Electrical computers and digital processing systems: multicomput – Remote data accessing – Accessing a remote server
Reexamination Certificate
2000-04-18
2004-06-15
Cardone, Jason D. (Department: 2142)
Electrical computers and digital processing systems: multicomput
Remote data accessing
Accessing a remote server
C709S241000, C345S473000
Reexamination Certificate
active
06751655
ABSTRACT:
BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
This invention relates to the field of computer network communication, and, more specifically, to the transportation of scenegraph information across a network.
Sun, Sun Microsystems, the Sun logo, Java, Java 3D and all Java-based trademarks and logos are trademarks or registered trademarks of Sun Microsystems, Inc. in the United States and other countries. All SPARC trademarks are used under license and are trademarks of SPARC International, Inc. in the United States and other countries. Products bearing SPARC trademarks are based upon an architecture developed by Sun Microsystems, Inc.
2. BACKGROUND ART
In present computer systems, it is possible to create a visual representation of a scene in which the scene description contains information regarding three physical dimensions. The use of such “3D” scenes is becoming increasingly important as a way to create “user friendly” interfaces to complex software applications, for example. In current practice, 3D scene descriptions are frequently organized in the form of directed acyclic graphs called scenegraphs. A scenegraph is a tree structure comprising a multiplicity of nodes interconnected in a hierarchical manner. This hierarchical structure provides a well-organized framework for describing a 3D scene, and one in which functionality may be easily augmented through the addition of one or more nodes to an existing scenegraph.
A consideration in the use of scenegraphs is that computer systems are frequently operated in conjunction with a network. It is therefore desirable to transfer scenegraph information across the network in a platform and application independent manner. There presently exist schemes that attempt to accomplish such a transfer of scenegraph information. One such scheme involves representing scenegraph information in the “Virtual Reality Modeling Language” (VRML), and transmitting the VRML data in an editable text file across a network using standard network protocols, such as http and ftp. These techniques use a textually represented (e.g., ASCII) sequence of symbols as a least common denominator for reliably transferring scenegraph descriptions. Sometimes the textual sequences are compressed into a binary format for transmission purposes.
A problem with using VRML and other passive, fixed-format mechanisms for transporting scenegraph information is that the receiving client application must include a mechanism for parsing and interpreting the received scenegraph information to construct the 3D scene. There is little flexibility for altering the representation of the scenegraph information for transmission, even if more efficient representations are developed, because the client's implementation of the parser/interpreter is fixed. A new format would require reprogramming of the client application to add the necessary parsing and interpreting support.
Scenegraph Techniques
The scenegraph programming model provides a simple and flexible mechanism for representing and rendering scenes. Individual graphics elements are constructed as separate node objects and connected together in a treelike structure. Those node objects are then manipulated using their predefined accessor, mutator and node-linking methods.
For reference, an object is a programming unit that groups together a data structure (one or more instance variables) and the operations (methods) that can use or affect that data. Thus, an object consists of data and one or more operations or procedures that can be performed on that data. An object can be instructed to perform one of its methods when it receives a “message.” A message is a command or instruction sent to the object to execute a certain method. A message consists of a method selection (e.g., method name) and zero or more arguments. A message tells the receiving object what operations to perform.
Any given object is an “instance” of a particular class. A class provides a definition for an object which typically includes both fields (e.g., variables) and methods. (The term “object” by itself is often used interchangeably to refer to a particular class or a particular instance.) An instance of a class includes the variables and methods defined for that class. Multiple instances can be created from the same class.
The scenegraph contains a complete description of the entire scene, or virtual universe. This includes the geometric data, the attribute information, and the viewing information needed to render the scene from a particular point of view. In the case of a 3D scene, the scenegraph hierarchy promotes a spatial grouping of geometric objects found at the leaves (i.e., end nodes) of the scenegraph. Internal nodes act to group their children together. A group node may also define a spatial bound that contains all the geometry defined by its descendants. Spatial grouping allows for efficient implementation of operations such as proximity detection, collision detection, view frustrum culling and occlusion culling.
Node objects of a scenegraph may be separated into “group node” objects and “leaf node” objects. Group node objects group together one or more child nodes, and can be used to define behavior or relationships common to those child nodes. Leaf node objects contain the actual definitions of shapes (geometry), lights, fog, sound, etc. A leaf node has no children and only one parent. The state of a leaf node includes any state in a direct path between the leaf node and the source or “root” node of the scenegraph. When a scene is rendered, the renderer incorporates all state changes made in a direct path from the root node of the scenegraph to a leaf node object in the drawing of that leaf node object.
FIG. 1
illustrates a general scenegraph structure used to represent a 3D scene in accordance, for example, with scenegraph policies as described in the Java 3D™ API Specification available from Sun Microsystems, Inc. The scenegraph of
FIG. 1
comprises a single root node, referred to as virtual universe (VU)
100
, one or more locale nodes (LO)
101
, one or more branch group nodes (BG)
102
, one or more group nodes (GN)
103
, and one or more leaf nodes (LN)
104
.
Virtual universe
100
represents the center of the scene, with all child nodes being positioned relative to it. One or more high-resolution locale nodes
101
are coupled to virtual universe
100
. Each such locale node
101
specifies a relative offset position with respect to virtual universe
100
. This relative offset is represented in a high-resolution format to accommodate distance relationships comparable to the smallest and largest conceived distances in the real world. Each locale node
101
may be used to attach one or more branch group nodes
102
, whose rendering positions are interpreted relative to the given locale node
101
.
Branch group nodes
102
generally act as a root node of a subgraph associated with the given parent locale node
101
. When a branch group node
102
is attached to a locale node
101
, and hence to a virtual universe
100
, the branch group node and its descendants are considered “live” (i.e., ready to render) with respect to the scene. One or more general group nodes
103
may be attached as child nodes to each branch group node
102
. Each group node
103
may support zero or more child nodes in the form of further group nodes
103
or leaf nodes
104
.
An example of an implementation of a group node
103
is as a transform node that contains a transform matrix used to scale, rotate, and position its descendants. Other group nodes implemented as “behavior” nodes may be used to embody algorithms for modifying the transform matrices of specified transform objects. Certain leaf node objects may also have references to component objects (not shown) which specify specific attributes of the given leaf node object (e.g., a shape leaf node may have as associated component objects a geometry component object, specifying a geometric shape of the shape leaf node, and an appearance component object, specifying the appearance of the shape in te
Deutsch Keith
Fernando Gerard
Shah Pallavi
Cardone Jason D.
O'Melveny & Myers LLP
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