Re: [Opensg-users] checking ray-scene collisions...

[Christoph Fuenfzig]

Hi, Dirk Reiners wrote: Hi folks, On Mon, 2004-02-16 at 05:18, Carsten Neumann wrote: I'm not sure if this is what you are asking for, but the IntersectAction starts the traversal at the Node you pass in (i.e. scene_root) and proceeds in the usual depth-first style. From the code you've given above I assume you only need the information if anything was hit, or maybe the geometry as well, but the IntersectAction will also determine the triangle that was hit. This is a likely the place where your performance hit comes from, as OpenSG has no special structure inside a Geometry to improve intersection on the triangle level. IIRC there is currently no way to turn off the triangle determination. does the intersect action use bounding boxes to fast discard negative collisions?? Yes, but this only helps if you have many Geometries, not when looking for a hit triangle inside a Geometry. Sorry, maybe someone else has some ideas here, hm, not much we can do here. The main reason dedicated ray-tracers are fast is because they add a lot of additional structure on the polygon level, which you don't need for OpenGL rendering, which is why we don't have any of that yet. Exception: polygon sorting for transparencies, which is why we might it someday, but not right now. The one thing that might help is Christoph Fuenfzig's work for OpenSG Plus, which does add these kinds of polygon-based structures for quick collision detection, for which ray intersection is a basic operation. Christoph, can you comment on how hard it is to use your code for simple ray intersection? Thanks Dirk Oh, there are also classes for simple ray intersection. There are two possibilities: You can use a k-DOP bounding volume hierarchy on the triangles of a given subtree, or you can use a regular grid to structure them. // create adapters with 18-dops for (NodePtr) scene typedef FaceBVolHierarchy<OpenSGTraits,OpenSGFaceInput<K18Dop> > Hierarchy; Hierarchy hier; OSGCache::the().setHierarchy(&hier); OSGCache::the().apply(scene); std::cout << "adapters with 18DOPs created.." << std::endl; // * ray intersect with bvol-hierarchy { // parameter: algorithm="LongestSideMedian", maxDepth=50, maxNumPrim=10  hier.setParameter("LongestSideMedian", 50, 10); hier.hierarchy(); BVolGroup<K18Dop>* root = hier.getRoot(); std::cout << "18DOP-hierarchy (max depth 50, max num primitives 10) build...." << std::endl; Ray ray(Pnt3f(0,0,10), Vec3f(0,0,-1)); Intersection in(ray); SingleEnterLeaveTraverser<OpenSGTraits,BVolRayIntersectTraits<OpenSGTraits> > trav; trav.getData().setIntersect(in); OSGCache::CacheData& data = "" trav.apply(data, root); if (trav.getData().getHit()) { std::cout << "bvol-hierarchy: hit found (" << "distance=" << in.getDist() << ", point=" << in.getPoint() << ")" << std::endl; in.clearData(); } else { std::cout << "bvol-hierarchy: no hit found" << std::endl; } } // * ray intersect with regular-grid { OSGCache::AdapterVector prim; OSGCache::the().collectAdapter(Hierarchy::AdapterType::getAdapterId(), prim); // create grid for scene extent // parameter: create prim.size() voxels in total OSGRegularGrid grid(AABox(root->getBoundingVolume()), prim.size(), RegularGridBase::MaxVoxels); // insert all adapters into the grid OSGRecursiveFillGrid(grid).fillVoxels(prim); std::cout << "regular-grid build...." << std::endl; Ray ray(Pnt3f(0,0,10), Vec3f(0,0,-1)); Intersection in(ray); if (grid.calcIntersect(in)) { std::cout << "regular-grid: hit found (" << "distance=" << in.getDist() << ", point=" << in.getPoint() << ")" << std::endl; in.clearData(); } else { std::cout << "regular-grid: no hit found" << std::endl; } } It looks a bit long, but it first builds the hierarchy or the regular grid and then performs one ray intersection. I will sent you the sources but currently I have no projectfile for Visual Studio .NET 2003 Bye, Christoph -- -------------------------------------------------------------------- Christoph Fünfzig Computer Graphics tel: +49 531 391-2105 TU Braunschweig fax: +49 531 391-2103 Muehlenpfordstr. 23 eMail: [EMAIL PROTECTED] D-38106 Braunschweig http://www.cg.cs.tu-bs.de/people/fuenfzig