Viewer Movement

Viewer Positioning

The scene graph in Figure 15-3 doesn't include the view branch graph; that branch is shown in Figure 15-7.

Figure 15-7. The view branch graph

The branch is created by a call to the SimpleUniverse constructor in the WrapCheckers3D( ) constructor:

     su = new SimpleUniverse(canvas3D);

SimpleUniverse offers simplified access to the view branch graph via the ViewingPlatform and Viewer classes, which are mapped to the graph (shown as dotted rectangles in Figure 15-7).

ViewingPlatform is used in initUserPosition( ) to access the transformGroup above the ViewPlatform node:

     ViewingPlatform vp = su.getViewingPlatform( );     TransformGroup steerTG = vp.getViewPlatformTransform( );

steerTG corresponds to the TG node in Figure 15-7. Its TRansform3D component is extracted and changed with the lookAt( ) and invert( ) methods:

     Transform3D t3d = new Transform3D( );     steerTG.getTransform(t3d);     t3d.lookAt( USERPOSN, new Point3d(0,0,0), new Vector3d(0,1,0));     t3d.invert( );     steerTG.setTransform(t3d);

lookAt( ) is a convenient way to set the viewer's position in the virtual world. The method requires the viewer's intended position, the point that she is looking at, and a vector specifying the upward direction. In this application, the viewer's position is USERPOSN (the (0, 5, 20) coordinate); she is looking toward the origin (0, 0, 0), and "up" is along the positive y-axis. This is illustrated by Figure 15-8.

Figure 15-8. lookAt( ) depicted graphically

invert( ) is required since the position is relative to the viewer rather than an object in the scene.