Re: [Algorithms] incremental triangulation for 2D collision detection broadphase
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Re: [Algorithms] incremental triangulation for 2D collision detection broadphase
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From: <Pau...@sc...> - 2010-02-05 16:42:14
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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Hi Samuel, At first glance this approach seems pretty complex and expensive for a broad phase? I can't see how you can do this without triangulation and thats not a cheap operation. Even then, you have to intersect polygons against AABBs which is actually quite a costly operation - not that far away from a full narrow phase. I would recommend sweep and prune, or multi-sweep and prune if your worlds are huge. We used sweep and prune in little big planet psp and it worked quite well. Just my 2p :) Cheers, Paul. Samuel Moll <sam...@go...> wrote on 03/02/2010 14:38:46: > @Ben: Thanks for the link, but I wanted to avoid doing full Delauney > triangulation since everything remotely Delauney-like suffices for > me... but I can probably use some of the methods in this paper. > @ Erwin: Thought I read somewhere that Box2D uses a hash... but the > source code looks alot like a AABB tree ;) > > > But I think I found something better, because I realized that I don't > really need a triangulation, only some partition for example using > polygons... > > Okay, here's the outline to my approach: > Every objects center is a "node", around the node is this objects > bounding volume (I think I'll use circles). > Then you build a graph that partitions the plane into (convex and > concave) polygons (You could make the graph so that only triangles are > used). On every corner of a polygon is an object, no object is on the > inside of a polygon. > > Now you test for every object which polygon its bounding volume > intersects. Obviously it intersects at least all polygons adjacent to > its node; if the bounding volumes are relatively tight, it should not > intersect more than these. > I think the average number of bounding volume tests for each object > should be around 6. > > Now all nodes move, and if the graph changes its topology, it needs to > be repaired. This is the part where I have no concrete algorithm > yet... but I guess I'll find one. I'm relatively sure that this step > should be fast ;) > > Then the graph is optimized: a few edges are swapped, inserted etc. to > avoid slivers and such. This should be easy. > > Greets, > Samuel > > > > On Wed, Feb 3, 2010 at 6:39 AM, Erwin Coumans <erw...@gm...> wrote: > > > > Hi Samuel, > > > > Box2d uses a dynamic AABB tree for the broadphase, based on the original > > implementation from our Bullet library in 3d. > > > > This tree is incrementally updated, faster than sweep and prune. > > > > No spatial hash. > > > > I'm interested in your approach. How do you 'triangulate' the centers, and > > compute connectivity? > > > > Thanks, > > Erwin > > > > Feel free to forward this to the list, I cannot mail to the list because of > > mail server issues. > > > > Sent from my iPhone > > > > On Feb 2, 2010, at 16:54, Samuel Moll <sam...@go...> wrote: > > > >> Hello all, > >> > >> I need a broadphase collision detection algorithm for 2D rigid body > >> physics (continuous collision detection, but that shouldn't matter for > >> the broadphase...). > >> > >> I have objects of wildly varying sizes, lots of free space and > >> possibly lots of clustering or even a single object very far away from > >> all the others, so a Quadtree (without some strange modifications, > >> wrapping the world came to mind) is not the best option. > >> > >> What I came up with is to take all the objects positions and > >> triangulate this point set. Then for each triangle I determine which > >> objects it overlaps and test all these objects for collision. > >> > >> This has a number of advantages, and I believe it could be competitive > >> to sweep and prune or Quadtrees (at least in 2D, in 3D its probably > >> not cool, but who knows?). I couldn't find anything about this method, > >> but if somebody already invented it I'd appreciate some pointers. > >> > >> What I need now is an (efficient :D) algorithm for updating the > >> triangulation when the points move. i.e. given a valid triangulation > >> (no triangles overlap, triangulates the convex hull of all points) and > >> movement vectors for all points, how can I "repair" the old > >> triangulation? > >> > >> The first part of the problem is how to maintain fat triangles > >> (slivers lead to poor collision rejection). I'm sure there are already > >> good algorithms to incrementally maintain a good triangulation, but I > >> couldn't find them. Also, the union of all triangles must stay convex. > >> > >> The second problem is how to detect and remove triangle overlaps that > >> arise due to fast-moving objects. I have no idea how to do this > >> robustly (theoretically, the points could teleport arbitrarily) > >> > >> I guess somebody already has solved this problem, but I could find no > >> relevant paper... > >> > >> Of course I'll release the finished implementation as open source, or > >> try to incorporate it into Box2D if they want it and if it proves > >> faster than their existing spatial hashing ;) > >> > >> > >> Sincerely, > >> Samuel Moll > >> > >> > >> > - ------------------------------------------------------------------------------ > >> The Planet: dedicated and managed hosting, cloud storage, colocation > >> Stay online with enterprise data centers and the best network in the > >> business > >> Choose flexible plans and management services without long-term contracts > >> Personal 24x7 support from experience hosting pros just a phone call away. > >> http://p.sf.net/sfu/theplanet-com > >> _______________________________________________ > >> GDAlgorithms-list mailing list > >> GDA...@li... > >> https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list > >> Archives: > >> http://sourceforge.net/mailarchive/forum.php?forum_name=gdalgorithms-list > > > > - ------------------------------------------------------------------------------ > The Planet: dedicated and managed hosting, cloud storage, colocation > Stay online with enterprise data centers and the best network in the business > Choose flexible plans and management services without long-term contracts > Personal 24x7 support from experience hosting pros just a phone call away. > http://p.sf.net/sfu/theplanet-com > _______________________________________________ > GDAlgorithms-list mailing list > GDA...@li... > https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list > Archives: > http://sourceforge.net/mailarchive/forum.php?forum_name=gdalgorithms-list ********************************************************************** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. 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