File indexing completed on 2024-12-29 03:29:28

 /*
 * Copyright (c) 2006-2011 Erin Catto http://www.box2d.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.
 */
 
 #include <Box2D/Dynamics/Joints/b2RevoluteJoint.h>
 #include <Box2D/Dynamics/b2Body.h>
 #include <Box2D/Dynamics/b2TimeStep.h>
 
 // Point-to-point constraint
 // C = p2 - p1
 // Cdot = v2 - v1
 //      = v2 + cross(w2, r2) - v1 - cross(w1, r1)
 // J = [-I -r1_skew I r2_skew ]
 // Identity used:
 // w k % (rx i + ry j) = w * (-ry i + rx j)
 
 // Motor constraint
 // Cdot = w2 - w1
 // J = [0 0 -1 0 0 1]
 // K = invI1 + invI2
 
 void b2RevoluteJointDef::Initialize(b2Body* bA, b2Body* bB, const b2Vec2& anchor)
 {
     bodyA = bA;
     bodyB = bB;
     localAnchorA = bodyA->GetLocalPoint(anchor);
     localAnchorB = bodyB->GetLocalPoint(anchor);
     referenceAngle = bodyB->GetAngle() - bodyA->GetAngle();
 }
 
 b2RevoluteJoint::b2RevoluteJoint(const b2RevoluteJointDef* def)
 : b2Joint(def)
 {
     m_localAnchorA = def->localAnchorA;
     m_localAnchorB = def->localAnchorB;
     m_referenceAngle = def->referenceAngle;
 
     m_impulse.SetZero();
     m_motorImpulse = 0.0f;
 
     m_lowerAngle = def->lowerAngle;
     m_upperAngle = def->upperAngle;
     m_maxMotorTorque = def->maxMotorTorque;
     m_motorSpeed = def->motorSpeed;
     m_enableLimit = def->enableLimit;
     m_enableMotor = def->enableMotor;
     m_limitState = e_inactiveLimit;
 }
 
 void b2RevoluteJoint::InitVelocityConstraints(const b2SolverData& data)
 {
     m_indexA = m_bodyA->m_islandIndex;
     m_indexB = m_bodyB->m_islandIndex;
     m_localCenterA = m_bodyA->m_sweep.localCenter;
     m_localCenterB = m_bodyB->m_sweep.localCenter;
     m_invMassA = m_bodyA->m_invMass;
     m_invMassB = m_bodyB->m_invMass;
     m_invIA = m_bodyA->m_invI;
     m_invIB = m_bodyB->m_invI;
 
     float32 aA = data.positions[m_indexA].a;
     b2Vec2 vA = data.velocities[m_indexA].v;
     float32 wA = data.velocities[m_indexA].w;
 
     float32 aB = data.positions[m_indexB].a;
     b2Vec2 vB = data.velocities[m_indexB].v;
     float32 wB = data.velocities[m_indexB].w;
 
     b2Rot qA(aA), qB(aB);
 
     m_rA = b2Mul(qA, m_localAnchorA - m_localCenterA);
     m_rB = b2Mul(qB, m_localAnchorB - m_localCenterB);
 
     // J = [-I -r1_skew I r2_skew]
     //     [ 0       -1 0       1]
     // r_skew = [-ry; rx]
 
     // Matlab
     // K = [ mA+r1y^2*iA+mB+r2y^2*iB,  -r1y*iA*r1x-r2y*iB*r2x,          -r1y*iA-r2y*iB]
     //     [  -r1y*iA*r1x-r2y*iB*r2x, mA+r1x^2*iA+mB+r2x^2*iB,           r1x*iA+r2x*iB]
     //     [          -r1y*iA-r2y*iB,           r1x*iA+r2x*iB,                   iA+iB]
 
     float32 mA = m_invMassA, mB = m_invMassB;
     float32 iA = m_invIA, iB = m_invIB;
 
     bool fixedRotation = (iA + iB == 0.0f);
 
     m_mass.ex.x = mA + mB + m_rA.y * m_rA.y * iA + m_rB.y * m_rB.y * iB;
     m_mass.ey.x = -m_rA.y * m_rA.x * iA - m_rB.y * m_rB.x * iB;
     m_mass.ez.x = -m_rA.y * iA - m_rB.y * iB;
     m_mass.ex.y = m_mass.ey.x;
     m_mass.ey.y = mA + mB + m_rA.x * m_rA.x * iA + m_rB.x * m_rB.x * iB;
     m_mass.ez.y = m_rA.x * iA + m_rB.x * iB;
     m_mass.ex.z = m_mass.ez.x;
     m_mass.ey.z = m_mass.ez.y;
     m_mass.ez.z = iA + iB;
 
     m_motorMass = iA + iB;
     if (m_motorMass > 0.0f)
     {
         m_motorMass = 1.0f / m_motorMass;
     }
 
     if (m_enableMotor == false || fixedRotation)
     {
         m_motorImpulse = 0.0f;
     }
 
     if (m_enableLimit && fixedRotation == false)
     {
         float32 jointAngle = aB - aA - m_referenceAngle;
         if (b2Abs(m_upperAngle - m_lowerAngle) < 2.0f * b2_angularSlop)
         {
             m_limitState = e_equalLimits;
         }
         else if (jointAngle <= m_lowerAngle)
         {
             if (m_limitState != e_atLowerLimit)
             {
                 m_impulse.z = 0.0f;
             }
             m_limitState = e_atLowerLimit;
         }
         else if (jointAngle >= m_upperAngle)
         {
             if (m_limitState != e_atUpperLimit)
             {
                 m_impulse.z = 0.0f;
             }
             m_limitState = e_atUpperLimit;
         }
         else
         {
             m_limitState = e_inactiveLimit;
             m_impulse.z = 0.0f;
         }
     }
     else
     {
         m_limitState = e_inactiveLimit;
     }
 
     if (data.step.warmStarting)
     {
         // Scale impulses to support a variable time step.
         m_impulse *= data.step.dtRatio;
         m_motorImpulse *= data.step.dtRatio;
 
         b2Vec2 P(m_impulse.x, m_impulse.y);
 
         vA -= mA * P;
         wA -= iA * (b2Cross(m_rA, P) + m_motorImpulse + m_impulse.z);
 
         vB += mB * P;
         wB += iB * (b2Cross(m_rB, P) + m_motorImpulse + m_impulse.z);
     }
     else
     {
         m_impulse.SetZero();
         m_motorImpulse = 0.0f;
     }
 
     data.velocities[m_indexA].v = vA;
     data.velocities[m_indexA].w = wA;
     data.velocities[m_indexB].v = vB;
     data.velocities[m_indexB].w = wB;
 }
 
 void b2RevoluteJoint::SolveVelocityConstraints(const b2SolverData& data)
 {
     b2Vec2 vA = data.velocities[m_indexA].v;
     float32 wA = data.velocities[m_indexA].w;
     b2Vec2 vB = data.velocities[m_indexB].v;
     float32 wB = data.velocities[m_indexB].w;
 
     float32 mA = m_invMassA, mB = m_invMassB;
     float32 iA = m_invIA, iB = m_invIB;
 
     bool fixedRotation = (iA + iB == 0.0f);
 
     // Solve motor constraint.
     if (m_enableMotor && m_limitState != e_equalLimits && fixedRotation == false)
     {
         float32 Cdot = wB - wA - m_motorSpeed;
         float32 impulse = -m_motorMass * Cdot;
         float32 oldImpulse = m_motorImpulse;
         float32 maxImpulse = data.step.dt * m_maxMotorTorque;
         m_motorImpulse = b2Clamp(m_motorImpulse + impulse, -maxImpulse, maxImpulse);
         impulse = m_motorImpulse - oldImpulse;
 
         wA -= iA * impulse;
         wB += iB * impulse;
     }
 
     // Solve limit constraint.
     if (m_enableLimit && m_limitState != e_inactiveLimit && fixedRotation == false)
     {
         b2Vec2 Cdot1 = vB + b2Cross(wB, m_rB) - vA - b2Cross(wA, m_rA);
         float32 Cdot2 = wB - wA;
         b2Vec3 Cdot(Cdot1.x, Cdot1.y, Cdot2);
 
         b2Vec3 impulse = -m_mass.Solve33(Cdot);
 
         if (m_limitState == e_equalLimits)
         {
             m_impulse += impulse;
         }
         else if (m_limitState == e_atLowerLimit)
         {
             float32 newImpulse = m_impulse.z + impulse.z;
             if (newImpulse < 0.0f)
             {
                 b2Vec2 rhs = -Cdot1 + m_impulse.z * b2Vec2(m_mass.ez.x, m_mass.ez.y);
                 b2Vec2 reduced = m_mass.Solve22(rhs);
                 impulse.x = reduced.x;
                 impulse.y = reduced.y;
                 impulse.z = -m_impulse.z;
                 m_impulse.x += reduced.x;
                 m_impulse.y += reduced.y;
                 m_impulse.z = 0.0f;
             }
             else
             {
                 m_impulse += impulse;
             }
         }
         else if (m_limitState == e_atUpperLimit)
         {
             float32 newImpulse = m_impulse.z + impulse.z;
             if (newImpulse > 0.0f)
             {
                 b2Vec2 rhs = -Cdot1 + m_impulse.z * b2Vec2(m_mass.ez.x, m_mass.ez.y);
                 b2Vec2 reduced = m_mass.Solve22(rhs);
                 impulse.x = reduced.x;
                 impulse.y = reduced.y;
                 impulse.z = -m_impulse.z;
                 m_impulse.x += reduced.x;
                 m_impulse.y += reduced.y;
                 m_impulse.z = 0.0f;
             }
             else
             {
                 m_impulse += impulse;
             }
         }
 
         b2Vec2 P(impulse.x, impulse.y);
 
         vA -= mA * P;
         wA -= iA * (b2Cross(m_rA, P) + impulse.z);
 
         vB += mB * P;
         wB += iB * (b2Cross(m_rB, P) + impulse.z);
     }
     else
     {
         // Solve point-to-point constraint
         b2Vec2 Cdot = vB + b2Cross(wB, m_rB) - vA - b2Cross(wA, m_rA);
         b2Vec2 impulse = m_mass.Solve22(-Cdot);
 
         m_impulse.x += impulse.x;
         m_impulse.y += impulse.y;
 
         vA -= mA * impulse;
         wA -= iA * b2Cross(m_rA, impulse);
 
         vB += mB * impulse;
         wB += iB * b2Cross(m_rB, impulse);
     }
 
     data.velocities[m_indexA].v = vA;
     data.velocities[m_indexA].w = wA;
     data.velocities[m_indexB].v = vB;
     data.velocities[m_indexB].w = wB;
 }
 
 bool b2RevoluteJoint::SolvePositionConstraints(const b2SolverData& data)
 {
     b2Vec2 cA = data.positions[m_indexA].c;
     float32 aA = data.positions[m_indexA].a;
     b2Vec2 cB = data.positions[m_indexB].c;
     float32 aB = data.positions[m_indexB].a;
 
     b2Rot qA(aA), qB(aB);
 
     float32 angularError = 0.0f;
     float32 positionError = 0.0f;
 
     bool fixedRotation = (m_invIA + m_invIB == 0.0f);
 
     // Solve angular limit constraint.
     if (m_enableLimit && m_limitState != e_inactiveLimit && fixedRotation == false)
     {
         float32 angle = aB - aA - m_referenceAngle;
         float32 limitImpulse = 0.0f;
 
         if (m_limitState == e_equalLimits)
         {
             // Prevent large angular corrections
             float32 C = b2Clamp(angle - m_lowerAngle, -b2_maxAngularCorrection, b2_maxAngularCorrection);
             limitImpulse = -m_motorMass * C;
             angularError = b2Abs(C);
         }
         else if (m_limitState == e_atLowerLimit)
         {
             float32 C = angle - m_lowerAngle;
             angularError = -C;
 
             // Prevent large angular corrections and allow some slop.
             C = b2Clamp(C + b2_angularSlop, -b2_maxAngularCorrection, 0.0f);
             limitImpulse = -m_motorMass * C;
         }
         else if (m_limitState == e_atUpperLimit)
         {
             float32 C = angle - m_upperAngle;
             angularError = C;
 
             // Prevent large angular corrections and allow some slop.
             C = b2Clamp(C - b2_angularSlop, 0.0f, b2_maxAngularCorrection);
             limitImpulse = -m_motorMass * C;
         }
 
         aA -= m_invIA * limitImpulse;
         aB += m_invIB * limitImpulse;
     }
 
     // Solve point-to-point constraint.
     {
         qA.Set(aA);
         qB.Set(aB);
         b2Vec2 rA = b2Mul(qA, m_localAnchorA - m_localCenterA);
         b2Vec2 rB = b2Mul(qB, m_localAnchorB - m_localCenterB);
 
         b2Vec2 C = cB + rB - cA - rA;
         positionError = C.Length();
 
         float32 mA = m_invMassA, mB = m_invMassB;
         float32 iA = m_invIA, iB = m_invIB;
 
         b2Mat22 K;
         K.ex.x = mA + mB + iA * rA.y * rA.y + iB * rB.y * rB.y;
         K.ex.y = -iA * rA.x * rA.y - iB * rB.x * rB.y;
         K.ey.x = K.ex.y;
         K.ey.y = mA + mB + iA * rA.x * rA.x + iB * rB.x * rB.x;
 
         b2Vec2 impulse = -K.Solve(C);
 
         cA -= mA * impulse;
         aA -= iA * b2Cross(rA, impulse);
 
         cB += mB * impulse;
         aB += iB * b2Cross(rB, impulse);
     }
 
     data.positions[m_indexA].c = cA;
     data.positions[m_indexA].a = aA;
     data.positions[m_indexB].c = cB;
     data.positions[m_indexB].a = aB;
     
     return positionError <= b2_linearSlop && angularError <= b2_angularSlop;
 }
 
 b2Vec2 b2RevoluteJoint::GetAnchorA() const
 {
     return m_bodyA->GetWorldPoint(m_localAnchorA);
 }
 
 b2Vec2 b2RevoluteJoint::GetAnchorB() const
 {
     return m_bodyB->GetWorldPoint(m_localAnchorB);
 }
 
 b2Vec2 b2RevoluteJoint::GetReactionForce(float32 inv_dt) const
 {
     b2Vec2 P(m_impulse.x, m_impulse.y);
     return inv_dt * P;
 }
 
 float32 b2RevoluteJoint::GetReactionTorque(float32 inv_dt) const
 {
     return inv_dt * m_impulse.z;
 }
 
 float32 b2RevoluteJoint::GetJointAngle() const
 {
     b2Body* bA = m_bodyA;
     b2Body* bB = m_bodyB;
     return bB->m_sweep.a - bA->m_sweep.a - m_referenceAngle;
 }
 
 float32 b2RevoluteJoint::GetJointSpeed() const
 {
     b2Body* bA = m_bodyA;
     b2Body* bB = m_bodyB;
     return bB->m_angularVelocity - bA->m_angularVelocity;
 }
 
 bool b2RevoluteJoint::IsMotorEnabled() const
 {
     return m_enableMotor;
 }
 
 void b2RevoluteJoint::EnableMotor(bool flag)
 {
     m_bodyA->SetAwake(true);
     m_bodyB->SetAwake(true);
     m_enableMotor = flag;
 }
 
 float32 b2RevoluteJoint::GetMotorTorque(float32 inv_dt) const
 {
     return inv_dt * m_motorImpulse;
 }
 
 void b2RevoluteJoint::SetMotorSpeed(float32 speed)
 {
     m_bodyA->SetAwake(true);
     m_bodyB->SetAwake(true);
     m_motorSpeed = speed;
 }
 
 void b2RevoluteJoint::SetMaxMotorTorque(float32 torque)
 {
     m_bodyA->SetAwake(true);
     m_bodyB->SetAwake(true);
     m_maxMotorTorque = torque;
 }
 
 bool b2RevoluteJoint::IsLimitEnabled() const
 {
     return m_enableLimit;
 }
 
 void b2RevoluteJoint::EnableLimit(bool flag)
 {
     if (flag != m_enableLimit)
     {
         m_bodyA->SetAwake(true);
         m_bodyB->SetAwake(true);
         m_enableLimit = flag;
         m_impulse.z = 0.0f;
     }
 }
 
 float32 b2RevoluteJoint::GetLowerLimit() const
 {
     return m_lowerAngle;
 }
 
 float32 b2RevoluteJoint::GetUpperLimit() const
 {
     return m_upperAngle;
 }
 
 void b2RevoluteJoint::SetLimits(float32 lower, float32 upper)
 {
     b2Assert(lower <= upper);
     
     if (lower != m_lowerAngle || upper != m_upperAngle)
     {
         m_bodyA->SetAwake(true);
         m_bodyB->SetAwake(true);
         m_impulse.z = 0.0f;
         m_lowerAngle = lower;
         m_upperAngle = upper;
     }
 }
 
 void b2RevoluteJoint::Dump()
 {
     int32 indexA = m_bodyA->m_islandIndex;
     int32 indexB = m_bodyB->m_islandIndex;
 
     b2Log("  b2RevoluteJointDef jd;\n");
     b2Log("  jd.bodyA = bodies[%d];\n", indexA);
     b2Log("  jd.bodyB = bodies[%d];\n", indexB);
     b2Log("  jd.collideConnected = bool(%d);\n", m_collideConnected);
     b2Log("  jd.localAnchorA.Set(%.15lef, %.15lef);\n", m_localAnchorA.x, m_localAnchorA.y);
     b2Log("  jd.localAnchorB.Set(%.15lef, %.15lef);\n", m_localAnchorB.x, m_localAnchorB.y);
     b2Log("  jd.referenceAngle = %.15lef;\n", m_referenceAngle);
     b2Log("  jd.enableLimit = bool(%d);\n", m_enableLimit);
     b2Log("  jd.lowerAngle = %.15lef;\n", m_lowerAngle);
     b2Log("  jd.upperAngle = %.15lef;\n", m_upperAngle);
     b2Log("  jd.enableMotor = bool(%d);\n", m_enableMotor);
     b2Log("  jd.motorSpeed = %.15lef;\n", m_motorSpeed);
     b2Log("  jd.maxMotorTorque = %.15lef;\n", m_maxMotorTorque);
     b2Log("  joints[%d] = m_world->CreateJoint(&jd);\n", m_index);
 }