Real-Time Physics Simulation Forum

When I look at the btGeneric6DofSpring2Constraint code I see many parameters that can be changed. Most of these have default values assigned in the various helper class ctors, while the frameInA and frameInB parameters are required input to the btGeneric6DofSpring2Constrain ctor. Those frame paramet...

When you move a kinematic object you don't need to give it non-zero velocities. If you do set its velocities non-zero it doesn't necessarily move forward in that way. Instead whenever the RigidBody needs to know its new transform external code must supply it (this is usually done via the MotionState...

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...

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...

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...

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...

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...

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...

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...

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...

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 ...

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.

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 ...

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...

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...