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CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
VRML
Virtual Reality Modeling LanguageVirtual Reality Modeling Language
http://www.parallelgraphics.com/products/cortona/http://www.parallelgraphics.com/products/cortona/
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
VRML
• In addition to HTML (HyperText Markup Language), that has become a standard authoring tool for the creation of home pages, VRML provides 3D worlds with integrated hyperlinks on the Web.
• Home pages become home spaces.
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
• A text file format • A simple language for describing 3-D shapes and interactive environments • A web standard
• VRML is endorsed by most 3-D graphics vendors and most web browser vendors
• Virtual environments are realized by a player (browser) that interprets, executes, and presents VRML files
1. What is VRML
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
You can write VRML files using: • Any text editor • Many world builder applications
You can view VRML files using: • A VRML browser • A VRML plug-in to an HTML browser
such as Cortona Player or Cosmo Player
Writing and Viewing VRML Files
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
VRML files contain:
• Header • Comments - notes to yourself • Nodes - nuggets of scene information • Fields - node attributes you can change • Field Values - attribute values • Node Names - names for reusable nodes
• Nodes have field and field values that describe their attributes. Shape nodes are used to define shapes with appearance and geometry.
VRML File Format
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Nodes can be named, and used repeatedly
DEF MyCylinder Shape { . . . } . . .
USE MyCylinder . . . USE MyCylinder
Defining Names for Nodes
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•Shapes are the building blocks of a VRML world •Primitive Shapes are standard building blocks:
• Box • Cone • Cylinder • Sphere
Example: prim.wrl
2. Building Primitive Shapes
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Understanding Shapes
• Shape nodes describe:
• geometry - form, or structure • appearance - color and texture
Shape { geometry . . . appearance . . . }
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
• Shape geometry is built with geometry nodes
• Standard, primitive geometry nodes include:
• Box { . . . } • Cone { . . . } • Cylinder { . . . } • Sphere { . . . }
Specifying Geometry
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
• Geometry node fields control dimensions
Box { size 2.0 0.5 3.0 } Cone { height 3.0 bottomRadius 0.75 } Cylinder { height 2.0 radius 1.5 } Sphere { radius 1.0 }
• Dimensions are usually in meters, but they can be anything
Setting Geometry Dimension
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
#VRML V2.0 utf8 # A Cylinder Shape { appearance Appearance { material Material { } } geometry Cylinder { height 2.0 radius 1.5 } }
Examples: cylinder.wrl
A Sample Primitive Shapes
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
• children - a list of member nodes for the group
Group { children [ Shape { . . . }, Shape { . . . }, . . . ] }
Understanding Groups
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
• Text Shapes build text in a VRML world
• Signs, notes, annotation, control panels
• Text shapes are flat and have no thickness
• You can choose the font family, style, size, etc.
3. Building Text Shapes
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•Text geometry nodes describe:
•text strings - the text to build •font style - how to build the text
Shape { geometry Text { string . . . fontStyle . . . } }
Understanding Text
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
• Text strings list the text to build
• Each string is built on its own line or column
Text { string [ "SIGGRAPH 96", "Conference" ] }
Building Text Strings
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Font styles have: •family - serif, sans, or typewriter •style - bold, italic, both, or none •size and spacing- character size and spacing
FontStyle { family "SERIF" style "BOLD" size 1.0 spacing 1.0 }
Specifying Font Style
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Font styles also have: •justification - begin, middle, end •direction - left/right, up/down
FontStyle { justify "BEGIN" horizontal TRUE leftToRight TRUE topToBottom TRUE }
Specifying Font Direction
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Shape { . . . geometry Text { string [ "SIGGRAPH 96", "Conference" ] fontStyle FontStyle { style "BOLD" } } }
Examples: sigtext.wrl
A Sample Text Shape
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
4. Transform Shapes
• By default, all shapes are built at the center of the world
• A transform enables you to
1. Translate shapes
2. Rotate shapes
3. Scale shapes
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•A VRML file builds components for a world
•A file's world components are built in the file's world coordinate system
Understanding Coordinate System
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
A transform creates a coordinate system that is translated, rotated, scaled relative to a parent coordinate system
Shapes built in the new coordinate system are translated, rotated, and scaled along with it
Understanding Coordinate System Transform
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
A Transform group node controls: •translation - position •rotation - orientation •scale - size
Transform { translation . . . rotation . . . scale . . . children [ . . . ] }
Specifying Transform
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•Translating positions a coordinate system in X, Y, and Z
Transform { # X Y Z translation 2.0 0.0 0.0 children [ . . . ] }
Translating
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•Rotating orients a coordinate system about a rotation axis by a rotation angle
•Angles are measured in radians
Transform { # X Y Z Angle rotation 0.0 0.0 1.0 0.52 children [ . . . ] }
Rotating
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
• A rotation axis defines a pole to rotate around
• Like the Earth's North-South pole
• Typical rotations are about the X, Y, or Z axes:
• Rotate about Axis X-Axis 1.0 0.0 0.0 Y-Axis 0.0 1.0 0.0 Z-Axis 0.0 0.0 1.0
Understanding Rotating Axis
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•Scaling grows or shrinks a coordinate system by a scaling factor in X, Y, and Z
Transform { # X Y Z scale 0.5 0.5 0.5 children [ . . . ] }
Scaling
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•Scale, Rotate, and Translate a coordinate system, one after the other
Transform { translation 2.0 0.0 0.0 rotation 0.0 0.0 1.0 0.52 scale 0.5 0.5 0.5 children [ . . . ] }
Scaling, Rotating & Translating
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Transform { translation 4.0 0.0 0.0 rotation 0.0 1.0 0.0 0.785 scale 0.5 0.5 0.5 children [ . . . ] }
Examples: archs.wrl
A Sample Transform Group
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
5. Controlling Appearance with Material
•The primitive shapes have a default emissive (glowing) white appearance
•You can control a shape's
Shading color Glow color Transparency
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
The appearance of a surface is defined by setting properties that define the material from which it is made. A texture can also be defined to improve the appearance of a surface.
•material properties - color, transparency, etc.
Shape { appearance Appearance { material . . . } geometry . . . }
Understanding Appearance
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•A Material node controls: •diffuse color - main shading color •emissive color - glowing color •transparency - opaque or not
Material { diffuseColor . . . emissiveColor . . . transparency . . . }
Understanding Materials
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Three types of Material Reflection
•diffuseColor Color of reflected light from diffuse reflection (light scattered randomly) •ambientIntensity Amount of background light the surface reflects •specularColor Color of reflected light from specular reflection (light reflected in a regular manner)
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•Colors specify: •A mixture of red, green, and blue light •Values between 0.0 (none) and 1.0 (lots)
•Color Red Green Blue
White 1.0 1.0 1.0 Black 0.0 0.0 0.0 Yellow 1.0 1.0 0.0 Magenta 1.0 0.0 1.0 Brown 0.5 0.2 0.0
Understanding Colors
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Shape { appearance Appearance { material Material { diffuseColor 1.0 1.0 1.0 } } geometry . . . }
Example: slabs.wrl
A Sample World using Appearance
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Making a Shape Shining
• By specifying "high" values for the Material node's shininess field, direct light will cause a specular hilight (or shiny spot) on a shape
• By specifying a value for the Material node's specularColor field, you can control the color of specular hilights (or shiny spots) on a shape
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
6. Grouping Nodes
•Shapes can be grouped to compose more complex shapes
•VRML has several grouping nodes, including: Group { . . . } Switch { . . . } Transform { . . . } Billboard { . . . }
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•The Group node creates a basic group
•Every child node in the group is displayed
Group { children [ . . . ] }
Understanding Basic Groups
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•The Transform group node creates a group with its own coordinate system
•Every child node in the group is displayed
Transform { translation . . . rotation . . . scale . . . children [ . . . ] }
Understanding Transform Groups
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•The Switch group node creates a switched group
•Only one child node in the group is displayed
•You select which child
Switch { whichChoice 0 choice [ . . . ] }
Understanding Switching Groups
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
• The Billboard group node creates a group with a special coordinate system
• Every child node in the group is displayed
• Coordinate system is turned to face viewer
Billboard { axisOfRotation . . . children [ . . . ] }
Understanding Billboard Groups
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•A rotation axis defines a pole to rotate round
•Similar to a Transform node's rotation field, but no angle (auto computed)
Billboard Rotation Axes
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Group { children [ Billboard { axisOfRotation 0.0 1.0 0.0 children [ ... ] }, Transform { . . . } ] }
Example: robobill.wrl
A Sample Billboard Group
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Inlining World Components
• VRML files describe components of a world: tables, chairs, lamps, walls, floors, doors
• Inlining combines files to build larger components: rooms, buildings, neighborhoods
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•The Inline node creates a special group
•Children are read from a VRML file selected by a URL
•Every child node in the group is displayed
Inline { url "table.wrl" }
Understanding Inlining
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
. . . Inline { url "table.wrl" }, . . . Transform { translation . . . children [ Inline { url "chair.wrl" } ] }, . . .
Example: dinette.wrl
A Sample Inlined File
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Adding Anchors to Your World
•Any shape or group of shapes can be an anchor
•Selecting the anchor jumps to a new VRML world •Like the <a href="page.html"> syntax of HTML
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
• The Anchor node creates a group
• Every child node in the group is displayed
• Selecting any child jumps to VRML file specified by URL
• The anchor can have a description string
Understanding Anchors
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
A Sample Anchor
Anchor { url "stairway.wrl" description "Floating Stairs" children [ . . . ] }
Example: anchor.wrl
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
7. Coordinate based Geometry: Points, Lines, and Faces
•Create more complex shapes than primitives
•Generate more efficient VRML worlds
•Have more control and flexibility than primitives
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
• Hard to build using primitives• There's a more flexible way to describe
shapes...
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
(1) Specifying Coordinates (Define location of "dots“)• Location of dots (points) using Coordinate node Coordinate { point [ 2.0 1.0 3.0, 4.0 2.5 5.3, . . . ] }
(2) Creating Geometry Using Coordinates (Connect the dots )• Three nodes have a coord field which accepts a Co
ordinate node • PointSet • IndexedLineSet • IndexedFaceSet
Describe Geometry in two steps
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
PointSet Node
•A dot is drawn at each point PointSet { coord Coordinate { point [ . . . ] } color Color { color [ . . . ] }}
•No control over size of dot
•Also supports color field for Color node
Example: ptplot.wrl
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•Straight lines are drawn between points
IndexedLineSet { coord Coordinate { point [ . . . ] } coordIndex [ 1, 0, 3, -1, . . . ] }
Example: lnplot.wrl
IndexedLineSet Node
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
coordIndex [ 1, 0, 3, -1, . . . ]
•Indexes reference ordered points of coord field •Index order is arbitrary (eg: 1, 0) •Indexes are Zero-based (eg: 0) •Can skip coordinates (eg: 0, 3) •Poly-line can be many points (eg: 1, 0, 3) •End of poly-line (eg: -1) •Multiple poly-lines (eg: . . .)
CoordIndex Value
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
IndexedFaceSet Node
•Faces are drawn within perimeter of points
IndexedFaceSet { coord Coordinate { point [ . . . ] } coordIndex [ 1, 0, 3, -1, . . . ] }
Example: vase1.wrl
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
8. Binding Color to Coordinate based Geometry
•Override Material node (overall color)
•Better color control for IndexedFaceSet, IndexedLineSet, PointSet, and ElevationGrid nodes
•Apply color per-face or per-vertex
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•The Color node is used as the color field value of IndexedFaceSet, IndexedLineSet, PointSet or ElevationGrid nodes
•The Color node contains a list of RGB values
Color { color [ 1.0 0.0 0.0, . . . ] }
Color Node
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
IndexedFaceSet { coord Coordinate { . . . } coordIndex [ . . . ] color Color { color [ 1.0 0.0 0.0, . . . ] } colorIndex [ 3, 0, 1, . . . ] colorPerVertex TRUE }
IndexedFaceSet using a color node
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•In IndexedFaceSet, IndexedLineSet nodes
•When colorPerVertex is TRUE, specify one color index per coordinate index (don't forget to account for the -1's !)
•When colorPerVertex is FALSE, specify one color index per face or line (eg. per -1)
ColorPerVertexField
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•Colored triangles: per-face and per-vertex
•Example: color_face.wrl, color_vertex.wrl
A sample Color Binding
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
9. Mapping Texture
•Wrap images around shapes •Apply an image as an opaque "decal" •Apply an image with transparent "holes"
•Wrap a movie's images around shapes
•Add realistic appearance to shapes
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•Texture color overrides Material node color
•Appearance node's texture field wraps an image around geometry
•The texture can be an ImageTexture, MovieTexture, or PixelTexture
Texture Property
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Appearance { material Material {} texture ImageTexture { url "myimage.jpg" } }
ImageTexture Node
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Appearance { texture MovieTexture { url "mymovie.mpg" speed 1 loop FALSE } }
MovieTexture Node
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•The PixelTexture node contains data stored as width, height, number of channels, followed by width*height hex values representing the image
•Example: A 2x4 RGB image
PixelTexture { image 2 4 3 0xFF0000 0x00FF00 0 0 0 0 0xFFFFFF 0xFFFF00 }
PixelTexture Node
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
10. Texture Control
When applying a texture, you sometimes need to control:
• What piece of a texture is extracted from an image
• How the piece of texture is applied to a face
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
I. Build cookie cutter of desired size and shape
II. Set position, rotation and scale over sheet
III. Extract a piece of dough from sheet, and apply extracted piece of dough onto shape
Three steps to apply a piece of texture
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
texCoord TextureCoordinate { point [ 0.2 0.2, 0.8 0.2, 0.8 0.8, 0.2 0.8 ] }
• Note: texCoord is a field of IndexedFaceSet, ElevationGrid nodes
I. Build Cookie Cutter Shape
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
• Appearance node's textureTransform field sets position, rotation and scale of cutter over the dough
TextureTransform { translation 0.5 0.5 rotation 0.0 scale 2.0 2.0 }
II. Texture Transform
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
• IndexedFaceSet extracts and applies the piece of texture to faces
IndexedFaceSet { coord Coordinate { . . . } coordIndex [ . . . ] texCoord TextureCoordinate { . . . } texCoordIndex [ . . . ] }
III. Extract and Apply Texture
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Texture Transform: Scale
TextureTransform { scale 3.0 3.0 }
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Texture Transform: Transform
TextureTransform { translation 0.166 0.0 } # 1/6
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Texture Transform: Rotation
TextureTransform { rotation 0.785 # 45 degrees }
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
11. Shading Control using Normals
•Normals define the direction of faces
•Faces used to approximate smooth surfaces, but normals can be used to control whether a surface is flat or smoothly shaded
•Default Normals are often good enough !
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•To control shading of ElevationGrid, and IndexedFaceSet nodes
•Specify normal, normalIndex, and normalPerVertex field values or…
•Set the creaseAngle field to automatically generate normals
Shading Control Tools
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•The normal field specifies face direction
Normal { vector [ 1.0 0.0 0.0, 0.0 1.0 0.0, 0.0 0.0 1.0, . . . ] }
Normal Node
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
CreaseAngle Field
•If angle between adjacent faces is larger than creaseAngle, then faces are flat shaded.•If angle between adjacent faces is smaller than creaseAngle, then faces are smoothly shaded.
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Shading
Flat• Surface colored uniformly according to its orientation towards light sources • Faceted appearance
Smooth (Gouraud)• Each vertex is assigned a color according to its orientation towards light sources and intermediate points are a blend of the surrounding vertex colors • Smooth shading • Can be too smooth (can smooth away detail)
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
12. Lights
•Light sources illuminate and effect shading of faces
•Several types of lights available for maximum control •Lights do not cast shadows
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•Three different light nodes
•PointLight, DirectionalLight, SpotLight
•Standard fields (common to all 3) and defaults:
•on TRUE •intensity 1.0 •ambientIntensity 0.0 •color 1.0 1.0 1.0
Light Node
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Point lights have a location and glow radially
PointLight { # Standard fields, plus: location 0.0 0.0 0.0 radius 1.0 #specifies the maximum distance for the light rays to travel
attenuation 1.0 0.0 0.0 }
PointLight Node
2
1
cdbdafactornattenuatio
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Directional lights point in a specified direction
DirectionalLight { # Standard fields, plus: direction 1.0 0.0 0.0 }
Directional Light
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Spot lights point in a direction and focus in a cone
SpotLight { # Standard fields, plus: location 0.0 0.0 0.0 direction 1.0 0.0 0.0 cutOffAngle 0.785 radius 1.0 attenuation 1.0 0.0 0.0 }
Spot Light
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•Backgrounds add realism to VRML worlds
•Backgrounds are cheaper than using geometry •Backgrounds always stay "infinitely distant"
13. Background
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•Two types of background (can be combined)
•Backdrop: Sky and Ground color gradients(Mapped to inside of a sphere)
•Panorama: Surrounding images(Mapped to inside faces of a cube)
Backdrop vs. Panorama
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•xxxColor specifies color values
•xxxAngle specifies angles in radians (0 .. PI)
Background { groundColor [ .14 .28 0, .09 .11 0, 0, 0, 0 ] groundAngle [ .785, 1.57 ] skyColor [ .02 0 .26, .02 0 .65, 0, 0, 0 ] skyAngle [ .785, 1.57 ] }
Example: m_bkgd1.wrl
Specifying Backdrop
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Specifying Panorama
•xxxUrl fields specify images
•Images overlay backdrop (if any)(backdrop shows through transparent regions)
Background { frontUrl "f_image.jpg" backUrl "b_image.jpg" leftUrl "l_image.jpg" rightUrl "r_image.jpg" }
Example: m_bkgd2.wrl
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•Fog is a "special effect" for added realism
•Exact effects (if any) are browser dependent
•Colors "fade" to a specified value over distance
14. Fog
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
VRML Fog Example#VRML V2.0 utf8 Group { children [ ... Fog { color 1.0 1.0 1.0 fogType "EXPONENTIAL" visibilityRange 30.0 } ] }
Fog Node
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•Fog can be used to provide a depth cue, add atmosphere, and increase realism
•Colors fade to value specified in color field.
•visibilityRange specifies distance at which fog color predominates. Value 0 disables node.
Example: fog1.wrl, fog2.wrl, fog4.wrl
Fog Example
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
15. Level of Detail
•LOD (Level Of Detail):
•Can reduce "upfront" download time(have simpler models loaded first)
•Can improve frame rate(use simpler models for far away objects)
•Useful as a depth cue
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
• An object is rendered with more detail when a user is close to it than when the user is far away
• An object can have several levels of detail, each valid for a different range of distances
• Hardware assist the transition between levels of detail to make them as smooth as possible
Levels of Detail
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•Range specifies distance from center of LOD to viewer (for each transition between levels) •Grouping node (one child displayed at a time).
LOD { range [ . . . ] center 0 0 0 level [ . . . ] }
LOD Node
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Using Ranges
•List range values in increasing order.
•Define children in order of highest to lowest detail.
•For N ranges, provide N+1 children
range [ 20, 100 ] < 20 m 1st child used >= 20 & < 100 m 2nd child used >= 100 m 3rd child used
Example: m_lod1.wrl, m_lod2.wrl
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•Making good levels of detail is tricky. •Two or three levels are usually enough. •Remove "details" that are easy to remove•Simplify geometry if appropriate
•Everything is a hint!(Browser decides which level to display.) •LOD can get large, use Inline for some kids.
•Don't use LOD to simulate behavior. •center is not a translation.
Optimizing Strategy
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•Primarily used to define named camera positions
•Browser will usually present a list of viewpoints using their description strings.
•Browser may animate between viewpoints.
16. Controlling the View Point
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Using Viewpoint
• Orientation defines direction of view and "up" direction (relative to default orientation). Rotation
Viewpoint { position 0 0 9 orientation 0 0 1 0 description "DefaultView" }
Example:m_vwpts1.wrl
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
• Sound adds realism and allows special effects • General uses:
1. Continuous background (traffic, muzak, ...) 2. Continuous localized (waterfall, monster, ...) 3. Triggered (bumping wall, clicking switch, ...)
17. Adding Sound
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•A Signal •AudioClip or MovieTexture Node •Think of this as the "CD player"
•A Location •Sound Node •Think of this as the "speaker"
CD Player vs. Speaker
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•AudioClip specifies a signal •Typically .wav or .mid file •Start time, pitch, looping or not
•Sound specifies a place •Location, direction, attenuation region •Intensity, "spatialized" or not
AudioClip vs. Sound
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•Playback started by: •Setting startTime field
•Setting loop to TRUE
AudioClip { url [ . . . ] loop FALSE startTime 0 }
AudioClip Node
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•Audible if clip is playing and node is "traversed"
Sound { source AudioClip { . . . } intensity 1 location 0 0 0 direction 0 0 1 spatialize TRUE }
Basic Sound Node
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Advanced Sound Node
•Defines two ellipsoids aligned with direction
•Full intensity within inner ellipsoid
•Intensity drops to zero between inner and outer
Sound { . . . minFront 1 maxFront 10 minBack 1 maxBack 10 }
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•In AudioClip node set •loop field to TRUE (Will start on entering world)
•In Sound node set •minFront and minBack to large values. •spatialize to FALSE (stereo clip will play as stereo)
Example: m_sound1.wrl
Continuous Background Sound
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•Set AudioClip node same as previous. •In Sound node set
•position and direction •minFront, maxFront, ... values •spatialize to TRUE (clip will play as monaural)
Example: m_sound2.wrl
Continuous Localized Sound
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
•In AudioClip node set •loop field to FALSE (for a "one shot") •startTime each time sound should play (discussed later)
•In Sound node set •location, direction, ... •spatialize to TRUE (usually)
Example: m_sound3.wrl
Triggered Sound
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
18. Fields and Events
• Each node has specific fields and events
1. Field : A stored value (parameter), eg. url 2. EventIn : An event node can receive, eg. set_url 3. EventOut : An event node can send, eg. url_changed
• Event: A message that contains a data value
CVVR Lab.@ National Dong Hwa Univ. 國立東華大學
Routes
•Route: Connects an EventOut to an EventIn
•A Route is not a node!
•Output type must match input type exactly
•Output may connect to multiple inputs (fan-out)
•Multiple outputs may connect to single input (fan-in)
•Nodes must be named in order to use Routes