Build Extruded Shapes

Motivation

Extruded shapes are very common

• Tubes, pipes, bars, vases, donuts
• Other tricky uses…

How can you do it:

• You can build extruded shapes using an IndexedFaceSet node.
• You can build extruded shapes more easily and efficiently using an Extrusion node.

Creating extruded shapes

Extruded shapes are described by:

• A 2-D cross-section
• A 3-D spine along which to sweep the cross-section

Extruded shapes are like long bubbles created with a bubble wand:

• The bubble wand’s outline is the cross-section
• The path along which you swing the wand is the spine

Syntax: Extrusion

An Extrusion geometry node creates extruded geometry:

• crossSection - 2-D cross-section
• spine - 3-D sweep path
• endCap and beginCap - cap ends

XML Encoding

<Shape>
  <Appearance><!-- ... --></Appearance>
  <Extrusion
      crossSection='...'
      spine='...'
      endCap='true'
      beginCap='true'
      ... />
</Shape>

Classic VRML Encoding

Shape {
  appearance Appearance { ... }
  geometry Extrusion {
    crossSection [ ... ]
    spine [ ...  ]
    endCap TRUE
    beginCap TRUE
    ...
  }
}

An Extrusion geometry node creates extruded geometry:

• solid - shape is solid
• ccw - faces are counter-clockwise
• convex - faces are convex

XML Encoding

<Shape>
  <Appearance><!-- ... --></Appearance>
  <Extrusion
      ...
      solid='true'
      ccw='true'
      convex='true'/>
</Shape>

Classic VRML Encoding

Shape {
  appearance Appearance { ... }
  geometry Extrusion {
    ...
    solid TRUE
    ccw TRUE
    convex TRUE
  }
}

Squishing and twisting extruded shapes

You can scale the cross-section along the spine:

• Vases, musical instruments
• Surfaces of revolution

You can rotate the cross-section along the spine

• Twisting ribbons

Syntax: Extrusion

An Extrusion geometry node creates geometry using:

• scale - cross-section scaling per spine point
• orientation - cross-section rotation per spine point

XML Encoding

<Shape>
  <Appearance><!-- ... --></Appearance>
  <Extrusion
      ...
      scale='...'
      orientation='...'/>
</Shape>

Classic VRML Encoding

Shape {
  appearance Appearance { ... }
  geometry Extrusion {
    ...
    scale [ ... ]
    orientation [ ... ]
  }
}

Summary

• An Extrusion node efficiently creates extruded shapes
• The crossSection field specifies the cross-section
• The spine field specifies the sweep path
• The scale and orientation fields specify scaling and rotation at each spine point