Hello Philipp,
Philipp Roßberger wrote:
> Hi,
> we want to build a distributed application with OpenSG that behaves like
> Croquet (http://www.opencroquet.org) regarding scene replication.
hm, I don't know Croquet, but from quickly reading a few paragraphs on
their site the they seem to distribute a scene to a large number of
users and then coordinate changes from each user. Is this, the ability
to allow everyone on a network changing the scene, what you are after ?
> We plan to have at least three computers in our setup, which share one
> scenegraph. Now it should be possible to manipulate the global shared
> scenegraph from every machine and replicate the changes to all other
> systems. Is it possible to do this with OpenSG?
The usual scenario for OpenSG clusters is one client that creates and
modifies the scene and a number of servers that receive the changes and
render images (client/server are used in the X11 sense here). However,
this is not the only possible setup, since you can transmit changes
between arbitrary machines, but you have to coordinate them yourself
(the single client, multiple server setup is easy to coordinate because
you only have to merge changes from the client into each severs scene,
so that might explain its popularity ;) )
> I scanned the mail archives and found several threads about scene
> replication. So far my understanding is, that it is possible to propagate
> scene graph manipulations via sendSync(). Is this the right direction?
Yes, but unlike Croquet there is no "universal time" that applies
changes in the correct chronological order. You will have to take care
of when to transmit changes to other machines and when and in what order
to apply them to the local copy of the scene.
> Finally I wonder how an architecture for the described setup should look
> like. One node, that receives all chances and notifys all other nodes? Or
> should the other nodes be directly notified by the node, that changed the
> scene graph?
Having a master node that collects all changes and then distributes an
up to date scene to the other nodes is probably much easier to implement
and seems to fit better with OpenSGs model. However, from what I've read
on the Croquet site their goal seems to avoid that master node and have
the slave nodes coordinate amongst themselves. This approach seems a lot
more difficult and you probably would have to implement similar
mechanisms as Croquet to coordinate changes between nodes. Basically
OpenSG provides the means to transmit changes to a scene over the
network, coordination of changes from multiple sources is up to the user.
Maybe one of the users who run applications on a cluster can give you
some more information.
Cheers,
Carsten
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