Creating New Node Types

Motivation

You can create new node types that encapsulate:

• Shapes
• Sensors
• Interpolators
• Scripts
• anything else …

This creates high-level nodes:

• Robots, menus, new shapes, etc.

Syntax: PROTO

A PROTO statement declares a new node type (a prototype):

• name - the new node type name
• fields, inputs, and outputs - interface to the prototype

XML Encoding

<ProtoDeclare name='BouncingBall'>
  <ProtoInterface>
    <field accessType='inputOutput' type='SFTime' name='cycleInterval' value='1'/>
    <field accessType='inputOutput' type='SFFloat' name='bounceHeight' value='1'/>
  </ProtoInterface>
  <ProtoBody>
    <!-- ... -->
  </ProtoBody>
</ProtoDeclare>

Classic VRML Encoding

PROTO BouncingBall [
  inputOutput SFTime  cycleInterval 1.0
  inputOutput SFFloat bounceHeight  1.0
]
{
  ...
}

Defining prototype bodies

PROTO defines:

• body - nodes and routes for the new node type

XML Encoding

<ProtoDeclare name='BouncingBall'>
  <ProtoInterface>
    <!-- ... -->
  </ProtoInterface>
  <ProtoBody>
    <Transform>
      <!-- children ... -->
    </Transform>
  </ProtoBody>
</ProtoDeclare>

Classic VRML Encoding

PROTO BouncingBall [
  ...
]
{
  Transform {
    children [ ... ]
  }
  ROUTE ...
}

Syntax: IS

The IS syntax connects a prototype interface field, input, or output to the body:

• Like an assignment statement
• Assigns interface field or input to body
• Assigns body outputs to interface

Interface items connected by IS need not have the same name as an item in the body, but often do:

XML Encoding

<ProtoDeclare name='BouncingBall'>
  <ProtoInterface>
    <field accessType='inputOutput' type='SFTime' name='cycleInterval' value='1'/>
    <field accessType='inputOutput' type='SFFloat' name='bounceHeight' value='1'/>
  </ProtoInterface>
  <ProtoBody>
    <!-- ... -->
    <TimeSensor DEF='Clock' ... >
      <IS>
        <connect nodeField='cycleInterval' protoField='cycleInterval'/>
        <!-- ... -->
      </IS>
    </TimeSensor>
    <!-- ... -->
  </ProtoBody>
</ProtoDeclare>

Classic VRML Encoding

PROTO BouncingBall [
  inputOutput SFTime  cycleInterval 1.0
  inputOutput SFFloat bounceHeight  1.0
]
{
  ...
  DEF Clock TimeSensor {
    cycleInterval IS cycleInterval
    ...
  }
  ...
}

Using IS

May IS to …

Interface	initializeOnly	inputOnly	outputOnly	inputOutput
initializeOnly	yes	no	no	yes
inputOnly	no	yes	no	yes
outputOnly	no	no	yes	yes
inputOutput	no	no	no	yes

Using prototyped nodes

The new node type can be used like any other type.

XML Encoding

<!-- Official Syntax -->
<ProtoInstance name='BouncingBall'>
  <fieldValue name='cycleInterval' value='2'/>
  <fieldValue name='bounceHeight' value='3'/>
</ProtoInstance>
<!-- Short Syntax -->
<BouncingBall
    cycleInterval='2'
    bounceHeight='3'/>

Classic VRML Encoding

BouncingBall {
  cycleInterval 2.0
  bounceHeight  3.0
}

Controlling usage rules

Recall that node use must be appropriate for the context:

• A Shape node specifies shape, not color
• A Material node specifies color, not shape
• A Box node specifies geometry, not shape or color

The context for a new node type depends upon the first node in the PROTO body.

For example, if the first node is a geometry node:

• The prototype creates a new geometry node type

The new node type can be used wherever the first node of the prototype body can be used.

• In XML the default value of the »containerField« attribute of a ProtoInstance element is »children«. Change this attribute to whatever value you need.

XML Encoding

<Shape>
  <!-- Official Syntax -->
  <ProtoInstance name='Torus' containerField='geometry'>
    <!-- ... -->
  </ProtoInstance>
</Shape>
<Shape>
  <!-- Short Syntax -->
  <Torus containerField='geometry' .../>
</Shape>

A sample prototype use

Create a BouncingBall node type that:

• Builds a beachball
  • Creates an animation clock
  • Using a PROTO field to select the cycle interval
• Bounces the beachball
  • Using the bouncing ball program script
  • Using a PROTO field to select the bounce height

Fields needed:

• Bounce height
• Cycle interval

XML Encoding

<ProtoDeclare name='BouncingBall'>
  <ProtoInterface>
    <field accessType='inputOutput' type='SFTime' name='cycleInterval' value='1'/>
    <field accessType='inputOutput' type='SFFloat' name='bounceHeight' value='1'/>
  </ProtoInterface>
  <ProtoBody>
    <!-- ... -->
  </ProtoBody>
</ProtoDeclare>

Classic VRML Encoding

PROTO BouncingBall [
  inputOutput SFTime  cycleInterval 1.0
  inputOutput SFFloat bounceHeight 1.0
]
{
  ...
}

Inputs and outputs needed:

• None - a TimeSensor node is built in to the new node

Body needed:

• A ball shape inside a transform
• An animation clock
• A bouncing ball program script
• Routes connecting it all together

XML Encoding

<ProtoDeclare name='BouncingBall'>
  <ProtoInterface>
    <!-- ... -->
  </ProtoInterface>
  <ProtoBody>
    <Transform DEF='Ball'>
      <Shape><!-- ... --></Shape>
    </Transform>
    <TimeSensor DEF='Clock' ... />
    <Script DEF='Bouncer' ... />
    <ROUTE ... />
  </ProtoBody>
</ProtoDeclare>

Classic VRML Encoding

PROTO BouncingBall [
  ...
]
{
  DEF Ball Transform {
    children [
      Shape { ... }
    ]
  }
  DEF Clock   TimeSensor { ... }
  DEF Bouncer Script { ... }
  ROUTE ...
}

Changing a prototype

If you change a prototype, all uses of that prototype change as well

• Prototypes enable world modularity
• Large worlds make heavy use of prototypes

For the BouncingBall prototype, adding a shadow to the prototype makes all balls have a shadow.

Syntax: EXTERNPROTO

Prototypes are typically in a separate external file, referenced by an EXTERNPROTO

• name, fields, events - as from PROTO, minus initial values
• url - the URL of the prototype file
• #name - name of PROTO in file

XML Encoding

<ExternProtoDeclare name='BouncingBall' url='"bounce.x3dv#BouncingBall", "bounce.x3d#BouncingBall"'>
  <field accessType='inputOutput' type='SFTime' name='cycleInterval'/>
  <field accessType='inputOutput' type='SFFloat' name='bounceHeight'/>
</ExternProtoDeclare>

Classic VRML Encoding

EXTERNPROTO BouncingBall [
  inputOutput SFTime  cycleInterval
  inputOutput SFFloat bounceHeight
]
[
  "bounce.x3dv#BouncingBall",
  "bounce.x3d#BouncingBall"
]

Summary

• PROTO declares a new node type and defines its node body
• EXTERNPROTO declares a new node type, specified by URL