From 81ce3f9030a7e9704fcaece5d4b23238b4828bdc Mon Sep 17 00:00:00 2001 From: Kevin Rushforth Date: Tue, 1 Nov 2005 17:13:23 +0000 Subject: 1. Finished inclusion of material from Specification Guide into javadoc spec. Added some links to new material. 2. Created a 1.4 ChangeLog git-svn-id: https://svn.java.net/svn/j3d-core~svn/trunk@456 ba19aa83-45c5-6ac9-afd3-db810772062c --- src/classes/share/javax/media/j3d/Behavior.java | 8 + src/classes/share/javax/media/j3d/Canvas3D.java | 8 + src/classes/share/javax/media/j3d/Locale.java | 6 + src/classes/share/javax/media/j3d/Node.java | 5 + .../share/javax/media/j3d/NodeComponent.java | 4 + .../share/javax/media/j3d/SceneGraphObject.java | 4 + src/classes/share/javax/media/j3d/Screen3D.java | 9 + src/classes/share/javax/media/j3d/View.java | 8 + .../share/javax/media/j3d/VirtualUniverse.java | 6 + .../share/javax/media/j3d/doc-files/Behaviors.html | 585 ++++++++++- .../share/javax/media/j3d/doc-files/Behaviors1.gif | Bin 0 -> 9067 bytes .../share/javax/media/j3d/doc-files/Behaviors2.gif | Bin 0 -> 2223 bytes .../share/javax/media/j3d/doc-files/Behaviors3.gif | Bin 0 -> 2189 bytes .../share/javax/media/j3d/doc-files/Behaviors4.gif | Bin 0 -> 2452 bytes 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src/classes/share/javax/media/j3d/doc-files/ViewModel4.gif create mode 100644 src/classes/share/javax/media/j3d/doc-files/ViewModel5.gif create mode 100644 src/classes/share/javax/media/j3d/doc-files/ViewModel6.gif create mode 100644 src/classes/share/javax/media/j3d/doc-files/ViewModel7.gif create mode 100644 src/classes/share/javax/media/j3d/doc-files/ViewModel8.gif create mode 100644 src/classes/share/javax/media/j3d/doc-files/ViewModel9.gif (limited to 'src/classes') diff --git a/src/classes/share/javax/media/j3d/Behavior.java b/src/classes/share/javax/media/j3d/Behavior.java index 6e00081..35e6c13 100644 --- a/src/classes/share/javax/media/j3d/Behavior.java +++ b/src/classes/share/javax/media/j3d/Behavior.java @@ -179,6 +179,14 @@ import java.util.Enumeration; * instance of a Behavior. Sharing wakeup criteria among different * instances of a Behavior is illegal. * + *

+ * Additional Information + *

+ * For more information, see the + * Introduction to the Java 3D API and + * Behaviors and Interpolators + * documents. + * * @see WakeupCondition */ diff --git a/src/classes/share/javax/media/j3d/Canvas3D.java b/src/classes/share/javax/media/j3d/Canvas3D.java index 6d887b9..c79b3c2 100644 --- a/src/classes/share/javax/media/j3d/Canvas3D.java +++ b/src/classes/share/javax/media/j3d/Canvas3D.java @@ -255,6 +255,14 @@ import java.util.*; * serialize a Canvas3D object will result in an * UnsupportedOperationException being thrown. * + *

+ * Additional Information + *

+ * For more information, see the + * Introduction to the Java 3D API and + * View Model + * documents. + * * @see Screen3D * @see View * @see GraphicsContext3D diff --git a/src/classes/share/javax/media/j3d/Locale.java b/src/classes/share/javax/media/j3d/Locale.java index 157cbde..95a0bfb 100644 --- a/src/classes/share/javax/media/j3d/Locale.java +++ b/src/classes/share/javax/media/j3d/Locale.java @@ -29,6 +29,12 @@ import java.util.ArrayList; * coordinates, and methods to add, remove, and enumerate the branch * graphs. * + *

+ * For more information, see the + * Introduction to the Java 3D API and + * Scene Graph Superstructure + * documents. + * * @see VirtualUniverse * @see HiResCoord * @see BranchGroup diff --git a/src/classes/share/javax/media/j3d/Node.java b/src/classes/share/javax/media/j3d/Node.java index 3853a63..eaf5d8e 100644 --- a/src/classes/share/javax/media/j3d/Node.java +++ b/src/classes/share/javax/media/j3d/Node.java @@ -20,6 +20,11 @@ import java.lang.reflect.Constructor; * The Node class provides an abstract class for all Group and Leaf Nodes. * It provides a common framework for constructing a Java 3D scene graph, * specifically bounding volumes. + * + *

+ * For more information, see the + * Introduction to the Java 3D API. + * *

* NOTE: Applications should not extend this class directly. */ diff --git a/src/classes/share/javax/media/j3d/NodeComponent.java b/src/classes/share/javax/media/j3d/NodeComponent.java index 9288d08..d40451d 100644 --- a/src/classes/share/javax/media/j3d/NodeComponent.java +++ b/src/classes/share/javax/media/j3d/NodeComponent.java @@ -16,6 +16,10 @@ import java.util.Hashtable; /** * NodeComponent is a common superclass for all scene graph node * component objects such as: Geometry, Appearance, Material, Texture, etc. + * + *

+ * For more information, see the + * Introduction to the Java 3D API. */ public abstract class NodeComponent extends SceneGraphObject { diff --git a/src/classes/share/javax/media/j3d/SceneGraphObject.java b/src/classes/share/javax/media/j3d/SceneGraphObject.java index 32c52b8..ffcfed1 100644 --- a/src/classes/share/javax/media/j3d/SceneGraphObject.java +++ b/src/classes/share/javax/media/j3d/SceneGraphObject.java @@ -46,6 +46,10 @@ import java.util.Hashtable; * ENABLE_PICK_REPORTING bits are not really capability bits, * although they are set with the setCapability method. The default value * for each of the ENABLE_*_REPORTING bits is false. + * + *

+ * For more information, see the + * Introduction to the Java 3D API. */ public abstract class SceneGraphObject extends Object { // Any global flags? (e.g., execution cullable, collideable) diff --git a/src/classes/share/javax/media/j3d/Screen3D.java b/src/classes/share/javax/media/j3d/Screen3D.java index 4b07e58..4f6ce05 100644 --- a/src/classes/share/javax/media/j3d/Screen3D.java +++ b/src/classes/share/javax/media/j3d/Screen3D.java @@ -68,6 +68,15 @@ import java.util.Hashtable; * specified (setHeadTrackerToLeftImagePlate and * setHeadTrackerToRightImagePlate methods).

*

+ * + *

+ * Additional Information + *

+ * For more information, see the + * Introduction to the Java 3D API and + * View Model + * documents. + * * @see Canvas3D * @see Canvas3D#getScreen3D */ diff --git a/src/classes/share/javax/media/j3d/View.java b/src/classes/share/javax/media/j3d/View.java index daf6cd4..ff6a964 100644 --- a/src/classes/share/javax/media/j3d/View.java +++ b/src/classes/share/javax/media/j3d/View.java @@ -389,6 +389,14 @@ import com.sun.j3d.utils.universe.*; // Needed for Support of DVR. * the viewing frustum for the left and right eye.

* * + *

+ * Additional Information + *

+ * For more information, see the + * Introduction to the Java 3D API and + * View Model + * documents. + * * @see Canvas3D * @see PhysicalBody * @see PhysicalEnvironment diff --git a/src/classes/share/javax/media/j3d/VirtualUniverse.java b/src/classes/share/javax/media/j3d/VirtualUniverse.java index 20c783b..60ececd 100644 --- a/src/classes/share/javax/media/j3d/VirtualUniverse.java +++ b/src/classes/share/javax/media/j3d/VirtualUniverse.java @@ -33,6 +33,12 @@ import java.util.Map; * A VirtualUniverse object defines methods to enumerate its Locale * objects and to remove them from the virtual universe. * + *

+ * For more information, see the + * Introduction to the Java 3D API and + * Scene Graph Superstructure + * documents. + * * @see Locale */ diff --git a/src/classes/share/javax/media/j3d/doc-files/Behaviors.html b/src/classes/share/javax/media/j3d/doc-files/Behaviors.html index 62d6fdd..7bcc4a2 100644 --- a/src/classes/share/javax/media/j3d/doc-files/Behaviors.html +++ b/src/classes/share/javax/media/j3d/doc-files/Behaviors.html @@ -7,7 +7,590 @@

Behaviors and Interpolators

-


+

Behavior 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.

+

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.

+

Behavior Object

+

A Behavior leaf node object contains a scheduling region and two +methods: an initialize method called once when the +behavior becomes "live" and a processStimulus +method called whenever appropriate by the Java 3D behavior +scheduler. +The Behavior object also contains the state information needed by its initialize +and processStimulus methods. +

+

The scheduling region defines a spatial volume that serves +to enable the scheduling of Behavior nodes. A Behavior node is active +(can receive stimuli) whenever an active ViewPlatform's activation +volume intersects a Behavior object's scheduling region. Only active +behaviors can receive stimuli. +

+

The scheduling interval 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. +

+

The processStimulus method receives and processes a +behavior's ongoing messages. The Java 3D behavior scheduler +invokes a +Behavior node's processStimulus +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 processStimulus 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. +

+

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: +

+ + +

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. +

+

Code Structure

+

When the Java 3D behavior scheduler invokes a Behavior object's +processStimulus +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. +

+

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 initialize +method or each time Java 3D invokes its processStimulus +method. +

+

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: +

+ + + + +

WakeupCondition Object

+

A WakeupCondition object is +an +abstract class specialized to fourteen +different WakeupCriterion objects and to four combining objects +containing multiple WakeupCriterion objects. +

+

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. +

+

+

+

WakeupCriterion Object

+

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 processStimulus +method whenever +

+ + + + + + + + + + + + + + +

A Behavior object constructs a WakeupCriterion +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. +

+

Composing WakeupCriterion +Objects

+

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: +

+ +
            WakeupCriterion && WakeupCriterion && ...
+ +
            WakeupCriterion || WakeupCriterion || ...
+ +
            WakeupOr && WakeupOr && ...
+ +
            WakeupAnd || WakeupAnd || ...
+

Composing Behaviors

+

Behavior objects can condition themselves to awaken only when +signaled +by another Behavior node. The WakeupOnBehaviorPost +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. +

+

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. +

+

+

+

Scheduling

+

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. +

+

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. +

+

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. +

+

Java 3D requires each behavior to have a scheduling region +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. +

+

+

+

How Java 3D Performs +Execution Culling

+

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"). +

+

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. +

+

In essence, the Java 3D scheduler performs the following +checks: +

+ + +

Java 3D's behavior scheduler executes those Behavior objects +that +have +been scheduled by calling the behavior's processStimulus +method. +

+

Interpolator Behaviors

+

This section describes Java 3D's predefined Interpolator behaviors. +They are called interpolators +because they smoothly interpolate between the two extreme values that +an interpolator can produce. Interpolators perform simple behavioral +acts, yet they provide broad functionality. +

+

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. +

+

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. +

+

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. +

+

Mapping Time to Alpha

+

Several parameters control the mapping of time onto an alpha value +(see +the javadoc for the Alpha 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. +

+

Figure +1 +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. +

+

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. +

+

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 α +increasing, α at 1, α decreasing, and +α at 0, all specify durations for +the corresponding values +of alpha. +

+

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. +

+

Time-to-Alpha Mapping +

+

+

+ +

+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 Figure +2. +

+

Alpha Increasing +

+

+

+ +

+In Figure +2, +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. +

+

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 Figure +3. +

+

In Figure +3, +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 α-decreasing value might be to combine it with a +rotation +interpolator to program a door closing. +

+

Alpha Decreasing +

+

+

+ +

+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 Figure +4. +

+

Alpha Increasing & Decreasing +

+

+

+ +

+In Figure +4, +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. +

+

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). +

+

We can construct looped versions of the waveforms shown in Figure +2, Figure +3, and Figure +4. Figure +5 shows a looping interpolator with mode flags set to enable +only the alpha-increasing and alpha-at-1 portion of the waveform. +

+

Alpha Increasing Infinite Loop +

+

+

+ +

+In Figure +5, alpha goes from 0 to 1 over a fixed duration of time, stays +at 1 for another fixed duration of time, and then repeats. +

+

Similarly, Figure +6 shows a looping interpolator with mode flags set to enable +only the alpha-decreasing and alpha-at-0 portion of the waveform. +

+

Alpha Decreasing Infinite Loop +

+

+

+ +

+Finally, Figure +7 shows a looping interpolator with both the increasing and +decreasing portions of the waveform enabled. +

+

In all three cases shown by Figure +5, Figure +6, and Figure +7, we can compute the exact value of alpha at any point in time. +

+

Alpha Increasing & Decreasing Infinite Loop +

+

+

+ +

+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. +

+

Acceleration of Alpha

+

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 increasingAlphaRampDuration +and the decreasing-AlphaRampDuration. +

+

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. Figure +8 shows three general examples of how the increasingAlphaRampDuration +method can be used to modify the alpha waveform. A value of 0 for the +increasing ramp duration implies that α +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 α is accelerated during the first half of the +period and +then decelerated during the second half of the period. For a value of n +that is less than 0.5, alpha is accelerated for duration n, +held constant for duration (1.0 - 2n), then decelerated for +duration n of the period. +

+

Alpha acceleration +

+

+

+ diff --git a/src/classes/share/javax/media/j3d/doc-files/Behaviors1.gif b/src/classes/share/javax/media/j3d/doc-files/Behaviors1.gif new file mode 100644 index 0000000..bb288ce Binary files /dev/null and b/src/classes/share/javax/media/j3d/doc-files/Behaviors1.gif differ diff --git a/src/classes/share/javax/media/j3d/doc-files/Behaviors2.gif b/src/classes/share/javax/media/j3d/doc-files/Behaviors2.gif new file mode 100644 index 0000000..005564f Binary files /dev/null and b/src/classes/share/javax/media/j3d/doc-files/Behaviors2.gif differ diff --git a/src/classes/share/javax/media/j3d/doc-files/Behaviors3.gif b/src/classes/share/javax/media/j3d/doc-files/Behaviors3.gif new file mode 100644 index 0000000..a8beb09 Binary files /dev/null and b/src/classes/share/javax/media/j3d/doc-files/Behaviors3.gif differ diff --git a/src/classes/share/javax/media/j3d/doc-files/Behaviors4.gif b/src/classes/share/javax/media/j3d/doc-files/Behaviors4.gif new file mode 100644 index 0000000..685bcb7 Binary files /dev/null and b/src/classes/share/javax/media/j3d/doc-files/Behaviors4.gif differ diff --git a/src/classes/share/javax/media/j3d/doc-files/Behaviors5.gif b/src/classes/share/javax/media/j3d/doc-files/Behaviors5.gif new file mode 100644 index 0000000..74783fb Binary files /dev/null and b/src/classes/share/javax/media/j3d/doc-files/Behaviors5.gif differ diff --git a/src/classes/share/javax/media/j3d/doc-files/Behaviors6.gif b/src/classes/share/javax/media/j3d/doc-files/Behaviors6.gif new file mode 100644 index 0000000..8614a4e Binary files /dev/null and b/src/classes/share/javax/media/j3d/doc-files/Behaviors6.gif differ diff --git a/src/classes/share/javax/media/j3d/doc-files/Behaviors7.gif b/src/classes/share/javax/media/j3d/doc-files/Behaviors7.gif new file mode 100644 index 0000000..0f2ce48 Binary files /dev/null and b/src/classes/share/javax/media/j3d/doc-files/Behaviors7.gif differ diff --git a/src/classes/share/javax/media/j3d/doc-files/Behaviors8.gif b/src/classes/share/javax/media/j3d/doc-files/Behaviors8.gif new file mode 100644 index 0000000..d048cfa Binary files /dev/null and b/src/classes/share/javax/media/j3d/doc-files/Behaviors8.gif differ diff --git a/src/classes/share/javax/media/j3d/doc-files/Concepts.html b/src/classes/share/javax/media/j3d/doc-files/Concepts.html index 1e0d389..7b005af 100644 --- a/src/classes/share/javax/media/j3d/doc-files/Concepts.html +++ b/src/classes/share/javax/media/j3d/doc-files/Concepts.html @@ -271,8 +271,8 @@ component becomes live or is compiled. It is best to set capabilities when you build your content. Listing 4 shows an example where we create a TransformGroup node and enable it for writing. -

Listing 4 – Capabilities Example +

Listing 4 – +Capabilities Example 

TransformGroup myTrans = new TransformGroup();
myTrans.setCapability(Transform.ALLOW_TRANSFORM_WRITE);
diff --git a/src/classes/share/javax/media/j3d/doc-files/Immediate.html b/src/classes/share/javax/media/j3d/doc-files/Immediate.html index c6f27f4..101fe22 100644 --- a/src/classes/share/javax/media/j3d/doc-files/Immediate.html +++ b/src/classes/share/javax/media/j3d/doc-files/Immediate.html @@ -7,7 +7,108 @@

Immediate-Mode Rendering

-


+

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.

+

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. +

+

+

+

Two Styles of Immediate-Mode +Rendering

+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. +

Pure Immediate-Mode +Rendering

+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. +
Note: Scene antialiasing is not supported +in pure immediate mode. +
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 Figure +1). +

Minimal Immediate-Mode Structure

+

+

+
    + Figure 1 – Minimal Immediate-Mode Structure +
+

+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. +

+

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. +

+

In pure immediate mode, the user must stop the Java 3D +renderer, via +the Canvas3D object stopRenderer() +method, prior to adding the Canvas3D object to an active View object +(that is, one that is attached to a live ViewPlatform object). +

+

+

+

Mixed-Mode Rendering

+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. +

The basic Java 3D stereo rendering loop, executed for +each +Canvas3D, is as follows: +

+

clear canvas (both eyes)
+
call preRender()                           // user-supplied method
set left eye view
render opaque scene graph objects
call renderField(FIELD_LEFT)               // user-supplied method
render transparent scene graph objects
set right eye view
render opaque scene graph objects again
call renderField(FIELD_RIGHT)              // user-supplied method
render transparent scene graph objects again
call postRender()                          // user-supplied method
synchronize and swap buffers
+
call postSwap()                            // user-supplied method

+The basic Java 3D monoscopic rendering loop is as +follows: +

clear canvas
+
call preRender()                            // user-supplied method
set view
render opaque scene graph objects
call renderField(FIELD_ALL)                 // user-supplied method
render transparent scene graph objects
call postRender()                           // user-supplied method
synchronize and swap buffers
+
call postSwap()                             // user-supplied method

+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 preRender, postRender, postSwap, +and/or renderField methods. diff --git a/src/classes/share/javax/media/j3d/doc-files/Immediate1.gif b/src/classes/share/javax/media/j3d/doc-files/Immediate1.gif new file mode 100644 index 0000000..2d549b1 Binary files /dev/null and b/src/classes/share/javax/media/j3d/doc-files/Immediate1.gif differ diff --git a/src/classes/share/javax/media/j3d/doc-files/Rendering.html b/src/classes/share/javax/media/j3d/doc-files/Rendering.html index a38f6eb..7415ce8 100644 --- a/src/classes/share/javax/media/j3d/doc-files/Rendering.html +++ b/src/classes/share/javax/media/j3d/doc-files/Rendering.html @@ -7,7 +7,142 @@

Execution and Rendering Model

-


+

Java 3D's execution and rendering model assumes the +existence of a VirtualUniverse +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. +

+

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. +

+

+

+

Three Major Rendering Modes

+

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. +

+

+

Immediate Mode

+

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 "Immediate-Mode Rendering" section.

+

+

+

Retained Mode

+

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. +

+

Java 3D's retained mode allows a programmer to construct +objects, +insert objects into a database, compose objects, and add behaviors to +objects. +

+

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. +

+

+

+

Compiled-Retained Mode

+

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. +

+

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. +

+

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. +

+

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." +

+

+

+

Instantiating the Render Loop

+

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. +

+

+

An Application-Level +Perspective

+

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 compile +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. +

+

+

Retained and +Compiled-Retained Rendering Modes

+

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.

diff --git a/src/classes/share/javax/media/j3d/doc-files/SceneGraphSharing.html b/src/classes/share/javax/media/j3d/doc-files/SceneGraphSharing.html index 478ea4d..ff80cb4 100644 --- a/src/classes/share/javax/media/j3d/doc-files/SceneGraphSharing.html +++ b/src/classes/share/javax/media/j3d/doc-files/SceneGraphSharing.html @@ -7,7 +7,244 @@

Reusing Scene Graphs

-


+

+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.

+

Sharing Subgraphs

+

An application that wishes to share a subgraph from multiple places +in +a scene graph must do so through the use of the Link +leaf node and an +associated SharedGroup 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. +

+

A SharedGroup node allows multiple Link leaf nodes to share its +subgraph as shown in Figure +1 below.
+

+

Sharing a Subgraph +

+
    + Figure 1 – Sharing a Subgraph +
+

Cloning Subgraphs

+

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. +

+

Java 3D provides the cloneTree +method for this +purpose. The cloneTree +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. +

+

References to Node Component +Objects

+

When cloneTree 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. +

+

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. +

+

Figure +2 +shows two instances of NodeComponent objects that are shared and one +NodeComponent element that is duplicated for the cloned subgraph. +

+

Referenced and Duplicated NodeComponent Objects +

+

+

+
    + Figure 2 – Referenced and Duplicated +NodeComponent Objects +
+

References to Other Scene +Graph Nodes

+Leaf nodes that contain references to other nodes +(for example, Light nodes reference a Group node) can create a problem +for the cloneTree method. After the cloneTree +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 Figure +3). +

To handle these ambiguities, a callback mechanism is provided. +

+

References to Other Scene Graph Nodes +

+
    + Figure 3 – References to Other Scene Graph +Nodes +
+

+A leaf node that needs to update referenced nodes upon being duplicated +by a call to cloneTree must implement the updateNodeReferences +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. +

+

Suppose, for instance, that the leaf node Lf1 in Figure +3 implemented the updateNodeReferences method. Once +all nodes had been duplicated, the clone-Tree method +would then call each cloned leaf's node updateNodeReferences +method. When cloned leaf node Lf2's method was called, Lf2 could ask if +the node N1 had been duplicated during the cloneTree +operation. If the node had been duplicated, leaf Lf2 could then update +its internal state with the cloned node, N2 (see Figure +4). +

+

Updated Subgraph after updateNodeReferences Call +

+

+

+
    + Figure 4 – Updated Subgraph after +updateNodeReferences Call +
+

+All predefined Java 3D nodes will automatically have their updateNodeReferences +method defined. Only subclassed nodes that reference other nodes need +to have this method overridden by the user. +

+

Dangling References

+Because cloneTree 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 (Figure +5). A dangling reference is discovered when a leaf node's updateNodeReferences +method calls the getNewNodeReference method and the +cloned subgraph does not contain a counterpart to the node being looked +up. +

Dangling Reference

+

+

+
    + Figure 5 – Dangling Reference: Bold Nodes +Are Being Cloned +
+

+When a dangling reference is discovered, cloneTree can +handle it in one of two ways. If cloneTree is called +without the allowDanglingReferences parameter set to true, +a dangling reference will result in a DanglingReferenceException +being thrown. The user can catch this exception if desired. If cloneTree +is called with the allowDanglingReferences parameter set +to true, the update-NodeReferences method +will return a reference to the same object passed into the getNewNodeReference +method. This will result in the cloneTree operation +completing with dangling references, as in Figure +5. +

+

Subclassing Nodes

+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 cloneTree. +

Leaf node subclasses (for example, Behaviors) that contain any user +node-specific data that needs to be duplicated during a cloneTree +operation must define the following two methods: +

+
Node cloneNode(boolean forceDuplicate);
void duplicateNode(Node n, boolean forceDuplicate)
+The cloneNode method consists of three lines: +

UserSubClass usc = new UserSubClass();
usc.duplicateNode(this, forceDuplicate);
return usc;

+The duplicateNode method must first call super.duplicateNode +before duplicating any necessary user-specific data or setting any +user-specific state. +

NodeComponent subclasses that contain any user node-specific data +must define the following two methods: +

+
NodeComponent cloneNodeComponent();
void duplicateNodeComponent(NodeComponent nc, boolean forceDuplicate);
+The cloneNodeComponent method consists of three lines: +

UserNodeComponent unc = new UserNodeComponent();
unc.duplicateNodeComponent(this, forceDuplicate);
return un;

+The duplicateNodeComponent must first call super.duplicateNodeComponent +and then can duplicate any user-specific data or set any user-specific +state as necessary. +

NodeReferenceTable Object

+The NodeReferenceTable object is used by a leaf node's updateNodeReferences +method called by the cloneTree +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. +

Example: User Behavior Node

+The following is an example of a user-defined Behavior object to show +properly how to define a node to be compatible with the cloneTree +operation. +
+
class RotationBehavior extends Behavior {
    TransformGroup objectTransform;
    WakeupOnElapsedFrames w;
+
    Matrix4d rotMat = new Matrix4d();
    Matrix4d objectMat = new Matrix4d();
    Transform3D t = new Transform3D();
+
    // Override Behavior's initialize method to set up wakeup
    // criteria
+
    public void initialize() {
+
        // Establish initial wakeup criteria
+
        wakeupOn(w);
   }
+
    // Override Behavior's stimulus method to handle the event
+
    public void processStimulus(Enumeration criteria) {
+
        // Rotate by another PI/120.0 radians
+
        objectMat.mul(objectMat, rotMat);
        t.set(objectMat);
        objectTransform.setTransform(t);
+
        // Set wakeup criteria for next time
+
        wakeupOn(w);
    }
+
    // Constructor for rotation behavior.
+
    public RotationBehavior(TransformGroup tg, int numFrames) {
        w = new WakeupOnElapsedFrames(numFrames);
        objectTransform = tg;
+
        objectMat.setIdentity();
+
        // Create a rotation matrix that rotates PI/120.0
        // radians per frame
        rotMat.rotX(Math.PI/120.0);
+
        // Note: When this object is duplicated via cloneTree,
        // the cloned RotationBehavior node needs to point to
        // the TransformGroup in the just-cloned tree.    
    }
+
    // Sets a new TransformGroup.
+
    public void setTransformGroup(TransformGroup tg) {
        objectTransform = tg;
+
    }
+
    // The next two methods are needed for cloneTree to operate
    // correctly.
    // cloneNode is needed to provide a new instance of the user
    // derived subclass.
+
    public Node cloneNode(boolean forceDuplicate) {
+
        // Get all data from current node needed for
        // the constructor
        int numFrames = w.getElapsedFrameCount();
+
        RotationBehavior r =
            new RotationBehavior(objectTransform, numFrames);
        r.duplicateNode(this, forceDuplicate);
        return r;
    }
+
    // duplicateNode is needed to duplicate all super class
    // data as well as all user data.
+
    public void duplicateNode(Node originalNode, boolean 
     forceDuplicate) {
        super.duplicateNode(originalNode, forceDuplicate);
+
        // Nothing to do here - all unique data was handled
        // in the constructor in the cloneNode routine.
    }
+
    // Callback for when this leaf is cloned. For this object
    // we want to find the cloned TransformGroup node that this
    // clone Leaf node should reference.
+
    public void updateNodeReferences(NodeReferenceTable t) {
+
        super.updateNodeReferences(t);
+
        // Update node's TransformGroup to proper reference
+
        TransformGroup newTg =
         (TransformGroup)t.getNewObjectReference(
            objectTransform);
        setTransformGroup(newTg);
    }
}
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View Model

-


+

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.

+

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. +

+

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. +

+

+

+

Why a New Model?

+

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. +

+

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." +

+

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. +

+

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. +

+

+

+

The Physical Environment +Influences the View

+

Letting the application control all viewing parameters is not +reasonable in systems in which the physical environment dictates some +of the view parameters. +

+

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. +

+

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. +

+

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 "View Model Details." +

+

+

+

Separation of Physical and +Virtual

+

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. +

+

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. +

+

+

+

The Virtual World

+

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. +

+

The Physical World

+

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. +

+

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. +

+

+

+

The Objects That Define the +View

+

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. Figure +1 shows graphically the central role of the View object and the +subsidiary role of its component objects. +

+

View Object + Other Components

+

+

+
    + Figure 1 – View Object, Its Component +Objects, and Their +Interconnection +
+

+The view-related objects shown in Figure +1 +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 "View Model +Details." +

+ +
    +
  • View: The main view object. +It contains many pieces of +view state.
    • +
+
    +
  • Canvas3D: 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.
    • +
+
    +
  • Screen3D: 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.
    • +
+
    +
  • PhysicalBody: An object that +contains calibration information +describing the user's physical body.
    • +
+
    +
  • PhysicalEnvironment: 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.
    • +
+

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. +

+

ViewPlatform: A Place in the +Virtual World

+

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. +

+

Figure +2 +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 Figure +2. +

+

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. +

+

View Platform Branch Graph +

+

+

+
    + Figure 2 – A Portion of a Scene Graph +Containing a ViewPlatform Object +
+

+

+

Moving through the Virtual +World

+

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. +

+

Controlling the ViewPlatform object can produce very interesting and +useful results. Our first simple scene graph (see "Introduction," Figure 1) +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. +

+

An alternative application scene graph, shown in Figure +3, +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. +

+

Had we populated this world with more objects, this scene graph +would allow navigation through the world via the Behavior node. +

+

Simple Scene Graph with View Control +

+

+

+
    + Figure 3 – A Simple Scene Graph with View +Control +
+

+Applications and behaviors manipulate a TransformGroup through its +access methods. These methods allow an application to retrieve and +set the Group node's Transform3D object. Transform3D Node methods +include getTransform and setTransform. +

+

+

+

Dropping in on a Favorite +Place

+

A scene graph may contain multiple ViewPlatform +objects. If a user detaches a View 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.

+

Associating Geometry with a +ViewPlatform

+

Java 3D does not have any built-in semantics for displaying a +visible +manifestation of a ViewPlatform within the virtual world (an avatar). +However, a developer can construct and manipulate an avatar using +standard Java 3D constructs. +

+

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 UserHeadToVworld +parameter (see "View Model +Details"). +The avatar's virtual head, represented by the shape node, will now move +around in lock-step with the ViewPlatform's TransformGroup and any +relative position and orientation changes of the user's actual physical +head (if a system has a head tracker). +

+

+

+

Generating a View

+

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 "View Model Details." +

+

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. +

+

+

+

Composing Model and Viewing +Transformations

+

Figure +4 +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. +

+

Object and ViewPlatform Transform

+

+

+
    + Figure 4 – Object and ViewPlatform +Transformations +
+

In our scene graph, what we would normally consider the +model transformation would consist of the following three +transformations: LT1T2. By +multiplying LT1T2 +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 (LTv1)-1 +or Tv1-1L-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. +

+

Fortunately, however, there is a solution to this problem. Composing +the model and view platform transformations gives us +

+
+

+
+
Tv1-1L-1LT1T2 += Tv1-1IT1T2 += Tv1-1T1T2, +
+
+

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 Tvn-1...Tv2-1Tv1-1T1T2...Tm. +

+

As mentioned earlier, the View object contains the remainder of the +view information, specifically, the eye matrix, E, +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, P, 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 PETv1-1T1T2. +In general this is PETvn-1...Tv2-1Tv1-1T1T2...Tm. +

+

The details of how Java 3D constructs the matrices E +and P in different end-user configurations are +described in "View Model Details." +

+

+

+

Multiple Locales

+

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 not attached +to the same Locale. +

+

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 LT1T2...Tm. +In our specific example, a point in Locale L2 would be transformed into +VirtualUniverse coordinates by L2T1T2...Tm. +The view platform transformation would be (L1Tv1Tv1...Tvn)-1 +or Tvn-1...Tv2-1Tv1-1L1-1. +Composing these two matrices gives us +

+
+

+
+
Tvn-1...Tv2-1Tv1-1L1-1L2T1T2...Tm. +
+
+

Thus, to render objects in another Locale, it is sufficient to +compute L1-1L2 +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 L1-1L2 +is a simple translation by L2 - L1. +Again, it is not actually necessary to transform points into +high-resolution VirtualUniverse coordinates. +

+

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." +

+

+

+

A Minimal Environment

+

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: +

+
    +
  • A VirtualUniverse object
    • +
+
    +
  • A high-resolution Locale object
    • +
+
    +
  • A BranchGroup node object
    • +
+
    +
  • A TransformGroup node object with associated transform
    • +
+
    +
  • A ViewPlatform leaf node object that defines the position and +orientation within the virtual universe for generating views
    • +
+
+

View Model Details

+

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. +

+

+

+

An Overview of the +Java 3D +View Model

+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. +

Java 3D must handle two rather different head-tracking +situations. +In one case, we rigidly attach a tracker's base, +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 sensor, 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. +

+

+

+

Physical Environments and +Their Effects

+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. +

The following two examples show how end-user environments can +significantly affect how an application must construct viewing +transformations. +

+

+

+

A Head-Mounted Example

+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. +

A Room-Mounted Example

+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. +

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. +

+

+

+

Impact of Head Position and +Orientation on the Camera

+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. +

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). +

+

Java 3D's view model incorporates the appropriate abstractions +to +compensate automatically for such variability in end-user hardware +environments. +

+

+

+

The Coordinate Systems

+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. +

Room-Mounted Coordinate +Systems

+The room-mounted coordinate system is divided into the virtual +coordinate system and the physical coordinate system. Figure +5 +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. +

The Virtual Coordinate +Systems

+
The Virtual World Coordinate System
+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 +x to the right, +y up, and +z toward +the viewer. +
The ViewPlatform Coordinate System
+The ViewPlatform coordinate system is the local coordinate system of +the ViewPlatform leaf node to which the View is attached. +

Display Rigidly Attached to Tracker Base

+

+

+
    + Figure 5 – Display Rigidly Attached to the +Tracker Base +
+

+

+
The Coexistence Coordinate System
+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. +

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. +

+

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. +

+

+

+

The Physical Coordinate +Systems

+
The Head Coordinate System
+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. +
The Image Plate Coordinate System
+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 XY +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. +
The Head Tracker Coordinate System
+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. +
The Tracker Base Coordinate System
+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. +

Head-Mounted Coordinate +Systems

+Head-mounted coordinate systems divide the same virtual coordinate +systems and the physical coordinate systems. Figure +6 +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. +
The Left Image Plate and Right Image Plate Coordinate Systems
+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 XY plane. Note that the left image plate's XY +plane does not necessarily lie parallel to the right image plate's XY +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. +

Display Rigidly Attached to Head Tracker

+

+

+
    + Figure 6 – Display Rigidly Attached to the +Head Tracker (Sensor) +
+

+

+

The Screen3D Object

+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. Figure +7 shows a scene graph fragment for a display environment designed +for such an end-user environment. Figure +8 shows a display environment that matches the scene graph +fragment in Figure +7. +

Environment with Single Screen3D Object

+

+

+
    + Figure 7 – A Portion of a Scene Graph +Containing a Single Screen3D +Object +
+

+Single-Screen Display Environment

+

+

+
    + Figure 8 – A Single-Screen Display +Environment +
+

+A multiple-projection wall display presents a more exotic environment. +Such environments have multiple screens, typically three or more. Figure +9 shows a scene graph fragment representing such a system, and Figure +10 shows the corresponding display environment. +

+

Environment with Three Screen3D Object +

+

+

+
    + Figure 9 – A Portion of a Scene Graph +Containing Three Screen3D +Objects +
+

+Three-Screen Display Environment

+

+

+
    + Figure 10 – A Three-Screen Display +Environment +
+

+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. +

+

+

+

Viewing in Head-Tracked Environments

+

The "Generating a View" 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. +

+

A Room-Mounted Display with +Head Tracking

+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. +

A Head-Mounted Display with +Head Tracking

+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. +

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. +

+

+

+

Compatibility Mode

+

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. +

+

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 setCompatibilityModeEnable +method turns compatibility mode on or off. Compatibility mode is +disabled by default. +

+
+

Note: 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. +

+
+

Overview of the +Camera-Based View Model

+The traditional camera-based view model, shown in Figure +11, +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. +

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. +

+

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. +

+

Camera-Based View Model +

+

+

+
    + Figure 11 – The Camera-Based View Model +
+

+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. +

+

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. +

+

+

+

Using the Camera-Based View +Model

+

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. +

+

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. +

+

+

+

Creating a Viewing Matrix

+

The Transform3D object provides a lookAt 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 VpcToEc +transform via the compatibility-mode viewing functions. The setVpcToEc +method is used to set the viewing matrix when in compatibility mode. +

+

Creating a Projection +Matrix

+

The Transform3D object provides three methods for +creating a projection matrix: frustum, perspective, +and ortho. 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 z += -1.
+

+

The frustum 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). +

+

The arguments define the frustum and its associated perspective +projection: (left, bottom, -near) +and (right, top, -near) +specify the point on the near clipping plane that maps onto the +lower-left and upper-right corners of the window, respectively. The -far +parameter specifies the far clipping plane. See Figure +12. +

+

The perspective method establishes a perspective +projection with the eye at the apex of a symmetric view frustum, +centered about the Z-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. +

+

The arguments define the frustum and its associated perspective +projection: -near and -far specify the near +and far clipping planes; fovx specifies the field of view +in the X dimension, in radians; and aspect +specifies the aspect ratio of the window. See Figure +13. +

+

Perspective Viewing Frustum +

+

+

+
    + Figure 12 – A Perspective Viewing Frustum +
+

+Perspective View Model Arguments

+

+

+
    + Figure 13 – Perspective View Model Arguments +
+

+The ortho 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. +

+

The arguments define a rectangular box used for projection: (left, +bottom, -near) and (right, top, +-near) +specify the point on the near clipping plane that maps onto the +lower-left and upper-right corners of the window, respectively. The -far +parameter specifies the far clipping plane. See Figure +14. +

+

Orthographic View Model +

+

+

+
    + Figure 14 – Orthographic View Model +
+

+

+

The setLeftProjection +and setRightProjection methods are used to set the +projection matrices for the left eye and right eye, respectively, when +in compatibility mode.

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-

-Application scene graph

+

Application +scene graph

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