencies for smoothing visual effects. I once
created a patch that makes beryl not using Xrandr, but then i run into the
second issue: there is a "well known" incompatibility problem between
xinerama and the composite extension - however, nobody could every
specify what exactly the problem is and how it would be possible to
overcome it :-(
For details, please check
(post #9 & #13)