学步园

在参考了多个例子后写了这么一个例子，总算明白了进行线段相交的各个步骤的含义了。

#include <osgViewer/Viewer>
#include <osgViewer/ViewerEventHandlers>
#include <osgGA/StateSetManipulator>
#include <osgDB/ReadFile>
#include <osgUtil/LineSegmentIntersector>
#include <osgUtil/IntersectionVisitor>
#include <osg/MatrixTransform>
#include <osg/Group>
#include <osg/Node>
int main()
{
	osg::ref_ptr<osg::Node> cow = osgDB::readNodeFile("cow.osg");//第一个节点
	osg::ref_ptr<osg::Node> axes = osgDB::readNodeFile("axes.osg");//第二个节点
	osg::ref_ptr<osg::MatrixTransform> mt_cow = new osg::MatrixTransform;
	mt_cow->setMatrix(osg::Matrix::scale(osg::Vec3(0.5,0.5,0.5))*osg::Matrix::translate(osg::Vec3(-10,0,0)));
	mt_cow->addChild(cow.get());
	osg::ref_ptr<osg::MatrixTransform> mt_axes = new osg::MatrixTransform;
	mt_axes->addChild(axes.get());
	osg::ref_ptr<osg::Group> root = new osg::Group;
	root->addChild(mt_cow.get());
	root->addChild(mt_axes.get());
	osgViewer::Viewer * viewer = new osgViewer::Viewer;
	viewer->addEventHandler(new osgGA::StateSetManipulator(viewer->getCamera()->getOrCreateStateSet()));
	/************************************************************************/
	/* 碰撞检测                                                             */
	/************************************************************************/
	osg::Vec3 p_start(-100,0,0);
	osg::Vec3 p_end(100,0,0);
	osgUtil::LineSegmentIntersector::Intersections _intersections;
	osg::ref_ptr< osgUtil::LineSegmentIntersector > _lineSegmentIntersector = new osgUtil::LineSegmentIntersector(p_start,p_end);
	osgUtil::IntersectionVisitor _iv(_lineSegmentIntersector.get());
	cow->accept(_iv);
	_intersections=_lineSegmentIntersector->getIntersections();
	int _intersectionNumber=_intersections.size();        
	if (_intersectionNumber!=0)
	{         
		osgUtil::LineSegmentIntersector::Intersections::iterator hitr = _intersections.begin();
		osg::Vec3 vec3_p1 =hitr->getWorldIntersectPoint()*mt_cow->getMatrix();//这样得到的交点就是绝对的世界坐标了。
		mt_axes->setMatrix(osg::Matrix::translate(vec3_p1));//把坐标系原点移动到交点，可以测试现在的坐标系原点是不是刚好和牛相交！
		hitr++;
		osg::Vec3 vec3_p2 =hitr->getWorldIntersectPoint()*mt_cow->getMatrix();
	}
	viewer->setSceneData(root.get());
	return viewer->run();
	
}