An interesting method to implement tetrahedral / bending constraint in a mass spring system (without using tetrahedral/bending constraint gradients).
http://physbam.stanford.edu/~fedkiw/pap ... 008-02.pdf
Nat.
Search found 78 matches
- Mon Jun 02, 2008 1:18 am
- Forum: Links, Papers, Libraries, Demos, Movies, Comparisons
- Topic: Deformables
- Replies: 0
- Views: 4726
- Wed May 21, 2008 1:18 pm
- Forum: General Bullet Physics Support and Feedback
- Topic: Softbody bug? Fit softbody rabbit mesh inside a tube mesh
- Replies: 5
- Views: 3832
Re: Softbody bug? Fit softbody rabbit mesh inside a tube mesh
I have been able to reproduce the problems. - Soft vs solid cylinder work as expected. - Soft vs Bvh/GImpact mesh is not yet implemented. - Soft vs Soft is at a very early stage of development, and is currently very unstable. Improvement of soft vs soft collisions is at the top of the priority list,...
- Sat May 17, 2008 9:19 am
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Collision detection for soft bodies
- Replies: 2
- Views: 6774
Re: Collision detection for soft bodies
Soft body versus soft body use discreet face/vertex collision only, it can handle self collision, but need some decomposition to avoid false positives not implemented yet (see http://gamma.cs.unc.edu/CDCD/ , and http://www.cs.unc.edu/~geom/RTRI/i3d08_RTRI.pdf ). The current implementation is very si...
- Sat May 17, 2008 8:30 am
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Decomposition of bodies intro tetrahedrons
- Replies: 3
- Views: 6183
Re: Decomposition of bodies intro tetrahedrons
For open source implementation there is http://tetgen.berlios.de/ . As for algorithms, Delaunay tetrahedralization (ex: http://citeseer.ist.psu.edu/frey96delaunay.html ) work well but is not as easy as triangulation to implement. In many cases, thin shell is enough to simulate deformable bodies, che...
- Wed May 07, 2008 4:26 pm
- Forum: General Bullet Physics Support and Feedback
- Topic: Bullet issues !?
- Replies: 17
- Views: 14598
Re: Bullet issues !?
For my comprehension, what you did is that you reduced the penetration length, am I that right ? Could that have any side effect somewhere else in the library ? Yes, you're right, basically, Bullet solve for velocities at contacts position such as velocityBodyA-velocityBodyB=-PenetrationDepth/Dt in...
- Mon May 05, 2008 3:54 pm
- Forum: General Bullet Physics Support and Feedback
- Topic: Bullet issues !?
- Replies: 17
- Views: 14598
Re: Bullet issues !?
As a quick fix, you can smooth out velocity drift correction by patching the method 'getDistance' in 'BulletCollision\NarrowPhaseCollision\btManifoldPoint.h' with that: btScalar getDistance() const { static const btScalar frames=16; const btScalar factor=btMin<btScalar>(1,(m_lifeTime/frames)); retur...
- Mon Apr 28, 2008 3:59 am
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: EPA
- Replies: 20
- Views: 19374
Re: EPA
How robust is it on polytopes without a margin? Have you tested degenerate configurations of intersecting boxes? I think this is where things start to can fall apart when trying to use EPA as a replacement for SAT. To test the EPA we only need to compare it with brute-force SAT. No optimizations ar...
- Sun Apr 27, 2008 9:12 am
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: EPA
- Replies: 20
- Views: 19374
Re: EPA
John, It will be nice to have a tests suite for gjk/epa in Bullet, something where we can add tests easily, compare accuracy (or failure) again SAT for polytopes of different implementations (epagjk,epagjk2,Solid,and yours), i don't have time to do that right now, but having a rock solid epa for Bul...
- Wed Apr 16, 2008 6:34 pm
- Forum: General Bullet Physics Support and Feedback
- Topic: Getting body velocity in local space
- Replies: 5
- Views: 6634
Re: Getting body velocity in local space
The function i gave you include angular velocity, call it with body->getCenterOfMassPosition() as worldposition if you only want linear velocity, or: static btVector3 getLinearVelocityInBodyFrame(btRigidBody* body) { return( body->getWorldTransform().getBasis().transpose() * body->getLinearVelocity(...
- Wed Apr 16, 2008 2:59 pm
- Forum: General Bullet Physics Support and Feedback
- Topic: Getting body velocity in local space
- Replies: 5
- Views: 6634
Re: Getting body velocity in local space
The following should work, btVector3 getVelocityAtWorldPosition(btRigidBody* body,const btVector3& worldposition,bool local) { /* That's the 'localpoint' */ const btVector3 relpos=worldposition-body->getCenterOfMassPosition(); /* That's velocity in world space */ const btVector3 wvel=body->getVe...
- Mon Apr 14, 2008 2:04 am
- Forum: Release Announcements
- Topic: Bullet 2.68 RC1: soft body preview (updated April 11)
- Replies: 7
- Views: 53746
Re: Bullet 2.68 RC1: soft body preview (updated April 11)
I've just seen that only convex shapes are supported for collision detection against soft bodies, is there any plan for the concave one, or should I stop using compound shape in my software :) ? Yes only convex shapes are supported for the moment, composites are work in progress, and trimeshs are p...
- Sun Mar 23, 2008 2:46 am
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Soft bodies early preview
- Replies: 41
- Views: 76418
Re: Soft bodies early preview
it happens but some methods seem numerically more robust and can recover gracefully I did test it, each application of gradient correction does in fact recover from sign inversion through (graceful:)) rotations, that could be a problem for one element, but usually more than one tetrahedron share a ...
- Sat Mar 22, 2008 2:15 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Soft bodies early preview
- Replies: 41
- Views: 76418
Re: Soft bodies early preview
However if you use only one rigid frame and move the vertices out from the object mass center it would not work well for many important cases. make a long straight cylinder and bend it in a U shape, the mass center is in the middle and it looks like that the intermediate "pulled" shapes w...
- Sat Mar 22, 2008 1:32 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Soft bodies early preview
- Replies: 41
- Views: 76418
Re: Soft bodies early preview
We have a tetrahedron having zero volume that would look like a triangle, given that you are trying to restore the volume by using a displacement relative to the mass center node a will never be able to escape b,c,d apparently? i called it a tetrahedron to give it more intuition but you can call it...
- Sat Mar 22, 2008 1:20 pm
- Forum: Research and development discussion about Collision Detection and Physics Simulation
- Topic: Soft bodies early preview
- Replies: 41
- Views: 76418
Re: Soft bodies early preview
When i switched between the 2 methods in a FEM solver i never noticed any artifacts and the QR code is just 4-5 lines of code without any iterations. However it can be argued that we are not talking about a FEM solver here so it's difficult to tell without trying it out. what method are you using f...