Cool stuff, thanks for addition... I could have done with it a few weeks ago before I wrote some it for a project here ;)
Best Regards Gordon __________________________________________________________ Gordon Tomlinson Email : gordon.tomlinson @ overwatch.com YIM/AIM: Gordon3dBrit MSN IM : Gordon3dBrit @ 3dSceneGraph.com __________________________________________________________ "Self defence is not a function of learning tricks but is a function of how quickly and intensely one can arouse one's instinct for survival" - Master Tambo Tetsura -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Robert Osfield Sent: Tuesday, October 31, 2006 10:43 AM To: osg users Subject: [osg-users] Introducing osgUtil::IntersectionVisitor,osgSim::LineOfSight and osgSim::HeightAboveTerrain Last week I mentioned that I'd be checking in some work on intersection testing, the first cut of it is now checked into CVS. The work is preliminary, but good enough to get testing with. In osgUtil you'll find: osgUtil::Intersector - a new base class for doing intersection tests between nodes and drawable leaves, the intersector stores the intersection hits as well as the abilty to clone and reproject itself into local coordinates. osgUtil::LineSegmentIntersector - a concrete implementation of an Intersector, that provides line segment intersection functionality. osgUtil::IntersectorGroup - a concrete implementation of an Intersector, that provides the ability to test a group of Intersectors. osgUtil::IntersectionVisitor - the base traverserser for new intersection support. All the actual intersection work is done by the Intersectors, so its a general purpose traverser. It also contains a callback to enable reading of external PagedLOD tiles, there isn't an implementation of the reading though, as osgUtil doesn't know about osgDB, and its only osgDB that can do the actual reading. In the future I expect to have osgUtil::PolytopeIntersector, and osgUtil::Pick/BoxIntersector that will work in window coordinates, as well as object coordinates like the existing LineSegmentIntersector does. Some more work needs to happen in IntersectionVisitor before this can happen, but the actual design work has been done, the architecture is designed to encompass screen picking requirements. In osgSim you'll find some specialist helper classes for vis-sim type work: osgUtil::LineOfSight - a class for setting up a group of line of sight tests and running the computation of the intersections. osgUtil::HeightAboveTerrain - class of setting a group of height above terrain tests and running the computation of the intersections. The later handles the local up vector that geocentric coordinates require if the model pass into the compute has a CoordinateSystemNode at the top - this allows you to handle whole earth database. In osgSim there is also a DatabaseCacheReadCallback that adds the support for reading paged databases along with the ability to cache these loads for later reuse. You can share a single DatabaseCacheReadCallback between multiple LineOfSight and HeightAboveTerrain operations so the cahce will be remain relevant across all your intersections tests. One important aspect to this work is that the support for paged database is such that you can automatically query the database for the highest resolution tile available - it'll automatically do all the nested loads for you. You can tweak the cache to balance how much memory you use. This database support feature is something I have been asked about from time to time, and I never gave a simple answer too, as I believed it'd be rather convoluted, suffer from high latencies and really thrash memory. This recent work lead me to an eureka moments when I realised that problem was actually quite a bit simpler if you avoided using the tradition osgDB::DatabasePager support, and did the reading directly within the traversal. So rather than try to explain how to do it, I can now simply point to the solution! The code also doesn't require the use of OpenGL graphics context so you do all the tests in non graphics applications, yes even I have to recognise that such applications do exist :-D There is also the beginnings on an osgintersection example, its a bit convoluted right now due to the needs of testing the code, but it should at least give you an inkling of how to use the new classes. There is possibility that the new design will stretch to doing multi-threaded intersection tests, this isn't implemented yet though, and won't be done straight away, but perhaps some point in the future we can tackle this. Please feel free to test the new classes out and give feedback. Have fun, Robert. _______________________________________________ osg-users mailing list osg-users@openscenegraph.net http://openscenegraph.net/mailman/listinfo/osg-users http://www.openscenegraph.org/ _______________________________________________ osg-users mailing list osg-users@openscenegraph.net http://openscenegraph.net/mailman/listinfo/osg-users http://www.openscenegraph.org/
