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3D computer graphics: Getting the hang of VRML

Learn about VRML and how you can use it to define your own virtual world

By Todd Sundsted, JavaWorld.com, 08/01/97

The combination of a URL, HTML, and HTTP made the Internet look like a vast universe of electronic pages -- flat, two-dimensional documents containing text, images, and links to other locations.

Most of us were satisfied with this new-found means of data gathering. Two dimensions, however, left a few folks feeling, well, a bit flat. While HTML was quickly gaining ground, several adventurous individuals, perhaps having digested a few too many Gibson-esque cyberpunk novels, were looking to add a third dimension to the Web.

The eventual result was the Virtual Reality Modeling Language (VRML). Based on the Open Inventor ASCII format from Silicon Graphics, VRML made it possible to describe three-dimensional scenes, complete with shapes, lights, textures, and other effects. VRML provided Web surfers with the added ability to interact with the Web via objects in the virtual world.

Java, as it turns out, it ideally suited for the task of implementing VRML. It is reasonably fast, portable, and, like VRML, tightly coupled with the Internet.

Let's begin our journey into three dimensions with a look at how a VRML document is structured.

The structure of a VRML document

Scene descriptions in VRML are made up of entities called nodes. Nodes can be shapes, properties, transformations, cameras, and lights. Nodes can also be clusters of other nodes, as we'll see a bit later.

A VRML description isn't just a haphazard collection of nodes; rather, the nodes are organized hierarchically in a structure called a scene graph. A VRML description consists of a single top-level node. That top-level node may contain other nodes, called children, as illustrated in the diagram below.

In this case, the top-level node is A, and nodes B, C, and F are its children. We can rearrange the figure to indicate containment, with descending line segments between adjacent nodes. This top-down arrangement is illustrated below.

The nodes that make up a scene graph are ordered -- a fact that has important implications during processing. Take a look at Traversing a node graph. The dotted line indicates the order in which nodes are processed, or traversed. Note that nodes E and G will be affected by the transformations indicated by nodes B and D. This order may seem odd because node D is in a different subtree than node G, but it is important to realize that nodes processed earlier affect nodes processed later no matter what subtree of the scene graph they are in. If node D defines a rotation, that rotation will be applied to all subsequent nodes, including both node E and G.