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# erwincoumans

Member Since 24 Jul 2005
Offline Last Active Jul 16 2016 10:01 PM

### #5301036Motor control redux

Posted by on 16 July 2016 - 10:04 PM

Bullet forums maybe? (they're mostly dead lately though): http://bulletphysics.org/Bullet/phpBB3/viewforum.php?f=4

I really like this project/idea

I've been barely visiting Bullet forums, because I have been working on control for robotics and articulated characters for a few years now, and now getting involved with deep learning in this context (I work in the Google Brain team nowadays where we create/use TensorFlow). I just replied:

http://bulletphysics.org/Bullet/phpBB3/viewtopic.php?p=37890#p37890

I'm going to add some more motor control and deep learning demos in Bullet for the upcoming release.

### #4797972OBB-OBB Collision data

Posted by on 13 April 2011 - 08:49 AM

One approximate way to generate contact points between two convex polyhedra A and B, is the following recipe:

1) find a separating axis between A and B using your favorite method (SAT, GJK etc)
2) find reference face on A and a incident face on B with a normal that is closest to this separating axis
3) perform Sutherland-Hodgman clipping on the vertices of this face on A against the polyhedron B
This clipping can be performed either in worldspace or in the local space of B, using the faces connected to face B

I recently implemented this method in the open source Bullet physics library, part of the Bullet 2.78 release, so you can test the implementation and read the code here:
http://code.google.c...actClipping.cpp in particular btPolyhedralContactClipping::clipHullAgainstHull and clipFace.

For general convex polyhedra you need to compute the connectivity and connected faces (m_connectedFaces in above code), Bullet uses the btConvexHullComputer for this. For the special case of OBB-OBB this information can be hard-coded, you can see the OBB-OBB clipping code in ODE/Bullet here: http://code.google.com/p/bullet/source/browse/trunk/src/BulletCollision/CollisionDispatch/btBoxBoxDetector.cpp#574

Thanks,
Erwin

### #4789766Rigid body contact scenario requiring global solver

Posted by on 23 March 2011 - 07:41 PM

Here is one global conflict scenario: the two dynamic objects are not aware that after CCD they end up in the same location.

There are more complicated cases, but this could be a start.

### #4781971Sweep test and physics

Posted by on 04 March 2011 - 09:10 PM

I created a proof of concept for predictive contacts in the Bullet SDK, thanks Paul for motivating me to do this. We discussed speculative contacts previously here.