Search found 849 matches

by drleviathan
Tue Sep 01, 2015 5:02 am
Forum: General Bullet Physics Support and Feedback
Topic: Simulation 3d
Replies: 16
Views: 11867

Re: Simulation 3d

Yes, Bullet could simulate that device. Since you'd be pursuing numerical accuracy you'd want to build Bullet with support for double precision to reduce floating point errors. The results may be sensitive to the details of how you set up the constraints. For example, the drawing shows the wheel's p...
by drleviathan
Sun Aug 23, 2015 1:40 pm
Forum: General Bullet Physics Support and Feedback
Topic: [SOLVED] Length, width, and height of a rigid body.
Replies: 8
Views: 9968

Re: Length, width, and height of a rigid body.

And if you want to compute the center of mass of an arbitrary mesh shape yourself here is some code for doing that (from this thread).
by drleviathan
Tue Aug 11, 2015 7:42 pm
Forum: General Bullet Physics Support and Feedback
Topic: Thread Safety in the Bullet API
Replies: 3
Views: 4997

Re: Thread Safety in the Bullet API

And there is a thread on these forums that talks about that multi-thread fork.
by drleviathan
Sun Aug 09, 2015 7:57 pm
Forum: General Bullet Physics Support and Feedback
Topic: [SOLVED] Check if rigidbody intersections are resolved
Replies: 4
Views: 5016

Re: Check if rigidbody intersections are resolved

I did some experimentation with one of the demos and I learned a few things: A btManifoldPoint between two colliding objects has a data member called distance which is negative when the objects penetrate each other. However, for one box resting on top of a second box the distance will tend to be neg...
by drleviathan
Mon Aug 03, 2015 8:09 pm
Forum: General Bullet Physics Support and Feedback
Topic: [Solved] Simulation speed is very inconsistent
Replies: 7
Views: 6938

Re: Simulation speed is very inconsistent

It is unclear to us why your simulation would start to run slow. You'll just have to profile your program. Bullet comes with a profiling framework: look for CProfileManager in the Demo code. You when it starts running slow you should dump that profile info and examine where the time is being spent. ...
by drleviathan
Fri Jul 31, 2015 2:49 pm
Forum: General Bullet Physics Support and Feedback
Topic: [SOLVED] Constrained box shapes experience heavy twitching
Replies: 3
Views: 3529

Re: Constrained box shapes experience heavy twitching

Are the boxes colliding with each other? In this recent thread we learned that the two constrained objects will collide by default so if your boxes overlap then the constraint may be unresolvable.
by drleviathan
Thu Jul 30, 2015 3:55 pm
Forum: General Bullet Physics Support and Feedback
Topic: do constrained objects collide?
Replies: 2
Views: 3193

Re: do constrained objects collide?

In Bullet-2.82 the declaration of btDiscreteDynamicsWorld::addConstraint() looks like this: virtual void addConstraint(btTypedConstraint* constraint, bool disableCollisionsBetweenLinkedBodies=false); The second argument can be used to make the linked bodies collide or not, but it defaults to having ...
by drleviathan
Mon Jul 27, 2015 3:22 pm
Forum: General Bullet Physics Support and Feedback
Topic: Simulation with a lot of objects
Replies: 1
Views: 2075

Re: Simulation with a lot of objects

One thing you need to know is that the computation cost of adding one new object to the world goes up as the number of objects already in the world increases. It could be that the cost gets unacceptably large before you reach 100k -- you'll have to test it yourself. However knowing this you can expe...
by drleviathan
Thu Jul 09, 2015 1:15 pm
Forum: General Bullet Physics Support and Feedback
Topic: reduce the AABB for spheres
Replies: 4
Views: 4555

Re: reduce the AABB for spheres

Oh hey, I also did a search and found this old post, although that wasn't the one I was thinking about.
by drleviathan
Thu Jul 09, 2015 6:00 am
Forum: General Bullet Physics Support and Feedback
Topic: reduce the AABB for spheres
Replies: 4
Views: 4555

Re: reduce the AABB for spheres

You're detecting the "collision" incorrectly. The recommended way to do it is to scan the contact manifold lists and keep a map of existing pairs of objects. When a new pair shows up then you would fire off a collision "start" event. Unfortunately such a system is not one of the ...
by drleviathan
Thu Jul 09, 2015 5:54 am
Forum: General Bullet Physics Support and Feedback
Topic: How can I increase the physical realism of my simulation?
Replies: 11
Views: 10847

Re: How can I increase the physical realism of my simulation

If damping were the cause then we'd expect the two descent curves to not align. According to the plots energy is lost on collision. As I recall there was a another recent post about how the measured accuracy of the simulation became worse on faster simulation steps. I don't have any theories as to w...
by drleviathan
Tue Jul 07, 2015 6:06 am
Forum: General Bullet Physics Support and Feedback
Topic: Importing shapes into Bullet
Replies: 4
Views: 5187

Re: Importing shapes into Bullet

The V-HACD library is just a lib that computes a list of convex hulls if you give it at mesh (points and triangle indices). From its output you'd have to generate your own btConvexHull shapes and put them into a btCompoundShape, or just load each convex hull as one object if they are all static (not...
by drleviathan
Tue Jul 07, 2015 5:49 am
Forum: General Bullet Physics Support and Feedback
Topic: Dynamic Object Slides on a Static Object
Replies: 3
Views: 3931

Re: Dynamic Object Slides on a Static Object

I wonder if your cube has a center of mass that it at the surface, or outside of, the shape itself. That is, are the mesh points in the local frame such that the origin is at their center (or at least inside the convex hull of points)? If not then the center of mass of the object will reside outside...
by drleviathan
Tue Jul 07, 2015 5:32 am
Forum: General Bullet Physics Support and Feedback
Topic: Intransigent Bodies - Still need to be able to set velocity
Replies: 2
Views: 3052

Re: Intransigent Bodies - Still need to be able to set veloc

Kinetic objects are not moved by the DynamicsWorld itself. Instead you need to give them a btMotionState (a custom derived version of course, since that is just a pure virtual interface class) that provides the new worldTransform whenever btMotionState::getWorldTransform() is called. Also, you need ...
by drleviathan
Mon Jun 29, 2015 1:54 pm
Forum: General Bullet Physics Support and Feedback
Topic: Importing shapes into Bullet
Replies: 4
Views: 5187

Re: Importing shapes into Bullet

As far as I know Bullet has no utilities for reading non-Bullet file formats. If you have an OBJ file then you'd have to find (or write) an OBJ parser and then write custom code to turn each mesh object into a btShape. Ideally you'd want to optimize the shapes: you wouldn't want to use a btBvhTriang...