Hello Peter,
In both cases, my intuition is that even the
worst-case AABB is still going to represent a much tighter bound than
the best-case bounding sphere, leading to unnecessary and expensive
tests against the actual geometry.
Actually, the osg::Node hierarchy uses bounding spheres, but the
osg::Drawable hierarchy uses AABBs. Once an intersection returns a
success against the BS, it will go down to the osg::Geodes, then loop
through the geode's drawables, checking their AABBs for intersection as
well. Only once one or more of these returns a success will it test
geometry.
See src/osgUtil/LineSegmentIntersector.cpp, method
intersect(IntersectionVisitor&, Drawable*):
void LineSegmentIntersector::intersect(osgUtil::IntersectionVisitor& iv,
osg::Drawable* drawable)
{
osg::Vec3d s(_start), e(_end);
if ( !intersectAndClip( s, e, drawable->getBound() ) ) return;
// ...
Here, intersectAndClip() checks the drawable's bounding box for
intersections and returns false if there were none.
So your intuition is right, but OSG already does this. You're welcome to
go down into the intersection visitor / line segment intersector and
improve upon this, of course.
J-S
--
______________________________________________________
Jean-Sebastien Guay jean-sebastien.g...@cm-labs.com
http://www.cm-labs.com/
http://whitestar02.webhop.org/
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