| Program Interactivity |
| It doesn't matter
which format you choose, VRML or YG for the CAVE,
interactivity will need to be programmed. VRML
is programmed using Virtual Reality Programming
Language and Ygdrasil, a scripting language, is
used to program for the CVAE. |
Types of Interactivity
Both VRML and YG allow for the
same type of interactivity. The user can navigate
through the space, be tracked throughout the scene,
the geometry can be changed with switches, proximity
sensors, and moved. In an urban planning simulation,
the user might want to swap out buildings, show
options of tree and street furniture, show traffic
flow, and scale buildings. |
YG For the CAVE
|
Documentation
for YG scripting was prepared by Alex Hill,
a PhD student in the Computer Science department
at UIC. YG is constantly being updated for ease
of use and complex event handling. To create interactivity,
a scene graph is constructed, models are imported,
scripts are written to control the models and
events, then the program is "Run" in
a Linux
or Unix environment. |
A scene graph for YG might resemble the following:
|
//set up wand trigger to toggle icons
on and off
#ifndef _HAZEL_INTERFACE_
node(User0.teleport(1523 610 0)+1)
#endif
#include "hazelInterface.scene"
//set up wand trigger to toggle icons on
and off
wandTrigger(when(buttonUp1,opp17mySlider.drop),
when(button2,opp17iconSwitchA.toggle,opp17iconSwitchB.toggle))
//create a value node to increment the
object orientation
value opp17objectRotate(integer,delta(90),
when(changed,opp17movedObjectB.orientation(0
0 $value)))
transform(position(1523 626 3))
{
//create a primary model
switch opp17objectSwitchA(on)
{
object (file(32and31.pfb))
switch opp17iconSwitchA(off)
{
pointAtTrigger(when(start,opp17icon1OnSwitchA.off,opp17icon1OffSwitchA.on),
when(stop,opp17icon1OffSwitchA.off,opp17icon1OnSwitchA.on),
when(button1,opp17objectSwitchA.off+0.1,opp17objectSwitchB.on+0.1))
{
transform (position(20 -30 2))
{
group opp17icon1GroupA()
{
switch opp17icon1OffSwitchA(on)
{
object (file(initmodelsselected.pfb))
}
switch opp17icon1OnSwitchA(off)
{
object (file(initmodels.pfb))
}
}
}
transform (position(45 30 35),size(10 10
1))
{
reference(node(opp17icon1GroupA))
}
}
}
}
} |
|
|
In the above example, I am teleporting
(repositioning) the User,
loading the interface scene graph,
creating icons and activating
icons with the PointAt Trigger (I created a set
of 3 icons for each parcel: rotation, switch between
models, and a slider that allowed me to move the
building.) The icons are similar to "rollovers"
on web pages. When the icon is activated via the
PointAt Trigger, the icon would light up. When
you press button1 on the CAVE Wand (the Cave's
mouse) the building could be swapped, moved, or
rotated depending on which icon you activated,
Here,
switch opp17objectSwitchA(on)
{
object (file(32and31.pfb))
I am loading the building named 32and31.pfb under
the SwitchA, when switch A is on, the model 32and31.pfb
will be visible. |
VRML For the Web
|
 |
In VRML, events are routed to each other
to control interactivity. The easiest
way to program interactivity in VRML is
to use Cosmo Worlds. In this program,
an outline editor will enable you visually
route objects to scripts. A toolbar (shown
left) will enable you to construct interactivity.
Proximity, touch, cylinder, sphere, plane,
time, and visibility sensors can be routed
to geometry. Additionally, interpolators
for points, colors, orientation and coordinates
are built in to Cosmo. A scene graph of
the constructed geometry and interactivity
can be seen in Cosmo. Below, a Level of
Detail (LOD) has been applied to a building.
The LOD enables different models of the
building to be switched out depending
on the range of the user within the world.
At 150 feet away, the most detailed model
is switched to the secondary model consisting
of less detail and a lower resolution
texture map. At 250 feet away, the secondary
model is switched off and no building
can be seen.
|
General Rules for Routing:
Events are of two types: outgoing
events send values, and incoming events receive
values. Many fields have both an outgoing event
(called an eventOut) and an incoming event (called
an eventIn) associated with them. The Outline
Editor uses a graphical shorthand arrow to show
these events.
The left-pointing arrow indicates the eventIn,
and the right-pointing arrow indicates the eventOut.
When you connect an eventOut to an eventIn (or
vice versa), the connection between them is
called a route (also sometimes referred to as
a wire).
The Outline Editor does not let you make "illegal"
routes.
Here's a list of rules for routing events:
- Incoming events are always routed to outgoing
events, and vice versa. You can't route two
incoming events to each other, or two outgoing
events to each other.
- The types of the events at both ends of the
route must be identical. For example, a single-valued
color event (SFColor) to a multi valued color
event (MFColor).
- You can't route an outgoing event to an incoming
event for the same field.
- You can’t route one SFNode event to
another if the two are not allowed to use the
same kind of node. For instance, you can’t
route a material event to or from a texture
event even though they’re both SFNode
events, because the material field requires
a Material node and the texture field requires
a texturing node.
- Detailed type-checking is not done on SFNode
events in prototypes and scripts; so the Outline
Editor allows you to create this last sort of
illegal route to or from events of a prototype
or a script. Check your prototypes and scripts
carefully to make sure that their SFNode events
send and receive legal nodes.
- You can't route from the 'children' field
of one grouping node to the children of one
of its descendants because this would cause
a cycle.
- This
tutorial for the Cosmo outline editor is very
helpful.
A portion of a scene graph for VRML might resemble
the following:
| #VRML V2.0 utf8 #Cosmo Worlds
V2.0
LOD {
center 338.82 4.05152 61.669
range [ 150, 250 ]
level [
Transform {
children [
Transform {
children Shape {
appearance Appearance {
material DEF _0 Material {
}
texture ImageTexture {
repeatS TRUE
repeatT TRUE
url "images/506_56th_1.png"
}
textureTransform NULL
}
geometry DEF _1 IndexedFaceSet {
coord Coordinate {
point [ -1 1 1,
-1 -1 1,
1 -1 1,
1 1 1 ]
}
coordIndex [ 0, 1, 2, 3, -1 ]
texCoord TextureCoordinate {
point [ 0 1,
0 0,
1 0,
1 1 ]
}
creaseAngle 0.5
normalIndex [ ]
texCoordIndex [ 0, 1, 2, 3, -1 ]
}
}
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