Reseting dynamic object's motion?

[suckho]

I'm very new to Bullet and I guess this is very basic (read: stupid) question, but I couldn't find the answer anywhere so here it comes..

I started integrating Bullet to my 3D engine and actually managed to do lot of things right.. My test scene consists of couple of static/kinematic 3d objects and 100 dynamic primitive shapes falling over them. These 100 falling objects are somewhere at Y=100 meters height in the beginning and then drop in free fall.

I wanted to prevent objects falling "away" so I did a check like "if (y<0) resetObject()", but couldnt get it working. My PhysObject class is derived from btMotionState and uses that for sync between gfx and phys engines. The problem is that I dont know how to reset dynamic btRigidBody's motionstate WITHOUT interpolation. I mean that when object is dropped to Y=0 level, I want it to warp back to Y=100 without interpolation and reset it's motion state (velocity, angular velocity, position, rotation, etc).

What is the proper way to do this? Let's say if I want to write a resetObject() function, what calls to btRigidBody should it include to reset everything to the state body were after creation? I want to keep the same instance, so making new object is not acceptable solution.

Thanks in advance.. I'll continue to figure this out by myself but any help is appreciated..

[suckho]

I think it works now, but I'm still not sure if this is done by the book.. Something missing? Something too much? Do I need to set those interpolation values?

Code: Select all

void BulletPhysObject::ResetMotionState()
{	
	btTransform t;
	Quaternion rot(geomNode->GetWorldToLocalMatrix());
	Vector4 pos=geomNode->GetLocalPosInWorldSpace(Vector4(0.0f,0.0f,0.0f,1.0f));
	t.setRotation(btQuaternion(rot.x, rot.y, rot.z, rot.w));
	t.setOrigin(btVector3(pos.x, pos.y, pos.z));
		
	body->setWorldTransform(t);
	body->setLinearVelocity(btVector3(0.0f,0.0f,0.0f));
	body->setAngularVelocity(btVector3(0.0f,0.0f,0.0f));
	
	body->setInterpolationWorldTransform(body->getWorldTransform());
	body->setInterpolationLinearVelocity(body->getLinearVelocity());
	body->setInterpolationAngularVelocity(body->getAngularVelocity());

	body->clearForces();
	body->activate();	
}

[suckho]

No.. It doesnt work.. Even if I try to reset object's motion this way I keep getting "old" values through MotionState's setWorldTransform().. Any ideas how this should be done?

[rrck]

Try to set transform using setCenterOfMassTransform (instead of setTransform) after resetting velocities.