谁能解释下

sky11811

#include <osgViewer/Viewer>
#include <osg/Group>
#include <osg/ref_ptr>
#include <osg/Geode>
#include <osg/Geometry>
#include <osg/Array>
#include <osg/NodeCallback>
#include <osgGA/FirstPersonManipulator>
#include <osg/Drawable>
#include <osgdb/ReadFile>


FILE * fp;

class xxCallback : public osg::NodeCallback
{
public:
        xxCallback(osgViewer::Viewer * v)
        {
                viewer = v;
        }
        virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
        {
                osg::Vec3d eye,center,up;
                viewer->getCamera()->getViewMatrixAsLookAt(eye,center,up);
                fprintf(fp,"update      %f,%f,%f  %f,%f,%f  %f,%f,%f\n",eye.x(),eye.y(),eye.z(),center.x(),center.y(),center.z(),up.x(),up.y(),up.z());
                traverse(node,nv);
        }
private:
        osgViewer::Viewer * viewer;
};

int main()
{
        osgViewer::Viewer viewer;
        osg::Group * root = new osg::Group();
        root->addChild(osgDB::readNodeFile("c:/osg_data/cow.osg"));
        root->setUpdateCallback(new xxCallback(&viewer));
        viewer.setCameraManipulator(new osgGA::FirstPersonManipulator());
        viewer.setSceneData( root );

        fp = fopen("G:\\1.txt","wt");
        while(!viewer.done())
        {
                viewer.frame();
                osg::Vec3d eye,center,up;
                viewer.getCamera()->getViewMatrixAsLookAt(eye,center,up);
                fprintf(fp,"frame执行后 %f,%f,%f  %f,%f,%f  %f,%f,%f\n",eye.x(),eye.y(),eye.z(),center.x(),center.y(),center.z(),up.x(),up.y(),up.z());
        }
}

代码里两次打印视点参数，在移动鼠标的情况下，两次输出不一样。按理说不可能啊。