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diff --git a/doc-files/Behaviors.html b/doc-files/Behaviors.html new file mode 100644 index 0000000..7bcc4a2 --- /dev/null +++ b/doc-files/Behaviors.html @@ -0,0 +1,596 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<html> +<head> + <meta content="text/html; charset=ISO-8859-1" + http-equiv="content-type"> + <title>Java 3D API - Behaviors and Interpolators</title> +</head> +<body> +<h2>Behaviors and Interpolators</h2> +<p><a href="../Behavior.html">Behavior</a> nodes provide the means for +animating objects, processing keyboard and mouse inputs, reacting to +movement, and enabling and processing pick events. Behavior nodes +contain Java code and state variables. A Behavior node's Java code can +interact with Java objects, change node values within a Java 3D +scene +graph, change the behavior's internal state-in general, perform any +computation it wishes. +</p> +<p>Simple behaviors can add surprisingly interesting effects to a scene +graph. For example, one can animate a rigid object by using a Behavior +node to repetitively modify the TransformGroup node that points to the +object one wishes to animate. Alternatively, a Behavior node can track +the current position of a mouse and modify portions of the scene graph +in response.</p> +<h2>Behavior Object</h2> +<p>A Behavior leaf node object contains a scheduling region and two +methods: an <code>initialize</code> method called once when the +behavior becomes "live" and a <code>processStimulus</code> +method called whenever appropriate by the Java 3D behavior +scheduler. +The Behavior object also contains the state information needed by its <code>initialize</code> +and <code>processStimulus</code> methods. +</p> +<p>The <em>scheduling region</em> defines a spatial volume that serves +to enable the scheduling of Behavior nodes. A Behavior node is <em>active</em> +(can receive stimuli) whenever an active ViewPlatform's activation +volume intersects a Behavior object's scheduling region. Only active +behaviors can receive stimuli. +</p> +<p>The <em>scheduling interval</em> defines a +partial order of execution for behaviors that wake up in response to +the same wakeup condition (that is, those behaviors that are processed +at the same "time"). Given a set of behaviors whose wakeup conditions +are satisfied at the same time, the behavior scheduler will execute all +behaviors in a lower scheduling interval before executing any behavior +in a higher scheduling interval. Within a scheduling interval, +behaviors can be executed in any order, or in parallel. Note that this +partial ordering is only guaranteed for those behaviors that wake up at +the same time in response to the same wakeup condition, for example, +the set of behaviors that wake up every frame in response to a +WakeupOnElapsedFrames(0) wakeup condition. +</p> +<p>The <code>processStimulus</code> method receives and processes a +behavior's ongoing messages. The Java 3D behavior scheduler +invokes a +Behavior node's <code>processStimulus</code> +method when an active ViewPlatform's activation volume intersects a +Behavior object's scheduling region and all of that behavior's wakeup +criteria are satisfied. The <code>processStimulus</code> method +performs its computations and actions (possibly including the +registration of state change information that could cause Java 3D +to +wake other Behavior objects), establishes its next wakeup condition, +and finally exits. +</p> +<p>A typical behavior will modify one or more nodes or node components +in +the scene graph. These modifications can happen in parallel with +rendering. In general, applications cannot count on behavior execution +being synchronized with rendering. There are two exceptions to this +general rule: +</p> +<ul> + <li>All modifications to scene graph objects (not including geometry +by-reference or texture by-reference) made from the <code>processStimulus</code> +method of a single behavior instance are guaranteed to take effect in +the same rendering frame</li> +</ul> +<ul> + <li>All modifications to scene graph objects (not including geometry +by-reference or texture by-reference) made from the <code>processStimulus</code> +methods of the set of behaviors that wake up in response to a +WakeupOnElapsedFrames(0) wakeup condition are guaranteed to take effect +in the same rendering frame.</li> +</ul> +<p>Note that modifications to geometry by-reference or texture +by-reference are not guaranteed to show up in the same frame as other +scene graph changes. +</p> +<h3>Code Structure</h3> +<p>When the Java 3D behavior scheduler invokes a Behavior object's +<code>processStimulus</code> +method, that method may perform any computation it wishes. Usually, it +will change its internal state and specify its new wakeup conditions. +Most probably, it will manipulate scene graph elements. However, the +behavior code can change only those aspects of a scene graph element +permitted by the capabilities associated with that scene graph element. +A scene graph's capabilities restrict behavioral manipulation to those +manipulations explicitly allowed. +</p> +<p>The application must provide the Behavior object with references to +those scene graph elements that the Behavior object will manipulate. +The application provides those references as arguments to the +behavior's constructor when it creates the Behavior object. +Alternatively, the Behavior object itself can obtain access to the +relevant scene graph elements either when Java 3D invokes its <code>initialize</code> +method or each time Java 3D invokes its <code>processStimulus</code> +method. +</p> +<p>Behavior methods have a very rigid structure. Java 3D assumes +that +they +always run to completion (if needed, they can spawn threads). Each +method's basic structure consists of the following: +</p> +<ul> + <li>Code to decode and extract references from the WakeupCondition +enumeration that caused the object's awakening.</li> +</ul> +<ul> + <li>Code to perform the manipulations associated with the +WakeupCondition.</li> +</ul> +<ul> + <li>Code to establish this behavior's new WakeupCondition.</li> +</ul> +<ul> + <li>A path to Exit (so that execution returns to the Java 3D +behavior +scheduler).</li> +</ul> +<h3>WakeupCondition Object</h3> +<p>A <a href="../WakeupCondition.html">WakeupCondition</a> object is +an +abstract class specialized to fourteen +different WakeupCriterion objects and to four combining objects +containing multiple WakeupCriterion objects. +</p> +<p>A Behavior node provides the Java 3D behavior scheduler with a +WakeupCondition object. When that object's WakeupCondition has been +satisfied, the behavior scheduler hands that same WakeupCondition back +to the Behavior via an enumeration. +</p> +<p> +</p> +<h3>WakeupCriterion Object</h3> +<p>Java 3D provides a rich set of wakeup criteria that Behavior +objects +can use in specifying a complex WakeupCondition. These wakeup criteria +can cause Java 3D's behavior scheduler to invoke a behavior's <code>processStimulus</code> +method whenever +</p> +<ul> + <li>The center of an active ViewPlatform enters a specified region.</li> +</ul> +<ul> + <li>The center of an active ViewPlatform exits a specified region.</li> +</ul> +<ul> + <li>A behavior is activated.</li> +</ul> +<ul> + <li>A behavior is deactivated.</li> +</ul> +<ul> + <li>A specified TransformGroup node's transform changes.</li> +</ul> +<ul> + <li>Collision is detected between a specified Shape3D node's Geometry +object and any other object.</li> +</ul> +<ul> + <li>Movement occurs between a specified Shape3D node's Geometry +object and any other object with which it collides.</li> +</ul> +<ul> + <li>A specified Shape3D node's Geometry object no longer collides +with any other object.</li> +</ul> +<ul> + <li>A specified Behavior object posts a specific event.</li> +</ul> +<ul> + <li>A specified AWT event occurs.</li> +</ul> +<ul> + <li>A specified time interval elapses.</li> +</ul> +<ul> + <li>A specified number of frames have been drawn.</li> +</ul> +<ul> + <li>The center of a specified Sensor enters a specified region.</li> +</ul> +<ul> + <li>The center of a specified Sensor exits a specified region.</li> +</ul> +<p>A Behavior object constructs a <a href="../WakeupCriterion.html">WakeupCriterion</a> +by constructing the +appropriate criterion object. The Behavior object must provide the +appropriate arguments (usually a reference to some scene graph object +and possibly a region of interest). Thus, to specify a +WakeupOnViewPlatformEntry, a behavior would specify the region that +will cause the behavior to execute if an active ViewPlatform enters it. +</p> +<h3>Composing WakeupCriterion +Objects</h3> +<p>A Behavior object can combine multiple WakeupCriterion objects into +a +more powerful, composite WakeupCondition. Java 3D behaviors +construct a +composite WakeupCondition in one of the following ways: +</p> +<ul> + <li><a href="../WakeupAnd.html">WakeupAnd</a>: An array of +WakeupCriterion objects ANDed together.</li> +</ul> +<pre> WakeupCriterion && WakeupCriterion && ...<br></pre> +<ul> + <li><a href="../WakeupOr.html">WakeupOr</a>: An array of +WakeupCriterion objects ORed together.</li> +</ul> +<pre> WakeupCriterion || WakeupCriterion || ...<br></pre> +<ul> + <li><a href="../WakeupAndOfOrs.html">WakeupAndOfOrs</a>: An array of +WakeupOr WakeupCondition objects that +are then ANDed together.</li> +</ul> +<pre> WakeupOr && WakeupOr && ...<br></pre> +<ul> + <li><a href="../WakeupOrOfAnds.html">WakeupOrOfAnds</a>: An array of +WakeupAnd WakeupCondition objects +that are then ORed together.</li> +</ul> +<pre> WakeupAnd || WakeupAnd || ...<br></pre> +<h2>Composing Behaviors</h2> +<p>Behavior objects can condition themselves to awaken only when +signaled +by another Behavior node. The <a href="../WakeupOnBehaviorPost.html">WakeupOnBehaviorPost</a> +WakeupCriterion +takes as arguments a reference to a Behavior node and an integer. These +two arguments allow a behavior to limit its wakeup criterion to a +specific post by a specific behavior. +</p> +<p>The WakeupOnBehaviorPost WakeupCriterion permits behaviors to chain +their computations, allowing parenthetical computations-one behavior +opens a door and the second closes the same door, or one behavior +highlights an object and the second unhighlights the same object. +</p> +<p> +</p> +<h2>Scheduling</h2> +<p>As a virtual universe grows large, Java 3D must carefully +husband +its +resources to ensure adequate performance. In a 10,000-object virtual +universe with 400 or so Behavior nodes, a naive implementation of Java +3D could easily end up consuming the majority of its compute cycles in +executing the behaviors associated with the 400 Behavior objects before +it draws a frame. In such a situation, the frame rate could easily drop +to unacceptable levels. +</p> +<p>Behavior objects are usually associated with geometric objects in +the +virtual universe. In our example of 400 Behavior objects scattered +throughout a 10,000-object virtual universe, only a few of these +associated geometric objects would be visible at a given time. A +sizable fraction of the Behavior nodes-those associated with nonvisible +objects-need not be executed. Only those relatively few Behavior +objects that are associated with visible objects must be executed. +</p> +<p>Java 3D mitigates the problem of a large number of Behavior +nodes in +a +high-population virtual universe through execution culling-choosing to +invoke only those behaviors that have high relevance. +</p> +<p>Java 3D requires each behavior to have a <em>scheduling region</em> +and to post a wakeup condition. Together a behavior's scheduling region +and wakeup condition provide Java 3D's behavior scheduler with +sufficient domain knowledge to selectively prune behavior invocations +and invoke only those behaviors that absolutely need to be executed. +</p> +<p> +</p> +<h2>How Java 3D Performs +Execution Culling</h2> +<p>Java 3D finds all scheduling regions associated with Behavior +nodes +and +constructs a scheduling/volume tree. It also creates an AND/OR tree +containing all the Behavior node wakeup criteria. These two data +structures provide the domain knowledge Java 3D needs to prune +unneeded +behavior execution (to perform "execution triage"). +</p> +<p>Java 3D must track a behavior's wakeup conditions only if an +active +ViewPlatform object's activation volume intersects with that Behavior +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 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 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 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 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>α</b> +increasing, <b>α</b> at 1, <b>α</b> decreasing, and +<b>α</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> – 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> – 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>α</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> – 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 & Decreasing" + title="Alpha Increasing & Decreasing" src="Behaviors4.gif"> +</p> +<p> +</p> +<ul> + <font size="-1"><b><i>Figure 4</i> – 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> – 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> – 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 & Decreasing Infinite Loop" + title="Alpha Increasing & Decreasing Infinite Loop" + src="Behaviors7.gif"> +</p> +<p> +</p> +<ul> + <font size="-1"><b><i>Figure 7</i> – An Interpolator Set to Loop +Infinitely and Mode Flags Set +to Enable All Portions of the Waveform</b></font> +</ul> +<p> +Java 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>α</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>α</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> – How an Alpha-Increasing Waveform +Changes with Various +Values of increasing-AlphaRampDuration</b></font> +</ul> +</body> +</html> diff --git a/doc-files/Behaviors1.gif b/doc-files/Behaviors1.gif Binary files differnew file mode 100644 index 0000000..bb288ce --- /dev/null +++ b/doc-files/Behaviors1.gif diff --git a/doc-files/Behaviors2.gif b/doc-files/Behaviors2.gif Binary files differnew file mode 100644 index 0000000..005564f --- /dev/null +++ b/doc-files/Behaviors2.gif diff --git a/doc-files/Behaviors3.gif b/doc-files/Behaviors3.gif Binary files differnew file mode 100644 index 0000000..a8beb09 --- /dev/null +++ b/doc-files/Behaviors3.gif diff --git a/doc-files/Behaviors4.gif b/doc-files/Behaviors4.gif Binary files differnew file mode 100644 index 0000000..685bcb7 --- /dev/null +++ b/doc-files/Behaviors4.gif diff --git a/doc-files/Behaviors5.gif b/doc-files/Behaviors5.gif Binary files differnew file mode 100644 index 0000000..74783fb --- /dev/null +++ b/doc-files/Behaviors5.gif diff --git a/doc-files/Behaviors6.gif b/doc-files/Behaviors6.gif Binary files differnew file mode 100644 index 0000000..8614a4e --- /dev/null +++ b/doc-files/Behaviors6.gif diff --git a/doc-files/Behaviors7.gif b/doc-files/Behaviors7.gif Binary files differnew file mode 100644 index 0000000..0f2ce48 --- /dev/null +++ b/doc-files/Behaviors7.gif diff --git a/doc-files/Behaviors8.gif b/doc-files/Behaviors8.gif Binary files differnew file mode 100644 index 0000000..d048cfa --- /dev/null +++ b/doc-files/Behaviors8.gif diff --git a/doc-files/Concepts.html b/doc-files/Concepts.html new file mode 100644 index 0000000..7b005af --- /dev/null +++ b/doc-files/Concepts.html @@ -0,0 +1,291 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<html> +<head> + <meta content="text/html; charset=ISO-8859-1" + http-equiv="content-type"> + <title>Java 3D API - Concepts</title> +</head> +<body> +<h2>Java 3D Concepts</h2> +<p>The Java 3D API specification serves to define objects, methods, and +their actions precisely. Describing how to use an API belongs in a +tutorial or programmer's +reference manual, and is well beyond the scope of this specification. +However, a short introduction to the main concepts in Java 3D will +provide the context for understanding the detailed, but isolated, +specification found in the class and method descriptions. We introduce +some of the key Java 3D concepts and illustrate them with some simple +program fragments. +</p> +<p> +</p> +<h2>Basic Scene Graph Concepts</h2> +<p>A scene graph is a "tree" structure that contains data arranged in a +hierarchical manner. The scene graph consists of parent nodes, child +nodes, and data objects. The parent nodes, called Group nodes, organize +and, in some cases, control how Java 3D interprets their descendants. +Group nodes serve as the glue that holds a scene graph together. Child +nodes can be either Group nodes or Leaf nodes. Leaf nodes have no +children. They encode the core semantic elements of a scene graph- for +example, what to draw (geometry), what to play (audio), how to +illuminate objects (lights), or what code to execute (behaviors). Leaf +nodes refer to data objects, called NodeComponent objects. +NodeComponent objects are not scene graph nodes, but they contain the +data that Leaf nodes require, such as the geometry to draw or the sound +sample to play. +</p> +<p>A Java 3D application builds and manipulates a scene graph by +constructing Java 3D objects and then later modifying those objects by +using their methods. A Java 3D program first constructs a scene graph, +then, once built, hands that scene graph to Java 3D for processing. +</p> +<p>The structure of a scene graph determines the relationships among +the +objects in the graph and determines which objects a programmer can +manipulate as a single entity. Group nodes provide a single point for +handling or manipulating all the nodes beneath it. A programmer can +tune a scene graph appropriately by thinking about what manipulations +an application will need to perform. He or she can make a particular +manipulation easy or difficult by grouping or regrouping nodes in +various ways. +</p> +<p> +</p> +<h3>Constructing a Simple Scene +Graph</h3> +<p>The following code constructs a simple scene graph consisting of a +group node and two leaf +nodes.<br> +</p> +<p><font size="-1"><b><a name="Listing_1"> +<i>Listing 1</i> – Code for Constructing a Simple Scene Graph +</a></b></font></p> +<hr> +<pre>Shape3D myShape1 = new Shape3D(myGeometry1, myAppearance1);<br>Shape3D myShape2 = new Shape3D(myGeometry2);<br>myShape2.setAppearance(myAppearance2);<br><br>Group myGroup = new Group();<br>myGroup.addChild(myShape1);<br>myGroup.addChild(myShape2);<br></pre> +<hr> +<p>It first constructs one leaf node, the first of two Shape3D +nodes, using a constructor that takes both a Geometry and an Appearance +NodeComponent object. It then constructs the second Shape3D node, with +only a Geometry object. Next, since the second Shape3D node was created +without an Appearance object, it supplies the missing Appearance object +using the Shape3D node's <code>setAppearance</code> method. At this +point both leaf nodes have been fully constructed. The code next +constructs a group node to hold the two leaf nodes. It +uses the Group node's <code>addChild</code> method to add the two leaf +nodes as children to the group node, finishing the construction of the +scene graph. <a href="#Figure_1">Figure +1</a> +shows the constructed scene graph, all the nodes, the node component +objects, and the variables used in constructing the scene graph. +</p> +<p><a name="Figure_1"></a><img style="width: 491px; height: 279px;" + alt="A Simple Scene Graph" title="A Simple Scene Graph" + src="Concepts1.gif"> +</p> +<ul> + <font size="-1"><b><i>Figure 1</i> – A Simple Scene Graph</b></font> +</ul> +<h3>A Place For Scene Graphs</h3> +Once a scene graph has been constructed, the +question becomes what to do with it? Java 3D cannot start rendering a +scene graph until a program "gives" it the scene graph. The program +does this by inserting the scene graph into the virtual universe. +<p>Java 3D places restrictions on how a program can insert a scene +graph +into a universe. +</p> +<p>A Java 3D environment consists of two superstructure objects, +VirtualUniverse and Locale, and one or more graphs, rooted by a special +BranchGroup node. <a href="#Figure_2">Figure 2</a> shows these objects +in context with other scene graph objects. +</p> +<p>The VirtualUniverse object defines a universe. A universe allows a +Java +3D program to create a separate and distinct arena for defining objects +and their relationships to one another. Typically, Java 3D programs +have only one VirtualUniverse object. Programs that have more than one +VirtualUniverse may share NodeComponent objects but not scene graph +node objects. +</p> +<p>The Locale object specifies a fixed position within the universe. +That +fixed position defines an origin for all scene graph nodes beneath it. +The Locale object allows a programmer to specify that origin very +precisely and with very high dynamic range. A Locale can accurately +specify a location anywhere in the known physical universe and at the +precision of Plank's distance. Typically, Java 3D programs have only +one Locale object with a default origin of (0, 0, 0). Programs that +have more than one Locale object will set the location of the +individual Locale objects so that they provide an appropriate local +origin for the nodes beneath them. For example, to model the Mars +landing, a programmer might create one Locale object with an origin at +Cape Canaveral and another with an origin located at the landing site +on Mars. +</p> +<p><a name="Figure_2"></a><img style="width: 500px; height: 286px;" + alt="Content Branch, View Branch, Superstructure" + title="Superstructure" src="Concepts2.gif"> +</p> +<ul> + <font size="-1"><b><i>Figure 2</i> – Content Branch, View Branch, and +Superstructure</b></font> +</ul> +<p> +The BranchGroup node serves as the root of a <em>branch graph</em>. +Collectively, the BranchGroup node and all of its children form the +branch graph. The two kinds of branch graphs are called content +branches and view branches. A <em>content branch</em> contains only +content-related leaf nodes, while a <em>view branch</em> +contains a ViewPlatform leaf node and may contain other content-related +leaf nodes. Typically, a universe contains more than one branch +graph-one view branch, and any number of content branches. +</p> +<p>Besides serving as the root of a branch graph, the BranchGroup node +has +two special properties: It alone may be inserted into a Locale object, +and it may be compiled. Java 3D treats uncompiled and compiled branch +graphs identically, though compiled branch graphs will typically render +more efficiently. +</p> +<p>We could not insert the scene graph created by our simple example (<a + href="#Listing_1">Listing +1</a>) into a Locale because it does not have a BranchGoup node for +its root. <a href="#Listing_2">Listing 2</a> +shows a modified version of our first code example that creates a +simple content branch graph and the minimum of superstructure objects. +Of special note, Locales do not have children, and they are not part of +the scene graph. The method for inserting a branch graph is <code>addBranchGraph</code>, +whereas <code>addChild</code> is the method for adding children to all +group nodes.</p> +<p><font size="-1"><b> +<i><a name="Listing_2"></a>Listing 2</i> – Code for Constructing a +Scene Graph and Some +Superstructure Objects +</b></font></p> +<hr> +<pre>Shape3D myShape1 = new Shape3D(myGeometry1, myAppearance1);<br>Shape3D myShape2 = new Shape3D(myGeometry2, myAppearance2);<br><br>BranchGroup myBranch = new BranchGroup();<br>myBranch.addChild(myShape1);<br>myBranch.addChild(myShape2);<br>myBranch.compile();<br><br>VirtualUniverse myUniverse = new VirtualUniverse();<br>Locale myLocale = new Locale(myUniverse);<br>myLocale.addBranchGraph(myBranch);<br></pre> +<hr> +<h3>SimpleUniverse Utility</h3> +Most Java 3D programs build an identical set of superstructure and view +branch objects, so the Java 3D utility packages provide a <code>universe</code> +package for constructing and manipulating the objects in a view branch. +The classes in the <code>universe</code> package provide a quick means +for building a single view (single window) application. <a + href="#Listing_3">Listing 3</a> +shows a code fragment for using the SimpleUniverse class. Note that the +SimpleUniverse constructor takes a Canvas3D as an argument, in this +case referred to by the variable <code>myCanvas</code>. +<p><font size="-1"><b><i><a name="Listing_3"></a>Listing 3</i> – Code +for Constructing a Scene Graph Using the Universe +Package +</b></font></p> +<hr> +<pre>import com.sun.j3d.utils.universe.*;<br><br>Shape3D myShape1 = new Shape3D(myGeometry1, myAppearance1);<br>Shape3D myShape2 = new Shape3D(myGeometry2, myAppearance2);<br><br>BranchGroup myBranch = new BranchGroup();<br>myBranch.addChild(myShape1);<br>myBranch.addChild(myShape2);<br>myBranch.compile();<br><br>SimpleUniverse myUniv = new SimpleUniverse(myCanvas);<br>myUniv.addBranchGraph(myBranch);<br></pre> +<hr> +<h3>Processing a Scene Graph</h3> +When given a scene graph, Java 3D processes that scene graph as +efficiently as possible. How a Java 3D implementation processes a scene +graph can vary, as long as the implementation conforms to the semantics +of the API. In general, a Java 3D implementation will render all +visible objects, play all enabled sounds, execute all triggered +behaviors, process any identified input devices, and check for and +generate appropriate collision events. +<p>The order that a particular Java 3D implementation renders objects +onto +the display is carefully not defined. One implementation might render +the first Shape3D object and then the second. Another might first +render the second Shape3D node before it renders the first one. Yet +another implementation may render both Shape3D nodes in parallel. +</p> +<p> +</p> +<h2>Features of Java 3D</h2> +Java 3D allows a programmer to specify a broad range of information. It +allows control over the shape of objects, their color, and +transparency. It allows control over background effects, lighting, and +environmental effects such as fog. It allows control over the placement +of all objects (even nonvisible objects such as lights and behaviors) +in the scene graph and over their orientation and scale. It allows +control over how those objects move, rotate, stretch, shrink, or morph +over time. It allows control over what code should execute, what sounds +should play, and how they should sound and change over time. +<p>Java 3D provides different techniques for controlling the effect of +various features. Some techniques act fairly locally, such as getting +the color of a vertex. Other techniques have broader influence, such as +changing the color or appearance of an entire object. Still other +techniques apply to a broad number of objects. In the first two cases, +the programmer can modify a particular object or an object associated +with the affected object. In the latter case, Java 3D provides a means +for specifying more than one object spatially. +</p> +<p> +</p> +<h3>Bounds</h3> +Bounds objects allow a programmer to define a volume in space. There +are three ways to specify this volume: as a box, a sphere, or a set of +planes enclosing a space. +<p>Bounds objects specify a volume in which particular operations +apply. +Environmental effects such as lighting, fog, alternate appearance, and +model clipping planes use bounds objects to specify their region of +influence. Any object that falls within the space defined by the bounds +object has the particular environmental effect applied. The proper use +of bounds objects can ensure that these environmental effects are +applied only to those objects in a particular volume, such as a light +applying only to the objects within a single room. +</p> +<p>Bounds objects are also used to specify a region of action. +Behaviors +and sounds execute or play only if they are close enough to the viewer. +The use of behavior and sound bounds objects allows Java 3D to cull +away those behaviors and sounds that are too far away to affect the +viewer (listener). By using bounds properly, a programmer can ensure +that only the relevant behaviors and sounds execute or play. +</p> +<p>Finally, bounds objects are used to specify a region of application +for +per-view operations such as background, clip, and soundscape selection. +For example, the background node whose region of application is closest +to the viewer is selected for a given view. +</p> +<p> +</p> +<h3>Nodes</h3> +All scene graph nodes have an implicit location in space of (0, 0, 0). +For objects that exist in space, this implicit location provides a +local coordinate system for that object, a fixed reference point. Even +abstract objects that may not seem to have a well-defined location, +such as behaviors and ambient lights, have this implicit location. An +object's location provides an origin for its local coordinate system +and, just as importantly, an origin for any bounding volume information +associated with that object. +<h3>Live and/or Compiled</h3> +All scene graph objects, including nodes and node component objects, +are either part of an active universe or not. An object is said to be <em>live</em> +if it is part of an active universe. Additionally, branch graphs are +either <em>compiled</em> +or not. When a node is either live or compiled, Java 3D enforces access +restrictions to nodes and node component objects. Java 3D allows only +those operations that are enabled by the program before a node or node +component becomes live or is compiled. It is best to set capabilities +when you build your content. <a href="#Listing_4">Listing 4</a> shows +an example where we create a TransformGroup node and +enable it for writing. +<p><font size="-1"><b><i><a name="Listing_4"></a>Listing 4</i> – +Capabilities Example +</b></font></p> +<hr> +<pre>TransformGroup myTrans = new TransformGroup();<br>myTrans.setCapability(Transform.ALLOW_TRANSFORM_WRITE);<br></pre> +<hr> +<p>By setting the capability to write the transform, Java 3D will allow +the following code to execute: +</p> +<pre>myTrans.setTransform3D(myT3D);<br></pre> +<p>It is important to ensure that all needed capabilities are set and +that +unnecessary capabilities are not set. The process of compiling a branch +graph examines the capability bits and uses that information to reduce +the amount of computation needed to run a program. +</p> +</body> +</html> diff --git a/doc-files/Concepts1.gif b/doc-files/Concepts1.gif Binary files differnew file mode 100644 index 0000000..8aa0dbc --- /dev/null +++ b/doc-files/Concepts1.gif diff --git a/doc-files/Concepts2.gif b/doc-files/Concepts2.gif Binary files differnew file mode 100644 index 0000000..f21e085 --- /dev/null +++ b/doc-files/Concepts2.gif diff --git a/doc-files/DAG.gif b/doc-files/DAG.gif Binary files differnew file mode 100644 index 0000000..8479136 --- /dev/null +++ b/doc-files/DAG.gif diff --git a/doc-files/HelloUniverse.html b/doc-files/HelloUniverse.html new file mode 100644 index 0000000..5e37bd6 --- /dev/null +++ b/doc-files/HelloUniverse.html @@ -0,0 +1,21 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<html> +<head> + <meta content="text/html; charset=ISO-8859-1" + http-equiv="content-type"> + <title>HelloUniverse</title> +</head> +<body> +<h2>HelloUniverse: A Sample Java +3D Program</h2> +<p>Here are code fragments from a simple program, <code>HelloUniverse.java</code>, +that creates a cube and a RotationInterpolator behavior object that +rotates the cube at a constant rate of pi/2 radians per second. The +HelloUniverse class creates the branch graph +that includes the cube and the RotationInterpolator behavior. It then +adds this branch graph to the Locale object generated by the +SimpleUniverse utility. +</p> +<pre><hr><br>public class HelloUniverse ... {<br> public BranchGroup createSceneGraph() {<br><i> // Create the root of the branch graph<br></i> BranchGroup objRoot = new BranchGroup();<br><br><i> // Create the TransformGroup node and initialize it to the<br> // identity. Enable the TRANSFORM_WRITE capability so that<br> // our behavior code can modify it at run time. Add it to<br> // the root of the subgraph.<br></i> TransformGroup objTrans = new TransformGroup();<br> objTrans.setCapability(<br> TransformGroup.ALLOW_TRANSFORM_WRITE);<br> objRoot.addChild(objTrans);<br><br><i> // Create a simple Shape3D node; add it to the scene graph.<br></i> objTrans.addChild(new ColorCube(0.4));<br><br><i> // Create a new Behavior object that will perform the<br> // desired operation on the specified transform and add<br> // it into the scene graph.<br></i> Transform3D yAxis = new Transform3D();<br> Alpha rotationAlpha = new Alpha(-1, 4000);<br> RotationInterpolator rotator = new RotationInterpolator(<br> rotationAlpha, objTrans, yAxis,<br> 0.0f, (float) Math.PI*2.0f);<br> BoundingSphere bounds =<br> new BoundingSphere(new Point3d(0.0,0.0,0.0), 100.0);<br> rotator.setSchedulingBounds(bounds);<br> objRoot.addChild(rotator);<br><br><i> // Have Java 3D perform optimizations on this scene graph.</i><br> objRoot.compile();<br><br> return objRoot;<br> }<br><br> public HelloUniverse() {<br><i> <set layout of container, construct canvas3d, add canvas3d><br><br> // Create the scene; attach it to the virtual universe<br></i> BranchGroup scene = createSceneGraph();<br> SimpleUniverse u = new SimpleUniverse(canvas3d);<br> u.getViewingPlatform().setNominalViewingTransform();<br> u.addBranchGraph(scene);<br> }<br>}</pre> +</body> +</html> diff --git a/doc-files/Immediate.html b/doc-files/Immediate.html new file mode 100644 index 0000000..101fe22 --- /dev/null +++ b/doc-files/Immediate.html @@ -0,0 +1,114 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<html> +<head> + <meta content="text/html; charset=ISO-8859-1" + http-equiv="content-type"> + <title>Java 3D API - Immediate-Mode Rendering</title> +</head> +<body> +<h2>Immediate-Mode Rendering</h2> +<p>Java 3D is fundamentally a scene graph-based API. Most of +the constructs in the API are biased toward retained mode and +compiled-retained mode rendering. However, there are some applications +that want both the control and the flexibility that immediate-mode +rendering offers. +</p> +<p>Immediate-mode applications can either use or ignore Java 3D's +scene +graph structure. By using immediate mode, end-user applications have +more freedom, but this freedom comes at the expense of performance. In +immediate mode, Java 3D has no high-level information concerning +graphical objects or their composition. Because it has minimal global +knowledge, Java 3D can perform only localized optimizations on +behalf +of the application programmer. +</p> +<p> +</p> +<h2>Two Styles of Immediate-Mode +Rendering</h2> +Use of Java 3D's immediate mode falls into one of two categories: +pure +immediate-mode rendering and mixed-mode rendering in which immediate +mode and retained or compiled-retained mode interoperate and render to +the same canvas. The Java 3D renderer is idle in pure immediate +mode, +distinguishing it from mixed-mode rendering. +<h3>Pure Immediate-Mode +Rendering</h3> +Pure immediate-mode rendering provides for those applications and +applets that do not want Java 3D to do any automatic rendering of +the +scene graph. Such applications may not even wish to build a scene graph +to represent their graphical data. However, they use Java 3D's +attribute objects to set graphics state and Java 3D's geometric +objects +to render geometry. +<hr noshade="noshade"><b>Note:</b> Scene antialiasing is not supported +in pure immediate mode. +<hr noshade="noshade">A pure immediate mode application must create a +minimal set of Java 3D +objects before rendering. In addition to a Canvas3D object, the +application must create a View object, with its associated PhysicalBody +and PhysicalEnvironment objects, and the following scene graph +elements: a VirtualUniverse object, a high-resolution Locale object, a +BranchGroup node object, a TransformGroup node object with associated +transform, and, finally, a ViewPlatform leaf node object that defines +the position and orientation within the virtual universe that generates +the view (see <a href="#Figure_1">Figure +1</a>). +<p><a name="Figure_1"></a><img style="width: 500px; height: 359px;" + alt="Minimal Immediate-Mode Structure" + title="Minimal Immediate-Mode Structure" src="Immediate1.gif"></p> +<p> +</p> +<ul> + <font size="-1"><b><i>Figure 1</i> – Minimal Immediate-Mode Structure</b></font> +</ul> +<p> +Java 3D provides utility functions that create much of this +structure +on behalf of a pure immediate-mode application, making it less +noticeable from the application's perspective-but the structure must +exist. +</p> +<p>All rendering is done completely under user control. It is necessary +for the user to clear the 3D canvas, render all geometry, and swap the +buffers. Additionally, rendering the right and left eye for stereo +viewing becomes the sole responsibility of the application. +</p> +<p>In pure immediate mode, the user must stop the Java 3D +renderer, via +the Canvas3D object <code>stopRenderer()</code> +method, prior to adding the Canvas3D object to an active View object +(that is, one that is attached to a live ViewPlatform object). +</p> +<p> +</p> +<h3>Mixed-Mode Rendering</h3> +Mixing immediate mode and retained or compiled-retained mode requires +more structure than pure immediate mode. In mixed mode, the +Java 3D +renderer is running continuously, rendering the scene graph into the +canvas. +<p>The basic Java 3D <em>stereo</em> rendering loop, executed for +each +Canvas3D, is as follows: +</p> +<pre><hr><br>clear canvas (both eyes)<br></pre> +<pre>call preRender() <strong><kbd>// user-supplied method<br></kbd></strong>set left eye view<br>render opaque scene graph objects<br>call renderField(FIELD_LEFT) <strong><kbd>// user-supplied method<br></kbd></strong>render transparent scene graph objects<br>set right eye view<br>render opaque scene graph objects again<br>call renderField(FIELD_RIGHT) <strong><kbd>// user-supplied method<br></kbd></strong>render transparent scene graph objects again<br>call postRender() <strong><kbd>// user-supplied method<br></kbd></strong>synchronize and swap buffers<br></pre> +<pre>call postSwap() <strong><kbd>// user-supplied method<br></kbd></strong><br><hr></pre> +The basic Java 3D <em>monoscopic</em> rendering loop is as +follows: +<pre><hr><br>clear canvas<br></pre> +<pre>call preRender() <strong><kbd>// user-supplied method<br></kbd></strong>set view<br>render opaque scene graph objects<br>call renderField(FIELD_ALL) <strong><kbd>// user-supplied method<br></kbd></strong>render transparent scene graph objects<br>call postRender() <strong><kbd>// user-supplied method<br></kbd></strong>synchronize and swap buffers<br></pre> +<pre>call postSwap() <strong><kbd>// user-supplied method<br></kbd></strong><br><hr></pre> +In both cases, the entire loop, beginning with clearing the canvas and +ending with swapping the buffers, defines a frame. The application is +given the opportunity to render immediate-mode geometry at any of the +clearly identified spots in the rendering loop. A user specifies his or +her own rendering methods by extending the Canvas3D class and +overriding the <code>preRender</code>, <code>postRender</code>, <code>postSwap</code>, +and/or <code>renderField</code> methods. +</body> +</html> diff --git a/doc-files/Immediate1.gif b/doc-files/Immediate1.gif Binary files differnew file mode 100644 index 0000000..2d549b1 --- /dev/null +++ b/doc-files/Immediate1.gif diff --git a/doc-files/Rendering.html b/doc-files/Rendering.html new file mode 100644 index 0000000..7415ce8 --- /dev/null +++ b/doc-files/Rendering.html @@ -0,0 +1,148 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<html> +<head> + <meta content="text/html; charset=ISO-8859-1" + http-equiv="content-type"> + <title>Java 3D API - Execution and Rendering Model</title> +</head> +<body> +<h2>Execution and Rendering Model</h2> +<p>Java 3D's execution and rendering model assumes the +existence of a <a href="../VirtualUniverse.html">VirtualUniverse</a> +object and an attached scene graph. This +scene graph can be minimal and not noticeable from an application's +perspective when using immediate-mode rendering, but it must exist. +</p> +<p>Java 3D's execution model intertwines with its rendering modes +and +with +behaviors and their scheduling. This chapter first describes the three +rendering modes, then describes how an application starts up a +Java 3D +environment, and finally it discusses how the various rendering modes +work within this framework. +</p> +<p> +</p> +<h2>Three Major Rendering Modes</h2> +<p>Java 3D supports three different modes for rendering scenes: +immediate +mode, retained mode, and compiled-retained mode. These three levels of +API support represent a potentially large variation in graphics +processing speed and in on-the-fly restructuring. +</p> +<p></p> +<h3>Immediate Mode</h3> +<p>Immediate mode allows maximum flexibility at some cost in rendering +speed. The application programmer can either use or ignore the scene +graph structure inherent in Java 3D's design. The programmer can +choose +to draw geometry directly or to define a scene graph. Immediate mode +can be either used independently or mixed with retained and/or +compiled-retained mode rendering. The immediate-mode API is described +in the "<a href="Immediate.html">Immediate-Mode Rendering</a>" section.</p> +<p> +</p> +<h3>Retained Mode</h3> +<p>Retained mode allows a great deal of the flexibility provided by +immediate mode while also providing a substantial increase in rendering +speed. All objects defined in the scene graph are accessible and +manipulable. The scene graph itself is fully manipulable. The +application programmer can rapidly construct the scene graph, create +and delete nodes, and instantly "see" the effect of edits. Retained +mode also allows maximal access to objects through a general pick +capability. +</p> +<p>Java 3D's retained mode allows a programmer to construct +objects, +insert objects into a database, compose objects, and add behaviors to +objects. +</p> +<p>In retained mode, Java 3D knows that the programmer has defined +objects, knows how the programmer has combined those objects into +compound objects or scene graphs, and knows what behaviors or actions +the programmer has attached to objects in the database. This knowledge +allows Java 3D to perform many optimizations. It can construct +specialized data structures that hold an object's geometry in a manner +that enhances the speed at which the Java 3D system can render it. +It +can compile object behaviors so that they run at maximum speed when +invoked. It can flatten transformation manipulations and state changes +where possible in the scene graph. +</p> +<p> +</p> +<h3>Compiled-Retained Mode</h3> +<p>Compiled-retained mode allows the Java 3D API to perform an +arbitrarily +complex series of optimizations including, but not restricted to, +geometry compression, scene graph flattening, geometry grouping, and +state change clustering. +</p> +<p>Compiled-retained mode provides hooks for end-user manipulation and +picking. Pick operations return the closest object (in scene graph +space) associated with the picked geometry. +</p> +<p>Java 3D's compiled-retained mode ensures effective graphics +rendering +speed in yet one more way. A programmer can request that Java 3D +compile an object or a scene graph. Once it is compiled, the programmer +has minimal access to the internal structure of the object or scene +graph. Capability flags provide access to specified components that the +application program may need to modify on a continuing basis. +</p> +<p>A compiled object or scene graph consists of whatever internal +structures Java 3D wishes to create to ensure that objects or +scene +graphs render at maximal rates. Because Java 3D knows that the +majority +of the compiled object's or scene graph's components will not change, +it can perform an extraordinary number of optimizations, including the +fusing of multiple objects into one conceptual object, turning an +object into compressed geometry or even breaking an object up into +like-kind components and reassembling the like-kind components into new +"conceptual objects." +</p> +<p> +</p> +<h2>Instantiating the Render Loop</h2> +<p>From an application's perspective, Java 3D's render loop runs +continuously. Whenever an application adds a scene branch to the +virtual world, that scene branch is instantly visible. This high-level +view of the render loop permits concurrent implementations of +Java 3D +as well as serial implementations. The remainder of this section +describes the Java 3D render loop bootstrap process from a +serialized +perspective. Differences that would appear in concurrent +implementations are noted as well. +</p> +<p></p> +<h3>An Application-Level +Perspective</h3> +<p>First the application must construct its scene graphs. It does this +by +constructing scene graph nodes and component objects and linking them +into self-contained trees with a BranchGroup node as a root. The +application next must obtain a reference to any constituent nodes or +objects within that branch that it may wish to manipulate. It sets the +capabilities of all the objects to match their anticipated use and only +then compiles the branch using the BranchGroup's <code>compile</code> +method. Whether it compiles the branch, the application can add it to +the virtual universe by adding the BranchGroup to a Locale object. The +application repeats this process for each branch it wishes to create. +Note that for concurrent Java 3D implementations, whenever an +application adds a branch to the active virtual universe, that branch +becomes visible. +</p> +<p></p> +<h3>Retained and +Compiled-Retained Rendering Modes</h3> +<p>This initialization process is identical for retained and +compiled-retained modes. In both modes, the application builds a scene +graph. In compiled-retained mode, the application compiles the scene +graph. Then the application inserts the (possibly compiled) scene graph +into the virtual universe. +</p> +</body> +</html> diff --git a/doc-files/SceneGraphOverview.html b/doc-files/SceneGraphOverview.html new file mode 100644 index 0000000..f1616df --- /dev/null +++ b/doc-files/SceneGraphOverview.html @@ -0,0 +1,226 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<html> +<head> + <meta content="text/html; charset=ISO-8859-1" + http-equiv="content-type"> + <title>Java 3D API - Scene Graph Overview</title> +</head> +<body> +<h2>Scene Graph Basics</h2> +<p>A scene graph consists of Java 3D +objects, called <em>nodes</em>, +arranged in a tree structure. The user creates one or more scene +subgraphs and attaches them to a virtual universe. The individual +connections between Java 3D nodes always represent a directed +relationship: parent to child. Java 3D restricts scene graphs in one +major way: Scene graphs may not contain cycles. Thus, a Java 3D scene +graph is a directed acyclic graph (DAG). See <a href="#Figure_1">Figure +1</a>. +</p> +<p>Java 3D refines the <a href="../Node.html">Node</a> object class +into two subclasses: <a href="../Group.html">Group</a> +and +<a href="../Leaf.html">Leaf</a> node objects. Group node objects group +together one or more child +nodes. A group node can point to zero or more children but can have +only one parent. The SharedGroup node cannot have any parents (although +it allows sharing portions of a scene graph, as described in "<a + href="SceneGraphSharing.html">Reusing Scene Graphs</a>"). +Leaf node objects contain the actual definitions of shapes (geometry), +lights, fog, sounds, and so forth. A leaf node has no children and only +one parent. The semantics of the various group and leaf nodes are +described in subsequent chapters. </p> +<h2>Scene Graph Structure</h2> +<p>A scene graph organizes and controls the rendering +of its constituent objects. The Java 3D renderer draws a scene graph in +a consistent way that allows for concurrence. The Java 3D renderer can +draw one object independently of other objects. Java 3D can allow such +independence because its scene graphs have a particular form and cannot +share state among branches of a tree. +</p> +<h3>Spatial Separation</h3> +<p>The hierarchy of the scene graph encourages a natural spatial +grouping +on the geometric objects found at the leaves of the graph. Internal +nodes act to group their children together. A group node also defines a +spatial bound that contains all the geometry defined by its +descendants. Spatial grouping allows for efficient implementation of +operations such as proximity detection, collision detection, view +frustum culling, and occlusion culling. +</p> +<p><a name="Figure_1"></a><img style="width: 500px; height: 341px;" + alt="Directed Acyclic Graph" title="Directed Acyclic Graph" + src="DAG.gif"></p> +<p> </p> +<ul> + <font size="-1"><b><i>Figure 1</i> – A Java +3D Scene Graph Is a DAG +(Directed Acyclic Graph)</b></font> +</ul> +<p> </p> +<h3>State Inheritance</h3> +<p>A leaf node's state is defined by the nodes in a direct path between +the scene graph's root and the leaf. Because a leaf's graphics context +relies only on a linear path between the root and that node, the Java +3D renderer can decide to traverse the scene graph in whatever order it +wishes. It can traverse the scene graph from left to right and top to +bottom, in level order from right to left, or even in parallel. The +only exceptions to this rule are spatially bounded attributes such as +lights and fog. +</p> +<p>This characteristic is in marked contrast to many older scene +graph-based APIs (including PHIGS and SGI's Inventor) where, if a node +above or to the left of a node changes the graphics state, the change +affects the graphics state of all nodes below it or to its right. </p> +<p>The most common node object, along the path from the root to the +leaf, +that changes the graphics state is the TransformGroup object. The +TransformGroup object can change the position, orientation, and scale +of the objects below it. </p> +<p>Most graphics state attributes are set by a Shape3D leaf node +through +its constituent Appearance object, thus allowing parallel rendering. +The Shape3D node also has a constituent Geometry object that specifies +its geometry-this permits different shape objects to share common +geometry without sharing material attributes (or vice versa). </p> +<p> </p> +<h3>Rendering</h3> +<p>The Java 3D renderer incorporates all graphics state changes made in +a +direct path from a scene graph root to a leaf object in the drawing of +that leaf object. Java 3D provides this semantic for both retained and +compiled-retained modes. +</p> +<p> </p> +<h2>Scene Graph Objects</h2> +<p>A Java 3D scene graph consists of a collection of Java 3D node +objects +connected in a tree structure. These node objects reference other scene +graph objects called <em>node component objects</em>. +All scene graph node and component objects are subclasses of a common +<a href="../SceneGraphObject.html">SceneGraphObject</a> class. The +SceneGraphObject class is an abstract class +that defines methods that are common among nodes and component objects. +</p> +<p>Scene graph objects are constructed by creating a new instance of +the +desired class and are accessed and manipulated using the object's <code>set</code> +and <code>get</code> +methods. Once a scene graph object is created and connected to other +scene graph objects to form a subgraph, the entire subgraph can be +attached to a virtual universe---via a high-resolution <a + href="../Locale.html">Locale</a> +object-making the object <em>live</em>. Prior to attaching a subgraph +to a virtual +universe, the entire subgraph can be <em>compiled</em> into an +optimized, internal format (see the +<code><a href="../BranchGroup.html#compile%28%29">BranchGroup.compile()</a></code> +method). </p> +<p>An important characteristic of all scene graph objects is that +they can +be accessed or modified only during the creation of a scene graph, +except where explicitly allowed. Access to most <code>set</code> and <code>get</code> +methods of objects that are part of a live or compiled scene graph is +restricted. Such restrictions provide the scene graph compiler with +usage information it can use in optimally compiling or rendering a +scene graph. Each object has a set of capability bits that enable +certain functionality when the object is live or compiled. By default, +all capability bits are disabled (cleared). Only those <code>set</code> +and <code>get</code> +methods corresponding to capability bits that are explicitly enabled +(set) prior to the object being compiled or made live are legal.<br> +</p> +<p> </p> +<h2>Scene Graph Superstructure +Objects</h2> +Java 3D defines two scene graph superstructure objects, +<a href="../VirtualUniverse.html">VirtualUniverse</a> +and <a href="../Locale.html">Locale</a>, which are used to contain +collections of subgraphs that +comprise the scene graph. These objects are described in more detail in +"<a href="VirtualUniverse.html">Scene Graph Superstructure</a>." +<p> </p> +<h3>VirtualUniverse Object</h3> +A <a href="../VirtualUniverse.html">VirtualUniverse</a> object +consists of a list of Locale objects that +contain a collection of scene graph nodes that exist in the universe. +Typically, an application will need only one VirtualUniverse, even for +very large virtual databases. Operations on a VirtualUniverse include +enumerating the Locale objects contained within the universe. +<p> </p> +<h3>Locale Object</h3> +The <a href="../Locale.html">Locale</a> object acts as a container for +a collection of subgraphs of +the scene graph that are rooted by a BranchGroup node. A Locale also +defines a location within the virtual universe using high-resolution +coordinates (HiResCoord) to specify its position. The HiResCoord serves +as the origin for all scene graph objects contained within the Locale. +<p>A Locale has no parent in the scene graph but is implicitly +attached to +a virtual universe when it is constructed. A Locale may reference an +arbitrary number of BranchGroup nodes but has no explicit children. </p> +<p>The coordinates of all scene graph objects are relative to the +HiResCoord of the Locale in which they are contained. Operations on a +Locale include setting or getting the HiResCoord of the Locale, adding +a subgraph, and removing a subgraph. </p> +<p> </p> +<h2>Scene Graph Viewing Objects</h2> +Java 3D defines five scene graph viewing objects that are not part of +the scene graph per se but serve to define the viewing parameters and +to provide hooks into the physical world. These objects are <a + href="../Canvas3D.html">Canvas3D</a>, +<a href="../Screen3D.html">Screen3D</a>, <a href="../View.html">View</a>, +<a href="../PhysicalBody.html">PhysicalBody</a>, and <a + href="../PhysicalEnvironment.html">PhysicalEnvironment</a>. They are +described in more detail in the "<a href="ViewModel.html">View Model</a>" +document.<br> +<p> </p> +<h3>Canvas3D Object</h3> +The <a href="../Canvas3D.html">Canvas3D</a> object encapsulates all of +the parameters associated with +the window being rendered into. +When a Canvas3D object is attached to a View object, the Java 3D +traverser renders the specified view onto the canvas. Multiple Canvas3D +objects can point to the same View object. +<p> </p> +<h3>Screen3D Object</h3> +The <a href="../Screen3D.html">Screen3D</a> object encapsulates all of +the +parameters associated with the physical screen containing the canvas, +such as the width and height of the screen in pixels, the physical +dimensions of the screen, and various physical calibration values. +<p> </p> +<h3>View Object</h3> +The <a href="../View.html">View</a> object specifies information +needed to render the scene graph. +<a href="#Figure_2">Figure +2</a> shows a View object attached to a simple scene graph for +viewing the scene. +<p>The View object is the central Java 3D object for coordinating all +aspects of viewing. +All viewing parameters in Java 3D are directly contained either within +the View object or within objects pointed to by a View object. Java 3D +supports multiple simultaneously active View objects, each of which can +render to one or more canvases. </p> +<p> </p> +<h3>PhysicalBody Object</h3> +The PhysicalBody object encapsulates all of the +parameters associated with the physical body, such as head position, +right and left eye position, and so forth. +<p> </p> +<h3>PhysicalEnvironment Object</h3> +<p>The PhysicalEnvironment object encapsulates all of the parameters +associated with the physical environment, such as calibration +information for the tracker base for the head or hand tracker.<br> +</p> +<p><a name="Figure_2"></a><br> +</p> +<p><img style="width: 489px; height: 339px;" alt="Viewing a Scene Graph" + title="Viewing a Scene Graph" src="ViewBranch.gif"> +</p> +<p> </p> +<ul> + <font size="-1"><b><i>Figure 2</i> – Viewing a Scene Graph</b></font> +</ul> +</body> +</html> diff --git a/doc-files/SceneGraphSharing.html b/doc-files/SceneGraphSharing.html new file mode 100644 index 0000000..c289c15 --- /dev/null +++ b/doc-files/SceneGraphSharing.html @@ -0,0 +1,250 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<html> +<head> + <meta content="text/html; charset=ISO-8859-1" + http-equiv="content-type"> + <title>Java 3D API - Reusing Scene Graphs</title> +</head> +<body> +<h2>Reusing Scene Graphs</h2> +<p> +Java 3D provides application programmers +with two different means for reusing scene graphs. First, multiple +scene graphs can share a common subgraph. Second, the node hierarchy of +a common subgraph can be cloned, while still sharing large component +objects such as geometry and texture objects. In the first case, +changes in the shared subgraph affect all scene graphs that refer to +the shared subgraph. In the second case, each instance is unique-a +change in one instance does not affect any other instance. +</p> +<h2>Sharing Subgraphs</h2> +<p>An application that wishes to share a subgraph from multiple places +in +a scene graph must do so through the use of the <a href="../Link.html">Link</a> +leaf node and an +associated <a href="../SharedGroup.html">SharedGroup</a> node. The +SharedGroup node serves as the root of +the shared subgraph. The Link leaf node refers to the SharedGroup node. +It does not incorporate the shared scene graph directly into its scene +graph. +</p> +<p>A SharedGroup node allows multiple Link leaf nodes to share its +subgraph as shown in <a href="#Figure_1">Figure +1</a> below.<br> +</p> +<p><a name="Figure_1"></a><img style="width: 500px; height: 476px;" + alt="Sharing a Subgraph" title="Sharing a Subgraph" + src="SceneGraphSharing1.gif"> +</p> +<ul> + <font size="-1"><b><i>Figure 1</i> – Sharing a Subgraph</b></font> +</ul> +<h2>Cloning Subgraphs</h2> +<p>An application developer may wish to reuse a common subgraph without +completely sharing that subgraph. For example, the developer may wish +to create a parking lot scene consisting of multiple cars, each with a +different color. The developer might define three basic types of cars, +such as convertible, truck, and sedan. To create the parking lot scene, +the application will instantiate each type of car several times. Then +the application can change the color of the various instances to create +more variety in the scene. Unlike shared subgraphs, each instance is a +separate copy of the scene graph definition: Changes to one instance do +not affect any other instance. +</p> +<p>Java 3D provides the <a href="../Node.html#cloneTree%28%29"><code>cloneTree</code></a> +method for this +purpose. The <code>cloneTree</code> +method allows the programmer to change some attributes (NodeComponent +objects) in a scene graph, while at the same time sharing the majority +of the scene graph data-the geometry. +</p> +<h3>References to Node Component +Objects</h3> +<p>When <code>cloneTree</code> reaches a leaf node, +there are two possible actions for handling the leaf node's +NodeComponent objects (such as Material, Texture, and so forth). First, +the cloned leaf node can reference the original leaf node's +NodeComponent object-the NodeComponent object itself is not duplicated. +Since the cloned leaf node shares the NodeComponent object with the +original leaf node, changing the data in the NodeComponent object will +effect a change in both nodes. This mode would also be used for objects +that are read-only at run time. +</p> +<p>Alternatively, the NodeComponent object can be duplicated, in which +case the new leaf node would reference the duplicated object. This mode +allows data referenced by the newly created leaf node to be modified +without that modification affecting the original leaf node. +</p> +<p><a href="#Figure_2">Figure +2</a> +shows two instances of NodeComponent objects that are shared and one +NodeComponent element that is duplicated for the cloned subgraph. +</p> +<p><a name="Figure_2"></a><img style="width: 499px; height: 287px;" + alt="Referenced and Duplicated NodeComponent Objects" + title="Referenced / Duplicated NodeComponens" + src="SceneGraphSharing2.gif"> +</p> +<p> +</p> +<ul> + <font size="-1"><b><i>Figure 2</i> – Referenced and Duplicated +NodeComponent Objects</b></font> +</ul> +<h3>References to Other Scene +Graph Nodes</h3> +Leaf nodes that contain references to other nodes +(for example, Light nodes reference a Group node) can create a problem +for the <code>cloneTree</code> method. After the <code>cloneTree</code> +operation is performed, the reference in the cloned leaf node will +still refer to the node in the original subgraph-a situation that is +most likely incorrect (see <a href="#Figure_3">Figure +3</a>). +<p>To handle these ambiguities, a callback mechanism is provided. +</p> +<p><a name="Figure_3"></a><img style="width: 499px; height: 240px;" + alt="References to Other Scene Graph Nodes" + title="References to Other Nodes" src="SceneGraphSharing3.gif"> +</p> +<ul> + <font size="-1"><b><i>Figure 3</i> – References to Other Scene Graph +Nodes</b></font> +</ul> +<p> +A leaf node that needs to update referenced nodes upon being duplicated +by a call to <code>cloneTree</code> must implement the <code>updateNodeReferences</code> +method. By using this method, the cloned leaf node can determine if any +nodes referenced by it have been duplicated and, if so, update the +appropriate references to their cloned counterparts. +</p> +<p>Suppose, for instance, that the leaf node Lf1 in <a href="#Figure_3">Figure +3</a> implemented the <code>updateNodeReferences</code> method. Once +all nodes had been duplicated, the <code>clone-Tree</code> method +would then call each cloned leaf's node <code>updateNodeReferences</code> +method. When cloned leaf node Lf2's method was called, Lf2 could ask if +the node N1 had been duplicated during the <code>cloneTree</code> +operation. If the node had been duplicated, leaf Lf2 could then update +its internal state with the cloned node, N2 (see <a href="#Figure_4">Figure +4</a>). +</p> +<p><a name="Figure_4"></a><img style="width: 499px; height: 190px;" + alt="Updated Subgraph after updateNodeReferences Call" + title="Subgraph after updateNodeReferences" + src="SceneGraphSharing4.gif"> +</p> +<p> +</p> +<ul> + <font size="-1"><b><i>Figure 4</i> – Updated Subgraph after +updateNodeReferences Call</b></font> +</ul> +<p> +All predefined Java 3D nodes will automatically have their <code>updateNodeReferences</code> +method defined. Only subclassed nodes that reference other nodes need +to have this method overridden by the user. +</p> +<h3>Dangling References</h3> +Because <code>cloneTree</code> is able to start +the cloning operation from any node, there is a potential for creating +dangling references. A dangling reference can occur only when a leaf +node that contains a reference to another scene graph node is cloned. +If the referenced node is not cloned, a dangling reference situation +exists: There are now two leaf nodes that access the same node (<a + href="#Figure_5">Figure +5</a>). A dangling reference is discovered when a leaf node's <code>updateNodeReferences</code> +method calls the <code>getNewNodeReference</code> method and the +cloned subgraph does not contain a counterpart to the node being looked +up. +<p><a name="Figure_5"></a><img style="width: 499px; height: 232px;" + alt="Dangling Reference" title="Dangling Reference" + src="SceneGraphSharing5.gif"></p> +<p> +</p> +<ul> + <font size="-1"><b><i>Figure 5</i> – Dangling Reference: Bold Nodes +Are Being Cloned</b></font> +</ul> +<p> +When a dangling reference is discovered, <code>cloneTree</code> can +handle it in one of two ways. If <code>cloneTree</code> is called +without the <code>allowDanglingReferences</code> parameter set to <code>true</code>, +a dangling reference will result in a <code>DanglingReferenceException</code> +being thrown. The user can catch this exception if desired. If <code>cloneTree</code> +is called with the <code>allowDanglingReferences</code> parameter set +to <code>true</code>, the <code>update-NodeReferences</code> method +will return a reference to the same object passed into the <code>getNewNodeReference</code> +method. This will result in the <code>cloneTree</code> operation +completing with dangling references, as in <a href="#Figure_5">Figure +5</a>. +</p> +<h3>Subclassing Nodes</h3> +All Java 3D predefined nodes (for example, Interpolators and LOD +nodes) +automatically handle all node reference and duplication operations. +When a user subclasses a Leaf object or a NodeComponent object, certain +methods must be provided in order to ensure the proper operation of <code>cloneTree</code>. +<p>Leaf node subclasses (for example, Behaviors) that contain any user +node-specific data that needs to be duplicated during a <code>cloneTree</code> +operation must define the following two methods: +</p> +<pre><b>Node cloneNode(boolean forceDuplicate);<br>void duplicateNode(Node n, boolean forceDuplicate)<br></b></pre> +The <code>cloneNode</code> method consists of three lines: +<pre><hr><br><code>UserSubClass usc = new UserSubClass();<br>usc.duplicateNode(this, forceDuplicate);</code><br>return usc;<br><br><hr></pre> +The <code>duplicateNode</code> method must first call <code>super.duplicateNode</code> +before duplicating any necessary user-specific data or setting any +user-specific state. +<p>NodeComponent subclasses that contain any user node-specific data +must define the following two methods: +</p> +<pre><b>NodeComponent cloneNodeComponent();<br>void duplicateNodeComponent(NodeComponent nc, boolean forceDuplicate);<br></b></pre> +The <code>cloneNodeComponent</code> method consists of three lines: +<pre><hr><br><code>UserNodeComponent unc = new UserNodeComponent();<br>unc.duplicateNodeComponent(this, forceDuplicate);</code><br>return un;<br><br><hr></pre> +The <code>duplicateNodeComponent</code> must first call <code>super.duplicateNodeComponent</code> +and then can duplicate any user-specific data or set any user-specific +state as necessary. +<h3>NodeReferenceTable Object</h3> +The NodeReferenceTable object is used by a leaf node's <code>updateNodeReferences</code> +method called by the <code>cloneTree</code> +operation. The NodeReferenceTable maps nodes from the original subgraph +to the new nodes in the cloned subgraph. This information can than be +used to update any cloned leaf node references to reference nodes in +the cloned subgraph. This object can be created only by Java 3D. +<h3>Example: User Behavior Node</h3> +The following is an example of a user-defined Behavior object to show +properly how to define a node to be compatible with the <code>cloneTree</code> +operation. +<hr> +<pre>class RotationBehavior extends Behavior {<br> TransformGroup objectTransform;<br> WakeupOnElapsedFrames w;<br></pre> +<pre> Matrix4d rotMat = new Matrix4d();<br> Matrix4d objectMat = new Matrix4d();<br> Transform3D t = new Transform3D();<br></pre> +<pre><i> // Override Behavior's initialize method to set up wakeup<br> // criteria<br></i></pre> +<pre> public void initialize() {<br></pre> +<pre><i> // Establish initial wakeup criteria<br></i></pre> +<pre> wakeupOn(w);<br> }<br></pre> +<pre><i> // Override Behavior's stimulus method to handle the event<br></i></pre> +<pre> public void void processStimulus(Iterator<WakeupCriterion> criteria) {<br></pre> +<pre><i> // Rotate by another PI/120.0 radians<br></i></pre> +<pre> objectMat.mul(objectMat, rotMat);<br> t.set(objectMat);<br> objectTransform.setTransform(t);<br></pre> +<pre><i> // Set wakeup criteria for next time<br></i></pre> +<pre> wakeupOn(w);<br> }<br></pre> +<pre><i> // Constructor for rotation behavior.<br></i></pre> +<pre> public RotationBehavior(TransformGroup tg, int numFrames) {<br> w = new WakeupOnElapsedFrames(numFrames);<br> objectTransform = tg;<br></pre> +<pre><i> objectMat.setIdentity();<br></i></pre> +<pre><i> // Create a rotation matrix that rotates PI/120.0<br> // radians per frame<br> rotMat.rotX(Math.PI/120.0);<br></i></pre> +<pre><i> // Note: When this object is duplicated via cloneTree,<br> // the cloned RotationBehavior node needs to point to<br> // the TransformGroup in the just-cloned tree. <br> }<br></i></pre> +<pre><i> // Sets a new TransformGroup.<br></i></pre> +<pre> public void setTransformGroup(TransformGroup tg) {<br> objectTransform = tg;<br></pre> +<pre><i> }<br></i></pre> +<pre><i> // The next two methods are needed for cloneTree to operate<br> // correctly.<br> // cloneNode is needed to provide a new instance of the user<br> // derived subclass.<br></i></pre> +<pre> public Node cloneNode(boolean forceDuplicate) {<br></pre> +<pre><i> // Get all data from current node needed for<br> // the constructor<br> int numFrames = w.getElapsedFrameCount();<br></i></pre> +<pre> RotationBehavior r =<br> new RotationBehavior(objectTransform, numFrames);<br> r.duplicateNode(this, forceDuplicate);<br> return r;<br> }<br></pre> +<pre><i> // duplicateNode is needed to duplicate all super class<br> // data as well as all user data.<br></i></pre> +<pre> public void duplicateNode(Node originalNode, boolean <br> forceDuplicate) {<br> super.duplicateNode(originalNode, forceDuplicate);<br></pre> +<pre><i> // Nothing to do here - all unique data was handled<br> // in the constructor in the cloneNode routine.<br> }<br></i></pre> +<pre><i> // Callback for when this leaf is cloned. For this object<br> // we want to find the cloned TransformGroup node that this<br> // clone Leaf node should reference.<br></i></pre> +<pre> public void updateNodeReferences(NodeReferenceTable t) {<br></pre> +<pre><i> super.updateNodeReferences(t);<br></i></pre> +<pre><i> // Update node's TransformGroup to proper reference<br></i></pre> +<pre> TransformGroup newTg =<br> (TransformGroup)t.getNewObjectReference(<br> objectTransform);<br> setTransformGroup(newTg);<br> }<br>}<br></pre> +</body> +</html> diff --git a/doc-files/SceneGraphSharing1.gif b/doc-files/SceneGraphSharing1.gif Binary files differnew file mode 100644 index 0000000..f6ca47c --- /dev/null +++ b/doc-files/SceneGraphSharing1.gif diff --git a/doc-files/SceneGraphSharing2.gif b/doc-files/SceneGraphSharing2.gif Binary files differnew file mode 100644 index 0000000..c062c81 --- /dev/null +++ b/doc-files/SceneGraphSharing2.gif diff --git a/doc-files/SceneGraphSharing3.gif b/doc-files/SceneGraphSharing3.gif Binary files differnew file mode 100644 index 0000000..325cab1 --- /dev/null +++ b/doc-files/SceneGraphSharing3.gif diff --git a/doc-files/SceneGraphSharing4.gif b/doc-files/SceneGraphSharing4.gif Binary files differnew file mode 100644 index 0000000..78aeaab --- /dev/null +++ b/doc-files/SceneGraphSharing4.gif diff --git a/doc-files/SceneGraphSharing5.gif b/doc-files/SceneGraphSharing5.gif Binary files differnew file mode 100644 index 0000000..2ff6547 --- /dev/null +++ b/doc-files/SceneGraphSharing5.gif diff --git a/doc-files/ViewBranch.gif b/doc-files/ViewBranch.gif Binary files differnew file mode 100644 index 0000000..75cc40d --- /dev/null +++ b/doc-files/ViewBranch.gif diff --git a/doc-files/ViewModel.html b/doc-files/ViewModel.html new file mode 100644 index 0000000..3cc9ece --- /dev/null +++ b/doc-files/ViewModel.html @@ -0,0 +1,1064 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<html> +<head> + <meta content="text/html; charset=ISO-8859-1" + http-equiv="content-type"> + <title>Java 3D API - View Model</title> +</head> +<body> +<h2>View Model</h2> +<p>Java 3D introduces a new view model that takes Java's +vision of "write once, run anywhere" and generalizes it to include +display devices and six-degrees-of-freedom input peripherals such as +head trackers. This "write once, view everywhere" nature of the new +view model means that an application or applet written using the Java +3D view model can render images to a broad range of display devices, +including standard computer displays, multiple-projection display +rooms, and head-mounted displays, without modification of the scene +graph. It also means that the same application, once again without +modification, can render stereoscopic views and can take advantage of +the input from a head tracker to control the rendered view. +</p> +<p>Java 3D's view model achieves this versatility by cleanly +separating +the virtual and the physical world. This model distinguishes between +how an application positions, orients, and scales a ViewPlatform object +(a viewpoint) within the virtual world and how the Java 3D +renderer +constructs the final view from that viewpoint's position and +orientation. The application controls the ViewPlatform's position and +orientation; the renderer computes what view to render using this +position and orientation, a description of the end-user's physical +environment, and the user's position and orientation within the +physical environment. +</p> +<p>This document first explains why Java 3D chose a different view +model +and some of the philosophy behind that choice. It next describes how +that model operates in the simple case of a standard computer screen +without head tracking—the most common case. Finally, it presents +advanced material that was originally published in Appendix C of the +API specification guide. +</p> +<p> +</p> +<h2>Why a New Model?</h2> +<p>Camera-based view models, as found in low-level APIs, give +developers +control over all rendering parameters. This makes sense when dealing +with custom applications, less sense when dealing with systems that +wish to have broader applicability: systems such as viewers or browsers +that load and display whole worlds as a single unit or systems where +the end users view, navigate, display, and even interact with the +virtual world. +</p> +<p>Camera-based view models emulate a camera in the virtual world, not +a +human in a virtual world. Developers must continuously reposition a +camera to emulate "a human in the virtual world." +</p> +<p>The Java 3D view model incorporates head tracking directly, if +present, +with no additional effort from the developer, thus providing end users +with the illusion that they actually exist inside a virtual world. +</p> +<p>The Java 3D view model, when operating in a non-head-tracked +environment and rendering to a single, standard display, acts very much +like a traditional camera-based view model, with the added +functionality of being able to generate stereo views transparently. +</p> +<p> +</p> +<h3>The Physical Environment +Influences the View</h3> +<p>Letting the application control all viewing parameters is not +reasonable in systems in which the physical environment dictates some +of the view parameters. +</p> +<p>One example of this is a head-mounted display (HMD), where the +optics +of the head-mounted display directly determine the field of view that +the application should use. Different HMDs have different optics, +making it unreasonable for application developers to hard-wire such +parameters or to allow end users to vary that parameter at will. +</p> +<p>Another example is a system that automatically computes view +parameters +as a function of the user's current head position. The specification of +a world and a predefined flight path through that world may not exactly +specify an end-user's view. HMD users would expect to look and thus see +to their left or right even when following a fixed path through the +environment-imagine an amusement park ride with vehicles that follow +fixed paths to present content to their visitors, but visitors can +continue to move their heads while on those rides. +</p> +<p>Depending on the physical details of the end-user's environment, the +values of the viewing parameters, particularly the viewing and +projection matrices, will vary widely. The factors that influence the +viewing and projection matrices include the size of the physical +display, how the display is mounted (on the user's head or on a table), +whether the computer knows the user's head location in three space, the +head mount's actual field of view, the display's pixels per inch, and +other such parameters. For more information, see "<a + href="#View_Model_Details">View Model Details</a>." +</p> +<p> +</p> +<h2>Separation of Physical and +Virtual</h2> +<p>The Java 3D view model separates the virtual environment, where +the +application programmer has placed objects in relation to one another, +from the physical environment, where the user exists, sees computer +displays, and manipulates input devices. +</p> +<p>Java 3D also defines a fundamental correspondence between the +user's +physical world and the virtual world of the graphic application. This +physical-to-virtual-world correspondence defines a single common space, +a space where an action taken by an end user affects objects within the +virtual world and where any activity by objects in the virtual world +affects the end user's view. +</p> +<p> +</p> +<h3>The Virtual World</h3> +<p>The virtual world is a common space in which virtual objects exist. +The +virtual world coordinate system exists relative to a high-resolution +Locale-each Locale object defines the origin of virtual world +coordinates for all of the objects attached to that Locale. The Locale +that contains the currently active ViewPlatform object defines the +virtual world coordinates that are used for rendering. Java3D +eventually transforms all coordinates associated with scene graph +elements into this common virtual world space. +</p> +<h3>The Physical World</h3> +<p>The physical world is just that-the real, physical world. This is +the +space in which the physical user exists and within which he or she +moves his or her head and hands. This is the space in which any +physical trackers define their local coordinates and in which several +calibration coordinate systems are described. +</p> +<p>The physical world is a space, not a common coordinate system +between +different execution instances of Java 3D. So while two different +computers at two different physical locations on the globe may be +running at the same time, there is no mechanism directly within +Java 3D +to relate their local physical world coordinate systems with each +other. Because of calibration issues, the local tracker (if any) +defines the local physical world coordinate system known to a +particular instance of Java 3D. +</p> +<p> +</p> +<h2>The Objects That Define the +View</h2> +<p>Java 3D distributes its view model parameters across several +objects, +specifically, the View object and its associated component objects, the +PhysicalBody object, the PhysicalEnvironment object, the Canvas3D +object, and the Screen3D object. <a href="#Figure_1">Figure +1</a> shows graphically the central role of the View object and the +subsidiary role of its component objects. +</p> +<p><a name="Figure_1"></a><img style="width: 500px; height: 355px;" + alt="View Object + Other Components" + title="View Object + Other Components" src="ViewModel1.gif"></p> +<p> +</p> +<ul> + <font size="-1"><b><i>Figure 1</i> – View Object, Its Component +Objects, and Their +Interconnection</b></font> +</ul> +<p> +The view-related objects shown in <a href="#Figure_1">Figure +1</a> +and their roles are as follows. For each of these objects, the portion +of the API that relates to modifying the virtual world and the portion +of the API that is relevant to non-head-tracked standard display +configurations are derived in this chapter. The remainder of the +details are described in "<a href="#View_Model_Details">View Model +Details</a>." +</p> +<ul> + <li><a href="../ViewPlatform.html"><em>ViewPlatform</em></a>: A leaf +node that locates a view within a +scene graph. The ViewPlatform's parents specify its location, +orientation, and scale within the virtual universe. See "<a + href="#ViewPlatform_Place">ViewPlatform: A Place in the Virtual World</a>," +for more +information. </li> +</ul> +<ul> + <li><a href="../View.html"><em>View</em></a>: The main view object. +It contains many pieces of +view state.</li> +</ul> +<ul> + <li><a href="../Canvas3D.html"><em>Canvas3D</em></a>: The 3D version +of the Abstract Windowing +Toolkit +(AWT) Canvas object. It represents a window in which Java 3D will +draw +images. It contains a reference to a Screen3D object and information +describing the Canvas3D's size, shape, and location within the Screen3D +object.</li> +</ul> +<ul> + <li><a href="../Screen3D.html"><em>Screen3D</em></a>: An object that +contains information describing +the display screen's physical properties. Java 3D places +display-screen +information in a separate object to prevent the duplication of screen +information within every Canvas3D object that shares a common screen.</li> +</ul> +<ul> + <li><a href="../PhysicalBody.html">PhysicalBody</a>: An object that +contains calibration information +describing the user's physical body.</li> +</ul> +<ul> + <li><a href="../PhysicalEnvironment.html">PhysicalEnvironment</a>: An +object that contains calibration +information describing the physical world, mainly information that +describes the environment's six-degrees-of freedom tracking hardware, +if present.</li> +</ul> +<p>Together, these objects describe the geometry of viewing rather than +explicitly providing a viewing or projection matrix. The Java 3D +renderer uses this information to construct the appropriate viewing and +projection matrices. The geometric focus of these view objects provides +more flexibility in generating views-a flexibility needed to support +alternative display configurations. +</p> +<h2><a name="ViewPlatform_Place"></a>ViewPlatform: A Place in the +Virtual World</h2> +<p>A ViewPlatform leaf node defines a coordinate system, and thus a +reference frame with its associated origin or reference point, within +the virtual world. The ViewPlatform serves as a point of attachment for +View objects and as a base for determining a renderer's view. +</p> +<p><a href="#Figure_2">Figure +2</a> +shows a portion of a scene graph containing a ViewPlatform node. The +nodes directly above a ViewPlatform determine where that ViewPlatform +is located and how it is oriented within the virtual world. By +modifying the Transform3D object associated with a TransformGroup node +anywhere directly above a ViewPlatform, an application or behavior can +move that ViewPlatform anywhere within the virtual world. A simple +application might define one TransformGroup node directly above a +ViewPlatform, as shown in <a href="#Figure_2">Figure +2</a>. +</p> +<p>A VirtualUniverse may have many different ViewPlatforms, but a +particular View object can attach itself only to a single ViewPlatform. +Thus, each rendering onto a Canvas3D is done from the point of view of +a single ViewPlatform. +</p> +<p><a name="Figure_2"></a><img style="width: 500px; height: 359px;" + alt="View Platform Branch Graph" title="View Platform Branch Graph" + src="ViewModel2.gif"> +</p> +<p> +</p> +<ul> + <font size="-1"><b><i>Figure 2</i> – A Portion of a Scene Graph +Containing a ViewPlatform Object</b></font> +</ul> +<p> +</p> +<h3>Moving through the Virtual +World</h3> +<p>An application navigates within the virtual world by modifying a +ViewPlatform's parent TransformGroup. Examples of applications that +modify a ViewPlatform's location and orientation include browsers, +object viewers that provide navigational controls, applications that do +architectural walkthroughs, and even search-and-destroy games. +</p> +<p>Controlling the ViewPlatform object can produce very interesting and +useful results. Our first simple scene graph (see <a + href="intro.html#Figure_1">"Introduction," Figure 1</a>) +defines a scene graph for a simple application that draws an object in +the center of a window and rotates that object about its center point. +In that figure, the Behavior object modifies the TransformGroup +directly above the Shape3D node. +</p> +<p>An alternative application scene graph, shown in <a href="#Figure_3">Figure +3</a>, +leaves the central object alone and moves the ViewPlatform around the +world. If the shape node contains a model of the earth, this +application could generate a view similar to that seen by astronauts as +they orbit the earth. +</p> +<p>Had we populated this world with more objects, this scene graph +would allow navigation through the world via the Behavior node. +</p> +<p><a name="Figure_3"></a><img style="width: 500px; height: 289px;" + alt="Simple Scene Graph with View Control" + title="Simple Scene Graph with View Control" src="ViewModel3.gif"> +</p> +<p> +</p> +<ul> + <font size="-1"><b><i>Figure 3</i> – A Simple Scene Graph with View +Control</b></font> +</ul> +<p> +Applications and behaviors manipulate a <a + href="../TransformGroup.html">TransformGroup</a> through its +access methods. These methods allow an application to retrieve and +set the Group node's Transform3D object. Transform3D Node methods +include <code>getTransform</code> and <code>setTransform</code>. +</p> +<p> +</p> +<h3>Dropping in on a Favorite +Place</h3> +<p>A scene graph may contain multiple <a href="../ViewPlatform.html">ViewPlatform</a> +objects. If a user detaches a <a href="../View.html">View</a> object +from a ViewPlatform and then +reattaches that View to a different ViewPlatform, the image on the +display will now be rendered from the point of view of the new +ViewPlatform.</p> +<h3>Associating Geometry with a +ViewPlatform</h3> +<p>Java 3D does not have any built-in semantics for displaying a +visible +manifestation of a ViewPlatform within the virtual world (an <em>avatar</em>). +However, a developer can construct and manipulate an avatar using +standard Java 3D constructs. +</p> +<p>A developer can construct a small scene graph consisting of a +TransformGroup node, a behavior leaf node, and a shape node and insert +it directly under the BranchGroup node associated with the ViewPlatform +object. The shape node would contain a geometric model of the avatar's +head. The behavior node would change the TransformGroup's transform +periodically to the value stored in a View object's <code>UserHeadToVworld</code><strong> +</strong>parameter (see "<a href="#View_Model_Details">View Model +Details</a>"). +The avatar's virtual head, represented by the shape node, will now move +around in lock-step with the ViewPlatform's TransformGroup<em> and </em>any +relative position and orientation changes of the user's actual physical +head (if a system has a head tracker). +</p> +<p> +</p> +<h2><a name="Generating_View"></a>Generating a View</h2> +<p>Java 3D generates viewing matrices in one of a few different +ways, +depending on whether the end user has a head-mounted or a room-mounted +display environment and whether head tracking is enabled. This section +describes the computation for a non-head-tracked, room-mounted +display-a standard computer display. Other environments are described +in "<a href="#View_Model_Details">View Model Details</a>." +</p> +<p>In the absence of head tracking, the ViewPlatform's origin specifies +the virtual eye's location and orientation within the virtual world. +However, the eye location provides only part of the information needed +to render an image. The renderer also needs a projection matrix. In the +default mode, Java 3D uses the projection policy, the specified +field-of-view information, and the front and back clipping distances to +construct a viewing frustum. +</p> +<p> +</p> +<h3>Composing Model and Viewing +Transformations</h3> +<p><a href="#Figure_4">Figure +4</a> +shows a simple scene graph. To draw the object labeled "S," +Java 3D +internally constructs the appropriate model, view platform, eye, and +projection matrices. Conceptually, the model transformation for a +particular object is computed by concatenating all the matrices in a +direct path between the object and the VirtualUniverse. The view matrix +is then computed-again, conceptually-by concatenating all the matrices +between the VirtualUniverse object and the ViewPlatform attached to the +current View object. The eye and projection matrices are constructed +from the View object and its associated component objects. +</p> +<p><a name="Figure_4"></a><img style="width: 500px; height: 332px;" + alt="Object and ViewPlatform Transform" + title="Object and ViewPlatform Transform" src="ViewModel4.gif"></p> +<p> +</p> +<ul> + <font size="-1"><b><i>Figure 4</i> – Object and ViewPlatform +Transformations</b></font> +</ul> +<p>In our scene graph, what we would normally consider the +model transformation would consist of the following three +transformations: <strong>LT</strong>1<strong>T</strong>2. By +multiplying <strong>LT</strong>1<strong>T</strong>2 +by a vertex in the shape object, we would transform that vertex into +the virtual universe's coordinate system. What we would normally +consider the view platform transformation would be (<strong>LT</strong>v1)-1 +or <strong>T</strong>v1<sup>-1</sup><strong>L</strong>-1. +This presents a problem since coordinates in the virtual universe are +256-bit fixed-point values, which cannot be used to represent +transformed points efficiently. +</p> +<p>Fortunately, however, there is a solution to this problem. Composing +the model and view platform transformations gives us +</p> +<dl> + <dt><br> + </dt> + <dd> <strong>T</strong>v1<sup>-1</sup><strong>L</strong>-1<strong>LT</strong>1<strong>T</strong>2 += <strong>T</strong>v1<sup>-1</sup><strong>IT</strong>1<strong>T</strong>2 += <strong>T</strong>v1<sup>-1</sup><strong>T</strong>1<strong>T</strong>2, + </dd> +</dl> +<p>the matrix that takes vertices in an object's local coordinate +system +and places them in the ViewPlatform's coordinate system. Note that the +high-resolution Locale transformations cancel each other out, which +removes the need to actually transform points into high-resolution +VirtualUniverse coordinates. The general formula of the matrix that +transforms object coordinates to ViewPlatform coordinates is <strong>T</strong>vn<sup>-1</sup>...<strong>T</strong>v2<sup>-1</sup><strong>T</strong>v1<sup>-1</sup><strong>T</strong>1<strong>T</strong>2...<strong>T</strong>m. +</p> +<p>As mentioned earlier, the View object contains the remainder of the +view information, specifically, the eye matrix, <strong>E</strong>, +that takes points in the View-Platform's local coordinate system and +translates them into the user's eye coordinate system, and the +projection matrix, <strong>P</strong>, that projects objects in the +eye's coordinate system into clipping coordinates. The final +concatenation of matrices for rendering our shape object "S" on the +specified Canvas3D is <strong>PET</strong>v1<sup>-1</sup><strong>T</strong>1<strong>T</strong>2. +In general this is <strong>PET</strong>vn<sup>-1</sup>...<strong>T</strong>v2<sup>-1</sup><strong>T</strong>v1<sup>-1</sup><strong>T</strong>1<strong>T</strong>2...<strong>T</strong>m. +</p> +<p>The details of how Java 3D constructs the matrices <strong>E</strong> +and <strong>P</strong> in different end-user configurations are +described in "<a href="#View_Model_Details">View Model Details</a>." +</p> +<p> +</p> +<h3>Multiple Locales</h3> +<p>Java 3D supports multiple high-resolution Locales. In some +cases, +these +Locales are close enough to each other that they can "see" each other, +meaning that objects can be rendered even though they are not in the +same Locale as the ViewPlatform object that is attached to the View. +Java 3D automatically handles this case without the application +having +to do anything. As in the previous example, where the ViewPlatform and +the object being rendered are attached to the same Locale, Java 3D +internally constructs the appropriate matrices for cases in which the +ViewPlatform and the object being rendered are <em>not</em> attached +to the same Locale. +</p> +<p>Let's take two Locales, L1 and L2, with the View attached to a +ViewPlatform in L1. According to our general formula, the modeling +transformation-the transformation that takes points in object +coordinates and transforms them into VirtualUniverse coordinates-is <strong>LT</strong>1<strong>T</strong>2...<strong>T</strong>m. +In our specific example, a point in Locale L2 would be transformed into +VirtualUniverse coordinates by <strong>L</strong>2<strong>T</strong>1<strong>T</strong>2...<strong>T</strong>m. +The view platform transformation would be (<strong>L</strong>1<strong>T</strong>v1<strong>T</strong>v1...<strong>T</strong>vn)-1 +or <strong>T</strong>vn<sup>-1</sup>...<strong>T</strong>v2<sup>-1</sup><strong>T</strong>v1<sup>-1</sup><strong>L</strong>1<sup>-1</sup>. +Composing these two matrices gives us +</p> +<dl> + <dt><br> + </dt> + <dd> <strong>T</strong>vn<sup>-1</sup>...<strong>T</strong>v2<sup>-1</sup><strong>T</strong>v1<sup>-1</sup><strong>L</strong>1<sup>-1</sup><strong>L</strong>2<strong>T</strong>1<strong>T</strong>2...<strong>T</strong>m. + </dd> +</dl> +<p>Thus, to render objects in another Locale, it is sufficient to +compute <strong>L</strong>1<sup>-1</sup><strong>L</strong>2 +and use that as the starting matrix when composing the model +transformations. Given that a Locale is represented by a single +high-resolution coordinate position, the transformation <strong>L</strong>1<sup>-1</sup><strong>L</strong>2 +is a simple translation by <strong>L</strong>2 - <strong>L</strong>1. +Again, it is not actually necessary to transform points into +high-resolution VirtualUniverse coordinates. +</p> +<p>In general, Locales that are close enough that the difference in +their +high-resolution coordinates can be represented in double precision by a +noninfinite value are close enough to be rendered. In practice, more +sophisticated culling techniques can be used to render only those +Locales that really are "close enough." +</p> +<p> +</p> +<h2>A Minimal Environment</h2> +<p>An application must create a minimal set of Java 3D objects +before +Java +3D can render to a display device. In addition to a Canvas3D object, +the application must create a View object, with its associated +PhysicalBody and PhysicalEnvironment objects, and the following scene +graph elements: +</p> +<ul> + <li>A VirtualUniverse object</li> +</ul> +<ul> + <li>A high-resolution Locale object</li> +</ul> +<ul> + <li>A BranchGroup node object</li> +</ul> +<ul> + <li>A TransformGroup node object with associated transform</li> +</ul> +<ul> + <li>A ViewPlatform leaf node object that defines the position and +orientation within the virtual universe for generating views</li> +</ul> +<hr> +<h2><a name="View_Model_Details"></a>View Model Details</h2> +<p>An application programmer writing a 3D +graphics program that will deploy on a variety of platforms must +anticipate the likely end-user environments and must carefully +construct the view transformations to match those characteristics using +a low-level API. This appendix addresses many of the issues an +application must face and describes the sophisticated features that +Java 3D's advanced view model provides. +</p> +<p> +</p> +<h2>An Overview of the +Java 3D +View Model</h2> +Both camera-based and Java 3D-based view models allow a programmer +to +specify the shape of a view frustum and, under program control, to +place, move, and reorient that frustum within the virtual environment. +However, how they do this varies enormously. Unlike the camera-based +system, the Java 3D view model allows slaving the view frustum's +position and orientation to that of a six-degrees-of-freedom tracking +device. By slaving the frustum to the tracker, Java 3D can +automatically modify the view frustum so that the generated images +match the end-user's viewpoint exactly. +<p>Java 3D must handle two rather different head-tracking +situations. +In one case, we rigidly attach a tracker's <em>base</em>, +and thus its coordinate frame, to the display environment. This +corresponds to placing a tracker base in a fixed position and +orientation relative to a projection screen within a room, to a +computer display on a desk, or to the walls of a multiple-wall +projection display. In the second head-tracking situation, we rigidly +attach a tracker's <em>sensor</em>, not its base, to the display +device. This corresponds to rigidly attaching one of that tracker's +sensors to a head-mounted display and placing the tracker base +somewhere within the physical environment. +</p> +<p> +</p> +<h2>Physical Environments and +Their Effects</h2> +Imagine an application where the end user sits on a magic carpet. The +application flies the user through the virtual environment by +controlling the carpet's location and orientation within the virtual +world. At first glance, it might seem that the application also +controls what the end user will see-and it does, but only +superficially. +<p>The following two examples show how end-user environments can +significantly affect how an application must construct viewing +transformations. +</p> +<p> +</p> +<h3>A Head-Mounted Example</h3> +Imagine that the end user sees the magic carpet and the virtual world +with a head-mounted display and head tracker. As the application flies +the carpet through the virtual world, the user may turn to look to the +left, to the right, or even toward the rear of the carpet. Because the +head tracker keeps the renderer informed of the user's gaze direction, +it might not need to draw the scene directly in front of the magic +carpet. The view that the renderer draws on the head-mount's display +must match what the end user would see if the experience had occurred +in the real world. +<h3>A Room-Mounted Example</h3> +Imagine a slightly different scenario where the end user sits in a +darkened room in front of a large projection screen. The application +still controls the carpet's flight path; however, the position and +orientation of the user's head barely influences the image drawn on the +projection screen. If a user looks left or right, then he or she sees +only the darkened room. The screen does not move. It's as if the screen +represents the magic carpet's "front window" and the darkened room +represents the "dark interior" of the carpet. +<p>By adding a left and right screen, we give the magic carpet rider a +more complete view of the virtual world surrounding the carpet. Now our +end user sees the view to the left or right of the magic carpet by +turning left or right. +</p> +<p> +</p> +<h3>Impact of Head Position and +Orientation on the Camera</h3> +In the head-mounted example, the user's head position and orientation +significantly affects a camera model's camera position and orientation +but hardly has any effect on the projection matrix. In the room-mounted +example, the user's head position and orientation contributes little to +a camera model's camera position and orientation; however, it does +affect the projection matrix. +<p>From a camera-based perspective, the application developer must +construct the camera's position and orientation by combining the +virtual-world component (the position and orientation of the magic +carpet) and the physical-world component (the user's instantaneous head +position and orientation). +</p> +<p>Java 3D's view model incorporates the appropriate abstractions +to +compensate automatically for such variability in end-user hardware +environments. +</p> +<p> +</p> +<h2>The Coordinate Systems</h2> +The basic view model consists of eight or nine coordinate systems, +depending on whether the end-user environment consists of a +room-mounted display or a head-mounted display. First, we define the +coordinate systems used in a room-mounted display environment. Next, we +define the added coordinate system introduced when using a head-mounted +display system. +<h3>Room-Mounted Coordinate +Systems</h3> +The room-mounted coordinate system is divided into the virtual +coordinate system and the physical coordinate system. <a + href="#Figure_5">Figure +5</a> +shows these coordinate systems graphically. The coordinate systems +within the grayed area exist in the virtual world; those outside exist +in the physical world. Note that the coexistence coordinate system +exists in both worlds. +<h4>The Virtual Coordinate +Systems</h4> +<h5> The Virtual World Coordinate System</h5> +The virtual world coordinate system encapsulates +the unified coordinate system for all scene graph objects in the +virtual environment. For a given View, the virtual world coordinate +system is defined by the Locale object that contains the ViewPlatform +object attached to the View. It is a right-handed coordinate system +with +<em>x</em> to the right, +<em>y</em> up, and +<em>z</em> toward +the viewer. +<h5> The ViewPlatform Coordinate System</h5> +The ViewPlatform coordinate system is the local coordinate system of +the ViewPlatform leaf node to which the View is attached. +<p><a name="Figure_5"></a><img style="width: 500px; height: 181px;" + alt="Display Rigidly Attached to Tracker Base" + title="Display Rigidly Attached to Tracker Base" src="ViewModel5.gif"></p> +<p> +</p> +<ul> + <font size="-1"><b><i>Figure 5</i> – Display Rigidly Attached to the +Tracker Base</b></font> +</ul> +<p> +</p> +<h5> The Coexistence Coordinate System</h5> +A primary implicit goal of any view model is to map a specified local +portion of the physical world onto a specified portion of the virtual +world. Once established, one can legitimately ask where the user's head +or hand is located within the virtual world or where a virtual object +is located in the local physical world. In this way the physical user +can interact with objects inhabiting the virtual world, and vice versa. +To establish this mapping, Java 3D defines a special coordinate +system, +called coexistence coordinates, that is defined to exist in both the +physical world and the virtual world. +<p>The coexistence coordinate system exists half in the virtual world +and +half in the physical world. The two transforms that go from the +coexistence coordinate system to the virtual world coordinate system +and back again contain all the information needed to expand or shrink +the virtual world relative to the physical world. It also contains the +information needed to position and orient the virtual world relative to +the physical world. +</p> +<p>Modifying the transform that maps the coexistence coordinate system +into the virtual world coordinate system changes what the end user can +see. The Java 3D application programmer moves the end user within +the +virtual world by modifying this transform. +</p> +<p> +</p> +<h4>The Physical Coordinate +Systems</h4> +<h5> The Head Coordinate System</h5> +The head coordinate system allows an application to import its user's +head geometry. The coordinate system provides a simple consistent +coordinate frame for specifying such factors as the location of the +eyes and ears. +<h5> The Image Plate Coordinate System</h5> +The image plate coordinate system corresponds with the physical +coordinate system of the image generator. The image plate is defined as +having its origin at the lower left-hand corner of the display area and +as lying in the display area's <em>XY</em> +plane. Note that image plate is a different coordinate system than +either left image plate or right image plate. These last two coordinate +systems are defined in head-mounted environments only. +<h5> The Head Tracker Coordinate System</h5> +The head tracker coordinate system corresponds to the +six-degrees-of-freedom tracker's sensor attached to the user's head. +The head tracker's coordinate system describes the user's instantaneous +head position. +<h5> The Tracker Base Coordinate System</h5> +The tracker base coordinate system corresponds to the emitter +associated with absolute position/orientation trackers. For those +trackers that generate relative position/orientation information, this +coordinate system is that tracker's initial position and orientation. +In general, this coordinate system is rigidly attached to the physical +world. +<h3>Head-Mounted Coordinate +Systems</h3> +Head-mounted coordinate systems divide the same virtual coordinate +systems and the physical coordinate systems. <a href="#Figure_6">Figure +6</a> +shows these coordinate systems graphically. As with the room-mounted +coordinate systems, the coordinate systems within the grayed area exist +in the virtual world; those outside exist in the physical world. Once +again, the coexistence coordinate system exists in both worlds. The +arrangement of the coordinate system differs from those for a +room-mounted display environment. The head-mounted version of +Java 3D's +coordinate system differs in another way. It includes two image plate +coordinate systems, one for each of an end-user's eyes. +<h5> The Left Image Plate and Right Image Plate Coordinate Systems</h5> +The left image plate and right image plate +coordinate systems correspond with the physical coordinate system of +the image generator associated with the left and right eye, +respectively. The image plate is defined as having its origin at the +lower left-hand corner of the display area and lying in the display +area's <em>XY</em> plane. Note that the left image plate's <em>XY</em> +plane does not necessarily lie parallel to the right image plate's <em>XY</em> +plane. Note that the left image plate and the right image plate are +different coordinate systems than the room-mounted display +environment's image plate coordinate system. +<p><a name="Figure_6"></a><img style="width: 499px; height: 162px;" + alt="Display Rigidly Attached to Head Tracker" + title="Display Rigidly Attached to Head Tracker" src="ViewModel6.gif"></p> +<p> +</p> +<ul> + <font size="-1"><b><i>Figure 6</i> – Display Rigidly Attached to the +Head Tracker (Sensor)</b></font> +</ul> +<p> +</p> +<h2>The Screen3D Object</h2> +A Screen3D object represents one independent display device. The most +common environment for a Java 3D application is a desktop computer +with +or without a head tracker. <a href="#Figure_7">Figure +7</a> shows a scene graph fragment for a display environment designed +for such an end-user environment. <a href="#Figure_8">Figure +8</a> shows a display environment that matches the scene graph +fragment in <a href="#Figure_7">Figure +7</a>. +<p><a name="Figure_7"></a><img style="width: 499px; height: 185px;" + alt="Environment with Single Screen3D Object" + title="Environment with Single Screen3D Object" src="ViewModel7.gif"></p> +<p> +</p> +<ul> + <font size="-1"><b><i>Figure 7</i> – A Portion of a Scene Graph +Containing a Single Screen3D +Object</b></font> +</ul> +<p> +<a name="Figure_8"></a><img style="width: 500px; height: 237px;" + alt="Single-Screen Display Environment" + title="Single-Screen Display Environment" src="ViewModel8.gif"></p> +<p> +</p> +<ul> + <font size="-1"><b><i>Figure 8</i> – A Single-Screen Display +Environment</b></font> +</ul> +<p> +A multiple-projection wall display presents a more exotic environment. +Such environments have multiple screens, typically three or more. <a + href="#Figure_9">Figure +9</a> shows a scene graph fragment representing such a system, and <a + href="#Figure_10">Figure +10</a> shows the corresponding display environment. +</p> +<p><a name="Figure_9"></a><img style="width: 500px; height: 196px;" + alt="Environment with Three Screen3D Object" + title="Environment with Three Screen3D Object" src="ViewModel9.gif"> +</p> +<p> +</p> +<ul> + <font size="-1"><b><i>Figure 9</i> – A Portion of a Scene Graph +Containing Three Screen3D +Objects</b></font> +</ul> +<p> +<a name="Figure_10"></a><img style="width: 700px; height: 241px;" + alt="Three-Screen Display Environment" + title="Three-Screen Display Environment" src="ViewModel10.gif"></p> +<p> +</p> +<ul> + <font size="-1"><b><i>Figure 10</i> – A Three-Screen Display +Environment</b></font> +</ul> +<p> +A multiple-screen environment requires more care during the +initialization and calibration phase. Java 3D must know how the +Screen3Ds are placed with respect to one another, the tracking device, +and the physical portion of the coexistence coordinate system. +</p> +<p> +</p> +<h2>Viewing in Head-Tracked Environments</h2> +<p>The "<a href="#Generating_View">Generating a View</a>" section +describes how Java 3D generates a view for a standard flat-screen +display with no head tracking. In this section, we describe how +Java 3D +generates a view in a room-mounted, head-tracked display +environment-either a computer monitor with shutter glasses and head +tracking or a multiple-wall display with head-tracked shutter glasses. +Finally, we describe how Java 3D generates view matrices in a +head-mounted and head-tracked display environment. +</p> +<h3>A Room-Mounted Display with +Head Tracking</h3> +When head tracking combines with a room-mounted +display environment (for example, a standard flat-screen display), the +ViewPlatform's origin and orientation serve as a base for constructing +the view matrices. Additionally, Java 3D uses the end-user's head +position and orientation to compute where an end-user's eyes are +located in physical space. Each eye's position serves to offset the +corresponding virtual eye's position relative to the ViewPlatform's +origin. Each eye's position also serves to specify that eye's frustum +since the eye's position relative to a Screen3D uniquely specifies that +eye's view frustum. Note that Java 3D will access the PhysicalBody +object to obtain information describing the user's interpupilary +distance and tracking hardware, values it needs to compute the +end-user's eye positions from the head position information. +<h3>A Head-Mounted Display with +Head Tracking</h3> +In a head-mounted environment, the ViewPlatform's origin and +orientation also serves as a base for constructing view matrices. And, +as in the head-tracked, room-mounted environment, Java 3D also +uses the +end-user's head position and orientation to modify the ViewPlatform's +position and orientation further. In a head-tracked, head-mounted +display environment, an end-user's eyes do not move relative to their +respective display screens, rather, the display screens move relative +to the virtual environment. A rotation of the head by an end user can +radically affect the final view's orientation. In this situation, Java +3D combines the position and orientation from the ViewPlatform with the +position and orientation from the head tracker to form the view matrix. +The view frustum, however, does not change since the user's eyes do not +move relative to their respective display screen, so Java 3D can +compute the projection matrix once and cache the result. +<p>If any of the parameters of a View object are updated, this will +effect +a change in the implicit viewing transform (and thus image) of any +Canvas3D that references that View object. +</p> +<p> +</p> +<h2>Compatibility Mode</h2> +<p>A camera-based view model allows application programmers to think +about +the images displayed on the computer screen as if a virtual camera took +those images. Such a view model allows application programmers to +position and orient a virtual camera within a virtual scene, to +manipulate some parameters of the virtual camera's lens (specify its +field of view), and to specify the locations of the near and far +clipping planes. +</p> +<p>Java 3D allows applications to enable compatibility mode for +room-mounted, non-head-tracked display environments or to disable +compatibility mode using the following methods. Camera-based viewing +functions are available only in compatibility mode. The <code>setCompatibilityModeEnable</code> +method turns compatibility mode on or off. Compatibility mode is +disabled by default. +</p> +<hr noshade="noshade"> +<p><b>Note:</b> Use of these view-compatibility +functions will disable some of Java 3D's view model features and +limit +the portability of Java 3D programs. These methods are primarily +intended to help jump-start porting of existing applications. +</p> +<hr noshade="noshade"> +<h3>Overview of the +Camera-Based View Model</h3> +The traditional camera-based view model, shown in <a href="#Figure_11">Figure +11</a>, +places a virtual camera inside a geometrically specified world. The +camera "captures" the view from its current location, orientation, and +perspective. The visualization system then draws that view on the +user's display device. The application controls the view by moving the +virtual camera to a new location, by changing its orientation, by +changing its field of view, or by controlling some other camera +parameter. +<p>The various parameters that users control in a +camera-based view model specify the shape of a viewing volume (known as +a frustum because of its truncated pyramidal shape) and locate that +frustum within the virtual environment. The rendering pipeline uses the +frustum to decide which objects to draw on the display screen. The +rendering pipeline does not draw objects outside the view frustum, and +it clips (partially draws) objects that intersect the frustum's +boundaries. +</p> +<p>Though a view frustum's specification may have many items in common +with those of a physical camera, such as placement, orientation, and +lens settings, some frustum parameters have no physical analog. Most +noticeably, a frustum has two parameters not found on a physical +camera: the near and far clipping planes. +</p> +<p><a name="Figure_11"></a><img style="width: 500px; height: 202px;" + alt="Camera-Based View Model" title="Camera-Based View Model" + src="ViewModel11.gif"> +</p> +<p> +</p> +<ul> + <font size="-1"><b><i>Figure 11</i> – The Camera-Based View Model</b></font> +</ul> +<p> +The location of the near and far clipping planes allows the application +programmer to specify which objects Java 3D should not draw. +Objects +too far away from the current eyepoint usually do not result in +interesting images. Those too close to the eyepoint might obscure the +interesting objects. By carefully specifying near and far clipping +planes, an application programmer can control which objects the +renderer will not be drawing. +</p> +<p>From the perspective of the display device, the virtual camera's +image +plane corresponds to the display screen. The camera's placement, +orientation, and field of view determine the shape of the view frustum. +</p> +<p> +</p> +<h3>Using the Camera-Based View +Model</h3> +<p>The camera-based view model allows Java 3D to bridge the gap +between +existing 3D code and Java 3D's view model. By using the +camera-based +view model methods, a programmer retains the familiarity of the older +view model but gains some of the flexibility afforded by Java 3D's +new +view model. +</p> +<p>The traditional camera-based view model is supported in Java 3D +by +helping methods in the Transform3D object. These methods were +explicitly designed to resemble as closely as possible the view +functions of older packages and thus should be familiar to most 3D +programmers. The resulting Transform3D objects can be used to set +compatibility-mode transforms in the View object. +</p> +<p> +</p> +<h4>Creating a Viewing Matrix</h4> +<p>The Transform3D object provides a <code>lookAt</code> utility +method +to create a +viewing matrix. This method specifies the position and orientation of +a viewing transform. It works similarly to the equivalent function in +OpenGL. The inverse of this transform can be used to control the +ViewPlatform object within the scene graph. Alternatively, this +transform can be passed directly to the View's <code>VpcToEc</code> +transform via the compatibility-mode viewing functions. The <code>setVpcToEc</code><code></code> +method is used to set the viewing matrix when in compatibility mode. +</p> +<h4>Creating a Projection +Matrix</h4> +<p>The Transform3D object provides three methods for +creating a projection matrix: <code>frustum</code>, <code>perspective</code>, +and <code>ortho</code>. All three map points from eye coordinates +(EC) to clipping coordinates (CC). Eye coordinates are defined such +that (0, 0, 0) is at the eye and the projection plane is at <em>z</em> += -1.<br> +</p> +<p>The <code>frustum</code> method +establishes a perspective projection with the eye at the apex of a +symmetric view frustum. The transform maps points from eye coordinates +to clipping coordinates. The clipping coordinates generated by the +resulting transform are in a right-handed coordinate system (as are all +other coordinate systems in Java 3D). +</p> +<p>The arguments define the frustum and its associated perspective +projection: <code>(left</code>, <code>bottom</code>, <code>-near)</code> +and <code>(right</code>, <code>top</code>, <code>-near)</code> +specify the point on the near clipping plane that maps onto the +lower-left and upper-right corners of the window, respectively. The <code>-far</code> +parameter specifies the far clipping plane. See <a href="#Figure_12">Figure +12</a>. +</p> +<p>The <code>perspective</code> method establishes a perspective +projection with the eye at the apex of a symmetric view frustum, +centered about the <em>Z</em>-axis, +with a fixed field of view. The resulting perspective projection +transform mimics a standard camera-based view model. The transform maps +points from eye coordinates to clipping coordinates. The clipping +coordinates generated by the resulting transform are in a right-handed +coordinate system. +</p> +<p>The arguments define the frustum and its associated perspective +projection: <code>-near</code> and <code>-far</code> specify the near +and far clipping planes; <code>fovx</code> specifies the field of view +in the <em>X</em> dimension, in radians; and <code>aspect</code> +specifies the aspect ratio of the window. See <a href="#Figure_13">Figure +13</a>. +</p> +<p><a name="Figure_12"></a><img style="width: 500px; height: 209px;" + alt="Perspective Viewing Frustum" title="Perspective Viewing Frustum" + src="ViewModel12.gif"> +</p> +<p> +</p> +<ul> + <font size="-1"><b><i>Figure 12</i> – A Perspective Viewing Frustum</b></font> +</ul> +<p> +<a name="Figure_13"></a><img style="width: 500px; height: 212px;" + alt="Perspective View Model Arguments" + title="Perspective View Model Arguments" src="ViewModel13.gif"></p> +<p> +</p> +<ul> + <font size="-1"><b><i>Figure 13</i> – Perspective View Model Arguments</b></font> +</ul> +<p> +The <code>ortho</code> method +establishes a parallel projection. The orthographic projection +transform mimics a standard camera-based video model. The transform +maps points from eye coordinates to clipping coordinates. The clipping +coordinates generated by the resulting transform are in a right-handed +coordinate system. +</p> +<p>The arguments define a rectangular box used for projection: <code>(left</code>, +<code>bottom</code>, <code>-near)</code> and <code>(right</code>, <code>top</code>, +<code>-near)</code> +specify the point on the near clipping plane that maps onto the +lower-left and upper-right corners of the window, respectively. The <code>-far</code> +parameter specifies the far clipping plane. See <a href="#Figure_14">Figure +14</a>. +</p> +<p><a name="Figure_14"></a><img style="width: 500px; height: 220px;" + alt="Orthographic View Model" title="Orthographic View Model" + src="ViewModel14.gif"> +</p> +<p> +</p> +<ul> + <font size="-1"><b><i>Figure 14</i> – Orthographic View Model</b></font> +</ul> +<p> +</p> +<p>The <code>setLeftProjection</code> +and <code>setRightProjection</code> methods are used to set the +projection matrices for the left eye and right eye, respectively, when +in compatibility mode.</p> +</body> +</html> diff --git a/doc-files/ViewModel1.gif b/doc-files/ViewModel1.gif Binary files differnew file mode 100644 index 0000000..e94743e --- /dev/null +++ b/doc-files/ViewModel1.gif diff --git a/doc-files/ViewModel10.gif b/doc-files/ViewModel10.gif Binary files differnew file mode 100644 index 0000000..aceb6e7 --- /dev/null +++ b/doc-files/ViewModel10.gif diff --git a/doc-files/ViewModel11.gif b/doc-files/ViewModel11.gif Binary files differnew file mode 100644 index 0000000..f943c15 --- /dev/null +++ b/doc-files/ViewModel11.gif diff --git a/doc-files/ViewModel12.gif b/doc-files/ViewModel12.gif Binary files differnew file mode 100644 index 0000000..787afe7 --- /dev/null +++ b/doc-files/ViewModel12.gif diff --git a/doc-files/ViewModel13.gif b/doc-files/ViewModel13.gif Binary files differnew file mode 100644 index 0000000..a8482ef --- /dev/null +++ b/doc-files/ViewModel13.gif diff --git a/doc-files/ViewModel14.gif b/doc-files/ViewModel14.gif Binary files differnew file mode 100644 index 0000000..f201443 --- /dev/null +++ b/doc-files/ViewModel14.gif diff --git a/doc-files/ViewModel2.gif b/doc-files/ViewModel2.gif Binary files differnew file mode 100644 index 0000000..2d549b1 --- /dev/null +++ b/doc-files/ViewModel2.gif diff --git a/doc-files/ViewModel3.gif b/doc-files/ViewModel3.gif Binary files differnew file mode 100644 index 0000000..5285015 --- /dev/null +++ b/doc-files/ViewModel3.gif diff --git a/doc-files/ViewModel4.gif b/doc-files/ViewModel4.gif Binary files differnew file mode 100644 index 0000000..ab9db1d --- /dev/null +++ b/doc-files/ViewModel4.gif diff --git a/doc-files/ViewModel5.gif b/doc-files/ViewModel5.gif Binary files differnew file mode 100644 index 0000000..859b456 --- /dev/null +++ b/doc-files/ViewModel5.gif diff --git a/doc-files/ViewModel6.gif b/doc-files/ViewModel6.gif Binary files differnew file mode 100644 index 0000000..2200595 --- /dev/null +++ b/doc-files/ViewModel6.gif diff --git a/doc-files/ViewModel7.gif b/doc-files/ViewModel7.gif Binary files differnew file mode 100644 index 0000000..ec84ac2 --- /dev/null +++ b/doc-files/ViewModel7.gif diff --git a/doc-files/ViewModel8.gif b/doc-files/ViewModel8.gif Binary files differnew file mode 100644 index 0000000..ee4b331 --- /dev/null +++ b/doc-files/ViewModel8.gif diff --git a/doc-files/ViewModel9.gif b/doc-files/ViewModel9.gif Binary files differnew file mode 100644 index 0000000..0cbf72c --- /dev/null +++ b/doc-files/ViewModel9.gif diff --git a/doc-files/VirtualUniverse.gif b/doc-files/VirtualUniverse.gif Binary files differnew file mode 100644 index 0000000..4d713a8 --- /dev/null +++ b/doc-files/VirtualUniverse.gif diff --git a/doc-files/VirtualUniverse.html b/doc-files/VirtualUniverse.html new file mode 100644 index 0000000..2f9dd14 --- /dev/null +++ b/doc-files/VirtualUniverse.html @@ -0,0 +1,265 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<html> +<head> + <meta content="text/html; charset=ISO-8859-1" + http-equiv="content-type"> + <title>Java 3D API - Scene Graph Superstructure</title> +</head> +<body> +<h2>Scene Graph Superstructure</h2> +<p>Java 3D's superstructure consists of one or more +VirtualUniverse objects, each of which contains a set of one or more +high-resolution Locale objects. The Locale objects, in turn, contain +collections of subgraphs that comprise the scene graph (see <a + href="#Figure_1">Figure +1</a>). +</p> +<p> +</p> +<h2>The Virtual Universe</h2> +Java 3D defines the concept of a <em>virtual universe</em> +as a three-dimensional space with an associated set of objects. Virtual +universes serve as the largest unit of aggregate representation, and +can also be thought of as databases. Virtual universes can be very +large, both in physical space units and in content. Indeed, in most +cases a single virtual universe will serve an application's entire +needs. +<p>Virtual universes are separate entities in that no node object may +exist in more than one virtual universe at any one time. Likewise, the +objects in one virtual universe are not visible in, nor do they +interact with objects in, any other virtual universe. +</p> +<p>To support large virtual universes, Java 3D introduces the concept +of Locales that have <em>high-resolution coordinates</em> +as an origin. Think of high-resolution coordinates as "tie-downs" that +precisely anchor the locations of objects specified using less precise +floating-point coordinates that are within the range of influence of +the high-resolution coordinates. +</p> +<p>A Locale, with its associated high-resolution coordinates, serves as +the next level of representation down from a virtual universe. All +virtual universes contain one or more high-resolution-coordinate +Locales, and all other objects are attached to a Locale. +High-resolution coordinates act as an upper-level translation-only +transform node. For example, the coordinates of all objects that are +attached to a particular Locale are all relative to the location of +that Locale's high-resolution coordinates. +</p> +<p><a name="Figure_1"></a><img style="width: 500px; height: 340px;" + alt="The Virtual Universe" title="The Virtual Universe" + src="VirtualUniverse.gif"> +</p> +<p> +</p> +<ul> + <font size="-1"><b><i>Figure 1</i> – The Virtual Universe</b></font> +</ul> +<p> +While a virtual universe is similar to the traditional computer +graphics concept of a scene graph, a given virtual universe can become +so large that it is often better to think of a scene graph as the +descendant of a high-resolution-coordinate Locale. +</p> +<p> +</p> +<h2>Establishing a Scene</h2> +To construct a three-dimensional scene, the programmer must execute a +Java 3D program. The Java 3D application must first create a +VirtualUniverse object and attach at least one Locale to it. Then the +desired scene graph is constructed, starting with a BranchGroup node +and including at least one ViewPlatform object, and the scene graph is +attached to the Locale. Finally, a View object that references the +ViewPlatform object (see "<a href="intro.html#Structuring">Structuring +the Java 3D Program</a>") +is constructed. As soon as a scene graph containing a ViewPlatform is +attached to the VirtualUniverse, Java 3D's rendering loop is engaged, +and the scene will appear on the drawing canvas(es) associated with the +View object. +<h2>Loading a Virtual Universe</h2> +Java 3D is a runtime application programming +interface (API), not a file format. As an API, Java 3D provides no +direct mechanism for loading or storing a virtual universe. +Constructing a scene graph involves the execution of a Java 3D program. +However, loaders to convert a number of standard 3D file formats to or +from Java 3D virtual universes are expected to be generally available. +<h2>Coordinate Systems</h2> +By default, Java 3D coordinate systems are right-handed, with the +orientation semantics being that +<em>y</em> is the local gravitational +up, +<em>x</em> is horizontal to the right, and +<em>z</em> is directly +toward the viewer. The default units are meters. +<h2>High-Resolution Coordinates</h2> +Double-precision floating-point, single-precision floating-point, or +even fixed-point representations of three-dimensional coordinates are +sufficient to represent and display rich 3D scenes. Unfortunately, +scenes are not worlds, let alone universes. If one ventures even a +hundred miles away from the (0.0, 0.0, 0.0) origin using only +single-precision floating-point coordinates, representable points +become quite quantized, to at very best a third of an inch (and much +more coarsely than that in practice). +<p>To "shrink" down to a small size (say the size of an IC transistor), +even very near (0.0, 0.0, 0.0), the same problem arises. +</p> +<p>If a large contiguous virtual universe is to be supported, some form +of +higher-resolution addressing is required. Thus the choice of 256-bit +positional components for "high-resolution" positions. +</p> +<p> +</p> +<h3>Java 3D High-Resolution +Coordinates</h3> +Java 3D high-resolution coordinates consist of three 256-bit +fixed-point numbers, one each for <em>x</em>, <em>y</em>, and <em>z</em>. +The fixed point is at bit 128, and the value 1.0 is defined to be +exactly 1 meter. This coordinate system is sufficient to describe a +universe in excess of several hundred billion light years across, yet +still define objects smaller than a proton (down to below the planck +length). <a href="#Table_1">Table +1</a> shows how many bits are needed above or below the fixed point +to represent the range of interesting physical dimensions. +<p><a name="Table_1"></a> +<table bordercolorlight="#FFFFFF" bordercolordark="#000000" border="1" + cellpadding="5" cellspacing="0"> + <caption><font size="-1"><b> <i>Table 1</i> – +Java 3D High-Resolution Coordinates </b></font></caption><tbody> + <tr bgcolor="#cccccc" valign="top"> + <th><font color="#003366" size="-1">2<sup>n</sup> Meters </font></th> + <th><font color="#003366" size="-1">Units </font></th> + </tr> + <tr valign="top"> + <td> 87.29</td> + <td>Universe (20 billion light years) <br> + </td> + </tr> + <tr valign="top"> + <td> 69.68</td> + <td>Galaxy (100,000 light years) </td> + </tr> + <tr valign="top"> + <td> 53.07</td> + <td>Light year </td> + </tr> + <tr valign="top"> + <td> 43.43</td> + <td>Solar system diameter </td> + </tr> + <tr valign="top"> + <td> 23.60</td> + <td>Earth diameter </td> + </tr> + <tr valign="top"> + <td> 10.65</td> + <td>Mile </td> + </tr> + <tr valign="top"> + <td> 9.97</td> + <td>Kilometer </td> + </tr> + <tr valign="top"> + <td> 0.00</td> + <td>Meter </td> + </tr> + <tr valign="top"> + <td> -19.93</td> + <td>Micron </td> + </tr> + <tr valign="top"> + <td> -33.22</td> + <td>Angstrom </td> + </tr> + <tr valign="top"> + <td> -115.57</td> + <td>Planck length </td> + </tr> + </tbody> +</table> +</p> +<p>A 256-bit fixed-point number also has the advantage of being able to +directly represent nearly any reasonable single-precision +floating-point value <em>exactly</em>. +</p> +<p>High-resolution coordinates in Java 3D are used only to embed more +traditional floating point coordinate systems within a much +higher-resolution substrate. In this way a visually seamless virtual +universe of any conceivable size or scale can be created, without worry +about numerical accuracy. +</p> +<p> +</p> +<h3>Java 3D Virtual World +Coordinates</h3> +Within a given virtual world coordinate system, positions are expressed +by three floating point numbers. The virtual world coordinate scale is +in meters, but this can be affected by scale changes in the object +hierarchy. +<h3>Details of High-Resolution +Coordinates</h3> +High-resolution coordinates are represented as signed, +two's-complement, fixed-point numbers consisting of 256 bits. Although +Java 3D keeps the internal representation of high-resolution +coordinates opaque, users specify such coordinates using 8-element +integer arrays. Java 3D treats the integer found at index 0 as +containing the most significant bits and the integer found at index 7 +as containing the least significant bits of the high-resolution +coordinate. The binary point is located at bit position 128, or between +the integers at index 3 and 4. A high-resolution coordinate of 1.0 is 1 +meter. +<p>The semantics of how file loaders deal with high-resolution +coordinates +is up to the individual file loader, as Java 3D does not directly +define any file-loading semantics. However, some general advice can be +given (note that this advice is <em>not</em> officially part of the +Java 3D specification). +</p> +<p>For "small" virtual universes (on the order of hundreds of meters +across in relative scale), a single Locale with high-resolution +coordinates at location (0.0, 0.0, 0.0) as the root node (below the +VirtualUniverse object) is sufficient; a loader can automatically +construct this node during the loading process, and the point in +high-resolution coordinates does not need any direct representation in +the external file. +</p> +<p>Larger virtual universes are expected to be constructed usually like +computer directory hierarchies, that is, as a "root" virtual universe +containing mostly external file references to embedded virtual +universes. In this case, the file reference object (user-specific data +hung off a Java 3D group or hi-res node) defines the location for the +data to be read into the current virtual universe. +</p> +<p>The data file's contents should be parented to the file object node +while being read, thus inheriting the high-resolution coordinates of +the file object as the new relative virtual universe origin of the +embedded scene graph. If this scene graph itself contains +high-resolution coordinates, it will need to be offset (translated) by +the amount in the file object's high-resolution coordinates and then +added to the larger virtual universe as new high-resolution +coordinates, with their contents hung off below them. Once again, this +procedure is not part of the official Java 3D specification, but some +more details on the care and use of high-resolution coordinates in +external file formats will probably be available as a Java 3D +application note. +</p> +<p>Authoring tools that directly support high-resolution coordinates +should create additional high-resolution coordinates as a user creates +new geometry "sufficiently" far away (or of different scale) from +existing high-resolution coordinates. +</p> +<p><strong>Semantics of widely moving objects</strong>. Most fixed and +nearly-fixed objects stay attached to the same high-resolution Locale. +Objects that make wide changes in position or scale may periodically +need to be reparented to a more appropriate high-resolution Locale. If +no appropriate high-resolution Locale exists, the application may need +to create a new one. +</p> +<p><strong>Semantics of viewing</strong>. The ViewPlatform object and +the +associated nodes in its hierarchy are very often widely moving objects. +Applications will typically attach the view platform to the most +appropriate high-resolution Locale. For display, all objects will first +have their positions translated by the difference between the location +of their high-resolution Locale and the view platform's high-resolution +Locale. (In the common case of the Locales being the same, no +translation is necessary.) +</p> +</body> +</html> diff --git a/doc-files/intro.gif b/doc-files/intro.gif Binary files differnew file mode 100644 index 0000000..503f818 --- /dev/null +++ b/doc-files/intro.gif diff --git a/doc-files/intro.html b/doc-files/intro.html new file mode 100644 index 0000000..f5ea134 --- /dev/null +++ b/doc-files/intro.html @@ -0,0 +1,337 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<html> +<head> + <meta content="text/html; charset=ISO-8859-1" + http-equiv="content-type"> + <title>The Java 3D API - Introduction</title> +</head> +<body> +<h2>Disclaimer</h2> +<p> +<i>This guide, which contains documentation formerly +published separately from the javadoc-generated API documentation, +is <b>not</b> an +official API specification. This documentation may contain references to +Java and Java 3D, both of which are trademarks of Sun Microsystems, Inc. +Any reference to these and other trademarks of Sun Microsystems are +for explanatory purposes only. Their use does impart any rights beyond +those listed in the source code license. In particular, Sun Microsystems +retains all intellectual property and trademark rights as described in +the proprietary rights notice in the COPYRIGHT.txt file. +</i> +</p> +<hr> +<h2>Introduction to the Java 3D API</h2> +<p>The Java 3D API is an application +programming interface used for writing three-dimensional graphics +applications and applets. It gives developers high-level constructs for +creating and manipulating 3D geometry and for constructing the +structures used in rendering that geometry. Application developers can +describe very large virtual worlds using these constructs, which +provide Java 3D with enough information to render these worlds +efficiently. +</p> +<p>Java 3D delivers Java's "write once, run anywhere" +benefit to +developers of 3D graphics applications. Java 3D is part of the +JavaMedia suite of APIs, making it available on a wide range of +platforms. It also integrates well with the Internet because +applications and applets written using the Java 3D API have access to +the entire set of Java classes. +</p> +<p>The Java 3D API draws its ideas from existing +graphics APIs and from +new technologies. Java 3D's low-level graphics constructs synthesize +the best ideas found in low-level APIs such as Direct3D, OpenGL, +QuickDraw3D, and XGL. Similarly, its higher-level constructs synthesize +the best ideas found in several scene graph-based systems. Java 3D +introduces some concepts not commonly considered part of the graphics +environment, such as 3D spatial sound. Java 3D's sound capabilities +help to provide a more immersive experience for the user.<br> +</p> +<!-- +<p><i>NOTE: Prior to version 1.4, the +Java 3D API was formally specified by a +separate Java 3D API Specification Guide, published separately +from the javadoc. As of version 1.4, +the javadoc-generated API reference is definitive. Relevant portions of +the guide have been included here and supersede any previously +published +information.</i> +</p> +--> +<p> +</p> +<h2>Programming Paradigm</h2> +Java 3D is an object-oriented API. Applications construct individual +graphics elements as separate objects and connect them together into a +treelike structure called a <em>scene graph</em>. The application +manipulates these objects using their predefined accessor, mutator, and +node-linking methods. +<h3>The Scene Graph Programming +Model</h3> +Java 3D's scene graph-based programming model provides a simple and +flexible mechanism for representing and rendering scenes. The scene +graph contains a complete description of the entire scene, or virtual +universe. This includes the geometric data, the attribute information, +and the viewing information needed to render the scene from a +particular point of view. The "<a href="SceneGraphOverview.html">Scene +Graph Basics</a>" document provides more information on the Java 3D +scene graph programming model. +<p>The Java 3D API improves on previous graphics APIs +by eliminating many +of the bookkeeping and programming chores that those APIs impose. Java +3D allows the programmer to think about geometric objects rather than +about triangles-about the scene and its composition rather than about +how to write the rendering code for efficiently displaying the scene. +</p> +<p> +</p> +<h3>Rendering Modes</h3> +Java 3D includes three different rendering modes: immediate mode, +retained mode, and compiled-retained mode (see "<a href="Rendering.html">Execution +and Rendering Model</a>"). +Each successive rendering mode allows Java 3D more freedom in +optimizing an application's execution. Most Java 3D applications will +want to take advantage of the convenience and performance benefits that +the retained and compiled-retained modes provide. +<h4>Immediate Mode</h4> +Immediate mode leaves little room for global +optimization at the scene graph level. Even so, Java 3D has raised the +level of abstraction and accelerates immediate mode rendering on a +per-object basis. An application must provide a Java 3D draw method +with a complete set of points, lines, or triangles, which are then +rendered by the high-speed Java 3D renderer. Of course, the application +can build these lists of points, lines, or triangles in any manner it +chooses. +<h4>Retained Mode</h4> +Retained mode requires an application to construct a scene graph and +specify which elements of that scene graph may change during rendering. +The scene graph describes the objects in the virtual universe, the +arrangement of those objects, and how the application animates those +objects. +<h4>Compiled-Retained Mode</h4> +Compiled-retained mode, like retained mode, requires the application to +construct a scene graph and specify which elements of the scene graph +may change during rendering. Additionally, the application can compile +some or all of the subgraphs that make up a complete scene graph. Java +3D compiles these graphs into an internal format. The compiled +representation of the scene graph may bear little resemblance to the +original tree structure provided by the application, however, it is +functionally equivalent. Compiled-retained mode provides the highest +performance. +<h3>Extensibility</h3> +Most Java 3D classes expose only accessor and mutator methods. Those +methods operate only on that object's internal state, making it +meaningless for an application to override them. Therefore, Java 3D +does not provide the capability to override the behavior of Java 3D +attributes. To make Java 3D work correctly, applications must call "<code>super.setXxxxx</code>" +for any attribute state set method that is overridden. +<p>Applications can extend Java 3D's classes and add +their own methods. +However, they may not override Java 3D's scene graph traversal +semantics because the nodes do not contain explicit traversal and draw +methods. Java 3D's renderer retains those semantics internally. +</p> +<p>Java 3D <em>does</em> provide hooks for mixing +Java 3D-controlled scene graph rendering and user-controlled rendering +using Java 3D's immediate mode constructs (see "<a + href="Immediate.html#Mixed">Mixed-Mode Rendering</a>"). Alternatively, +the application can +stop Java 3D's renderer and do all its drawing in immediate mode (see "<a + href="Immediate.html#PureImmediate">Pure Immediate-Mode Rendering</a>"). +</p> +<p>Behaviors require applications to extend the +Behavior object and to +override its methods with user-written Java code. These extended +objects should contain references to those scene graph objects that +they will manipulate at run time. The "<a href="Behaviors.html">Behaviors +and Interpolators</a>" document describes Java 3D's behavior +model. +</p> +<p> +</p> +<h2>High Performance</h2> +Java 3D's programming model allows the Java 3D API to do the mundane +tasks, such as scene graph traversal, managing attribute state changes, +and so forth, thereby simplifying the application's job. Java 3D does +this without sacrificing performance. At first glance, it might appear +that this approach would create more work for the API; however, it +actually has the opposite effect. Java 3D's higher level of abstraction +changes not only the amount but, more important, also the kind of work +the API must perform. Java 3D does not need to impose the same type of +constraints as do APIs with a lower level of abstraction, thus allowing +Java 3D to introduce optimizations not possible with these lower-level +APIs. +<p>Additionally, leaving the details of rendering to +Java 3D allows it to +tune the rendering to the underlying hardware. For example, relaxing +the strict rendering order imposed by other APIs allows parallel +traversal as well as parallel rendering. Knowing which portions of the +scene graph cannot be modified at run time allows Java 3D to flatten +the tree, pretransform geometry, or represent the geometry in a native +hardware format without the need to keep the original data. +</p> +<p> +</p> +<h3>Layered Implementation</h3> +Besides optimizations at the scene graph level, one of the more +important factors that determines the performance of Java 3D is the +time it takes to render the visible geometry. Java 3D implementations +are layered to take advantage of the native, low-level API that is +available on a given system. In particular, Java 3D implementations +that use Direct3D and OpenGL are available. This means that Java 3D +rendering will be accelerated across the same wide range of systems +that are supported by these lower-level APIs. +<h3>Target Hardware Platforms</h3> +Java 3D is aimed at a wide range of 3D-capable hardware and software +platforms, from low-cost PC game cards and software renderers at the +low end, through midrange workstations, all the way up to very +high-performance specialized 3D image generators. +<p>Java 3D implementations are expected to provide +useful rendering rates +on most modern PCs, especially those with 3D graphics accelerator +cards. On midrange workstations, Java 3D is expected to provide +applications with nearly full-speed hardware performance. +</p> +<p>Finally, Java 3D is designed to scale as the +underlying hardware +platforms increase in speed over time. Tomorrow's 3D PC game +accelerators will support more complex virtual worlds than high-priced +workstations of a few years ago. Java 3D is prepared to meet this +increase in hardware performance. +</p> +<p> +</p> +<h2><a name="Structuring"></a>Structuring the Java 3D Program</h2> +<p>This section illustrates how a developer might +structure a Java 3D application. The simple application in this example +creates a scene graph that draws an object in the middle of a window +and rotates the object about its center point. +</p> +<h3>Java 3D Application Scene +Graph</h3> +<p>The scene graph for the sample application is shown below. +</p> +<p>The scene graph consists of superstructure +components—a VirtualUniverse +object and a Locale object—and a set of branch graphs. Each branch +graph is a subgraph that is rooted by a BranchGroup node that is +attached to the superstructure. For more information, see "<a + href="SceneGraphOverview.html">Scene Graph Basics</a>." +</p> +<p><a name="Figure_1"></a><img style="width: 500px; height: 263px;" + alt="Application +scene graph" title="Application scene graph" + src="intro.gif"></p> +<p> +</p> +<ul> + <font size="-1"><b><i>Figure 1 – </i>Application Scene Graph</b></font> +</ul> +<p> +A VirtualUniverse object defines a named universe. Java 3D permits the +creation of more than one universe, though the vast majority of +applications will use just one. The VirtualUniverse object provides a +grounding for scene graphs. All Java 3D scene graphs must connect to a +VirtualUniverse object to be displayed. For more information, see "<a + href="VirtualUniverse.html">Scene Graph Superstructure</a>." +</p> +<p>Below the VirtualUniverse object is a Locale object. +The Locale object +defines the origin, in high-resolution coordinates, of its attached +branch graphs. A virtual universe may contain as many Locales as +needed. In this example, a single Locale object is defined with its +origin at (0.0, 0.0, 0.0). +</p> +<p>The scene graph itself starts with the <a href="../BranchGroup.html">BranchGroup</a> +nodes. +A BranchGroup serves as the root of a +subgraph, called a <em>branch graph</em>, of the scene graph. Only +BranchGroup objects can attach to Locale objects. +</p> +<p>In this example there are two branch graphs and, +thus, two BranchGroup +nodes. Attached to the left BranchGroup are two subgraphs. One subgraph +consists of a user-extended Behavior leaf node. The Behavior node +contains Java code for manipulating the transformation matrix +associated with the object's geometry. +</p> +<p>The other subgraph in this BranchGroup consists of a +TransformGroup +node that specifies the position (relative to the Locale), orientation, +and scale of the geometric objects in the virtual universe. A single +child, a Shape3D leaf node, refers to two component objects: a Geometry +object and an Appearance object. The Geometry object describes the +geometric shape of a 3D object (a cube in our simple example). The +Appearance object describes the appearance of the geometry (color, +texture, material reflection characteristics, and so forth). +</p> +<p>The right BranchGroup has a single subgraph that +consists of a +TransformGroup node and a ViewPlatform leaf node. The TransformGroup +specifies the position (relative to the Locale), orientation, and scale +of the ViewPlatform. This transformed ViewPlatform object defines the +end user's view within the virtual universe. +</p> +<p>Finally, the ViewPlatform is referenced by a View +object that specifies +all of the parameters needed to render the scene from the point of view +of the ViewPlatform. Also referenced by the View object are other +objects that contain information, such as the drawing canvas into which +Java 3D renders, the screen that contains the canvas, and information +about the physical environment. +</p> +<p> +</p> +<h3>Recipe for a Java 3D Program</h3> +<p>The following steps are taken by the example program to create the +scene graph elements and link them together. Java 3D will then render +the scene graph and display the graphics in a window on the screen:</p> +<ul> +1. Create a Canvas3D object and add it to the Applet panel. + <p>2. Create a BranchGroup as the root of the scene branch graph.</p> + <p>3. Construct a Shape3D node with a TransformGroup node above it.</p> + <p>4. Attach a RotationInterpolator behavior to the TransformGroup.</p> + <p>5. Call the simple universe utility function to do the following:</p> + <ul> +a. Establish a virtual universe with a single high-resolution Locale +(see "<a href="SceneGraphOverview.html">Scene Graph Basics</a>"). + <p>b. Create the PhysicalBody, PhysicalEnvironment, View, and +ViewPlat-form objects.</p> + <p>c. Create a BranchGroup as the root of the view platform branch +graph.</p> + <p>d. Insert the view platform branch graph into the Locale.</p> + </ul> +6. Insert the scene branch graph into the simple universe's Locale. +</ul> +<p>The Java 3D renderer then starts running in an infinite loop. The +renderer conceptually performs the following operations:</p> +<pre> while(true) {<br> Process input<br> If (request to exit) break<br> Perform Behaviors<br> Traverse the scene graph and render visible objects<br> }<br> Cleanup and exit<br></pre> +<h3>HelloUniverse: A Sample Java +3D Program</h3> +<p><a href="HelloUniverse.html">Click here</a> to see code fragments +from a simple program, <code>HelloUniverse.java</code>, +that creates a cube and a RotationInterpolator behavior object that +rotates the cube at a constant rate of pi/2 radians per second.<br> +</p> +<h2>Other Documents<br> +</h2> +<p>Here are other documents that provide explanatory material, +previously included as part of +the Java 3D API Specification Guide.<br> +</p> +<ul> + <li><a href="Concepts.html">Java 3D Concepts</a></li> + <li><a href="SceneGraphOverview.html">Scene Graph Basics</a></li> + <li><a href="VirtualUniverse.html">Scene Graph Superstructure</a></li> + <li><a href="SceneGraphSharing.html">Reusing Scene Graphs</a></li> + <li><a href="ViewModel.html">View Model</a></li> + <li><a href="Behaviors.html">Behaviors and Interpolators</a></li> + <li><a href="Rendering.html">Execution and Rendering Model</a></li> + <li><a href="Immediate.html">Immediate-Mode Rendering</a></li> +</ul> +<p><br> +</p> +</body> +</html> |
