Graphics Programs Reference
In-Depth Information
means a more detailed position tracking
(but more bandwidth is required!!)
When a user hits a WebTalk04 HTML page
in the Internet, the Shockwave player embedded
is loaded and the user of a WebTalk application
sees a browser window, which is split in two parts.
The upper half is a W3D movie showing the
3D representation of the world, in which the visitor
can move and interact with objects. In this portion
of the screen the user can also see other visitors
moving and performing actions. A human-shaped
figurine (avatar) represents every visitor. In the
lower half of the screen a chat window is provided
as a flash flat panel in which visitors can write
messages to other visitors and can read incoming
messages. Figure 6.
In order to build a general application, the
W3D portion does not embed 3D geometries but
the system builds the virtual scene in real time,
fetching the separate geometries and textures from
a repository; the geometries can be in any of the
most common formats currently available, be it
3DS, Plasma, Maya or Lightwave.
The collaboration logic, via the WebTalk
Interaction Engine (WtIE), detects every event
generated both in 2D or 3D interface and forwards
them, through the Real Time Message Protocol
(RTMP), to the Server. Likewise, every other event
generated in the same moment from other clients
connected to the same webpage, is distributed by
the Flash Communication Server to the Shockwave
plug-in on the client side, which passes them up
the stack into the W3D worlds.
Users can thus see each other's avatars (human-
shaped figurines which mark every user's posi-
tion) and can see objects moving and operating
in response to the manipulation of other users.
All the system architecture is built up around
the MVC (Model View Controller) design pat-
tern, in which the model represents the shared
world state, the view represents each client web
application and the controller is the programming
logic that builds up and regulates each end user
GUI as well as the shared state.
The architecture of WebTalk04 is shown in
Figure 7. Let us now describe all its components:
As seen, we can use a specific XML file in order
to set up different bandwidth speed on different
client machines. In this way we allow clients with
dissimilar connection speeds to access together and
simultaneously the same virtual world, ensuring
the world share state consistency.
System Architecture
The WebTalk04 project makes extensive use
of Macromedia technology, while keeping the
goals of web-accessibility and use of standard
components.
The choice of using Macromedia is strategic
because of the large spread of the Macromedia
Shockwave player, with over 200 million instal-
lations all over the world and at the same time
allowing the use of a solid, tested and free soft-
ware player without the need of implementing
another one.
The WebTalk04 system architecture is written
in different programming languages: Lingo (Direc-
tor coding) with all its extensions made available
in recent times as Netlingo and 3D Lingo, Action
Script 2 (Flash coding).
The architecture is deeply based over a client/
server paradigm and exploits an application server
hosting a Web Server for static and dynamic con-
tents and a Communication Server (Macromedia
Flashcomm) for sharing data in cooperative and
distributed applications.
While the server is appointed to listen to cli-
ent connections and distribute events between
the participants, maintaining a centralized state
repository, the client side is composed by a Shock-
wave plug-in which runs inside a regular internet
browser such as Netscape or Explorer.
The chances are that the average surfer already
has Netscape/Explorer, with Shockwave plug-in
installed on the system.
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