behaviors.html

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object's scheduling region. If the ViewPlatform object's activation
volume does not intersect with a behavior's scheduling region,
Java 3D
can safely ignore that behavior's wakeup criteria.
</p>
<p>In essence, the Java&nbsp;3D scheduler performs the following
checks:
</p>
<ul>
  <li>Find all Behavior objects with scheduling regions that intersect
the active ViewPlatform object's activation volume.</li>
</ul>
<ul>
  <li>For each Behavior object within the ViewPlatform's activation
volume, if that behavior's WakeupCondition is <code>true</code>,
schedule that Behavior object for execution.</li>
</ul>
<p>Java&nbsp;3D's behavior scheduler executes those Behavior objects
that
have
been scheduled by calling the behavior's <code>processStimulus</code>
method.
</p>
<h2>Interpolator Behaviors</h2>
<p>This section describes Java&nbsp;3D's predefined <a
 href="../Interpolator.html">Interpolator</a> behaviors.
They are called <em>interpolators</em>
because they smoothly interpolate between the two extreme values that
an interpolator can produce. Interpolators perform simple behavioral
acts, yet they provide broad functionality.
</p>
<p>The Java&nbsp;3D API provides interpolators for a number of
functions:
manipulating transforms within a TransformGroup, modifying the values
of a Switch node, and modifying Material attributes such as color and
transparency.
</p>
<p>These predefined Interpolator behaviors share the same mechanism for
specifying and later for converting a temporal value into an alpha
value. Interpolators consist of two portions: a generic portion that
all interpolators share and a domain-specific portion.
</p>
<p>The generic portion maps time in milliseconds onto a value in the
range
[0.0, 1.0] inclusive. The domain-specific portion maps an alpha value
in the range [0.0, 1.0] onto a value appropriate to the predefined
behavior's range of outputs. An alpha value of 0.0 generates an
interpolator's minimum value, an alpha value of 1.0 generates an
interpolator's maximum value, and an alpha value somewhere in between
generates a value proportionally in between the minimum and maximum
values.
</p>
<h3>Mapping Time to Alpha</h3>
<p>Several parameters control the mapping of time onto an alpha value
(see
the javadoc for the <a href="../Alpha.html">Alpha</a> object for a
description of the API).
That mapping is deterministic as long as its parameters do not change.
Thus, two different interpolators with the same parameters will
generate the same alpha value given the same time value. This means
that two interpolators that do not communicate can still precisely
coordinate their activities, even if they reside in different threads
or even different processors-as long as those processors have
consistent clocks.
</p>
<p><a href="#Figure_1">Figure
1</a>
shows the components of an interpolator's time-to-alpha mapping. Time
is represented on the horizontal axis. Alpha is represented on the
vertical axis. As we move from left to right, we see the alpha value
start at 0.0, rise to 1.0, and then decline back to 0.0 on the
right-hand side.
</p>
<p>On the left-hand side, the trigger time defines
when this interpolator's waveform begins in milliseconds. The region
directly to the right of the trigger time, labeled Phase Delay, defines
a time period where the waveform does not change. During phase delays
alpha is either 0 or 1, depending on which region it precedes.
</p>
<p>Phase delays provide an important means for offsetting multiple
interpolators from one another, especially where the interpolators have
all the same parameters. The next four regions, labeled <b>&#945;</b>
increasing, <b>&#945;</b> at 1, <b>&#945;</b> decreasing, and
<b>&#945;</b> at 0, all specify durations for
the corresponding values
of alpha.
</p>
<p>Interpolators have a loop count that determines how many times to
repeat the sequence of alpha increasing, alpha at 1, alpha decreasing,
and alpha at 0; they also have associated mode flags that enable either
the increasing or decreasing portions, or both, of the waveform.
</p>
<p><a name="Figure_1"></a><img style="width: 500px; height: 141px;"
 alt="Time-to-Alpha Mapping" title="Time-to-Alpha Mapping"
 src="Behaviors1.gif">
</p>
<p>
</p>
<ul>
  <font size="-1"><b><i>Figure 1</i> &#8211; An Interpolator's Generic
Time-to-Alpha Mapping Sequence</b></font>
</ul>
<p>
Developers can use the loop count in conjunction with the mode flags to
generate various kinds of actions. Specifying a loop count of 1 and
enabling the mode flag for only the alpha-increasing and alpha-at-1
portion of the waveform, we would get the waveform shown in <a
 href="#Figure_2">Figure
2</a>.
</p>
<p><a name="Figure_2"></a><img style="width: 241px; height: 100px;"
 alt="Alpha Increasing" title="Alpha Increasing" src="Behaviors2.gif">
</p>
<p>
</p>
<ul>
  <font size="-1"><b><i>Figure 2</i> &#8211; An Interpolator Set to a Loop
Count of 1 with Mode Flags Set to Enable
Only the Alpha-Increasing and Alpha-at-1 Portion of the Waveform</b></font>
</ul>
<p>
In <a href="#Figure_2">Figure
2</a>,
the alpha value is 0 before the combination of trigger time plus the
phase delay duration. The alpha value changes from 0 to 1 over a
specified interval of time, and thereafter the alpha value remains 1
(subject to the reprogramming of the interpolator's parameters). A
possible use of a single alpha-increasing value might be to combine it
with a rotation interpolator to program a door opening.
</p>
<p>Similarly, by specifying a loop count of 1 and
a mode flag that enables only the alpha-decreasing and alpha-at-0
portion of the waveform, we would get the waveform shown in <a
 href="#Figure_3">Figure
3</a>.
</p>
<p>In <a href="#Figure_3">Figure
3</a>,
the alpha value is 1 before the combination of trigger time plus the
phase delay duration. The alpha value changes from 1 to 0 over a
specified interval; thereafter the alpha value remains 0 (subject to
the reprogramming of the interpolator's parameters). A possible use of
a single <b>&#945;</b>-decreasing value might be to combine it with a
rotation
interpolator to program a door closing.
</p>
<p><a name="Figure_3"></a><img style="width: 241px; height: 88px;"
 alt="Alpha Decreasing" title="Alpha Decreasing" src="Behaviors3.gif">
</p>
<p>
</p>
<ul>
  <font size="-1"><b><i>Figure 3</i> &#8211; An Interpolator Set to a Loop
Count of 1 with Mode Flags Set to Enable
Only the Alpha-Decreasing and Alpha-at-0 Portion of the Waveform</b></font>
</ul>
<p>
We can combine both of the above waveforms by specifying a loop count
of 1 and setting the mode flag to enable both the alpha-increasing and
alpha-at-1 portion of the waveform as well as the alpha-decreasing and
alpha-at-0 portion of the waveform. This combination would result in
the waveform shown in <a href="#Figure_4">Figure
4</a>.
</p>
<p><a name="Figure_4"></a><img style="width: 241px; height: 100px;"
 alt="Alpha Increasing &amp; Decreasing"
 title="Alpha Increasing &amp; Decreasing" src="Behaviors4.gif">
</p>
<p>
</p>
<ul>
  <font size="-1"><b><i>Figure 4</i> &#8211; An Interpolator Set to a Loop
Count of 1 with Mode Flags
Set to Enable All Portions of the Waveform</b></font>
</ul>
<p>
In <a href="#Figure_4">Figure
4</a>,
the alpha value is 0 before the combination of trigger time plus the
phase delay duration. The alpha value changes from 0 to 1 over a
specified period of time, remains at 1 for another specified period of
time, then changes from 1 to 0 over a third specified period of time;
thereafter the alpha value remains 0 (subject to the reprogramming of
the interpolator's parameters). A possible use of an alpha-increasing
value followed by an alpha-decreasing value might be to combine it with
a rotation interpolator to program a door swinging open and then
closing.
</p>
<p>By increasing the loop count, we can get
repetitive behavior, such as a door swinging open and closed some
number of times. At the extreme, we can specify a loop count of -1
(representing infinity).
</p>
<p>We can construct looped versions of the waveforms shown in <a
 href="#Figure_2">Figure
2</a>, <a href="#Figure_3">Figure
3</a>, and <a href="#Figure_4">Figure
4</a>. <a href="#Figure_5">Figure
5</a> shows a looping interpolator with mode flags set to enable
only the alpha-increasing and alpha-at-1 portion of the waveform.
</p>
<p><a name="Figure_5"></a><img style="width: 500px; height: 99px;"
 alt="Alpha Increasing Infinite Loop"
 title="Alpha Increasing Infinite Loop" src="Behaviors5.gif">
</p>
<p>
</p>
<ul>
  <font size="-1"><b><i>Figure 5</i> &#8211; An Interpolator Set to Loop
Infinitely and Mode Flags Set to Enable
Only the Alpha-Increasing and Alpha-at-1 Portion of the Waveform</b></font>
</ul>
<p>
In <a href="#Figure_5">Figure
5</a>, alpha goes from 0 to 1 over a fixed duration of time, stays
at 1 for another fixed duration of time, and then repeats.
</p>
<p>Similarly, <a href="#Figure_6">Figure
6</a> shows a looping interpolator with mode flags set to enable
only the alpha-decreasing and alpha-at-0 portion of the waveform.
</p>
<p><a name="Figure_6"></a><img style="width: 500px; height: 97px;"
 alt="Alpha Decreasing Infinite Loop"
 title="Alpha Decreasing Infinite Loop" src="Behaviors6.gif">
</p>
<p>
</p>
<ul>
  <font size="-1"><b><i>Figure 6</i> &#8211; An Interpolator Set to Loop
Infinitely and Mode Flags Set to Enable
Only the Alpha-Decreasing and Alpha-at-0 Portion of the Waveform</b></font>
</ul>
<p>
Finally, <a href="#Figure_7">Figure
7</a> shows a looping interpolator with both the increasing and
decreasing portions of the waveform enabled.
</p>
<p>In all three cases shown by <a href="#Figure_5">Figure
5</a>, <a href="#Figure_6">Figure
6</a>, and <a href="#Figure_7">Figure
7</a>, we can compute the exact value of alpha at any point in time.
</p>
<p><a name="Figure_7"></a><img style="width: 500px; height: 99px;"
 alt="Alpha Increasing &amp; Decreasing  Infinite Loop"
 title="Alpha Increasing &amp; Decreasing  Infinite Loop"
 src="Behaviors7.gif">
</p>
<p>
</p>
<ul>
  <font size="-1"><b><i>Figure 7</i> &#8211; An Interpolator Set to Loop
Infinitely and Mode Flags Set
to Enable All Portions of the Waveform</b></font>
</ul>
<p>
Java&nbsp;3D's preprogrammed behaviors permit other behaviors to change
their parameters. When such a change occurs, the alpha value changes to
match the state of the newly parameterized interpolator.
</p>
<h3>Acceleration of Alpha</h3>
<p>Commonly, developers want alpha to change slowly at first and then
to
speed up until the change in alpha reaches some appropriate rate. This
is analogous to accelerating your car up to the speed limit-it does not
start off immediately at the speed limit. Developers specify this
"ease-in, ease-out" behavior through two additional parameters, the <code>increasingAlphaRampDuration</code>
and the <code>decreasing-AlphaRampDuration</code>.
</p>
<p>Each of these parameters specifies a period within the increasing or
decreasing alpha duration region during which the "change in alpha" is
accelerated (until it reaches its maximum per-unit-of-time step size)
and then symmetrically decelerated. <a href="#Figure_8">Figure
8</a> shows three general examples of how the <code>increasingAlphaRampDuration</code>
method can be used to modify the alpha waveform. A value of 0 for the
increasing ramp duration implies that <b>&#945;</b>
is not accelerated; it changes at a constant rate. A value of 0.5 or
greater (clamped to 0.5) for this increasing ramp duration implies that
the change in <b>&#945;</b> is accelerated during the first half of the
period and
then decelerated during the second half of the period. For a value of <em>n</em>
that is less than 0.5, alpha is accelerated for duration <em>n</em>,
held constant for duration (1.0 - 2<em>n</em>), then decelerated for
duration <em>n</em> of the period.
</p>
<p><a name="Figure_8"></a><img style="width: 500px; height: 354px;"
 alt="Alpha acceleration" title="Alpha acceleration"
 src="Behaviors8.gif">
</p>
<p>
</p>
<ul>
  <font size="-1"><b><i>Figure 8</i> &#8211; How an Alpha-Increasing Waveform
Changes with Various
Values of increasing-AlphaRampDuration</b></font>
</ul>
</body>
</html>