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Techniques of Perception in VRML97
by n_polys 08_2001
Visual
Perception
- We need light and an eye (camera)
to see anything!
- On a 2D screen, the environment
is actively rendered from a user ‘Viewpoint’.
Depth information
is recovered in the Field of View by occlusion and relative size. Recent advances in stereo-optic goggle displays means that the environment
can be rendered for 2
eyes, giving the added spatial effect of ‘binocular disparity’.
- fieldOfView effects visual mapping
of scene to screen(like a Fish-eye lens or telescope)
- You can use the Binding Stack
and ROUTEs to dynamically change the current Viewpoint
node. The first bind-able
node encountered in the file will the bound and placed at the
top of the binding stack.
- Viewpoints can be animated in the
same way as a movie-camera runs through a shot.
They are also affected by their parent Transform(s).
A
‘Transform’ node manifests and locates its children nodes within
the world space and scene hierarchy.
‘ROUTEs’ allow events and information to pass between nodes. In most cases, a named (DEF’d) Transform node acts as the
ROUTE destination for animating the translation and rotation
of objects. The Viewpoint node’s ‘position’ field is also
exposed and so can receive similar animation data. This idea of nested parent/child nodes and
their results has been explored in many other tutorials and books,
so we will not delve into it here. It is important to remember that
it is a compounding, cumulative process as one adds additional parent
Transforms.
We
will, however, emphasize that good story-board planning and scene
design will determine the most efficient scene graph (node hierarchy).
The
Viewpoint Node:
- position
- orientation
- fieldOfView
- description
- jump
- set_bind
Viewpoint
example
| Explore
this solar system and space station by paging through the different
viewpoints. If you see any red balls, see if you can guess
what Viewpoint field theyare
animating. |
Lighting Nodes:
on, intensity, ambientIntensity, color
- Pointlight
(attenuation)
- DirectionalLight (like
sun, lights sibling and offspring)
- Spotlight
(direction, beamWidth, cutOffAngle)
Light
Example: types
| The
Dials control the fields of different lights in the scene and
spheres turn the lights off and on.
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| Spheres:
Top:
Spotlight on/off
Middle:
Directional Light on/off
Bottom:
PointLight on/off
|
Dials:
Pointlight:Red
Green
Blue
Intensity
DirectionalLight:
intensity
Spotlight:
beamWidth
|
|
Click
and drag on different objects in the scene- you can rotate
them with a SphereSensor node.
|
Illuminating
objects:
- Normals (for
tight lighting control)
- Appearance
and Materials:
shininess, transparency, specular, emmisive, and diffuse colors
in RGB
- creaseAngle
: shading across polygons of the mesh
- Textures with (or without) alpha channels
(transparency) can be applied and mapped to geometry as fixed
or animated maps. Standard
formats: .png, .jpg, .gif
- Currently, shadows must be faked with
textures or other techniques.
Multi-texturing and advanced appearance functionality
was shown by leading browser companies recently in X3D extensions
dealing with these exact issues.
Lighting
example: objects
| These objects show the effect of creaseAngle
values. the demo also
has dials to interactively control an object’s transparency
and shininess. |
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