© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING Chapter 2 – Basic VRML

© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING Structure of VRML File  A VRML file consists of the following major functional components  the VRML header  the scene graph which includes  Shapes  Interpolators  sensors and scripts  the prototypes  event routing

© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING #VRML V2.0 utf8 # A brown hut Group { children [ # Draw the hut walls Shape { appearance DEF Brown Appearance { material Material { diffuseColor } geometry Cylinder { height 2.0 radius 2.0 } },

© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING # Draw the hut roof Transform { translation children Shape { appearance USE Brown geometry Cone { height 2.0 bottomRadius 2.5 } ] }

© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING VRML Header  For easy identification of VRML files, every VRML file shall begin with  #VRML V2.0  The is either " utf8 " or any other authorized values defined in other parts of ISO/IEC  In this course, we are using " utf8" which indicates a clear text encoding that allows for international characters to be displayed in VRML

© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING UTF-8 File Format  # character begins a comment  Only the first comment (the file header) has semantic meaning  The only exception is within double-quoted SFString and MFString fields where the # character is defined to be part of the string  Commas, spaces, tabs, linefeeds, and carriage-returns are separator characters wherever they appear outside of string fields  One or more separator characters separate the syntactical entities in VRML  The separator characters collectively are termed whitespace

© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING VRML Statements  VRML file may contain any combination of the following :  Any number of PROTO or EXTERNPROTO statements  Any number of root children node statements  Any number of USE statements  Any number of ROUTE statements

© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING Scene Graph  The scene graph contains nodes, which describe objects and their properties  It contains hierarchically grouped geometry to provide an audio-visual representation of objects  It also provides a means for nodes to participate in the event generation and routing mechanism

© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING Nodes  Nodes are used to describe shapes and properties of the world such as:  shapes  colors  lights  viewpoints, how to position and orient shapes  animation times, sensors and interpolators

© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING Nodes  A node contains the following information:  type of nodes  a set of curly brackets  fields  For example, a cylinder node could be described: cylinder { height 2.0 radius 2.0 }

© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING Fields and Field Values  Fields define the attributes of a node  In the above example, the height field defines the height of the cylinder  Fields are optional within the nodes  If the values are not given, then a default value would be assigned  For example, the default values of cylinder have radius = 1.0 units and height = 2.0 units  Field values defines the attributes like color, size or position

© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING Defining and Using Node Name  Any node can be defined in the world  The name of the node must begin with a letter, followed by any combination of characters and/or digits  DEF node_name name_type  Once a node has a name, we could reuse the node.  The node with defined name is called original node while the reuse nodes are called instances  USE node_name  Note that the node names are case-sensitive

© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING Describing Shapes  A VRML shape has appearance (based on material), color and surface texture  These attributes are specified by the field values within a shape node  VRML supports several primitives shape geometries that include boxes, cylinders, cones, and shapes  VRML also supports advanced shape geometries like extruded shapes and elevation grids  Using these primitive shapes, we could group them and build more complex shapes  Shapes can be grouped by the Group node

© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING Event Routing  Some VRML nodes generate events in response to environmental changes or user interaction  Event routing provides a mechanism, which allow events to be propagated to effect changes in other nodes  Once generated, events are sent to their routed destinations in time order and processed by the receiving node  This processing can change the state of the node, generate additional events, or change the structure of the scene graph

© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING Event Routing  In order to build a dynamic world and propagate events based on environmental changes, we need “wiring instructions”  This process involves  a pair of nodes to wire together  a wiring route or path between these two nodes  Once the nodes are wired, messages could be sent along that route  Such message is called events which contains communicating values

© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING Event Routing  For a successful routing, nodes must have eventIn and the corresponding eventOut  An eventIn receives events when it is connected to a route and a message is being sent to it  An eventOut sends the events out along the connected route  VRML “wiring” architecture is built by describing a route from one node’s eventOut to another node’s eventIn

© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING Event Routing  The receiving node reacts based on the event depends on the following:  type of node receiving the event  node input jack to which the route is wired  values contained in the event  current activities of the node

© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING Presentation and Interaction  The interpretation, execution, and presentation of VRML files will typically be undertaken a browser, which displays the shapes and sounds in the scene graph  This presentation is known as a virtual world and is navigated in the browser by a human or mechanical entity, known as a user  The world is displayed as if experienced from a particular location; that position and orientation in the world is known as the viewer

© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING Presentation and Interaction  The browser may define navigation paradigms (such as walking or flying) that enables the user to move the viewer through the virtual world  The browser may provide a mechanism allowing the user to interact with the world through sensor nodes in the scene graph hierarchy  Sensors respond to user interaction with geometric objects in the world, the movement of the user through the world, or the passage of time

© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING Presentation and Interaction  The visual presentation of geometric objects in a VRML world follows a conceptual model designed to resemble the physical characteristics of light  The VRML lighting model describes how appearance properties and lights in the world are combined to produce displayed colours  Refer to the diagram for the conceptual model of the VRML browser

© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING Presentation and Interaction Conceptual Model of VRML Browser

© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING USE Statement  The USE statement enables us to reuse all the objects that we have defined earlier in the scene graph  A USE statement consists of the USE keyword followed by a node name as follows:  USE

© TMC Computer School HC20203 VRML HIGHER DIPLOMA IN COMPUTING ROUTE Statement  A ROUTE statement provides the message passing mechanism from one node to another  A ROUTE statement consists of the ROUTE keyword followed in order by a node name, a period character, a field name, the TO keyword, a node name, a period character, and a field name.  Whitespace is allowed but not required before or after the period characters:  ROUTE. TO.  All these commands will be covered in more details as the course proceeds