Chapter 32.   Networked Tour3D

NetTour3D is a very simple networked virtual environment (NVE) which allows sprites representing users (clients) on different machines to move about in a shared world. The world is the familiar checkboard, with scenery and obstacles (red poles).

NetTour3D is essentially a combination of two earlier examples: Tour3D from Chapter 18 which introduced the Sprite3D class, and networking code from the multi-threaded chat application in Chapter 30. It would be a good idea to (re-)read those chapters before starting on this one.

NetTour3D is a client/server application, with each client running a copy of the shared world, with messages passing between the clients via the server.

The image at the top of the page shows NetTour3D being run by two clients. Each window is a particular client's view of the shared world (a third person camera which follows the client's sprite). Each client can see their own sprite and, when in the right location, the sprites of the other visitors. A client can move his sprite around using the usual keyboard controls. All the visitors use the same robot image but their own names are floating above the robots. The world includes a castle and several obstacles.

Key features:

• Each user (client) is represented by two kinds of sprite: a sprite local to the user's machine, and a distributed sprite utilized on other machines. Both types have the same appearance (a robot) but are updated in different ways;
• The local and distributed sprites are subclasses of a common Sprite3D class, so are functionally very similar;
• Local sprites are updated directly, without the client first communicating with the server, so reducing latency;
• The world scenery is created by each client, not transmitted from the server, so conserving bandwidth. The scenery is specified in a 'tour' file and loaded by a PropManager object (first seen in Chapter 16), so different worlds can be easily specified.

A major weakness of this example is that the users cannot interact, apart from gliding about the checkboard. However, it wouldn't be difficult to graft a multi-user chat component onto NetTour3D. This would involve integrating more of the multi-threaded chat example of Chapter 30 into NetTour3D.

In this chapter, we begin by discussing the features of a fully fledged Networked Virtual Environment (NVE), and then consider the considerably simpler NetTour3D example.

Downloads

• The PDF file for the draft chapter (the old ch.21) (280 KB). Last updated: 30th July 2003.
  
• Zipped Source code (87 KB). It requires NCSA Portfolio as a separate download.
  Last updated: 20th April 2005. The book's code.
  
• NCSA Portfolio (zipped) (402 KB).
  

• Up to the Killer Game Programming in Java Index Page
• Back to Chapter 31. A Networked Two-Person Game
• On to Chapter 33. Using Web Service APIs

Dr. Andrew Davison
E-mail: ad@coe.psu.ac.th
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