Re: [vwrap] Consensus? What exactly should be in the protocol

[David W Levine <[e-mail]>]

So, of course we're building in the web space. I hope nobody is denying
that. In fact if you look at everything described in VWRAP is starts with
an assumption that most services are delivered as REST or REST like
services. I think its safe to say that the people who have been discussing
this for over two years are aware of Roy's work, and have thought about how
REST applies to virtual worlds. REST represents a lot of thinking about how
the web delivers content, and in particular why not to turn the web into a
distributed object model, or a shared state model, but rather to leverage
the observed successful patterns of the web in managing distributed
programming problems.

But..  (There is always a but) The very core thing that a virtual world
does doesn't fit terribly well into the mainstream web model.  The heart of
a virtual world is delivering (and Morgaine's phrase serves very well here)
a visual mashup of things to users 30-60 times a second, updating
continually to reflect the input of  the physical simulation, any user
inputs, and any scripted inputs. Our core problem is taking in the inputs,
deriving the new state and sharing it out to the users. This isn't really
what the web has historically done. The fact that it isn't, that there are
some really interesting distributed system challenges at the very heart of
this, is part of its technical appeal to me.

Life is made harder by the fact that the virtual space is being constantly
asked to accept new things to deal with. Every time an avatar arrives it
brings a set of stuff
which has to be melded into the scenegraph.  Again, we all know this.
Rezing an avatar means adding a bunch of new content to the virtual space,
and it means pushing
it back out to all the observers.

In the traditional web you go to a URL, you do a get, and you get handed a
huge slab of stuff to render.(some of which may require fetches, plugins,
etc.)  In the more dynamic 2.0 style stuff, the stuff you get may include
dynamic elements which fetch and update more stuff. In the virtual worlds
space, we bring to to a fever pitch. we take inputs from all the present
users, from a simulation, including the scripted changes within the
simulation. We then turn around and want to show this to the user.

How do we present this to the user. Well, we currently use Linden's
UDP/http/longpoll tangle. Fine. But. how could we do it?

We could create a video stream and stream it. (WHich isn't very web page
like at all, but has some nice properties)
We could do something like OnLive where we would create a very tailored
stream and deliver it to a client with very specialized coupled inputs (And
life with a lot of
constraints and again isn't very web page like)
We could send a stateless update every frame for the client to render
(Well, with ulimited bandwidth and processor power)
Or.. we could do what we currently do, just cleaner. which, roughly
speaking is send down initial state and then send down a series of updates
to that state. Woah, not
exactly a traditional web page. Worse still.. where do we post the inputs
from the client to the world?

At the same time, we also get to ask "How do we get all the "stuff" into
the region. In Linden's world, the answer is easy. They use a proprietary
protocol and fetch it from
their creaking central servers. In OpenSim, a similar answer obtains. And
for added pain which we have all shared, the current set of clients push
all the stuff related to
the user via the region.

VWRAP attempts to describe nothing more than a set of REST web services
which represent the region and the services. It attempts to leverage what's
been learned from REST, and Linden's system, and in fact OpenSim, to
describe a simple, extensible set of services which can describe: Regions,
Auth services, how to rez and unrez avatars, how to (when we get some
writing down) fetch and manipulate assets, inventory lists and so on.

What you end up with is built deeply on web principals, but not a web page,
but mostly because a virtual world is not, at its heart a web page,but a
set of services collaborating to
share state in a pretty unusual way.

- David
~Zha