implement 'mimic' joint constraint or 'gear' constraint for btMultiBody, add example in pybullet/examples/mimicJointConstraint.py

src/BulletDynamics/CMakeLists.txt

@@ -37,6 +37,7 @@ SET(BulletDynamics_SRCS
 	Featherstone/btMultiBodyFixedConstraint.cpp
 	Featherstone/btMultiBodySliderConstraint.cpp
 	Featherstone/btMultiBodyJointMotor.cpp
+	Featherstone/btMultiBodyGearConstraint.cpp
 	MLCPSolvers/btDantzigLCP.cpp
 	MLCPSolvers/btMLCPSolver.cpp
 	MLCPSolvers/btLemkeAlgorithm.cpp
@@ -98,6 +99,7 @@ SET(Featherstone_HDRS
 	Featherstone/btMultiBodyFixedConstraint.h
 	Featherstone/btMultiBodySliderConstraint.h
 	Featherstone/btMultiBodyJointMotor.h
+	Featherstone/btMultiBodyGearConstraint.h	
 )
 
 SET(MLCPSolvers_HDRS

src/BulletDynamics/Featherstone/btMultiBodyConstraint.h

@@ -183,6 +183,7 @@ public:
 
 	virtual void debugDraw(class btIDebugDraw* drawer)=0;
 
+	virtual void setGearRatio(btScalar ratio) {}
 };
 
 #endif //BT_MULTIBODY_CONSTRAINT_H

src/BulletDynamics/Featherstone/btMultiBodyGearConstraint.cpp

@@ -0,0 +1,169 @@
+/*
+Bullet Continuous Collision Detection and Physics Library
+Copyright (c) 2013 Erwin Coumans  http://bulletphysics.org
+
+This software is provided 'as-is', without any express or implied warranty.
+In no event will the authors be held liable for any damages arising from the use of this software.
+Permission is granted to anyone to use this software for any purpose,
+including commercial applications, and to alter it and redistribute it freely,
+subject to the following restrictions:
+
+1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
+2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
+3. This notice may not be removed or altered from any source distribution.
+*/
+
+///This file was written by Erwin Coumans
+
+#include "btMultiBodyGearConstraint.h"
+#include "btMultiBody.h"
+#include "btMultiBodyLinkCollider.h"
+#include "BulletCollision/CollisionDispatch/btCollisionObject.h"
+
+btMultiBodyGearConstraint::btMultiBodyGearConstraint(btMultiBody* bodyA, int linkA, btMultiBody* bodyB, int linkB, const btVector3& pivotInA, const btVector3& pivotInB, const btMatrix3x3& frameInA, const btMatrix3x3& frameInB)
+	:btMultiBodyConstraint(bodyA,bodyB,linkA,linkB,1,false),
+	m_gearRatio(1)
+{
+   
+}
+
+void btMultiBodyGearConstraint::finalizeMultiDof()
+{
+	
+	allocateJacobiansMultiDof();
+	
+	m_numDofsFinalized = m_jacSizeBoth;
+}
+
+btMultiBodyGearConstraint::~btMultiBodyGearConstraint()
+{
+}
+
+
+int btMultiBodyGearConstraint::getIslandIdA() const
+{
+
+	if (m_bodyA)
+	{
+		btMultiBodyLinkCollider* col = m_bodyA->getBaseCollider();
+		if (col)
+			return col->getIslandTag();
+		for (int i=0;i<m_bodyA->getNumLinks();i++)
+		{
+			if (m_bodyA->getLink(i).m_collider)
+				return m_bodyA->getLink(i).m_collider->getIslandTag();
+		}
+	}
+	return -1;
+}
+
+int btMultiBodyGearConstraint::getIslandIdB() const
+{
+	if (m_bodyB)
+	{
+		btMultiBodyLinkCollider* col = m_bodyB->getBaseCollider();
+		if (col)
+			return col->getIslandTag();
+
+		for (int i=0;i<m_bodyB->getNumLinks();i++)
+		{
+			col = m_bodyB->getLink(i).m_collider;
+			if (col)
+				return col->getIslandTag();
+		}
+	}
+	return -1;
+}
+
+
+void btMultiBodyGearConstraint::createConstraintRows(btMultiBodyConstraintArray& constraintRows,
+		btMultiBodyJacobianData& data,
+		const btContactSolverInfo& infoGlobal)
+{
+    // only positions need to be updated -- data.m_jacobians and force
+    // directions were set in the ctor and never change.
+	
+	if (m_numDofsFinalized != m_jacSizeBoth)
+	{
+        finalizeMultiDof();
+	}
+
+	//don't crash
+	if (m_numDofsFinalized != m_jacSizeBoth)
+		return;
+
+	
+	if (m_maxAppliedImpulse==0.f)
+		return;
+	
+	// note: we rely on the fact that data.m_jacobians are
+	// always initialized to zero by the Constraint ctor
+	int linkDoF = 0;
+	unsigned int offsetA = 6 + (m_bodyA->getLink(m_linkA).m_dofOffset + linkDoF);
+	unsigned int offsetB = 6 + (m_bodyB->getLink(m_linkB).m_dofOffset + linkDoF);
+
+	// row 0: the lower bound
+	jacobianA(0)[offsetA] = 1;
+	jacobianB(0)[offsetB] = m_gearRatio;
+
+	const btScalar posError = 0;
+	const btVector3 dummy(0, 0, 0);
+	btScalar erp = infoGlobal.m_erp;
+	btScalar kp = 1;
+	btScalar kd = 1;
+	int numRows = getNumRows();
+
+	for (int row=0;row<numRows;row++)
+	{
+		btMultiBodySolverConstraint& constraintRow = constraintRows.expandNonInitializing();
+
+
+        int dof = 0;
+        btScalar currentPosition = m_bodyA->getJointPosMultiDof(m_linkA)[dof];
+        btScalar currentVelocity = m_bodyA->getJointVelMultiDof(m_linkA)[dof];
+
+		//btScalar positionStabiliationTerm = erp*(m_desiredPosition-currentPosition)/infoGlobal.m_timeStep;
+        //btScalar velocityError = (m_desiredVelocity - currentVelocity);
+
+        btScalar desiredRelativeVelocity =   0;
+    
+		fillMultiBodyConstraint(constraintRow,data,jacobianA(row),jacobianB(row),dummy,dummy,dummy,dummy,posError,infoGlobal,-m_maxAppliedImpulse,m_maxAppliedImpulse,false,1,false,desiredRelativeVelocity);
+
+		constraintRow.m_orgConstraint = this;
+		constraintRow.m_orgDofIndex = row;
+		{
+			//expect either prismatic or revolute joint type for now
+			btAssert((m_bodyA->getLink(m_linkA).m_jointType == btMultibodyLink::eRevolute)||(m_bodyA->getLink(m_linkA).m_jointType == btMultibodyLink::ePrismatic));
+			switch (m_bodyA->getLink(m_linkA).m_jointType)
+			{
+				case btMultibodyLink::eRevolute:
+				{
+					constraintRow.m_contactNormal1.setZero();
+					constraintRow.m_contactNormal2.setZero();
+					btVector3 revoluteAxisInWorld = quatRotate(m_bodyA->getLink(m_linkA).m_cachedWorldTransform.getRotation(),m_bodyA->getLink(m_linkA).m_axes[0].m_topVec);
+					constraintRow.m_relpos1CrossNormal=revoluteAxisInWorld;
+					constraintRow.m_relpos2CrossNormal=-revoluteAxisInWorld;
+					
+					break;
+				}
+				case btMultibodyLink::ePrismatic:
+				{
+					btVector3 prismaticAxisInWorld = quatRotate(m_bodyA->getLink(m_linkA).m_cachedWorldTransform.getRotation(),m_bodyA->getLink(m_linkA).m_axes[0].m_bottomVec);
+					constraintRow.m_contactNormal1=prismaticAxisInWorld;
+					constraintRow.m_contactNormal2=-prismaticAxisInWorld;
+					constraintRow.m_relpos1CrossNormal.setZero();
+					constraintRow.m_relpos2CrossNormal.setZero();					
+					break;
+				}
+				default:
+				{
+					btAssert(0);
+				}
+			};
+			
+		}
+
+	}
+
+}
+

src/BulletDynamics/Featherstone/btMultiBodyGearConstraint.h

@@ -0,0 +1,103 @@
+/*
+Bullet Continuous Collision Detection and Physics Library
+Copyright (c) 2013 Erwin Coumans  http://bulletphysics.org
+
+This software is provided 'as-is', without any express or implied warranty.
+In no event will the authors be held liable for any damages arising from the use of this software.
+Permission is granted to anyone to use this software for any purpose,
+including commercial applications, and to alter it and redistribute it freely,
+subject to the following restrictions:
+
+1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
+2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
+3. This notice may not be removed or altered from any source distribution.
+*/
+
+///This file was written by Erwin Coumans
+
+#ifndef BT_MULTIBODY_GEAR_CONSTRAINT_H
+#define BT_MULTIBODY_GEAR_CONSTRAINT_H
+
+#include "btMultiBodyConstraint.h"
+
+class btMultiBodyGearConstraint : public btMultiBodyConstraint
+{
+protected:
+
+	btRigidBody*	m_rigidBodyA;
+	btRigidBody*	m_rigidBodyB;
+	btVector3		m_pivotInA;
+	btVector3		m_pivotInB;
+  btMatrix3x3     m_frameInA;
+  btMatrix3x3     m_frameInB;
+	btScalar			m_gearRatio;
+	
+public:
+
+	btMultiBodyGearConstraint(btMultiBody* body, int link, btRigidBody* bodyB, const btVector3& pivotInA, const btVector3& pivotInB, const btMatrix3x3& frameInA, const btMatrix3x3& frameInB);
+	btMultiBodyGearConstraint(btMultiBody* bodyA, int linkA, btMultiBody* bodyB, int linkB, const btVector3& pivotInA, const btVector3& pivotInB, const btMatrix3x3& frameInA, const btMatrix3x3& frameInB);
+
+	virtual ~btMultiBodyGearConstraint();
+
+	virtual void finalizeMultiDof();
+
+	virtual int getIslandIdA() const;
+	virtual int getIslandIdB() const;
+
+	virtual void createConstraintRows(btMultiBodyConstraintArray& constraintRows,
+		btMultiBodyJacobianData& data,
+		const btContactSolverInfo& infoGlobal);
+
+    const btVector3& getPivotInA() const
+    {
+        return m_pivotInA;
+    }
+    
+    void setPivotInA(const btVector3& pivotInA)
+    {
+        m_pivotInA = pivotInA;
+    }
+
+	const btVector3& getPivotInB() const
+	{
+		return m_pivotInB;
+	}
+
+	virtual void setPivotInB(const btVector3& pivotInB)
+	{
+		m_pivotInB = pivotInB;
+	}
+    
+    const btMatrix3x3& getFrameInA() const
+    {
+        return m_frameInA;
+    }
+    
+    void setFrameInA(const btMatrix3x3& frameInA)
+    {
+        m_frameInA = frameInA;
+    }
+    
+    const btMatrix3x3& getFrameInB() const
+    {
+        return m_frameInB;
+    }
+    
+    virtual void setFrameInB(const btMatrix3x3& frameInB)
+    {
+        m_frameInB = frameInB;
+    }
+
+	virtual void debugDraw(class btIDebugDraw* drawer)
+	{
+		//todo(erwincoumans)
+	}
+	
+	virtual void setGearRatio(btScalar gearRatio)
+	{
+		m_gearRatio = gearRatio;
+	}
+
+};
+
+#endif //BT_MULTIBODY_GEAR_CONSTRAINT_H