Gordon Tomlinsons OSG Samples : Bounding Box Calculation

How to Calculate the Bounding Box of an osg::node

OSG Code Example

This example function illustrates one possible method of calculating a tight bounding box on a given osg::Node :

How to create and derive a class from an osg osg::NodeVisitor
How to use an osg::NodeVisitor on a given node
How to take account of any osg::MatrixTransform in the osg::Node children
How to create and use a osg::BoundingBox
How to get the number of osg::Drawable's from an osg::Geode
How to traverse the osg::Drawable's and retrieve/use each osg::Drawable of each osg::Geode
How to retrieve a osg::BoundingBox from an osg::Drawable
How to retrieve athe osg::Matrix from a osg::MatrixTransform node

Note this code/example is based on a several postings to the OSG mailing list and has been mangled into this form by myself

Code :

--

// +----------------------------------------------------------------------------------+

// |

// | Simple Node Visitor to calculate the Bounding Box extents of the visited Node

// |

// | usage example:

// |

// | CcalculateBoundingBox bbox ;

// |

// | node->accept( bbox );

// |

// | osg::BoundingBox boxExtents = bboxCalc.bbox();

// |

// +----------------------------------------------------------------------------------+

#include <osg/NodeVisitor>

#include <osg/BoundingBox>

#include <osg/BoundingSphere>

#include <osg/MatrixTransform>

#include <osg/Billboard>

class CcalculateBoundingBox : public osg::NodeVisitor {

public:

CcalculateBoundingBox() : NodeVisitor( NodeVisitor::TRAVERSE_ALL_CHILDREN ) {

// ----------------------------------------------------------------------

// Default Public Class Constructor

// ----------------------------------------------------------------------

m_transformMatrix.makeIdentity();

}

virtual ~CcalculateBoundingBox() {}

virtual

void apply( osg::Geode &geode ) {

// -------------------------------------------

// Handle nodes of the type osg::Geode

// -------------------------------------------

osg::BoundingBox bbox;

// update bounding box for each drawable

for( unsigned int i = 0; i < geode.getNumDrawables(); ++i ){

// expand the overall bounding box

bbox.expandBy( geode.getDrawable( i )->getBound());

}

// transform corners by current matrix

osg::BoundingBox bboxTrans;

for( unsigned int i = 0; i < 8; ++i ) {

osg::Vec3 xvec = bbox.corner( i ) * m_transformMatrix;

bboxTrans.expandBy( xvec );

}

// update the overall bounding box size

m_boundingBox.expandBy( bboxTrans );

// continue traversing through the graph

traverse( geode );

} // ::apply(osg::Geode &geode)

virtual

void apply( osg::MatrixTransform &node ) {

// ---------------------------------------------------------

// Handle nodes of the type osg::MatrixTransform

// ---------------------------------------------------------

m_transformMatrix *= node.getMatrix();

// continue traversing through the graph

traverse( node );

} // ::apply(osg::MatrixTransform &node)

virtual

void apply( osg::Billboard &node ){

// -----------------------------------------------

// Handle nodes of the type osg::Billboard

// -----------------------------------------------

// important to handle billboard so that its size will

// not affect the geode size continue traversing the graph

traverse( node );

} // ::apply(osg::MatrixTransform &node)

// return teh bounding box

osg::BoundingBox &getBoundBox() { return m_boundingBox; }

protected :

osg::BoundingBox m_boundingBox; // the overall resultant bounding box

osg::Matrix m_transformMatrix; // the current transform matrix

}; // class CcalculateBoundingBox

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