Search found 549 matches

by drleviathan
Fri Sep 20, 2019 3:26 pm
Forum: General Bullet Physics Support and Feedback
Topic: Moving a rigid object to mouse position
Replies: 2
Views: 152

Re: Moving a rigid object to mouse position

I realized after writing it up: the algorithm above is limited to rotation and scale transformations. It doesn't handle translations. For that you have to use 4D vectors where each vector looks like: v = <x, y, z, 1> and you would need four pairs of corresponding points to build the two 4x4 matrices...
by drleviathan
Thu Sep 19, 2019 8:37 pm
Forum: General Bullet Physics Support and Feedback
Topic: Angulating a rigidBody not known
Replies: 3
Views: 112

Re: Angulating a rigidBody not known

What you're asking about is called "inverse kinematics". You know the final destination and the problem is to determine the path to get there, or whether a valid path exists or not. I don't have the time or expertise to write up tutorial here. I recommend you research the subject to see what info yo...
by drleviathan
Thu Sep 19, 2019 4:23 pm
Forum: General Bullet Physics Support and Feedback
Topic: Moving a rigid object to mouse position
Replies: 2
Views: 152

Re: Moving a rigid object to mouse position

This sounds a math question about how to transform from one frame to another. Given some 2D point on the screen (frameA) you want to compute the corresponding 3D point in the world-frame of the physics simulation (frameB). There exists a transform that does what you want such that: pointInB = transf...
by drleviathan
Thu Sep 19, 2019 4:01 pm
Forum: General Bullet Physics Support and Feedback
Topic: Angulating a rigidBody not known
Replies: 3
Views: 112

Re: Angulating a rigidBody not known

It is unclear to me exactly what you want to do so I will describe two solutions: (1) If you want a btRigidBody to "tumble" about some point at its end then you would set its center of mass (COM) at that point. The COM is the <0,0,0> point in the btCollisionShape's local frame, and it is the "transl...
by drleviathan
Thu Sep 05, 2019 6:03 am
Forum: General Bullet Physics Support and Feedback
Topic: Is Bullet Physics for Unity right for me? Subframe logic and callbacks.
Replies: 4
Views: 224

Re: Is Bullet Physics for Unity right for me? Subframe logic and callbacks.

Dead reckoning Sorry, I looked at the extrapolation code I have and decided: it is wrong. It could only ever work for objects whose inertia tensor has uniform eigenvalues (e.g. the inertia tensor of a sphere or similarly symmetric mass distribution), so I won't post it. A correct generalized versio...
by drleviathan
Wed Sep 04, 2019 7:19 pm
Forum: General Bullet Physics Support and Feedback
Topic: Is Bullet Physics for Unity right for me? Subframe logic and callbacks.
Replies: 4
Views: 224

Re: Is Bullet Physics for Unity right for me? Subframe logic and callbacks.

Subframe logic Bullet's CCD sweeps a spherical Proxy shape along the path of the center of the Object and if it hits something I think it (a) truncates the Object's forward motion by the fraction where the Proxy hit and (b) includes the sphere's contact points to those of the Object's contact manif...
by drleviathan
Tue Sep 03, 2019 4:44 am
Forum: General Bullet Physics Support and Feedback
Topic: Is Bullet Physics for Unity right for me? Subframe logic and callbacks.
Replies: 4
Views: 224

Re: Is Bullet Physics for Unity right for me? Subframe logic and callbacks.

Subframe logic You can't add new objects mid-subframe. Instead: at the beginning of each subframe add the fresh bullets in the right spots after you've done all of your math and logic. If you're really worried about "tunnelling" because of extrapolated bullet creation behind nearby targets then her...
by drleviathan
Fri Aug 30, 2019 3:49 am
Forum: General Bullet Physics Support and Feedback
Topic: Bullet as an external library
Replies: 3
Views: 333

Re: Bullet as an external library

What OS are you using? My main OS is linux and the build_cmake_single.sh script works for me. It builds all of the libs and examples. When it is done I have an actual executable file and a symbolic link to it: build_cmake/examples/TwoJoint/App_TwoJoint-2.88 build_cmake/examples/TwoJoint/App_TwoJoint...
by drleviathan
Wed Aug 28, 2019 2:40 am
Forum: General Bullet Physics Support and Feedback
Topic: Bullet as an external library
Replies: 3
Views: 333

Re: Bullet as an external library

TwoJoint is a stand-alone executable that uses the example utility code to make an in-process "physics server". In a while loop it submits "commands" to the server, steps the server, then harvests the results through the finite set of "handles" to its known demo objects. If you want to use the same ...
by drleviathan
Fri Aug 16, 2019 3:45 pm
Forum: General Bullet Physics Support and Feedback
Topic: Multi-Agent Representation
Replies: 1
Views: 250

Re: Multi-Agent Representation

If you're doing Deep Robotic Learning (DRI) and Human Robot Interactions (HRI) then you probably want to be using pybullet and asking your questions in the pybullet forum channel.
by drleviathan
Thu Aug 15, 2019 4:10 pm
Forum: General Bullet Physics Support and Feedback
Topic: Attribute ?
Replies: 1
Views: 224

Re: Attribute ?

The statement: "when I add a polygon to a btTriangleShape" does not quite make sense. A btTriangleShape is just a triangle with three vertices and doesn't have polygons. Perhaps you meant a btTriangleMeshShape? btTriangleMeshShape is a pure virtual base class. The first non-virtual derived class is ...
by drleviathan
Thu Aug 15, 2019 3:28 pm
Forum: General Bullet Physics Support and Feedback
Topic: Problems occurred when the validation of the Bullet's accuracy with a bouncing ball test
Replies: 5
Views: 395

Re: Problems occurred when the validation of the Bullet's accuracy with a bouncing ball test

It has been reported in previous forum posts (which I wasn't able to find with a quick search) that an object will sometimes NOT bounce on collision when the substep is too small. Since I couldn't find those threads I have to rely on my memory which tells me the problem was seen at substeps of 1/100...
by drleviathan
Tue Aug 13, 2019 4:56 pm
Forum: General Bullet Physics Support and Feedback
Topic: Problems occurred when the validation of the Bullet's accuracy with a bouncing ball test
Replies: 5
Views: 395

Re: Problems occurred when the validation of the Bullet's accuracy with a bouncing ball test

This might affect things, you'll have to test: I don't think your world->stepSimulation() is doing what you think it is. You're specifying the "step" but not the "substep" duration and hence it uses the default substep of 1/60 sec. So your world "steps" forward in 1/600 sec increments and does nothi...
by drleviathan
Mon Aug 12, 2019 2:50 pm
Forum: General Bullet Physics Support and Feedback
Topic: Problems occurred when the validation of the Bullet's accuracy with a bouncing ball test
Replies: 5
Views: 395

Re: Problems occurred when the validation of the Bullet's accuracy with a bouncing ball test

I dunno the answer but I have some questions about your simulation: (1) What was your simulation stepping strategy? Fixed substep? If so, what was its duration? How man max substeps? (2) Are you using single or double precision? (3) Your ball was an implicit btSphereShape , I assume, but what shape ...
by drleviathan
Tue Aug 06, 2019 9:54 pm
Forum: General Bullet Physics Support and Feedback
Topic: Soft Body rendering from OBJ model (data extraction)
Replies: 2
Views: 291

Re: Soft Body rendering from OBJ model (data extraction)

I started looking at the btSoftBody code to see if I could provide some insight. I don't fully understand it yet but it looks like btSoftBody::m_faces is a btAllignedObjectArray<btSoftBody::Face> and a Face is a "triangle" that has pointers to three Nodes . struct Face : Feature { Node* m_n[3]; // N...