How to rotate an object in Bullet Physics

Question

Here I have a problem with object rotation in Bullet. What I want to implement is to rotate an object around global x,y,z axis at the same time. (here global means the axis x,y,z will not be changed during rotation) I have the code below

btQuaternion m_lastRot;
btTransform tranf =  _obj[idx]->mp_btRidObj->getCenterOfMassTransform();
tranf.getBasis().getRotation(m_lastRot);
btQuaternion qx(btVector3(1,0,0),angX);
btQuaternion qy(btVector3(0,1,0),angY);
btQuaternion qz(btVector3(0,0,1),angZ);
tranf.setRotation(qz * qy * qx * m_lastRot);
_obj[idx]->mp_btRidObj->setCenterOfMassTransform(tranf);

But it does not work as I expected. By the way, the code below which rotateing a object around one of x,y,z axis each time works well.

btQuaternion m_lastRot;
btTransform tranf =  _obj[idx]->mp_btRidObj->getCenterOfMassTransform();
tranf.getBasis().getRotation(_obj[idx]->m_lastRot);
btQuaternion qx(btVector3(1,0,0),angX);
btQuaternion qy(btVector3(0,1,0),angY);
btQuaternion qz(btVector3(0,0,1),angZ);
if(x)
tranf.setRotation(qx * m_lastRot);
else if(y)
tranf.setRotation(qy * m_lastRot);
else if(z)
tranf.setRotation(qz * m_lastRot);

_obj[idx]->mp_btRidObj->setCenterOfMassTransform(tranf);

Is there anyone can tell me how to solve this problem?

related http://stackoverflow.com/questions/8196634/how-to-apply-rotation-to-a-body-in-bullet-physics-engine — Ciro Santilli OurBigBook.com, May 02 '16 at 11:18

score 1 · Answer 1 · answered Dec 09 '14 at 05:58

1

I do it like this:

//this is my bullet object currently reading data from:
bulletobject->getMotionState()->getWorldTransform(trans);
btQuaternion rot = trans.getRotation();
myquat.w = rot.w();
myquat.x = rot.x();
myquat.y = rot.z();
myquat.z = rot.y();
//I then apply the quat to my object that I want to move in my graphics application.

you have to remember to get the 'w' also if you do it this way, if not the rotations will be wrong.

answered Dec 09 '14 at 05:58

IAmNoone

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Although I haven't tried your method but I have a question that it seems your "myquat"is just from the quaternion of the object, have you changed the value of "myquat" before you apply it to your object? – Peng Yang Dec 11 '14 at 17:14

score 0 · Answer 2 · answered Dec 08 '14 at 20:20

0

In Jbullet I belive there is a method called setOrientation(Quat4f r) implemented in Bullet RigidBody that does what you want. I assume it's also in the standard Bullet lib.

answered Dec 08 '14 at 20:20

new Objekt

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Thanks for your reply.I have tried to find a function named setOrientation but I have not found it at least in rigidbody class.Instead, I have found an alternative way to solve the problem.Thank you all the same. – Peng Yang Dec 11 '14 at 17:20
Go ahead and add your solution as an anwser to the question for anyone else who happens upoun this while searching then. Sorry I wasn't of much help and good luck with your project. – new Objekt Dec 11 '14 at 18:03

How to rotate an object in Bullet Physics

2 Answers2