8.5. Calculating a Bounding Box

The bounding-box action computes a 3D bounding box that encloses the shapes in a subgraph under a node or defined by a path. This action also computes the center point of these shapes (see Example 8.1, “ Setting the Center Field of a Transform Node ”). SoGet-BoundingBoxAction is typically called on a path, which enables you to obtain a bounding box for a specific object in world coordinates. This action returns an SbBox3f⁽^C++^|^Java⁾, which specifies a 3D box aligned with the x-, y-, and z-axes in world coordinate space.

Create an Instance of the Action

An example of creating an instance of SoGetBoundingBoxAction⁽^C++^|^Java^|^.NET⁾ is

C++

SbViewportRegion vpReg;
vpReg.setWindowSize(300, 200);
SoGetBoundingBoxAction bboxAction (vpReg);

.NET

SbViewportRegion vpReg = new SbViewportRegion();
vpReg.SetWindowSize(300, 200);
SoGetBoundingBoxAction bboxAction = new SoGetBoundingBoxAction(vpReg);

Java

SbViewportRegion vpReg = new SbViewportRegion();
vpReg.setWindowSize((short)300, (short)200);
SoGetBoundingBoxAction bboxAction = new SoGetBoundingBoxAction(vpReg);

This constructor has one parameter, the viewport region. This information is needed for computing the bounding box of screen-aligned or screen-sized objects, such as SoText2⁽^C++^|^Java^|^.NET⁾.

Apply the Action

SoGetBoundingBoxAction⁽^C++^|^Java^|^.NET⁾ can be applied to the root node of a subgraph, to a path, or to a path list.

Obtain Results

Three methods access the results of SoGetBoundingBoxAction⁽^C++^|^Java^|^.NET⁾:

getBoundingBox()	returns an SbBox3f⁽^C++^\|^Java⁾ bounding box that encloses the shape or shapes
getCenter()	returns the computed center point for the shapes
getXfBoundingBox()	returns an SbXfBox3f⁽^C++^\|^Java⁾ bounding box

The center point returned by getCenter() is defined differently for different objects. For example, the center of an SoFaceSet⁽^C++^|^Java^|^.NET⁾ is defined as the average of its vertices' coordinates. The center of a group is defined as the average of the centers of the objects in the group.

An SbXfBox3f⁽^C++^|^Java⁾ stores the original bounding box for a shape and the matrix that transforms it to the correct world space. The advantage to using an SbXfBox3f⁽^C++^|^Java⁾ instead of an SbBox3f⁽^C++^|^Java⁾ is that the bounding box isn't enlarged unnecessarily. You may want to use this class if you need to perform additional transformations on the bounding box.

Example 8.1, “ Setting the Center Field of a Transform Node ” shows using an SoGetBoundingBoxAction⁽^C++^|^Java^|^.NET⁾ (bboxAction) to return the center of the graph rooted by a node so that rotations can be made around it.

Example 8.1. Setting the Center Field of a Transform Node

C++

SbViewportRegion myViewport;
SoTransform *myTransform;

SoGetBoundingBoxAction bboxAction(myViewport);
bboxAction.apply(root);
myTransform->center = bboxAction.getCenter();

.NET

SbViewportRegion myViewport = new SbViewportRegion();
SoTransform myTransform = new SoTransform();

SoGetBoundingBoxAction bboxAction = new SoGetBoundingBoxAction(myViewport);
bboxAction.Apply(root);
myTransform.center.Value = bboxAction.GetCenter();

Java

SbViewportRegion myViewport = new SbViewportRegion();
SoTransform myTransform = new SoTransform();

SoGetBoundingBoxAction bboxAction = new SoGetBoundingBoxAction(myViewport);
bboxAction.apply(root);
myTransform.center.setValue(bboxAction.getCenter());

Prev	Up	Next
8.4. Rendering	Home	8.6. Accumulating a Transformation Matrix