[osg-users] how to update the Camera

[Wu Xiaodong]

Hi, I am freshman in OpenSceneGrapph.  Now I have some issue on updating the
Camera when the Geode under it was updated.

the details of the issue is as following.

 1st step. I build a viewer and its scene graph with only one osg::Geometry
which contains nothing. and set a TrackballManipulator to the viewer's
camera;

*        osg::ref_ptr<osgGA::TrackballManipulator> trackBall = new
osgGA::TrackballManipulator;
        setCameraManipulator( trackBall.get() );
* 2nd step. I update the one Geometry by a object of  the class derived from
the Geometry node's UpdateCallBack class;

the default track ball center seems to be the (0,0,0); when the Gemetry is
updated, the Geometry node's center is changed into (x0,y0,z0); but the
track ball rotate around the vertex ( 0,0,0). How can I make it rotate
around the (x0,y0,z0 );

       I read the OSG's reference docs, may I can achieve it by
setPreDrawCallback<file:///E:/Oil/OpenSceneGraphReferenceDocs/a01059.html#a76>(
DrawCallback <file:///E:/Oil/OpenSceneGraphReferenceDocs/a01061.html> *cb) .

      Is there any advice about the application above, Thanks.

                                                               Xiaodong Wu
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