Search found 460 matches

by drleviathan
Sat Dec 08, 2018 5:54 pm
Forum: General Bullet Physics Support and Feedback
Topic: (conceptual) question about contact point generation
Replies: 2
Views: 65

Re: (conceptual) question about contact point generation

A good place to start would be a youtube video that shows the Bullet collision margin and how that changes the effective shape during collisions. The video points out Box-Box collisions don't use the margins, however Box-Sphere collisions do:

https://www.youtube.com/watch?v=BGAwRKPlpCw&t=2s
by drleviathan
Thu Dec 06, 2018 7:22 pm
Forum: General Bullet Physics Support and Feedback
Topic: Separate colliders and rigidbodies?
Replies: 4
Views: 66

Re: Separate colliders and rigidbodies?

I see. Then I think the translation from Unity's component system to Bullet would go something like this: Object with RigidBody and Collider components --> dynamic Bullet RigidBody with Shape Object with RigidBody component --> dynamic Bullet RigidBody with Shape but set collisionless Object with Co...
by drleviathan
Thu Dec 06, 2018 4:03 pm
Forum: General Bullet Physics Support and Feedback
Topic: Separate colliders and rigidbodies?
Replies: 4
Views: 66

Re: Separate colliders and rigidbodies?

I don't understand your distinctions between Unity (which is a game platform and can be configured to use Bullet for its physics engine) and Bullet (which is just a physics engine). It sounds to me like you're confusing the RigidBody (which would be your Collider) with a GameObject (which would repr...
by drleviathan
Wed Dec 05, 2018 4:08 pm
Forum: General Bullet Physics Support and Feedback
Topic: Performance problems
Replies: 2
Views: 130

Re: Performance problems

Alternatively, you could use the CProfileManager API to get some detailed information about where the time is being spent. Look in the btQuickprof.h file for see its API. In short you can call CProfileManager::reset() before your stepSimulation(), then CProfileManager::dumpAll() after.
by drleviathan
Tue Dec 04, 2018 12:00 am
Forum: General Bullet Physics Support and Feedback
Topic: Trouble with ray testing
Replies: 2
Views: 97

Re: Trouble with ray testing

In my experience that "Overflow in AABB, object removed from simulation" assert happens when NaN has been injected into the system. I've seen this happen in two ways: (a) dividing by zero somewhere or (b) every frame: using a transform to compute its new value and then neglecting to renormalize it.
by drleviathan
Fri Nov 16, 2018 4:51 pm
Forum: General Bullet Physics Support and Feedback
Topic: Problems with unstable rotation
Replies: 2
Views: 136

Re: Problems with unstable rotation

What are the values of BoxExtent ? If the eigenvalues of the inertia tensor have a high, mid, and low value AND you rotate the object around the axis parallel to eigenvector that corresponds to the "mid" eigenvalue then there is a natural instability where the spinning object will flip like that. Fo...
by drleviathan
Mon Nov 12, 2018 3:15 am
Forum: General Bullet Physics Support and Feedback
Topic: Poor performance when ghost object overlaps many btBoxShapes [with video]
Replies: 5
Views: 255

Re: Poor performance when ghost object overlaps many btBoxShapes [with video]

I wouldn't be surprised to learn that several btPairCachingGhostObjects each overlapping several other objects could put a heavy load on Bullet's simulation. Here is some ideas that might be helpful: (1) By default Bullet will update every Aabb of every static object every substep. Normally this def...
by drleviathan
Sun Nov 04, 2018 11:48 am
Forum: General Bullet Physics Support and Feedback
Topic: Client-side prediction of networked RaycastVehicle
Replies: 2
Views: 188

Re: Client-side prediction of networked RaycastVehicle

the body will disappear, to never come back even when the next update arrives
It sounds to me like there is an instability in your simulation. When NaN gets injected into BulletC++ it crashes but the JS implementation you are using may misbehave in other ways.
by drleviathan
Fri Nov 02, 2018 3:17 pm
Forum: General Bullet Physics Support and Feedback
Topic: Why bullet proposes value to clamp number of substeps?
Replies: 1
Views: 92

Re: Why bullet proposes value to clamp number of substeps?

There is a phenomenon known as the "physics simulation spiral of death" where the real time to compute the world's next state is larger than the timestep itself. On each step the simulation falls further behind. This can happen when the world has too many objects or the objects are too complex. A si...
by drleviathan
Tue Sep 18, 2018 3:14 pm
Forum: General Bullet Physics Support and Feedback
Topic: I need help
Replies: 2
Views: 317

Re: I need help

Yes, the angular velocity is capped for safety. Yes, you can change it. This thread has the info you seek.
by drleviathan
Fri Sep 07, 2018 3:46 pm
Forum: General Bullet Physics Support and Feedback
Topic: Convert mesh into dynamics data
Replies: 2
Views: 369

Re: Convert mesh into dynamics data

I too would like to have a really smart convex-decomposition tool that could suggest optimized shape approximations for mesh sub parts. I'll probably eventually try to write one myself but I think it is a year or two down the road. I've got a few ideas on how one would go about it, but they are most...
by drleviathan
Fri Sep 07, 2018 3:32 pm
Forum: General Bullet Physics Support and Feedback
Topic: Make gravity force opposite normal
Replies: 1
Views: 234

Re: Make gravity force opposite normal

Do you mean: "How to implement a planet's gravitational field in Bullet?" ? If so, here is some info: Bullet has a World gravity setting ( btDiscreteDynamicsWorld::setGravity() ) but it is uniform. You can override the World gravity on a per-object basis: btRigidBody::setGravity() . For a radial gra...
by drleviathan
Thu Sep 06, 2018 4:03 pm
Forum: General Bullet Physics Support and Feedback
Topic: Basic concave collision detection question
Replies: 1
Views: 269

Re: Basic concave collision detection question

btBvhTriangleMeshShape works fine for collisions with other shapes. However, RigidBodies that use btBvhTriangleMeshShape must be static , they can't be dynamic or kinematic. The reason, I think, is that Bullet has not implemented the btBvhTriangleMeshShape vs btBvhTriangleMeshShape collision algorit...
by drleviathan
Sun Sep 02, 2018 6:18 am
Forum: General Bullet Physics Support and Feedback
Topic: btRaycastVehicle roll after collision with wall
Replies: 4
Views: 419

Re: btRaycastVehicle roll after collision with wall

The extra low center of mass (COM) might be contributing to its "hop" into the air on collisions. Maybe try dialing it higher to see how it affects that problem. Perhaps there is a sweet spot for how low to make the COM. Dunno if these other ideas will work but they are what I would try: (1) Increas...
by drleviathan
Fri Aug 31, 2018 10:54 pm
Forum: General Bullet Physics Support and Feedback
Topic: btRaycastVehicle roll after collision with wall
Replies: 4
Views: 419

Re: btRaycastVehicle roll after collision with wall

I have one idea you could try: Give the vehicle a very low center of mass (COM). It is pretty easy to do this by wrapping your existing shape with a btCompoundShape. You can even put the COM outside the bounds of the body, below the wheels, which would make it automatically self-righting (unflippabl...