An Introduction to Virtual Reality Modeling Language 1.0 (VRML 1.0)

Steven K. Feiner
Department of Computer Science
Columbia University

Goal

• Universal language for specifying multi-user, interactive simulations:
  • 3D display
  • interaction
  • networking through Internet/WWW

Reality

• VRML Version v1.0 allows
  • static 3D models (worlds)
  • WWW links to other VRML models, HTML, and MIME.

• Browsers support
  • loading models
  • navigation
  • selecting links

Example Browser

• Template Graphics Software WebSpace Navigator v1.0

History

• Spring 1994, First WWW Conf., Geneva: Need expressed for common language for 3D scenes with WWW links ("HTML for VR"):
  • VRML (Virtual Reality Markup Language)

• Mailing list created. Moderator Mark Pesce announces intent to have draft spec ready for Fall 1994 WWW Conf.

• Decision not to extend HTML, but to adapt existing format.

• Choose SGI Open Inventor ASCII File Format:
  • Select subset
  • Extend for networking.

• Gavin Bell (SGI) adapts file format, Paul Strauss (SGI) develops parser to be released by SGI.

Language

• Node: Container for objects.

• Scene graph: Ordered hierarchy of nodes

• Scene graph has state: Earlier nodes can affect later ones

Syntax

• File header

  #VRML V1.0 ascii
  

  • Must start every file

• Comment

  #
  

  • All chars until next NL or CR are ignored (except if # is in string)

• Node definition (unnamed)

  objecttype { fields children }
  

  • objecttype: node type (e.g., cube, sphere, material, separator)
  • fields: optional parameters (e.g., sphere radius)
  • children: optional child nodes if node is a group node.

  Exactly one node definition follows the header.

Programs

• Example

  #VRML V1.0 ascii
  
  AsciiText {string "hello, virtual world" }
  

• File
  • Should have suffix ".wrl"

• Invocation
  • Try it!

    hello.wrl

Nodes

• Shape: Specify geometry
  • AsciiText, Cone, Cube, Cylinder, IndexedFaceSet, IndexedLineSet, PointSet, Sphere

    Sample shapes

• Property: Affect how shapes are drawn
  • Geometry/appearance: Coordinate3, FontStyle, Material, MaterialBinding, Normal, NormalBinding, Texture2, Texture2Transform, TextureCoordinate2, ShapeHints
  • Matrix/transform: MatrixTransform, Rotation, Scale, Transform, Translation
  • Camera: OrthographicCamera, PerspectiveCamera
  • Light: DirectionalLight, PointLight, SpotLight

• Group: Induce hierarchy, etc.
  • Traversal State: Separator
  • Conditional: LOD, Switch
  • Link: WWWAnchor, WWWInline

• Miscellaneous
  • Documentation: Info

Fields

• Single-valued: Name begins with "SF"
  • SFBitMask, SFBool, SFColor, SFEnum, SFFloat, SFImage, SFLong, SFMatrix, SFRotation, SFString, SFVec2f, SFVec3f
  • Examples:

    	SFFloat:	3.14
    	SFColor:	0.2 0.9 0.2
    	SFVec2f:	0 1
    

• Multiple-valued: Name begins with "MF"
  • MFColor, MFFloat, MFLong, MFString, MFVec2f, MFVec3f
  • Written as comma-separated values, enclosed in square brackets
  • Examples:

    	MFLong:		[ 128, 0x7FFF, 0xFFFF]
    	MFVec2f:	[ 0 1, 0.9 1 ]
    

Traversal State

• Traversal state:Value of all properties (geometry, appearance, transform, camera, light)

• Properties are global: affect/are affected by nodes in order enountered

• Separator: Pushes state, traverses children, pops state
  • Isolates children

Linking

• WWWAnchor: Loads new scene graph from WWW when one of its children is "chosen"
  • Scene graph is specified as a URL
  • Browser determines how children are chosen (e.g., by mouse click)
  • Acts like Separator

• WWWInline: Reads child from WWW
  • Child is specified as a URL

• Example:

  WWWAnchor {
      name "http://www.xxx.com/widgetLit.html"
      Separator {
  	Translation { translation 0 1.2 3.1}
  	WWWInline {
  	    name "http://www.xxx.com/vrml/widgetModel.wrl"
  	}
      }
  }
  

Instancing

• Node definition (named)

  DEF objectname objecttype { fields children }
  

  • Defines a named object and creates an instance of it

• Node instancing

  USE objectname
  

  • Creates instance of most recently defined node of that name
  • Names are not shared between files

• Example

  Separator {
      DEF Box Cube {width 1.5 height 3}
      Separator {
  	Translation {translation 4 0 0}
  	DEF Box Cube {width 1}
      }
      Translation {translation 0 4 0}
      USE Box
  }
  

  • Creates 2 instances of second, smaller Cube

Extensibility

• Non-standard nodes can be defined using a standard self-describing syntax:

  Cube {
      fields [ SFFloat width, SFFloat height, SFFloat depth ]
      width 2 height 2 depth 2
  }
  

  • A VRML 1.0 implementation must parse all properly defined nodes, but may ignore them.

  • It is not an error to specify fields for a standard VRML 1.0 node.

• Is-a relationships

  Die {
      fields [ MFString isA 
  	     SFFloat width, SFFloat height, SFFloat depth
  	     SFFloat bevel ]
      isA [ "BeveledCube" "Cube" ]
      width 2 height 2 depth 2
      bevel .1
  }	
  

  • Means that a Die will be treated, in order of preference, as a BeveledCube or Cube by a VRML 1.0 implementation that doesn't support Die.

Examples

References

VRML*Tech: The Virtual Reality Modeling Language Technical Forum

Virtual Reality Modeling Language Repository

Template Graphics Software, Inc., Template Graphics Software Home (Access to WebSpace Navigator v1.0)

National Center for Supercomputer Applications Relativity Group, NCSA Relativity Group VRML Page