Motivation
- If several shapes have the same geometry or appearance, you must use multiple duplicate nodes, one for each use
- Instead, define a name for the first occurrence of a node
- Later, use that name to share the same node in a new context
Syntax: DEF
The DEF syntax gives a name to a node.
XML Encoding
1
2
3
4
5
6
7
| <Shape>
<Appearance>
<Material DEF='RedColor'
diffuseColor='1.0 0.0 0.0'/>
</Appearance>
<!-- geometry ... -->
</Shape>
|
Classic VRML Encoding
1
2
3
4
5
6
7
8
| Shape {
appearance Appearance {
material DEF RedColor Material {
diffuseColor 1.0 0.0 0.0
}
}
geometry ...
}
|
Using DEF
- DEF must be in upper-case
- You can name any node
- Names can be most any sequence of letters and numbers
- Names must be unique within a file
Syntax: USE
The USE syntax uses a previously named node
XML Encoding
1
2
3
4
5
6
| <Shape>
<Appearance>
<Material USE='RedColor'/>
</Appearance>
<!-- geometry ... -->
</Shape>
|
Classic VRML Encoding
1
2
3
4
5
6
| Shape {
appearance Appearance {
material USE RedColor
}
geometry ...
}
|
Using USE
- USE must be in upper-case
- A re-use of a named node is called an instance
- A named node can have any number of instances
- Each instance shares the same node description
- You can only instance names defined in the same file
Using named nodes
Naming and using nodes:
- Saves typing
- Reduces file size
- Enables rapid changes to shapes with the same attributes
- Speeds browser processing
Names are also necessary for animation …
A sample use of node names
XML Encoding
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
| <Inline
url='"table.x3dv"'/>
<Transform
translation='0.95 0 0'>
<Inline DEF='Chair'
url='"chair.x3dv"'/>
</Transform>
<Transform
translation='-0.95 0 0'
rotation='0 1 0 3.14'>
<Inline USE='Chair'/>
</Transform>
<Transform
translation='0 0 0.95'
rotation='0 1 0 4.71318530717959'>
<Inline USE='Chair'/>
</Transform>
<Transform
translation='0 0 -0.95'
rotation='0 1 0 1.57'>
<Inline USE='Chair'/>
</Transform>
|
Classic VRML Encoding
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
| Inline {
url "table.x3dv"
}
Transform {
translation 0.95 0.0 0.0
children DEF Chair Inline {
url "chair.x3dv"
}
}
Transform {
translation -0.95 0.0 0.0
rotation 0.0 1.0 0.0 3.14
children USE Chair
}
Transform {
translation 0.0 0.0 0.95
rotation 0.0 1.0 0.0 -1.57
children USE Chair
}
Transform {
translation 0.0 0.0 -0.95
rotation 0.0 1.0 0.0 1.57
children USE Chair
}
|
Example
Summary
- DEF names a node
- USE uses a named node
