Does metacity compositor use acceleration?

[thibaut bethune]

chombee said "Does the compositor that you can enable in metacity in
hardy use 3D acceleration?"

( to enable compositor in metacity, run in a terminal :
gconftool-2 -s --type bool /apps/metacity/general/compositing_manager true )

Yes it is accelerated
Unlike Compiz Fusion that uses OpenGL acceleration, Metacity makes use
of XRender
http://en.wikipedia.org/wiki/XRender

More information here : http://blogs.gnome.org/metacity/category/compositing/
and specially here :
http://blogs.gnome.org/metacity/2007/11/16/adventures-in-compositation-land/

"Compositing at its simplest is a program telling the Xserver not to
draw the windows anymore because the program wants to do it instead.
So now X doesn't draw the window to the screen, but to a backing store
pixmap which the compositor program then draws on the screen. It makes
sense for this compositing program to be the window manager, because
it already knows all about screens and displays and what window goes
where when. . . etc, but it does not need to be (e.g. xcompmgr).
The trick is that when the compositor comes to draw the window's
backing pixmap to the screen it can really do whatever it wants with
it. It can paint it backwards, or with a red tint, or just simply
paint it normally to the screen. Compositors like Compiz draw the
window onto GL textures and then are able to do 3D transforms on them.
The compositor in Metacity just draws it to the screen using the
XRender extension."

"No, you don't need 3D acceleration for this compositor, so cards with
sucky GL will be able to use it. You will however need a good and fast
XRender implementation. I'm using the both the binary NVidia driver
and the opensource Intel driver. The NVidia driver works well, the
Intel one (as shipped by Gutsy) works ok, but CPU usage can get high.
I've been told the Fiesty Intel driver is quite slow"

Note that i have an ATI Radeon 8500 LE card (R200) and i've modified
my xorg.conf to boost performance through EXA (
http://en.wikipedia.org/wiki/EXA ) by adding two lines into it.
Here is the interesting part of my xorg.conf :
"Section "Device"
Identifier "Configured Video Device"
Option "AccelMethod" "EXA"
Option "MigrationHeuristic" "greedy"
EndSection

See also :
https://bugs.launchpad.net/xorg-server/+bug/88696
https://bugs.launchpad.net/ubuntu/+source/firefox-3.0/+bug/182038
http://xorg.freedesktop.org/wiki/ExaStatus
http://man.root.cz/4/radeon/