The Virtual Reality Modeling Language

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The Virtual Reality Modeling Language

Gavin Bell, Silicon Graphics, Inc.

Anthony Parisi, Intervista Software

Mark Pesce, VRML List Moderator

Acknowledgements

I want to thank three people who have been absolutely instrumental in the design process: Brian Behlendorf, whose drive (and disk space) made this process happen; and Tony Parisi and Gavin Bell, the final authors of this specification, who have put in a great deal of design work, ensuring that we have a satisfactory product. My hat goes off to all of them, and to all of you who have made this process a success.

Mark Pesce

I would like to add a personal note of thanks to Jan Hardenbergh of Oki Advanced Products for his diligent efforts to keep the specification process on track, and his invaluable editing assistance. I would also like to acknowledge Chris Marrin of Silicon Graphics for his timely contributions to the final design.

Tony Parisi

Revision History

•First Draft - November 2, 1994 •Second Draft - May 8, 1995 •Third Draft - May 26, 1995

Table of Contents

•Introduction

•VRML Mission Statement •History •Version 1.0 Requirements

•Language Specification

•Language Basics •Coordinate System •Fields •Nodes •Instancing •Extensibility •An Example

•Browser Considerations

•File Extensions •MIME Types

The Virtual Reality Modeling Language (VRML) is a language for describing multi-participant interactive simulations -- virtual worlds networked via the global Internet and hyperlinked with the World Wide Web. All aspects of virtual world display, interaction and internetworking can be specified using VRML. It is the intention of its designers that VRML become the standard language for interactive simulation within the World Wide Web.

The first version of VRML allows for the creation of virtual worlds with limited interactive behavior. These worlds can contain objects which have hyperlinks to other worlds, HTML documents or other valid MIME types. When the user selects an object with a hyperlink, the appropriate MIME viewer is launched. When the user selects a link to a VRML document from within a correctly configured WWW browser, a VRML viewer is launched. Thus VRML viewers are the perfect companion applications to standard WWW browsers for navigating and visualizing the Web. Future versions of VRML will allow for richer behaviors, including animations, motion physics and real-time multi-user interaction.

This document specifies the features and syntax of Version 1.0 of VRML.

The history of the development of the Internet has had three distinct phases; first, the development of the TCP/IP infrastructure which allowed documents and data to be stored in a proximally independent way; that is, Internet provided a layer of abstraction between data sets and the hosts which manipulated them. While this abstraction was useful, it was also confusing; without any clear sense of "what went where", access to Internet was restricted to the class of sysops/net surfers who could maintain internal cognitive maps of the data space.

Next, Tim Berners-Lee's work at CERN, where he developed the hypermedia system known as World Wide Web, added another layer of abstraction to the existing structure. This abstraction provided an "addressing" scheme, a unique identifier (the Universal Resource Locator), which could tell anyone "where to go and how to get there" for any piece of data within the Web. While useful, it lacked dimensionality; there's no there there within the web, and the only type of navigation permissible (other than surfing) is by direct reference. In other words, I can only tell you how to get to the VRML Forum home page by saying, "http://www.wired.com/", which is not human-centered data. In fact, I need to make an effort to remember it at all. So, while the World Wide Web provides a retrieval mechanism to complement the existing storage mechanism, it leaves a lot to be desired, particularly for human beings.

Finally, we move to "perceptualized" Internetworks, where the data has been sensualized, that is, rendered sensually. If something is represented sensually, it is possible to make sense of it. VRML is an attempt (how successful, only time and effort will tell) to place humans at the center of the Internet, ordering its universe to our whims. In order to do that, the most important single element is a standard that defines the particularities of perception. Virtual Reality Modeling Language is that standard, designed to be a universal description language for multi-participant simulations.

These three phases, storage, retrieval, and perceptualization are analogous to the human process of consciousness, as expressed in terms of semantics and cognitive science. Events occur and are recorded (memory); inferences are drawn from memory (associations), and from sets of related events, maps of the universe are created (cognitive perception). What is important to remember is that the map is not the territory, and we should avoid becoming trapped in any single representation or world-view. Although we need to design to avoid disorientation, we should always push the envelope in the kinds of experience we can bring into manifestation!

This document is the living proof of the success of a process that was committed to being open and flexible, responsive to the needs of a growing Web community. Rather than re-invent the wheel, we have adapted an existing specification (Open Inventor) as the basis from which our own work can grow, saving years of design work and perhaps many mistakes. Now our real work can begin; that of rendering our noospheric space.

VRML was conceived in the spring of 1994 at the first annual World Wide Web Conference in Geneva, Switzerland. Tim Berners-Lee and Dave Raggett organized a Birds-of-a-Feather (BOF) session to discuss Virtual Reality interfaces to the World Wide Web. Several BOF attendees described projects already underway to build three dimensional graphical visualization tools which interoperate with the Web. Attendees agreed on the need for these tools to have a common language for specifying 3D scene description and WWW hyperlinks -- an analog of HTML for virtual reality. The term Virtual Reality Markup Language (VRML) was coined, and the group resolved to begin specification work after the conference. The word 'Markup' was later changed to 'Modeling' to reflect the graphical nature of VRML.

Shortly after the Geneva BOF session, the www-vrml mailing list was created to discuss the development of a specification for the first version of VRML. The response to the list invitation was overwhelming: within a week, there were over a thousand members. After an initial settling-in period, list moderator Mark Pesce of Labyrinth Group announced his intention to have a draft version of the specification ready by the WWW Fall 1994 conference, a mere five months away. There was general agreement on the list that, while this schedule was aggressive, it was achievable provided that the requirements for the first version were not too ambitious and that VRML could be adapted from an existing solution. The list quickly agreed upon a set of requirements for the first version, and began a search for technologies which could be adapted to fit the needs of VRML.

The search for existing technologies turned up a several worthwhile candidates. After much deliberation the list came to a consensus: the Open Inventor ASCII File Format from Silicon Graphics, Inc. The Inventor File Format supports complete descriptions of 3D scenes with polygonally rendered objects, lighting, materials, ambient properties and realism effects. A subset of the Inventor File Format, with extensions to support networking, forms the basis of VRML. Gavin Bell of Silicon Graphics has adapted the Inventor File Format for VRML, with design input from the mailing list. SGI has publicly stated that the file format is available for use in the open market, and have contributed a file format parser into the public domain to bootstrap VRML viewer development.

VRML 1.0 is designed to meet the following requirements:

•Platform independence •Extensibility •Ability to work well over low-bandwidth connections

As with HTML, the above are absolute requirements for a network language standard; they should need little explanation here.

Early on the designers decided that VRML would not be an extension to HTML. HTML is designed for text, not graphics. Also, VRML requires even more finely tuned network optimizations than HTML; it is expected that a typical VRML scene will be composed of many more "inline" objects and served up by many more servers than a typical HTML document. Moreover, HTML is an accepted standard, with existing implementations that depend on it. To impede the HTML design process with VRML issues and constrain the VRML design process with HTML compatibility concerns would be to do both languages a disservice. As a network language, VRML will succeed or fail independent of HTML.

It was also decided that, except for the hyperlinking feature, the first version of VRML would not support interactive behaviors. This was a practical decision intended to streamline design and implementation. Design of a language for describing interactive behaviors is a big job, especially when the language needs to express behaviors of objects communicating on a network. Such languages do exist; if we had chosen one of them, we would have risked getting into a "language war." People don't get excited about the syntax of a language for describing polygonal objects; people get very excited about the syntax of real languages for writing programs. Religious wars can extend the design process by months or years. In addition, networked inter-object operation requires brokering services such as those provided by CORBA or OLE, services which don't exist yet within WWW; we would have had to invent them. Finally, by keeping behaviors out of Version 1, we have made it a much smaller task to implement a viewer. We acknowledge that support for arbitrary interactive behaviors is critical to the long-term success of VRML; they will be included in Version 2.

The language specification is divided into the following sections:

•Language Basics •Coordinate System •Fields •Nodes •Instancing •Extensibility •An Example

At the highest level of abstraction, VRML is just a way for objects to read and write themselves. Theoretically, the objects can contain anything -- 3D geometry, MIDI data, JPEG images, anything. VRML defines a set of objects useful for doing 3D graphics. These objects are called Nodes.

Nodes are arranged in hierarchical structures called scene graphs. Scene graphs are more than just a collection of nodes; the scene graph defines an ordering for the nodes. The scene graph has a notion of state -- nodes earlier in the scene can affect nodes that appear later in the scene. For example, a Rotation or Material node will affect the nodes after it in the scene. A mechanism is defined to limit the effects of properties (separator nodes), allowing parts of the scene graph to be functionally isolated from other parts.

A node has the following characteristics:

•What kind of object it is. A node might be a cube, a sphere, a texture map, a transformation, etc.

The parameters that distinguish this node from other nodes of the same type. For example, each Sphere node might have a different radius, and different texture maps nodes will certainly contain different images to use as the texture maps. These parameters are called Fields. A node can have 0 or more fields.

•A name to identify this node. Being able to name nodes and refer to them elsewhere is very powerful; it allows a scene's author to give hints to applications using the scene about what is in the scene, and creates possibilities for very powerful scripting extensions. Nodes do not have to be named, but if they are named, they can have only one name. However, names do not have to be unique-- several different nodes may be given the same name.

•Child nodes. Object hierarchy is implemented by allowing some types of nodes to contain other nodes. Parent nodes traverse their children in order during rendering. Nodes that may have children are referred to as group nodes. Group nodes can have zero or more children.

The syntax chosen to represent these pieces of information is straightforward:

DEF objectname objecttype { fields children }

Only the object type and curly braces are required; nodes may or may not have a name, fields, and children.

Node names must not begin with a digit, and must not contain spaces or control characters, single or double quote characters, backslashes, curly braces, the plus character or the period character.

For example, this file contains a simple scene defining a view of a red cone and a blue sphere, lit by a directional light:

#VRML V1.0 ascii

Separator {

DirectionalLight {

direction 0 0 -1 # Light shining from viewer into scene

}

PerspectiveCamera {

position -8.6 2.1 5.6

orientation -0.1352 -0.9831 -0.1233 1.1417

focalDistance 10.84

}

Separator { # The red sphere

Material {

diffuseColor 1 0 0 # Red

}

Translation { translation 3 0 1 }

Sphere { radius 2.3 }

}

Separator { # The blue cube

Material {

diffuseColor 0 0 1 # Blue

}

Transform {

translation -2.4 .2 1

rotation 0 1 1 .9

}

Cube {}

}

General Syntax

For easy identification of VRML files, every VRML file must begin with the characters:

#VRML V1.0 ascii

Any characters after these on the same line are ignored. The line is terminated by either the ASCII newline or carriage-return characters.

The '#' character begins a comment; all characters until the next newline or carriage return are ignored. The only exception to this is within string fields, where the '#' character will be part of the string.

Note: Comments and whitespace may not be preserved; in particular, a VRML document server may strip comments and extraneous whitespace from a VRML file before transmitting it. Info nodes should be used for persistent information like copyrights or author information. Info nodes could also be used for object descriptions.

Blanks, tabs, newlines and carriage returns are whitespace characters wherever they appear outside of string fields. One or more whitespace characters separates the syntactical entities in VRML files, where necessary.

After the required header, a VRML file contains exactly one VRML node. That node may of course be a group node, containing any number of other nodes.

VRML uses a cartesian, right-handed, 3-dimensional coordinate system. By default, objects are projected onto a 2-dimensional device by projecting them in the direction of the positive Z axis, with the positive X axis to the right and the positive Y axis up. A camera or modeling transformation may be used to alter this default projection.

The standard unit for lengths and distances specified is meters. The standard unit for angles is radians.

There are two general classes of fields; fields that contain a single value (where a value may be a single number, a vector, or even an image), and fields that contain multiple values. Single-valued fields all have names that begin with "SF", multiple-valued fields have names that begin with "MF". Each field type defines the format for the values it writes.

Multiple-valued fields are written as a series of values separated by commas, all enclosed in square brackets. If the field has zero values then only the square brackets ("[]") are written. The last may optionally be followed by a comma. If the field has exactly one value, the brackets may be omitted and just the value written. For example, all of the following are valid for a multiple-valued field containing the single integer value 1:

[1,]

[ 1 ]

SFBitMask

A single-value field that contains a mask of bit flags. Nodes that use this field class define mnemonic names for the bit flags. SFBitMasks are written to file as one or more mnemonic enumerated type names, in this format:

( flag1 | flag2 | ... )

If only one flag is used in a mask, the parentheses are optional. These names differ among uses of this field in various node classes.

SFBool

A field containing a single boolean (true or false) value. SFBools may be written as 0 (representing FALSE), 1, TRUE, or FALSE.

SFColor

A single-value field containing a color. SFColors are written to file as an RGB triple of floating point numbers in standard scientific notation, in the range 0.0 to 1.0.

SFEnum

A single-value field that contains an enumerated type value. Nodes that use this field class define mnemonic names for the values. SFEnums are written to file as a mnemonic enumerated type name. The name differs among uses of this field in various node classes.

SFFloat

A field that contains one single-precision floating point number. SFFloats are written to file in standard scientific notation.

SFImage

A field that contain an uncompressed 2-dimensional color or greyscale image.

SFImages are written to file as three integers representing the width, height and number of components in the image, followed by width*height hexadecimal values representing the pixels in the image, separated by whitespace. A one-component image will have one-byte hexadecimal values representing the intensity of the image. For example, 0xFF is full intensity, 0x00 is no intensity. A two-component image puts the intensity in the first (high) byte and the transparency in the second (low) byte. Pixels in a three-component image have the red component in the first (high) byte, followed by the green and blue components (so 0xFF0000 is red). Four-component images put the transparency byte after red/green/blue (so 0x0000FF80 is semi-transparent blue). A value of 1.0 is completely transparent, 0.0 is completely opaque. Note: each pixel is actually read as a single unsigned number, so a 3-component pixel with value "0x0000FF" can also be written as "0xFF" or "255" (decimal). Pixels are specified from left to right, bottom to top. The first hexadecimal value is the lower left pixel of the image, and the last value is the upper right pixel.

For example,

1 2 1 0xFF 0x00

is a 1 pixel wide by 2 pixel high greyscale image, with the bottom pixel white and the top pixel black. And:

2 4 3 0xFF0000 0xFF00 0 0 0 0 0xFFFFFF 0xFFFF00

is a 2 pixel wide by 4 pixel high RGB image, with the bottom left pixel red, the bottom right pixel green, the two middle rows of pixels black, the top left pixel white, and the top right pixel yellow.

SFLong

A field containing a single long (32-bit) integer. SFLongs are written to file as an integer in decimal, hexadecimal (beginning with '0x') or octal (beginning with '0') format.

SFMatrix

A field containing a transformation matrix. SFMatrices are written to file in row-major order as 16 floating point numbers separated by whitespace. For example, a matrix expressing a translation of 7.3 units along the X axis is written as:

1 0 0 0 0 1 0 0 0 0 1 0 7.3 0 0 1

SFRotation

A field containing an arbitrary rotation. SFRotations are written to file as four floating point values separated by whitespace. The 4 values represent an axis of rotation followed by the amount of right-handed rotation about that axis, in radians. For example, a 180 degree rotation about the Y axis is:

0 1 0 3.14159265

SFString

A field containing an ASCII string (sequence of characters). SFStrings are written to file as a sequence of ASCII characters in double quotes (optional if the string doesn't contain any whitespace). Any characters (including newlines) may appear within the quotes. To include a double quote character within the string, precede it with a backslash. For example:

Testing

"One, Two, Three"

"He said, \"Immel did it!\""

are all valid strings.

SFVec2f

Field containing a two-dimensional vector. SFVec2fs are written to file as a pair of floating point values separated by whitespace.

SFVec3f

Field containing a three-dimensional vector. SFVec3fs are written to file as three floating point values separated by whitespace.

MFColor

A multiple-value field that contains any number of RGB colors. MFColors are written to file as one or more RGB triples of floating point numbers in standard scientific notation. When more than one value is present, all of the values must be enclosed in square brackets and separated by commas. For example:

[ 1.0 0.0 0.0, 0 1 0, 0 0 1 ]

represents the three colors red, green, and blue.

MFLong

A multiple-value field that contains any number of long (32-bit) integers. MFLongs are written to file as one or more integer values, in decimal, hexadecimal or octal format. When more than one value is present, all the values are enclosed in square brackets and separated by commas; for example:

[ 17, -0xE20, -518820 ]

MFVec2f

A multiple-value field that contains any number of two-dimensional vectors. MFVec2fs are written to file as one or more pairs of floating point values separated by whitespace. When more than one value is present, all of the

[ 0 0, 1.2 3.4, 98.6 -4e1 ]

MFVec3f

A multiple-value field that contains any number of three-dimensional vectors. MFVec3fs are written to file as one or more triples of floating point values separated by whitespace. When more than one value is present, all of the values are enclosed in square brackets and separated by commas; for example:

[ 0 0 0, 1.2 3.4 5.6, 98.6 -4e1 212 ]

<Picture>Nodes

VRML defines several different classes of nodes. Most of the nodes can be classified into one of three categories; shape, property or group. Shape nodes define the geometry in the scene. Conceptually, they are the only nodes that draw anything. Property nodes affect the way shapes are drawn. And grouping nodes gather other nodes together, allowing collections of nodes to be treated as a single object. Some group nodes also control whether or not their children are drawn.

Nodes may contain zero or more fields. Each node type defines the type, name, and default value for each of its fields. The default value for the field is used if a value for the field is not specified in the VRML file. The order in which the fields of a node are read is not important; for example, "Cube { width 2 height 4 depth 6 }" and "Cube { height 4 depth 6 width 2 }" are equivalent.

Here are the 36 nodes grouped by type. The first group are the shape nodes. These specify geometry:

AsciiText, Cone, Cube, Cylinder, IndexedFaceSet, IndexedLineSet, PointSet, Sphere,

The second group are the properties. These can be further grouped into properties of the geometry and its appearance, matrix or transform properties, and cameras and lights: Coordinate3, FontStyle, Info, LOD, Material, MaterialBinding, Normal, NormalBinding, Texture2, Texture2Transform, TextureCoordinate2, ShapeHints

MatrixTransform, Rotation, Scale, Transform, Translation

OrthographicCamera, PerspectiveCamera

DirectionalLight, PointLight, SpotLight

These are the group nodes:

Group, Separator, Switch, TransformSeparator, WWWAnchor

Finally, the WWWInline node does not fit neatly into any category.

WWWInline

AsciiText

This node represents strings of text characters from the ASCII coded character set. The first string is rendered with its baseline at (0,0,0). All subsequent strings advance y by -(size * spacing). See FontStyle for a description of the size field. The justification field determines the placement of the strings in the x dimension. LEFT (the default) places the left edge of each string at x=0. CENTER places the center of each string at x=0. RIGHT places the right edge of each string at x=0. Text is rendered from left to right, top to bottom in the font set by FontStyle. The width field defines a suggested width constraint for each string. The default is to use the natural width of each string. Setting any value to 0 indicates the natural width should be used for that string.

The text is transformed by the current cumulative transformation and is drawn with the current material and texture.

Textures are applied to 3D text as follows. The texture origin is at the origin of the first string, as determined by the justification. The texture is scaled equally in both S and T dimensions, with the font height representing 1 unit. S increases to the right. The T origin can occur anywhere along each character, depending on how that character's outline is defined.

JUSTIFICATION

LEFT Align left edge of text to origin

CENTER Align center of text to origin

RIGHT Align right edge of text to origin

FILE FORMAT/DEFAULTS

AsciiText {

string "" # MFString

spacing 1 # SFFloat

justification LEFT # SFEnum

width 0 # MFFloat

}

Cone

This node represents a simple cone whose central axis is aligned with the y-axis. By default, the cone is centered at (0,0,0) and has a size of -1 to +1 in all three directions. The cone has a radius of 1 at the bottom and a height of 2, with its apex at 1 and its bottom at -1. The cone has two parts: the sides and the bottom.

The cone is transformed by the current cumulative transformation and is drawn with the current texture and material.

If the current material binding is PER_PART or PER_PART_INDEXED, the first current material is used for the sides of the cone, and the second is used for the bottom. Otherwise, the first material is used for the entire cone.

When a texture is applied to a cone, it is applied differently to the sides and bottom. On the sides, the texture wraps counterclockwise (from above) starting at the back of the cone. The texture has a vertical seam at the back, intersecting the yz-plane. For the bottom, a circle is cut out of the texture square and applied to the cone's base circle. The texture appears right side up when the top of the cone is rotated towards the -Z axis.

PARTS

SIDES The conical part

BOTTOM The bottom circular face

ALL All parts

FILE FORMAT/DEFAULTS

Cone {

parts ALL # SFBitMask

bottomRadius 1 # SFFloat

height 2 # SFFloat

}

Coordinate3

This node defines a set of 3D coordinates to be used by a subsequent IndexedFaceSet, IndexedLineSet, or PointSet node. This node does not produce a visible result during rendering; it simply replaces the current coordinates in the rendering state for subsequent nodes to use.

FILE FORMAT/DEFAULTS

Coordinate3 {

point 0 0 0 # MFVec3f

}

Cube

This node represents a cuboid aligned with the coordinate axes. By default, the cube is centered at (0,0,0) and measures 2 units in each dimension, from -1 to +1. The cube is transformed by the current cumulative transformation and is drawn with the current material and texture.

If the current material binding is PER_PART, PER_PART_INDEXED, PER_FACE, or PER_FACE_INDEXED, materials will be bound to the faces of the cube in this order: front (+Z), back (-Z), left (-X), right (+X), top (+Y), and bottom (-Y).

Textures are applied individually to each face of the cube; the entire texture goes on each face. On the front, back, right, and left sides of the cube, the texture is applied right side up. On the top, the texture appears right side up when the top of the cube is tilted toward the camera. On the bottom, the texture appears right side up when the top of the cube is tilted towards the -Z axis.

FILE FORMAT/DEFAULTS

Cube {

width 2 # SFFloat

height 2 # SFFloat

depth 2 # SFFloat

}

Cylinder

This node represents a simple capped cylinder centered around the y-axis. By default, the cylinder is centered at (0,0,0) and has a default size of -1 to +1 in all three dimensions. The cylinder has three parts: the sides, the top (y = +1) and the bottom (y = -1). You can use the radius and height fields to create a cylinder with a different size.

The cylinder is transformed by the current cumulative transformation and is drawn with the current material and texture.

If the current material binding is PER_PART or PER_PART_INDEXED, the first current material is used for the sides of the cylinder, the second is used for the top, and the third is used for the bottom. Otherwise, the first material is used for the entire cylinder.

When a texture is applied to a cylinder, it is applied differently to the sides, top, and bottom. On the sides, the texture wraps counterclockwise (from above) starting at the back of the cylinder. The texture has a vertical seam at the back, intersecting the yz-plane. For the top and bottom, a circle is cut out of the texture square and applied to the top or bottom circle. The top texture appears right side up when the top of the cylinder is tilted toward the +Z axis, and the bottom texture appears right side up when the top of the cylinder is tilted toward the -Z axis.

pARTS

SIDES The cylindrical part

TOP The top circular face

BOTTOM The bottom circular face

ALL All parts

FILE FORMAT/DEFAULTS

Cylinder {

parts ALL # SFBitMask

radius 1 # SFFloat

height 2 # SFFloat

}

DirectionalLight

This node defines a directional light source that illuminates along rays parallel to a given 3-dimensional vector.

A light node defines an illumination source that may affect subsequent shapes in the scene graph, depending on the current lighting style. Light sources are affected by the current transformation. A light node under a separator does not affect any objects outside that separator.

FILE FORMAT/DEFAULTS

DirectionalLight {

on TRUE # SFBool

intensity 1 # SFFloat

color 1 1 1 # SFColor

direction 0 0 -1 # SFVec3f

}

FontStyle

This node defines the current font style used for all subsequent AsciiText. Font attributes only are defined. It is up to the browser to assign specific fonts to the various attribute combinations. The size field specifies the height (in object space units) of glyphs rendered and determines the vertical spacing of adjacent lines of text.

FAMILY

SERIF Serif style (such as TimesRoman)

SANS Sans Serif Style (such as Helvetica)

TYPEWRITER Fixed pitch style (such as Courier)

STYLE

NONE No modifications to family

BOLD Embolden family

ITALIC Italicize or Slant family

FILE FORMAT/DEFAULTS

FontStyle {

size 10 # SFFloat

family SERIF # SFEnum

style NONE # SFBitMask

}

Group

This node defines the base class for all group nodes. Group is a node that contains an ordered list of child nodes. This node is simply a container for the child nodes and does not alter the traversal state in any way. During traversal, state accumulated for a child is passed on to each successive child and then to the parents of the group (Group does not push or pop traversal state as separator does).

FILE FORMAT/DEFAULTS

Group {

}

IndexedFaceSet

This node represents a 3D shape formed by constructing faces (polygons) from vertices located at the current coordinates. IndexedFaceSet uses the indices in its coordIndex field to specify the polygonal faces. An index of -1 indicates that the current face has ended and the next one begins.

The vertices of the faces are transformed by the current transformation matrix.

Treatment of the current material and normal binding is as follows: The PER_PART and PER_FACE bindings specify a material or normal for each face. PER_VERTEX specifies a material or normal for each vertex. The corresponding _INDEXED bindings are the same, but use the materialIndex or normalIndex indices. The DEFAULT material binding is equal to OVERALL. The DEFAULT normal binding is equal to PER_VERTEX_INDEXED; if insufficient normals exist in the state, vertex normals will be generated automatically.

Explicit texture coordinates (as defined by TextureCoordinate2) may be bound to vertices of an indexed shape by using the indices in the textureCoordIndex field. As with all vertex-based shapes, if there is a current texture but no texture coordinates are specified, a default texture coordinate mapping is calculated using the bounding box of the shape. The longest dimension of the bounding box defines the S coordinates, and the next longest defines the T coordinates. The value of the S coordinate ranges from 0 to 1, from one end of the bounding box to the other. The T coordinate ranges between 0 and the ratio of the second greatest dimension of the bounding box to the greatest dimension.

Be sure that the indices contained in the coordIndex, materialIndex, normalIndex, and textureCoordIndex fields are valid with respect to the current state, or errors will occur.

FILE FORMAT/DEFAULTS

IndexedFaceSet {

coordIndex 0 # MFLong

materialIndex -1 # MFLong

normalIndex -1 # MFLong

textureCoordIndex -1 # MFLong

}

IndexedLineSet

This node represents a 3D shape formed by constructing polylines from vertices located at the current coordinates. IndexedLineSet uses the indices in its coordIndex field to specify the polylines. An index of -1 indicates that the current polyline has ended and the next one begins.

The coordinates of the line set are transformed by the current cumulative transformation.

Treatment of the current material and normal binding is as follows: The PER_PART binding specifies a material or normal for each segment of the line. The PER_FACE binding specifies a material or normal for each polyline. PER_VERTEX specifies a material or normal for each vertex. The corresponding _INDEXED bindings are the same, but use the materialIndex or normalIndex indices. The DEFAULT material binding is equal to OVERALL. The DEFAULT normal binding is equal to PER_VERTEX_INDEXED; if insufficient normals exist in the state, the lines will be drawn unlit. The same rules for texture coordinate generation as IndexedFaceSet are used.

FILE FORMAT/DEFAULTS

IndexedLineSet {

coordIndex 0 # MFLong

materialIndex -1 # MFLong

normalIndex -1 # MFLong

textureCoordIndex -1 # MFLong

}

Info

This class defines an information node in the scene graph. This node has no effect during traversal. It is used to store information in the scene graph, typically for application-specific purposes, copyright messages, or other strings.

Info {

string "<Undefined info>" # SFString

}

LOD

This group node is used to allow applications to switch between various representations of objects automatically. The children of this node typically represent the same object or objects at varying levels of detail, from highest detail to lowest.

The specified center point of the LOD is transformed by the current transformation into world space, and the distance from the transformed center to the world-space eye point is calculated. If the distance is less than the first value in the ranges array, then the first child of the LOD group is drawn. If between the first and second values in the ranges array, the second child is drawn, etc. If there are N values in the ranges array, the LOD group should have N+1 children. Specifying too few children will result in the last child being used repeatedly for the lowest levels of detail; if too many children are specified, the extra children will be ignored. Each value in the ranges array should be less than the previous value, otherwise results are undefined.

FILE FORMAT/DEFAULTS

LOD {

range [ ] # MFFloat

center 0 0 0 # SFVec3f

}

Material

This node defines the current surface material properties for all subsequent shapes. Material sets several components of the current material during traversal. Different shapes interpret materials with multiple values differently. To bind materials to shapes, use a MaterialBinding node.

FILE FORMAT/DEFAULTS

Material {

ambientColor 0.2 0.2 0.2 # MFColor

diffuseColor 0.8 0.8 0.8 # MFColor

specularColor 0 0 0 # MFColor

emissiveColor 0 0 0 # MFColor

shininess 0.2 # MFFloat

transparency 0 # MFFloat

}

MaterialBinding

This node specifies how the current materials are bound to shapes that follow in the scene graph. Each shape node may interpret bindings differently. The current material always has a base value, which is defined by the first value of all material fields. Since material fields may have multiple values, the binding determines how these values are distributed over a shape.

The bindings for faces and vertices are meaningful only for shapes that are made from faces and vertices. Similarly, the indexed bindings are only used by the shapes that allow indexing.

When multiple material values are bound, the values are cycled through, based on the period of the material component with the most values. For example, the following table shows the values used when cycling through (or indexing into) a material with 2 ambient colors, 3 diffuse colors, and 1 of all other components in the current material. (The period of this material cycle is 3):

Material Ambient color Diffuse color Other

0 0 0 0

1 1 1 0

2 1 2 0

3 (same as 0) 0 0 0

BINDINGS

DEFAULT Use default binding

OVERALL Whole object has same material

PER_PART One material for each part of object

PER_PART_INDEXED One material for each part, indexed

PER_FACE One material for each face of object

PER_FACE_INDEXED One material for each face, indexed

PER_VERTEX One material for each vertex of object

PER_VERTEX_INDEXED One material for each vertex, indexed

FILE FORMAT/DEFAULTS

MaterialBinding {

value DEFAULT # SFEnum

}

MatrixTransform

This node defines a geometric 3D transformation with a 4 by 4 matrix. Note that some matrices (such as singular ones) may result in errors.

FILE FORMAT/DEFAULTS

MatrixTransform {

matrix 1 0 0 0 # SFMatrix

0 1 0 0

0 0 1 0

0 0 0 1

}

Normal

This node defines a set of 3D surface normal vectors to be used by vertex-based shape nodes (IndexedFaceSet, IndexedLineSet, PointSet) that follow it in the scene graph. This node does not produce a visible result during rendering; it simply replaces the current normals in the rendering state for subsequent nodes to use. This node contains one multiple-valued field that contains the normal vectors.

FILE FORMAT/DEFAULTS

Normal {

vector 0 0 1 # MFVec3f

}

NormalBinding

This node specifies how the current normals are bound to shapes that follow in the scene graph. Each shape node may interpret bindings differently.

The bindings for faces and vertices are meaningful only for shapes that are made from faces and vertices. Similarly, the indexed bindings are only used by the shapes that allow indexing. For bindings that require multiple normals, be sure to have at least as many normals defined as are necessary; otherwise, errors will occur.

BINDINGS

DEFAULT Use default binding

OVERALL Whole object has same normal

PER_PART One normal for each part of object

PER_PART_INDEXED One normal for each part, indexed

PER_FACE One normal for each face of object

PER_FACE_INDEXED One normal for each face, indexed

PER_VERTEX One normal for each vertex of object

PER_VERTEX_INDEXED One normal for each vertex, indexed

FILE FORMAT/DEFAULTS

NormalBinding {

value DEFAULT # SFEnum

}

OrthographicCamera

An orthographic camera defines a parallel projection from a viewpoint. This camera does not diminish objects with distance, as an PerspectiveCamera does. The viewing volume for an orthographic camera is a rectangular parallelepiped (a box).

By default, the camera is located at (0,0,1) and looks along the negative z-axis; the position and orientation fields can be used to change these values. The height field defines the total height of the viewing volume.

A camera can be placed in a VRML world to specify the initial location of the viewer when that world is entered. VRML browsers will typically modify the camera to allow a user to move through the virtual world.

Cameras are affected by the current transformation, so you can position a camera by placing a transformation node before it in the scene graph . The default position and orientation of a camera is at (0,0,1) looking along the negative z-axis.

FILE FORMAT/DEFAULTS

OrthographicCamera {

position 0 0 1 # SFVec3f

orientation 0 0 1 0 # SFRotation

focalDistance 5 # SFFloat

height 2 # SFFloat

}

PerspectiveCamera

A perspective camera defines a perspective projection from a viewpoint. The viewing volume for a perspective camera is a truncated right pyramid.

By default, the camera is located at (0,0,1) and looks along the negative z-axis; the position and orientation fields can be used to change these values. The heightAngle field defines the total vertical angle of the viewing volume.

See more on cameras in the OrthographicCamera description.

FILE FORMAT/DEFAULTS

PerspectiveCamera {

position 0 0 1 # SFVec3f

orientation 0 0 1 0 # SFRotation

focalDistance 5 # SFFloat

heightAngle 0.785398 # SFFloat

}

PointLight

This node defines a point light source at a fixed 3D location. A point source illuminates equally in all directions; that is, it is omni- directional.

FILE FORMAT/DEFAULTS

PointLight {

on TRUE # SFBool

intensity 1 # SFFloat

color 1 1 1 # SFColor

location 0 0 1 # SFVec3f

}

PointSet

This node represents a set of points located at the current coordinates. PointSet uses the current coordinates in order, starting at the index specified by the startIndex field. The number of points in the set is specified by the numPoints field. A value of -1 for this field indicates that all remaining values in the current coordinates are to be used as points.

The coordinates of the point set are transformed by the current cumulative transformation. The points are drawn with the current material and texture.

Treatment of the current material and normal binding is as follows: PER_PART, PER_FACE, and PER_VERTEX bindings bind one material or normal to each point. The DEFAULT material binding is equal to OVERALL. The DEFAULT normal binding is equal to PER_VERTEX. The startIndex is also used for materials or normals when the binding indicates that they should be used per vertex.

FILE FORMAT/DEFAULTS

PointSet {

startIndex 0 # SFLong

numPoints -1 # SFLong

}

Rotation

This node defines a 3D rotation about an arbitrary axis through the origin. The rotation is accumulated into the current transformation, which is applied to subsequent shapes.

FILE FORMAT/DEFAULTS

Rotation {

rotation 0 0 1 0 # SFRotation

}

See rotation field description for more information.

Scale

This node defines a 3D scaling about the origin. If the components of the scaling vector are not all the same, this produces a non-uniform scale.

FILE FORMAT/DEFAULTS

Scale {

scaleFactor 1 1 1 # SFVec3f

}

Separator

This group node performs a push (save) of the traversal state before traversing its children and a pop (restore) after traversing them. This isolates the separator's children from the rest of the scene graph. A separator can include lights, cameras, coordinates, normals, bindings, and all other properties.

Separators can also perform render culling. Render culling skips over traversal of the separator's children if they are not going to be rendered, based on the comparison of the separator's bounding box with the current view volume. Culling is controlled by the renderCulling field. These are set to AUTO by default, allowing the implementation to decide whether or not to cull.

CULLING ENUMS

ON Always try to cull to the view volume

OFF Never try to cull to the view volume

AUTO Implementation-defined culling behavior

FILE FORMAT/DEFAULTS

Separator {

renderCulling AUTO # SFEnum

}

ShapeHints

The ShapeHints node indicates that IndexedFaceSets are solid, contain ordered vertices, or contain convex faces.

These hints allow VRML implementations to optimize certain rendering features. Optimizations that may be performed include enabling back-face culling and disabling two-sided lighting. For example, if an object is solid and has ordered vertices, an implementation may turn on backface culling and turn off two-sided lighting. If the object is not solid but has ordered vertices, it may turn off backface culling and turn on two-sided lighting.

The ShapeHints node also affects how default normals are generated. When an IndexedFaceSet has to generate default normals, it uses the creaseAngle field to determine which edges should be smoothly shaded and which ones should have a sharp crease. The crease angle is the angle between surface normals on adjacent polygons. For example, a crease angle of .5 radians (the default value) means that an edge between two adjacent polygonal faces will be smooth shaded if the normals to the two faces form an angle that is less than .5 radians (about 30 degrees). Otherwise, it will be faceted.

VERTEX ORDERING ENUMS

UNKNOWN_ORDERING Ordering of vertices is unknown

CLOCKWISE Face vertices are ordered clockwise

(from the outside)

COUNTERCLOCKWISE Face vertices are ordered counterclockwise

(from the outside)

SHAPE TYPE ENUMS

UNKNOWN_SHAPE_TYPE Nothing is known about the shape

SOLID The shape encloses a volume

FACE TYPE ENUMS

UNKNOWN_FACE_TYPE Nothing is known about faces

CONVEX All faces are convex

FILE FORMAT/DEFAULTS

ShapeHints {

vertexOrdering UNKNOWN_ORDERING # SFEnum

shapeType UNKNOWN_SHAPE_TYPE # SFEnum

faceType CONVEX # SFEnum

creaseAngle 0.5 # SFFloat

}

Sphere

This node represents a sphere. By default, the sphere is centered at the origin and has a radius of 1. The sphere is transformed by the current cumulative transformation and is drawn with the current material and texture.

A sphere does not have faces or parts. Therefore, the sphere ignores material and normal bindings, using the first material for the entire sphere and using its own normals. When a texture is applied to a sphere, the texture covers the entire surface, wrapping counterclockwise from the back of the sphere. The texture has a seam at the back on the yz-plane.

FILE FORMAT/DEFAULTS

Sphere {

radius 1 # SFFloat

}

SpotLight

This node defines a spotlight light source. A spotlight is placed at a fixed location in 3-space and illuminates in a cone along a particular direction. The intensity of the illumination drops off exponentially as a ray of light diverges from this direction toward the edges of the cone. The rate of drop-off and the angle of the cone are controlled by the dropOffRate and cutOffAngle fields.

FILE FORMAT/DEFAULTS

SpotLight {

on TRUE # SFBool

intensity 1 # SFFloat

color 1 1 1 # SFVec3f

location 0 0 1 # SFVec3f

direction 0 0 -1 # SFVec3f

dropOffRate 0 # SFFloat

cutOffAngle 0.785398 # SFFloat

}

Switch

This group node traverses one, none, or all of its children. One can use this node to switch on and off the effects of some properties or to switch between different properties.

The whichChild field specifies the index of the child to traverse, where the first child has index 0.

A value of -1 (the default) means do not traverse any children. A value of -3 traverses all children, making the switch behave exactly like a regular Group.

FILE FORMAT/DEFAULTS

Switch {

whichChild -1 # SFLong

}

Texture2

This property node defines a texture map and parameters for that map. This map is used to apply texture to subsequent shapes as they are rendered.

The texture can be read from the URL specified by the filename field. To turn off texturing, set the filename field to an empty string ("").

Textures can also be specified inline by setting the image field to contain the texture data. Specifying both a URL and data inline will result in undefined behavior.

WRAP ENUM

REPEAT Repeats texture outside 0-1 texture coordinate range

CLAMP Clamps texture coordinates to lie within 0-1 range

FILE FORMAT/DEFAULTS

Texture2 {

filename "" # SFString

image 0 0 0 # SFImage

wrapS REPEAT # SFEnum

wrapT REPEAT # SFEnum

}

Texture2Transform

This node defines a 2D transformation applied to texture coordinates. This affects the way textures are applied to the surfaces of subsequent shapes. The transformation consists of (in order) a non-uniform scale about an arbitrary center point, a rotation about that same point, and a translation. This allows a user to change the size and position of the textures on shapes.

FILE FORMAT/DEFAULTS

Texture2Transform {

translation 0 0 # SFVec2f

rotation 0 # SFFloat

scaleFactor 1 1 # SFVec2f

center 0 0 # SFVec2f

}

TextureCoordinate2

This node defines a set of 2D coordinates to be used to map textures to the vertices of subsequent PointSet, IndexedLineSet, or IndexedFaceSet objects. It replaces the current texture coordinates in the rendering state for the shapes to use.

Texture coordinates range from 0 to 1 across the texture. The horizontal coordinate, called S, is specified first, followed by the vertical coordinate, T.

FILE FORMAT/DEFAULTS

TextureCoordinate2 {

point 0 0 # MFVec2f

}

Transform

This node defines a geometric 3D transformation consisting of (in order) a (possibly) non-uniform scale about an arbitrary point, a rotation about an arbitrary point and axis, and a translation.

FILE FORMAT/DEFAULTS

Transform {

translation 0 0 0 # SFVec3f

rotation 0 0 1 0 # SFRotation

scaleFactor 1 1 1 # SFVec3f

scaleOrientation 0 0 1 0 # SFRotation

center 0 0 0 # SFVec3f

}

The transform node

Transform {

translation T1

rotation R1

scaleFactor S

scaleOrientation R2

center T2

}

is equivalent to the sequence

Translation { translation T1 }

Translation { translation T2 }

Rotation { rotation R1 }

Rotation { rotation R2 }

Scale { scaleFactor S }

Rotation { rotation -R2 }

Translation { translation -T2 }

TransformSeparator

This group node is similar to the separator node in that it saves state before traversing its children and restores it afterwards. However, it saves only the current transformation; all other state is left as is. This node can be useful for positioning a camera, since the transformations to the camera will not affect the rest of the scene, even through the camera will view the scene. Similarly, this node can be used to isolate transformations to light sources or other objects.

FILE FORMAT/DEFAULTS

TransformSeparator {

}

Translation

This node defines a translation by a 3D vector.

FILE FORMAT/DEFAULTS

Translation {

translation 0 0 0 # SFVec3f

}

WWWAnchor

The WWWAnchor group node loads a new scene into a VRML browser when one of its children is chosen. Exactly how a user "chooses" a child of the WWWAnchor is up to the VRML browser; typically, clicking on one of its children with the mouse will result in the new scene replacing the current scene. A WWWAnchor with an empty ("") name does nothing when its children are chosen. The name is an arbitrary URL.

WWWAnchor behaves like a Separator, pushing the traversal state before traversing its children and popping it afterwards.

The description field in the WWWAnchor allows for a friendly prompt to be displayed as an alternative to the URL in the name field. Ideally, browsers will allow the user to choose the description, the URL or both to be displayed for a candidate WWWAnchor.

The WWWAnchor's map field is an enumerated value that can be either NONE (the default) or POINT. If it is POINT then the object-space coordinates of the point on the object the user chose will be added to the URL in the name field, with the syntax "?x,y,z".

MAP ENUM

NONE Do not add information to the URL

POINT Add object-space coordinates to URL

FILE FORMAT/DEFAULTS

WWWAnchor {

name "" # SFString

description "" # SFString

map NONE # SFEnum

}

WWWInline

The WWWInline node reads its children from anywhere in the World Wide Web. Exactly when its children are read is not defined; reading the children may be delayed until the WWWInline is actually displayed. A WWWInline with an empty name does nothing. The name is an arbitrary URL.

The effect of referring to a non-VRML URL in a WWWInline node is undefined.

If the WWWInline's bboxSize field specifies a non-empty bounding box (a bounding box is non-empty if at least one of its dimensions is greater than zero), then the WWWInline's object-space bounding box is specified by its bboxSize and bboxCenter fields. This allows an implementation to view-volume cull or LOD switch the WWWInline without reading its contents.

FILE FORMAT/DEFAULTS

WWWInline {

name "" # SFString

bboxSize 0 0 0 # SFVec3f

bboxCenter 0 0 0 # SFVec3f

}

A node may be the child of more than one group. This is called "instancing" (using the same instance of a node multiple times, called "aliasing" or "multiple references" by other systems), and is accomplished by using the "USE" keyword.

The DEF keyword both defines a named node, and creates a single instance of it. The USE keyword indicates that the most recently defined instance should be used again. If several nodes were given the same name, then the last DEF encountered during parsing "wins". DEF/USE is limited to a single file; there is no mechanism for USE'ing nodes that are DEF'ed in other files.

A name goes into scope as soon as the DEF is encountered, and does not go out of scope until another DEF of the same name or end-of-file are encountered. Nodes cannot be shared between files (you cannot USE a node that was DEF'ed inside the file to which a WWWInline refers).

For example, rendering this scene will result in three spheres being drawn. Both of the spheres are named 'Joe'; the second (smaller) sphere is drawn twice:

Separator {

DEF Joe Sphere { }

Translation { translation 2 0 0 }

Separator {

DEF Joe Sphere { radius .2 }

Translation { translation 2 0 0 }

}

USE Joe # radius .2 sphere will be used here

}

Extensions to VRML are supported by supporting self-describing nodes. Nodes that are not part of standard VRML must write out a description of their fields first, so that all VRML implementations are able to parse and ignore the extensions.

This description is written just after the opening curly-brace for the node, and consists of the keyword 'fields' followed by a list of the types and names of fields used by that node, all enclosed in square brackets and separated by commas. For example, if Cube was not a standard VRML node, it would be written like this:

Cube {

fields [ SFFloat width, SFFloat height, SFFloat depth ]

width 10 height 4 depth 3

}

Specifying the fields for nodes that ARE part of standard VRML is not an error; VRML parsers must silently ignore the field specification.

Is-a relationships

A new node type may also be a superset of an existing node that is part of the standard. In this case, if an implementation for the new node type cannot be found the new node type can be safely treated as as the existing node it is based on (with some loss of functionality, of course). To support this, new node types can define an MFString field called 'isA' containing the names of the types of which it is a superset. For example, a new type of Material called "ExtendedMaterial" that adds index of refraction as a material property can be written as:

ExtendedMaterial {

fields [ MFString isA, MFFloat indexOfRefraction,

MFColor ambientColor, MFColor diffuseColor,

MFColor specularColor, MFColor emissiveColor,

MFFloat shininess, MFFloat transparency ]

isA [ "Material" ]

indexOfRefraction .34

diffuseColor .8 .54 1

}

Multiple is-a relationships may be specified in order of preference; implementations are expected to use the first for which there is an implementation.

<Picture>An Example

This is a longer example of a VRML scene. It contains a simple model of a track-light consisting of primitive shapes, plus three walls (built out of polygons) and a reference to a shape defined elsewhere, both of which are illuminated by a spotlight. The shape acts as a hyperlink to some HTML text.

#VRML V1.0 ascii

Separator {

Separator { # Simple track-light geometry:

Translation { translation 0 4 0 }

Separator {

Material { emissiveColor 0.1 0.3 0.3 }

Cube {

width 0.1

height 0.1

depth 4

}

Rotation { rotation 0 1 0 1.57079 }

Separator {

Material { emissiveColor 0.3 0.1 0.3 }

Cylinder {

radius 0.1

height .2

}

Rotation { rotation -1 0 0 1.57079 }

Separator {

Material { emissiveColor 0.3 0.3 0.1 }

Rotation { rotation 1 0 0 1.57079 }

Translation { translation 0 -.2 0 }

Cone {

height .4

bottomRadius .2

}

Translation { translation 0 .4 0 }

Cylinder {

radius 0.02

height .4

}

SpotLight { # Light from above

location 0 4 0

direction 0 -1 0

intensity 0.9

cutOffAngle 0.7

}

Separator { # Wall geometry; just three flat polygons

Coordinate3 {

point [

-2 0 -2, -2 0 2, 2 0 2, 2 0 -2,

-2 4 -2, -2 4 2, 2 4 2, 2 4 -2]

}

IndexedFaceSet {

coordIndex [ 0, 1, 2, 3, -1,

0, 4, 5, 1, -1,

0, 3, 7, 4, -1

]

}

WWWAnchor { # A hyperlinked cow:

name "http://www.foo.edu/CowProject/AboutCows.html"

Separator {

Translation { translation 0 1 0 }

WWWInline { # Reference another object

name "http://www.foo.edu/3DObjects/cow.wrl"

}

This section describes the file naming and MIME conventions to be used in building VRML browsers and configuring WWW browsers to work with them.

The file extension for VMRL files is .wrl (for world).

The MIME type for VRML files is defined as follows:

x-world/x-vrml

The MIME major type for 3D world descriptions is x-world. The MIME minor type for VRML documents is x-vrml. Other 3D world descriptions, such as oogl for The Geometry Center's Object-Oriented Geometry Language, or iv, for SGI's Open Inventor ASCII format, can be supported by using different MIME minor types.