Chapter 3: Node Reference--The Annotated VRML97 Reference Manual

TECHNICAL NOTE: Extrusion and ElevationGrid are the only new geometry types added to VRML 2.0; all the rest were part of VRML 1.0. Like ElevationGrid, Extrusion was added because it is commonly used (many shapes can be created with Extrusion) and because the equivalent IndexedFaceSet is much larger. Extrusions are also much more convenient than IndexedFaceSet. Because implementations know the topology of an extrusion, normals are more easily generated. Texture coordinates are also easily generated and cannot be specified. You can use a TextureTransform node to modify the generated coordinates, but must use an IndexedFaceSet if you want complete control over texture map application.

Like ElevationGrid, several of Extrusion's fields are only partially exposed to make it easier to create optimized implementations--you can set them, but you cannot read their value.

EXAMPLE (click to run): The following example illustrates the three typical uses of the Extrusion node (see Figure 3-23). The first Extrusion node defines a surface-of-revolution object. The second Extrusion node defines a beveled, cookie cutter object. The third Extrusion node defines a bent-twisted-tapered object:

#VRML V2.0 utf8
Group { children [
  Transform {    # Surface of Revolution object
    translation -4 0 0
    children Shape {
      appearance DEF A Appearance {
        material Material {
          ambientIntensity 0.33
          diffuseColor 1 1 1
        }
        texture ImageTexture { url "marble2.gif" }
      }
      geometry DEF SOR Extrusion {
        crossSection [  1  0,  .866 -.5,    .5   -.866,
                        0 -1, -.5   -.866, -.866 -.5,
                       -1  0, -.866  .5,   -.5    .866,
                        0  1,  .5    .866,  .866  .5, 1 0 ]
        spine [ 0 0 0, 0 0.5 0, 0 1.5 0, 0 2 0, 0 2.5 0, 0 3 0,
                0 4 0, 0 4.5 0 ]
        scale [ 0.4 0.4, 1.2 1.2, 1.6 1.6, 1.5 1.5, 1.0 1.0,
                0.4 0.4, 0.4 0.4, 0.7 0.7 ]
      }
    }
  }
  Transform {   # Beveled cookie-cutter object
    children Shape {
      appearance USE A
      geometry DEF COOKIE Extrusion {
        crossSection [ 1 0, 0.25 -0.25, 0 -1, -0.25 -0.25, -1 0,
                       -0.25 0.25, 0 1, 0.25 0.25, 1 0 ]
        spine [ 0 0 0, 0 0.2 0, 0 1 0, 0 1.2 0 ]
        scale [ 1 1, 1.3 1.3, 1.3 1.3, 1 1 ]
      }
    }
  }
  Transform {   # Bend/twist/taper object
    translation 3 0 0 
    children Shape {
      appearance USE A
      geometry DEF BENDY Extrusion {
        crossSection [ 1 0, 0 -1, -1 0, 0 1, 1 0 ]
        spine [ 0 0 0, 0.5 0.5 0, 0.5 1 0, 0 1.5 0, 0 2 0,
                -0.5 2.5 0, -0.5 3 0, 0 3.5 0 ]
        scale [ .3 .3, .2 .2, .1 .1, .1 .1, .1 .1, .1 .1, .1 .1,
                .3 .3 ]
        orientation [ 0 1 0 0.0, 0 1 0 -.3, 0 1 0 -.6, 0 1 0 -.9,
        orientation [ 0 1 0 -1.2, 0 1 0 -1.5, 0 1 0 -1.8, 0 1 0 -2.1 ]
        creaseAngle 0.9
      }
    }
  }
  Background { skyColor 1 1 1 }
  DirectionalLight { direction 0 0 1 }
  NavigationInfo { type "EXAMINE" }
]}

3.18 Extrusion

3.18.1 Introduction

3.18.2 Algorithmic description

Figure 3-21: Spine-aligned cross-section plane at a spine point.

3.18.3 Special cases

3.18.4 Common cases

3.18.5 Other fields

Figure 3-22: Extrusion Node Examples

Figure 3-23: Extrusion Node Example with Image Texture