First look at the Scene Graph

The scene graph consists of superstructure components-a VirtualUniverse object and a Locale object-and a set of branch graphs. Each branch graph is a subgraph that is rooted by a BranchGroup node that is attached to the superstructure.

  A VirtualUniverse object defines a named universe. Java 3D permits the creation of more than one universe, though the vast majority of applications will use just one. The VirtualUniverse object provides a grounding for scene graphs. All Java 3D scene graphs must connect to a VirtualUniverse object to be displayed.

Below the VirtualUniverse object is a Locale object. The Locale object defines the origin, in high-resolution coordinates, of its attached branch graphs. A virtual universe may contain as many Locales as needed. In this example, a single Locale object is defined with its origin at (0.0, 0.0, 0.0).

The scene graph itself starts with the BranchGroup nodes. A BranchGroup serves as the root of a subgraph, called a branch graph, of the scene graph. Only BranchGroup objects can attach to Locale objects.

In this example there are two branch graphs and, thus, two BranchGroup nodes. Attached to the left BranchGroup are two subgraphs. One subgraph consists of a user-extended Behavior leaf node. The Behavior node contains Java code for manipulating the transformation matrix associated with the object's geometry.

The other subgraph in this BranchGroup consists of a TransformGroup node that specifies the position (relative to the Locale), orientation, and scale of the geometric objects in the virtual universe. A single child, a Shape3D leaf node, refers to two component objects: a Geometry object and an Appearance object. The Geometry object describes the geometric shape of a 3D object (a cube in our simple example). The Appearance object describes the appearance of the geometry (color, texture, material reflection characteristics, and so forth).

The right BranchGroup has a single subgraph that consists of a TransformGroup node and a ViewPlatform leaf node. The TransformGroup specifies the position (relative to the Locale), orientation, and scale of the ViewPlatform. This transformed ViewPlatform object defines the end user's view within the virtual universe.

Finally, the ViewPlatform is referenced by a View object that specifies all of the parameters needed to render the scene from the point of view of the ViewPlatform. Also referenced by the View object are other objects that contain information, such as the drawing canvas into which Java 3D renders, the screen that contains the canvas, and information about the physical environment.