Game Development Reference
In-Depth Information
looking for immersive visual feedback in their virtual worlds [32]. There is undoubtedly much more to come,
and for you, a designer of virtual environments, great challenges await.
1.3 HOW DO THEY WORK?
The best way to understand a virtual world is to visit one. There are hundreds of public virtual worlds online
that allow access free of charge or through a subscription. A list of the most popular virtual 3D worlds
includes Active Worlds, Minecraft, OpenSim-based worlds, Second Life, and The Sims Online.
Essentially, virtual worlds are persistent 3D spaces deined inside of a computer program running on a server.
When you log out of one, the place still remains, it is “persistent,” cycling through its daily settings and host-
ing other visitors to its location. Figure 1.2 shows the generic structure shared by most user content-generated
virtual worlds such as OpenSim and Second Life. As you can see, even this bare-bones description is fairly
complex. When you want to enter this world, you start with the viewer (or client) interface. This is a program
that you download and run on your computer. For the purposes of this topic, the Firestorm Viewer was selected
since it is the most popular one and provides a customized setup for use in OpenSim as well as Second Life.
Assuming that you have set up an avatar account previously with whatever virtual world you would like
to visit, let's look at the process of entering a virtual world.
After you have launched the viewer and logged in to your avatar account, your user name and password
are veriied by the login service, and if the account is valid, the avatar's last location or home location coor-
dinates ( x , y , z ) are found on the land map of the world. The login service coordinates with the viewer so
that the avatar can view the region it is entering and tells the simulator (sim) to expect an incoming avatar.
Once the avatar starts to appear, you can see the landscape on your screen and your avatar standing on it.
You are now in the simulator, and it is busy telling the grid service that you are there and that all the simula-
tors around your location should share their data with your avatar and viewer so you can look over at them.
There is lots going on in the simulator; it is the central backbone and a switchboard for information being sent
to and received from your avatar. The simulator is also running lots of calculations in its physics engine to
help objects and your avatar have realistic physics, like keeping your feet on the ground, providing solid walls
and open doorways, letting coconuts from the nearby palm tree fall with a soft thump and roll around. The
simulator is also keeping track of the objects in your inventory as well as the other assets in the region. This
includes information about who made the content you see, who currently owns it, and what kind of permis-
sions they have to modify it, sell it, or give it away. As you build stuff, especially large items like buildings
or mountains, the simulator talks to the map database in the grid service, and that updates the look of your
sim on the land map, which is shown in the viewer. The simulator also relays information to other servers and
services that keep track of who owns land, especially if it is divided into parcels. It relays information about
the lists of your friends and groups, what your social/privacy settings are, and other sorts of details regarding
your environment and afiliations.
In 2011, a group of fearless explorers called the Alchemy Sims Builders set off across the Metaverse in
search of more space and land they could call their own. They settled in on a server maintained by SimHost
(http://www.simhost.com) and established the Alchemy Sims Grid (ASG), a 16-region grid accessible via
the hypergrid (grid.alchemysims.com:8002:triton). Most of the content and pictures taken for this topic were
made on this grid, which runs OpenSim 0.7.5. In Figure 1.3, you can see what the “back end” of the system
looks like on a computer screen. As you can see there are 17 windows open all the time; 16 of them are
for the various regions on ASG, and 1 is for ROBUST, which coordinates the whole grid. Having a system
like this gives you the god-like power to make quick and dramatic changes to your terrains, create avatar
accounts and such. It also requires that you exercise responsible behavior and dedication to maintaining the
persistence of the grid. At least once a month, there are server updates that shut the server down, so you will
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