add btHingeAccumulatedAngleConstraint derived from btHingeConstraint,

that exposes a new method getAccumulatedHingeAngle
See also https://github.com/bulletphysics/bullet3/issues/42

src/BulletDynamics/ConstraintSolver/btHingeConstraint.cpp

@@ -285,8 +285,59 @@ void	btHingeConstraint::buildJacobian()
 #endif //__SPU__
 
 
+static inline btScalar btNormalizeAnglePositive(btScalar angle)
+{
+  return btFmod(btFmod(angle, 2.0*SIMD_PI) + 2.0*SIMD_PI, 2.0*SIMD_PI);
+}
+
+
+
+static btScalar btShortestAngularDistance(btScalar accAngle, btScalar curAngle)
+{
+	btScalar result = btNormalizeAngle(btNormalizeAnglePositive(btNormalizeAnglePositive(curAngle) -
+	btNormalizeAnglePositive(accAngle)));
+	return result;
+}
+
+static btScalar btShortestAngleUpdate(btScalar accAngle, btScalar curAngle)
+{
+	btScalar tol(0.3);
+	btScalar result = btShortestAngularDistance(accAngle, curAngle);
+
+	  if (btFabs(result) > tol)
+		return curAngle;
+	  else
+		return accAngle + result;
+
+	return curAngle;
+}
+
+
+btScalar btHingeAccumulatedAngleConstraint::getAccumulatedHingeAngle()
+{
+	btScalar hingeAngle = getHingeAngle();
+	m_accumulatedAngle = btShortestAngleUpdate(m_accumulatedAngle,hingeAngle);
+	return m_accumulatedAngle;
+}
+void	btHingeAccumulatedAngleConstraint::setAccumulatedHingeAngle(btScalar accAngle)
+{
+	m_accumulatedAngle  = accAngle;
+}
+
+void btHingeAccumulatedAngleConstraint::getInfo1(btConstraintInfo1* info)
+{
+	//update m_accumulatedAngle
+	btScalar curHingeAngle = getHingeAngle();
+	m_accumulatedAngle = btShortestAngleUpdate(m_accumulatedAngle,curHingeAngle);
+
+	btHingeConstraint::getInfo1(info);
+}
+
+
 void btHingeConstraint::getInfo1(btConstraintInfo1* info)
 {
+
+
 	if (m_useSolveConstraintObsolete)
 	{
 		info->m_numConstraintRows = 0;
@@ -606,6 +657,8 @@ void	btHingeConstraint::updateRHS(btScalar	timeStep)
 }
 
 
+
+
 btScalar btHingeConstraint::getHingeAngle()
 {
 	return getHingeAngle(m_rbA.getCenterOfMassTransform(),m_rbB.getCenterOfMassTransform());

src/BulletDynamics/ConstraintSolver/btHingeConstraint.h

@@ -236,6 +236,7 @@ public:
 	}
 
 
+	///The getHingeAngle gives the hinge angle in range [-PI,PI]
 	btScalar getHingeAngle();
 
 	btScalar getHingeAngle(const btTransform& transA,const btTransform& transB);
@@ -326,6 +327,43 @@ struct	btHingeConstraintDoubleData
 };
 #endif //BT_BACKWARDS_COMPATIBLE_SERIALIZATION
 
+///The getAccumulatedHingeAngle returns the accumulated hinge angle, taking rotation across the -PI/PI boundary into account
+ATTRIBUTE_ALIGNED16(class) btHingeAccumulatedAngleConstraint : public btHingeConstraint
+{
+protected:
+	btScalar	m_accumulatedAngle;
+public:
+
+	BT_DECLARE_ALIGNED_ALLOCATOR();
+	
+	btHingeAccumulatedAngleConstraint(btRigidBody& rbA,btRigidBody& rbB, const btVector3& pivotInA,const btVector3& pivotInB, const btVector3& axisInA,const btVector3& axisInB, bool useReferenceFrameA = false)
+	:btHingeConstraint(rbA,rbB,pivotInA,pivotInB, axisInA,axisInB, useReferenceFrameA )
+	{
+		m_accumulatedAngle=getHingeAngle();
+	}
+
+	btHingeAccumulatedAngleConstraint(btRigidBody& rbA,const btVector3& pivotInA,const btVector3& axisInA, bool useReferenceFrameA = false)
+	:btHingeConstraint(rbA,pivotInA,axisInA, useReferenceFrameA)
+	{
+		m_accumulatedAngle=getHingeAngle();
+	}
+	
+	btHingeAccumulatedAngleConstraint(btRigidBody& rbA,btRigidBody& rbB, const btTransform& rbAFrame, const btTransform& rbBFrame, bool useReferenceFrameA = false)
+	:btHingeConstraint(rbA,rbB, rbAFrame, rbBFrame, useReferenceFrameA )
+	{
+		m_accumulatedAngle=getHingeAngle();
+	}
+
+	btHingeAccumulatedAngleConstraint(btRigidBody& rbA,const btTransform& rbAFrame, bool useReferenceFrameA = false)
+	:btHingeConstraint(rbA,rbAFrame, useReferenceFrameA )
+	{
+		m_accumulatedAngle=getHingeAngle();
+	}
+	btScalar getAccumulatedHingeAngle();
+	void	setAccumulatedHingeAngle(btScalar accAngle);
+	virtual void getInfo1 (btConstraintInfo1* info);
+
+};
 
 struct	btHingeConstraintFloatData
 {