added angular limits to the Generic D6 constraint. Works for small angles. Will add a check for different combinations, and use different extraction of ordering of rotation from the diff quaternion.

Improved vehicle interpolation of wheels, and added Z-up axis option for the Demo
made 'getWorldTransform' const method in btMotionState
added future 'deactivationCallback'(not used yet)

Demos/ConstraintDemo/ConstraintDemo.cpp

@@ -47,8 +47,10 @@ int main(int argc,char** argv)
 }
 
 btTransform sliderTransform;
-btVector3 lowerSliderLimit = btVector3(-20,0,0);
+btVector3 lowerSliderLimit = btVector3(0,0,0);
-btVector3 hiSliderLimit = btVector3(10,0,0);
+btVector3 hiSliderLimit = btVector3(0,0,0);
+
+btRigidBody* d6body0 =0;
 
 void	drawLimit()
 {
@@ -59,9 +61,18 @@ void	drawLimit()
 		glColor3f(color.getX(), color.getY(), color.getZ());
 		glVertex3d(from.getX(), from.getY(), from.getZ());
 		glVertex3d(to.getX(), to.getY(), to.getZ());
+		if (d6body0)
+		{
+			from = d6body0->getWorldTransform().getOrigin();
+			to = from + d6body0->getWorldTransform().getBasis() * btVector3(0,0,10);
+			glVertex3d(from.getX(), from.getY(), from.getZ());
+			glVertex3d(to.getX(), to.getY(), to.getZ());
+		}
 		glEnd();
 }
 
+
+
 void	ConstraintDemo::initPhysics()
 {
 	//ConstraintSolver* solver = new btSequentialImpulseConstraintSolver;
@@ -108,26 +119,31 @@ void	ConstraintDemo::initPhysics()
 	{
 		mass = 1.f;
 		btVector3 sliderWorldPos(0,10,0);
-		btVector3 sliderAxis(0,0,1);
+		btVector3 sliderAxis(1,0,0);
-		btScalar angle=SIMD_RADS_PER_DEG * 10.f;
+		btScalar angle=0.f;//SIMD_RADS_PER_DEG * 10.f;
 		btMatrix3x3 sliderOrientation(btQuaternion(sliderAxis ,angle));
+		trans.setIdentity();
 		trans.setOrigin(sliderWorldPos);
-		trans.setBasis(sliderOrientation);
+		//trans.setBasis(sliderOrientation);
 		sliderTransform = trans;
 
-		btRigidBody* body0 = localCreateRigidBody( mass,trans,shape);
+		d6body0 = localCreateRigidBody( mass,trans,shape);
-		body0->setActivationState(DISABLE_DEACTIVATION);
+		d6body0->setActivationState(DISABLE_DEACTIVATION);
 		btRigidBody* fixedBody1 = localCreateRigidBody(0,trans,0);
 
 		btTransform frameInA, frameInB;
 		frameInA = btTransform::getIdentity();
 		frameInB = btTransform::getIdentity();
 		
-		btGeneric6DofConstraint* slider = new btGeneric6DofConstraint(*body0,*fixedBody1,frameInA,frameInB);
+		btGeneric6DofConstraint* slider = new btGeneric6DofConstraint(*d6body0,*fixedBody1,frameInA,frameInB);
 		slider->setLinearLowerLimit(lowerSliderLimit);
 		slider->setLinearUpperLimit(hiSliderLimit);
-		slider->setAngularLowerLimit(btVector3(1e30,0,0));
+//		slider->setAngularLowerLimit(btVector3(-3.1415*0.5f,0,0));
-		slider->setAngularUpperLimit(btVector3(-1e30,0,0));
+//		slider->setAngularUpperLimit(btVector3(3.1415*0.5f,0,0));
+
+		//range should be small, otherwise singularities will 'explode' the constraint
+		slider->setAngularLowerLimit(btVector3(0,-3.1415*0.25f,-3.1415*0.25f));
+		slider->setAngularUpperLimit(btVector3(0,3.1415*0.25f,3.1415*0.25f));
 
 		m_dynamicsWorld->addConstraint(slider);
 

Demos/VehicleDemo/VehicleDemo.cpp

@@ -301,7 +301,7 @@ void VehicleDemo::renderme()
 	for (i=0;i<m_vehicle->getNumWheels();i++)
 	{
 		//synchronize the wheels with the (interpolated) chassis worldtransform
-		m_vehicle->updateWheelTransform(i);
+		m_vehicle->updateWheelTransform(i,true);
 		//draw wheels (cylinders)
 		m_vehicle->getWheelInfo(i).m_worldTransform.getOpenGLMatrix(m);
 		GL_ShapeDrawer::drawOpenGL(m,&wheelShape,wheelColor,getDebugMode());
@@ -323,11 +323,14 @@ void VehicleDemo::clientMoveAndDisplay()
 	if (m_dynamicsWorld)
 	{
 		//during idle mode, just run 1 simulation step maximum
-		int maxSimSubSteps = m_idle ? 1 : 1;
+		int maxSimSubSteps = m_idle ? 1 : 2;
 		if (m_idle)
 			dt = 1.0/420.f;
 
 		int numSimSteps = m_dynamicsWorld->stepSimulation(dt,maxSimSubSteps);
+
+#define VERBOSE_FEEDBACK
+#ifdef VERBOSE_FEEDBACK
 		if (!numSimSteps)
 			printf("Interpolated transforms\n");
 		else
@@ -341,6 +344,7 @@ void VehicleDemo::clientMoveAndDisplay()
 				printf("Simulated (%i) steps\n",numSimSteps);
 			}
 		}
+#endif //VERBOSE_FEEDBACK
 
 	}
 
@@ -384,16 +388,20 @@ void VehicleDemo::clientMoveAndDisplay()
 void VehicleDemo::displayCallback(void) 
 {
 
+	clientMoveAndDisplay();
+	return;
+
 	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 
 
 
 	
-	m_dynamicsWorld->updateAabbs();
+	//m_dynamicsWorld->updateAabbs();
+	
 	//draw contactpoints
 	//m_physicsEnvironmentPtr->CallbackTriggers();
 
 
-	renderme();
+	//renderme();
 
 
 	glFlush();
@@ -416,7 +424,7 @@ void VehicleDemo::clientResetScene()
 		for (int i=0;i<m_vehicle->getNumWheels();i++)
 		{
 			//synchronize the wheels with the (interpolated) chassis worldtransform
-			m_vehicle->updateWheelTransform(i);
+			m_vehicle->updateWheelTransform(i,true);
 		}
 	}
 

src/BulletDynamics/ConstraintSolver/btGeneric6DofConstraint.cpp

@@ -127,6 +127,52 @@ void btGeneric6DofConstraint::buildJacobian()
 	}
 }
 
+float getMatrixElem(const btMatrix3x3& mat,int index)
+{
+	int row = index%3;
+	int col = index / 3;
+	return mat[row][col];
+}
+
+///MatrixToEulerXYZ from http://www.geometrictools.com/LibFoundation/Mathematics/Wm4Matrix3.inl.html
+bool	MatrixToEulerXYZ(const btMatrix3x3& mat,btVector3& xyz)
+{
+    // rot =  cy*cz          -cy*sz           sy
+    //        cz*sx*sy+cx*sz  cx*cz-sx*sy*sz -cy*sx
+    //       -cx*cz*sy+sx*sz  cz*sx+cx*sy*sz  cx*cy
+
+///	0..8
+
+	 if (getMatrixElem(mat,2) < 1.0f)
+    {
+        if (getMatrixElem(mat,2) > -1.0f)
+        {
+            xyz[0] = btAtan2(-getMatrixElem(mat,5),getMatrixElem(mat,8));
+            xyz[1] = btAsin(getMatrixElem(mat,2));
+            xyz[2] = btAtan2(-getMatrixElem(mat,1),getMatrixElem(mat,0));
+            return true;
+        }
+        else
+        {
+            // WARNING.  Not unique.  XA - ZA = -atan2(r10,r11)
+            xyz[0] = -btAtan2(getMatrixElem(mat,3),getMatrixElem(mat,4));
+            xyz[1] = -SIMD_HALF_PI;
+            xyz[2] = 0.0f;
+            return false;
+        }
+    }
+    else
+    {
+        // WARNING.  Not unique.  XAngle + ZAngle = atan2(r10,r11)
+        xyz[0] = btAtan2(getMatrixElem(mat,3),getMatrixElem(mat,4));
+        xyz[1] = SIMD_HALF_PI;
+        xyz[2] = 0.0;
+        return false;
+    }
+	 return false;
+}
+
+
 void	btGeneric6DofConstraint::solveConstraint(btScalar	timeStep)
 {
 	btScalar tau = 0.1f;
@@ -201,6 +247,18 @@ void	btGeneric6DofConstraint::solveConstraint(btScalar	timeStep)
 		}
 	}
 
+	btVector3	axis;
+	btScalar	angle;
+	btTransform	frameAWorld = m_rbA.getCenterOfMassTransform() * m_frameInA;
+	btTransform	frameBWorld = m_rbB.getCenterOfMassTransform() * m_frameInB;
+
+	btTransformUtil::calculateDiffAxisAngle(frameAWorld,frameBWorld,axis,angle);
+	btQuaternion diff(axis,angle);
+	btMatrix3x3 diffMat (diff);
+	btVector3 xyz;
+	///this is not perfect, we can first check which axis are limited, and choose a more appropriate order
+	MatrixToEulerXYZ(diffMat,xyz);
+
 	// angular
 	for (i=0;i<3;i++)
 	{
@@ -221,6 +279,35 @@ void	btGeneric6DofConstraint::solveConstraint(btScalar	timeStep)
 
 			btScalar rel_pos = kSign[i] * axisA.dot(axisB);
 
+			btScalar	lo = -1e30f;
+			btScalar	hi = 1e30f;
+		
+			//handle the twist limit
+			if (m_lowerLimit[i+3] < m_upperLimit[i+3])
+			{
+				//clamp the values
+				btScalar loLimit =  m_upperLimit[i+3] > -3.1415 ? m_lowerLimit[i+3] : -1e30f;
+				btScalar hiLimit = m_upperLimit[i+3] < 3.1415 ? m_upperLimit[i+3] : 1e30f;
+
+				float projAngle  = -2.*xyz[i];
+				
+				if (projAngle < loLimit)
+				{
+					hi = 0.f;
+					rel_pos = (loLimit - projAngle);
+				} else
+				{
+					if (projAngle > hiLimit)
+					{
+						lo = 0.f;
+						rel_pos = (hiLimit - projAngle);
+					} else
+					{
+						continue;
+					}
+				}
+			}
+		
 			//impulse
 			btScalar impulse = -(tau*rel_pos/timeStep + damping*rel_vel) * jacDiagABInv;
 			m_accumulatedImpulse[i + 3] += impulse;

src/BulletDynamics/Dynamics/btDiscreteDynamicsWorld.cpp

@@ -120,40 +120,7 @@ void	btDiscreteDynamicsWorld::synchronizeMotionStates()
 {
 	//debug vehicle wheels
 	
-	if (getDebugDrawer() && getDebugDrawer()->getDebugMode() & btIDebugDraw::DBG_DrawWireframe)
+	
-	{
-		for (unsigned int i=0;i<this->m_vehicles.size();i++)
-		{
-			for (int v=0;v<m_vehicles[i]->getNumWheels();v++)
-			{
-				btVector3 wheelColor(0,255,255);
-				if (m_vehicles[i]->getWheelInfo(v).m_raycastInfo.m_isInContact)
-				{
-					wheelColor.setValue(0,0,255);
-				} else
-				{
-					wheelColor.setValue(255,0,255);
-				}
-
-				//synchronize the wheels with the (interpolated) chassis worldtransform
-				m_vehicles[i]->updateWheelTransform(v);
-					
-				btVector3 wheelPosWS = m_vehicles[i]->getWheelInfo(v).m_worldTransform.getOrigin();
-
-				btVector3 axle = btVector3(	
-					m_vehicles[i]->getWheelInfo(v).m_worldTransform.getBasis()[0][m_vehicles[i]->getRightAxis()],
-					m_vehicles[i]->getWheelInfo(v).m_worldTransform.getBasis()[1][m_vehicles[i]->getRightAxis()],
-					m_vehicles[i]->getWheelInfo(v).m_worldTransform.getBasis()[2][m_vehicles[i]->getRightAxis()]);
-
-
-				//m_vehicles[i]->getWheelInfo(v).m_raycastInfo.m_wheelAxleWS
-				//debug wheels (cylinders)
-				m_debugDrawer->drawLine(wheelPosWS,wheelPosWS+axle,wheelColor);
-				m_debugDrawer->drawLine(wheelPosWS,m_vehicles[i]->getWheelInfo(v).m_raycastInfo.m_contactPointWS,wheelColor);
-
-			}
-		}
-	}
 	{
 		//todo: iterate over awake simulation islands!
 		for (unsigned int i=0;i<m_collisionObjects.size();i++)
@@ -196,6 +163,40 @@ void	btDiscreteDynamicsWorld::synchronizeMotionStates()
 		}
 	}
 
+	if (getDebugDrawer() && getDebugDrawer()->getDebugMode() & btIDebugDraw::DBG_DrawWireframe)
+	{
+		for (unsigned int i=0;i<this->m_vehicles.size();i++)
+		{
+			for (int v=0;v<m_vehicles[i]->getNumWheels();v++)
+			{
+				btVector3 wheelColor(0,255,255);
+				if (m_vehicles[i]->getWheelInfo(v).m_raycastInfo.m_isInContact)
+				{
+					wheelColor.setValue(0,0,255);
+				} else
+				{
+					wheelColor.setValue(255,0,255);
+				}
+
+				//synchronize the wheels with the (interpolated) chassis worldtransform
+				m_vehicles[i]->updateWheelTransform(v,true);
+					
+				btVector3 wheelPosWS = m_vehicles[i]->getWheelInfo(v).m_worldTransform.getOrigin();
+
+				btVector3 axle = btVector3(	
+					m_vehicles[i]->getWheelInfo(v).m_worldTransform.getBasis()[0][m_vehicles[i]->getRightAxis()],
+					m_vehicles[i]->getWheelInfo(v).m_worldTransform.getBasis()[1][m_vehicles[i]->getRightAxis()],
+					m_vehicles[i]->getWheelInfo(v).m_worldTransform.getBasis()[2][m_vehicles[i]->getRightAxis()]);
+
+
+				//m_vehicles[i]->getWheelInfo(v).m_raycastInfo.m_wheelAxleWS
+				//debug wheels (cylinders)
+				m_debugDrawer->drawLine(wheelPosWS,wheelPosWS+axle,wheelColor);
+				m_debugDrawer->drawLine(wheelPosWS,m_vehicles[i]->getWheelInfo(v).m_raycastInfo.m_contactPointWS,wheelColor);
+
+			}
+		}
+	}
 
 }
 
@@ -218,8 +219,15 @@ int	btDiscreteDynamicsWorld::stepSimulation( float timeStep,int maxSubSteps, flo
 		//variable timestep
 		fixedTimeStep = timeStep;
 		m_localTime = timeStep;
-		numSimulationSubSteps = 1;
+		if (btFuzzyZero(timeStep))
-		maxSubSteps = 1;
+		{
+			numSimulationSubSteps = 0;
+			maxSubSteps = 0;
+		} else
+		{
+			numSimulationSubSteps = 1;
+			maxSubSteps = 1;
+		}
 	}
 
 	//process some debugging flags
@@ -227,7 +235,7 @@ int	btDiscreteDynamicsWorld::stepSimulation( float timeStep,int maxSubSteps, flo
 	{
 		gDisableDeactivation = (getDebugDrawer()->getDebugMode() & btIDebugDraw::DBG_NoDeactivation) != 0;
 	}
-	if (!btFuzzyZero(timeStep) && numSimulationSubSteps)
+	if (numSimulationSubSteps)
 	{
 
 		saveKinematicState(fixedTimeStep);
@@ -238,6 +246,7 @@ int	btDiscreteDynamicsWorld::stepSimulation( float timeStep,int maxSubSteps, flo
 		for (int i=0;i<clampedSimulationSteps;i++)
 		{
 			internalSingleStepSimulation(fixedTimeStep);
+			synchronizeMotionStates();
 		}
 
 	} 
@@ -266,20 +275,23 @@ void	btDiscreteDynamicsWorld::internalSingleStepSimulation(float timeStep)
 	btContactSolverInfo infoGlobal;
 	infoGlobal.m_timeStep = timeStep;
 	
+
+
 	///solve non-contact constraints
 	solveNoncontactConstraints(infoGlobal);
 	
 	///solve contact constraints
 	solveContactConstraints(infoGlobal);
 
-	///update vehicle simulation
-	updateVehicles(timeStep);
-	
 	///CallbackTriggers();
 
 	///integrate transforms
 	integrateTransforms(timeStep);
-		
+
+	///update vehicle simulation
+	updateVehicles(timeStep);
+
+
 	updateActivationState( timeStep );
 
 	

src/BulletDynamics/Vehicle/btRaycastVehicle.cpp

@@ -76,8 +76,8 @@ btWheelInfo&	btRaycastVehicle::addWheel( const btVector3& connectionPointCS, con
 	
 	btWheelInfo& wheel = m_wheelInfo[getNumWheels()-1];
 	
-	updateWheelTransformsWS( wheel );
+	updateWheelTransformsWS( wheel , false );
-	updateWheelTransform(getNumWheels()-1);
+	updateWheelTransform(getNumWheels()-1,false);
 	return wheel;
 }
 
@@ -92,15 +92,18 @@ const btTransform&	btRaycastVehicle::getWheelTransformWS( int wheelIndex ) const
 
 }
 
-void	btRaycastVehicle::updateWheelTransform( int wheelIndex )
+void	btRaycastVehicle::updateWheelTransform( int wheelIndex , bool interpolatedTransform)
 {
 	
 	btWheelInfo& wheel = m_wheelInfo[ wheelIndex ];
-	updateWheelTransformsWS(wheel);
+	updateWheelTransformsWS(wheel,interpolatedTransform);
 	btVector3 up = -wheel.m_raycastInfo.m_wheelDirectionWS;
 	const btVector3& right = wheel.m_raycastInfo.m_wheelAxleWS;
 	btVector3 fwd = up.cross(right);
 	fwd = fwd.normalize();
+//	up = right.cross(fwd);
+//	up.normalize();
+
 	//rotate around steering over de wheelAxleWS
 	float steering = wheel.m_steering;
 	
@@ -139,16 +142,16 @@ void btRaycastVehicle::resetSuspension()
 	}
 }
 
-void	btRaycastVehicle::updateWheelTransformsWS(btWheelInfo& wheel )
+void	btRaycastVehicle::updateWheelTransformsWS(btWheelInfo& wheel , bool interpolatedTransform)
 {
 	wheel.m_raycastInfo.m_isInContact = false;
 
-	btTransform chassisTrans;
+	btTransform chassisTrans = getChassisWorldTransform();
-	if (getRigidBody()->getMotionState())
+	if (interpolatedTransform && (getRigidBody()->getMotionState()))
+	{
 		getRigidBody()->getMotionState()->getWorldTransform(chassisTrans);
-	else
+	}
-		chassisTrans = getRigidBody()->getCenterOfMassTransform();
+
-	
 	wheel.m_raycastInfo.m_hardPointWS = chassisTrans( wheel.m_chassisConnectionPointCS );
 	wheel.m_raycastInfo.m_wheelDirectionWS = chassisTrans.getBasis() *  wheel.m_wheelDirectionCS ;
 	wheel.m_raycastInfo.m_wheelAxleWS = chassisTrans.getBasis() * wheel.m_wheelAxleCS;
@@ -156,7 +159,7 @@ void	btRaycastVehicle::updateWheelTransformsWS(btWheelInfo& wheel )
 
 btScalar btRaycastVehicle::rayCast(btWheelInfo& wheel)
 {
-	updateWheelTransformsWS( wheel );
+	updateWheelTransformsWS( wheel,false);
 
 	
 	btScalar depth = -1;
@@ -240,12 +243,35 @@ btScalar btRaycastVehicle::rayCast(btWheelInfo& wheel)
 }
 
 
+const btTransform& btRaycastVehicle::getChassisWorldTransform() const
+{
+	/*if (getRigidBody()->getMotionState())
+	{
+		btTransform chassisWorldTrans;
+		getRigidBody()->getMotionState()->getWorldTransform(chassisWorldTrans);
+		return chassisWorldTrans;
+	}
+	*/
+
+	
+	return getRigidBody()->getCenterOfMassTransform();
+}
+
+
 void btRaycastVehicle::updateVehicle( btScalar step )
 {
+	{
+		for (int i=0;i<getNumWheels();i++)
+		{
+			updateWheelTransform(i,false);
+		}
+	}
+
 
 	m_currentVehicleSpeedKmHour = 3.6f * getRigidBody()->getLinearVelocity().length();
 	
-	const btTransform& chassisTrans = getRigidBody()->getCenterOfMassTransform();
+	const btTransform& chassisTrans = getChassisWorldTransform();
+
 	btVector3 forwardW (
 		chassisTrans.getBasis()[0][m_indexForwardAxis],
 		chassisTrans.getBasis()[1][m_indexForwardAxis],
@@ -305,10 +331,12 @@ void btRaycastVehicle::updateVehicle( btScalar step )
 
 		if (wheel.m_raycastInfo.m_isInContact)
 		{
+			const btTransform&	chassisWorldTransform = getChassisWorldTransform();
+
 			btVector3 fwd (
-				getRigidBody()->getCenterOfMassTransform().getBasis()[0][m_indexForwardAxis],
+				chassisWorldTransform.getBasis()[0][m_indexForwardAxis],
-				getRigidBody()->getCenterOfMassTransform().getBasis()[1][m_indexForwardAxis],
+				chassisWorldTransform.getBasis()[1][m_indexForwardAxis],
-				getRigidBody()->getCenterOfMassTransform().getBasis()[2][m_indexForwardAxis]);
+				chassisWorldTransform.getBasis()[2][m_indexForwardAxis]);
 
 			btScalar proj = fwd.dot(wheel.m_raycastInfo.m_contactNormalWS);
 			fwd -= wheel.m_raycastInfo.m_contactNormalWS * proj;

src/BulletDynamics/Vehicle/btRaycastVehicle.h

@@ -68,9 +68,8 @@ public:
 	virtual ~btRaycastVehicle() ;
 
 		
-
+	const btTransform& getChassisWorldTransform() const;
-
+	
-
 	btScalar rayCast(btWheelInfo& wheel);
 
 	virtual void updateVehicle(btScalar step);
@@ -86,7 +85,7 @@ public:
 
 	const btTransform&	getWheelTransformWS( int wheelIndex ) const;
 
-	void	updateWheelTransform( int wheelIndex );
+	void	updateWheelTransform( int wheelIndex, bool interpolatedTransform = true );
 	
 	void	setRaycastWheelInfo( int wheelIndex , bool isInContact, const btVector3& hitPoint, const btVector3& hitNormal,btScalar depth);
 
@@ -103,7 +102,7 @@ public:
 
 	btWheelInfo&	getWheelInfo(int index);
 
-	void	updateWheelTransformsWS(btWheelInfo& wheel );
+	void	updateWheelTransformsWS(btWheelInfo& wheel , bool interpolatedTransform = true);
 
 	
 	void setBrake(float brake,int wheelIndex);

src/LinearMath/btDefaultMotionState.h

@@ -19,16 +19,25 @@ struct	btDefaultMotionState : public btMotionState
 	}
 
 	///synchronizes world transform from user to physics
-	virtual void	getWorldTransform(btTransform& centerOfMassWorldTrans )
+	virtual void	getWorldTransform(btTransform& centerOfMassWorldTrans ) const 
 	{
 			centerOfMassWorldTrans = 	m_centerOfMassOffset.inverse() * m_graphicsWorldTrans ;
 	}
 
 	///synchronizes world transform from physics to user
+	///Bullet only calls the update of worldtransform for active objects
 	virtual void	setWorldTransform(const btTransform& centerOfMassWorldTrans)
 	{
 			m_graphicsWorldTrans = centerOfMassWorldTrans * m_centerOfMassOffset ;
 	}
+
+	///Bullet gives a callback for objects that are about to be deactivated (put asleep)
+	/// You can intercept this callback for your own bookkeeping. 
+	///Also you can return false to disable deactivation for this object this frame.
+	virtual bool deactivationCallback(void*	userPointer) {
+		return true;
+	}
+
 };
 
 #endif //DEFAULT_MOTION_STATE_H

src/LinearMath/btMotionState.h

@@ -29,10 +29,15 @@ class	btMotionState
 			
 		}
 		
-		virtual void	getWorldTransform(btTransform& worldTrans )=0;
+		virtual void	getWorldTransform(btTransform& worldTrans ) const =0;
 
+		//Bullet only calls the update of worldtransform for active objects
 		virtual void	setWorldTransform(const btTransform& worldTrans)=0;
-
+		
+		//future: when Bullet makes attempt to deactivate object, you can intercept this callback (return false to disable deactivation for this object this frame)
+		virtual bool deactivationCallback(void*	userPointer) {
+			return true;
+		}
 };
 
 #endif //BT_MOTIONSTATE_H

src/LinearMath/btTransformUtil.h

@@ -108,7 +108,16 @@ public:
 	static void	calculateVelocity(const btTransform& transform0,const btTransform& transform1,btScalar timeStep,btVector3& linVel,btVector3& angVel)
 	{
 		linVel = (transform1.getOrigin() - transform0.getOrigin()) / timeStep;
-#ifdef USE_QUATERNION_DIFF
+		btVector3 axis;
+		btScalar  angle;
+		calculateDiffAxisAngle(transform0,transform1,axis,angle);
+		angVel = axis * angle / timeStep;
+	}
+
+	static void calculateDiffAxisAngle(const btTransform& transform0,const btTransform& transform1,btVector3& axis,btScalar& angle)
+	{
+	
+	#ifdef USE_QUATERNION_DIFF
 		btQuaternion orn0 = transform0.getRotation();
 		btQuaternion orn1a = transform1.getRotation();
 		btQuaternion orn1 = orn0.farthest(orn1a);
@@ -118,9 +127,7 @@ public:
 		btQuaternion dorn;
 		dmat.getRotation(dorn);
 #endif//USE_QUATERNION_DIFF
-
+	
-		btVector3 axis;
-		btScalar  angle;
 		angle = dorn.getAngle();
 		axis = btVector3(dorn.x(),dorn.y(),dorn.z());
 		axis[3] = 0.f;
@@ -130,13 +137,8 @@ public:
 			axis = btVector3(1.f,0.f,0.f);
 		else
 			axis /= btSqrt(len);
-
-		
-		angVel = axis * angle / timeStep;
-
 	}
 
-
 };
 
 #endif //SIMD_TRANSFORM_UTIL_H