VRML 2.0 Prototype Concepts

• Prototypes are the mechanism used for expanding the VRML language
• A prototype has a new type name followed by a list of fields and events in brackets
• These may have default values associated with them (a good idea)
• Now VRML describing the prototype is written
• Fields and Nodes in the VRML section are associated with the fields of the prototype declaration using the word IS
• The prototype is invoked by referencing its name and supplying some or all of its field values within curly brackets (just like referencing an inbuilt node)
• If you want fields of the prototype to be able to receive events declare them as exposed
• The prototype can be referenced anywhere that a node which is the same type as the first node in its VRML section could be referenced
• The externproto declaration references a proto in another file by adding a url at the end of the declaration
• externproto is a convenient way to build up a library of prototypes that are reusable
• The field and event declartions of the externproto must be a subset of those in the prototype declaration
• The name of the externproto has no connection to the name of the prototype, only the url associates them

This will all become clearer with some examples.