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Prototypes

In addition to the more than 50 built-in nodes that VRML offers, developers are free to create their own custom nodes as well. Experienced VRML programmers can, in essence, extend the core capabilities of VRML by using the language's powerful PROTO mechanism (short for prototype). Through a corresponding EXTERNPROTO mechanism, which stands for external prototype, PROTO node definitions can reside in a file other than those in which they're actually used, allowing developers to create entire libraries of reusable custom nodes.

Prototypes are often used to construct reusable geometric shapes and models, interface elements (such as progress bars, sliders, buttons, dials, and toggle switches), animated objects, mathematical functions, custom appearances, and special effects (such as exploding objects). Because prototypes can be created using any number of VRML's built-in nodes, including Script nodes that contain programs written in languages such as Java and JavaScript, they can be quite sophisticated. A number of reusable prototype nodes are available on the Web, such as the freely available PROTO Repository (see "PROTO Repository"), which can save content authors a great deal of time and tedium when it comes to implementing advanced features in their VRML worlds.


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