File indexing completed on 2025-08-03 03:49:59

 /*
 * Copyright (c) 2007 Erin Catto http://www.gphysics.com
 *
 * 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/b2PulleyJoint.h>
 #include <Box2D/Dynamics/b2Body.h>
 #include <Box2D/Dynamics/b2TimeStep.h>
 
 // Pulley:
 // length1 = norm(p1 - s1)
 // length2 = norm(p2 - s2)
 // C0 = (length1 + ratio * length2)_initial
 // C = C0 - (length1 + ratio * length2) >= 0
 // u1 = (p1 - s1) / norm(p1 - s1)
 // u2 = (p2 - s2) / norm(p2 - s2)
 // Cdot = -dot(u1, v1 + cross(w1, r1)) - ratio * dot(u2, v2 + cross(w2, r2))
 // J = -[u1 cross(r1, u1) ratio * u2  ratio * cross(r2, u2)]
 // K = J * invM * JT
 //   = invMass1 + invI1 * cross(r1, u1)^2 + ratio^2 * (invMass2 + invI2 * cross(r2, u2)^2)
 //
 // Limit:
 // C = maxLength - length
 // u = (p - s) / norm(p - s)
 // Cdot = -dot(u, v + cross(w, r))
 // K = invMass + invI * cross(r, u)^2
 // 0 <= impulse
 
 void b2PulleyJointDef::Initialize(b2Body* b1, b2Body* b2,
                 const b2Vec2& ga1, const b2Vec2& ga2,
                 const b2Vec2& anchor1, const b2Vec2& anchor2,
                 qreal r)
 {
     bodyA = b1;
     bodyB = b2;
     groundAnchorA = ga1;
     groundAnchorB = ga2;
     localAnchorA = bodyA->GetLocalPoint(anchor1);
     localAnchorB = bodyB->GetLocalPoint(anchor2);
     b2Vec2 d1 = anchor1 - ga1;
     lengthA = d1.Length();
     b2Vec2 d2 = anchor2 - ga2;
     lengthB = d2.Length();
     ratio = r;
     b2Assert(ratio > b2_epsilon);
     qreal C = lengthA + ratio * lengthB;
     maxLengthA = C - ratio * b2_minPulleyLength;
     maxLengthB = (C - b2_minPulleyLength) / ratio;
 }
 
 b2PulleyJoint::b2PulleyJoint(const b2PulleyJointDef* def)
 : b2Joint(def)
 {
     m_groundAnchor1 = def->groundAnchorA;
     m_groundAnchor2 = def->groundAnchorB;
     m_localAnchor1 = def->localAnchorA;
     m_localAnchor2 = def->localAnchorB;
 
     b2Assert(def->ratio != 0.0f);
     m_ratio = def->ratio;
 
     m_constant = def->lengthA + m_ratio * def->lengthB;
 
     m_maxLength1 = b2Min(def->maxLengthA, m_constant - m_ratio * b2_minPulleyLength);
     m_maxLength2 = b2Min(def->maxLengthB, (m_constant - b2_minPulleyLength) / m_ratio);
 
     m_impulse = 0.0f;
     m_limitImpulse1 = 0.0f;
     m_limitImpulse2 = 0.0f;
 }
 
 void b2PulleyJoint::InitVelocityConstraints(const b2TimeStep& step)
 {
     b2Body* b1 = m_bodyA;
     b2Body* b2 = m_bodyB;
 
     b2Vec2 r1 = b2Mul(b1->GetTransform().R, m_localAnchor1 - b1->GetLocalCenter());
     b2Vec2 r2 = b2Mul(b2->GetTransform().R, m_localAnchor2 - b2->GetLocalCenter());
 
     b2Vec2 p1 = b1->m_sweep.c + r1;
     b2Vec2 p2 = b2->m_sweep.c + r2;
 
     b2Vec2 s1 = m_groundAnchor1;
     b2Vec2 s2 = m_groundAnchor2;
 
     // Get the pulley axes.
     m_u1 = p1 - s1;
     m_u2 = p2 - s2;
 
     qreal length1 = m_u1.Length();
     qreal length2 = m_u2.Length();
 
     if (length1 > b2_linearSlop)
     {
         m_u1 *= 1.0f / length1;
     }
     else
     {
         m_u1.SetZero();
     }
 
     if (length2 > b2_linearSlop)
     {
         m_u2 *= 1.0f / length2;
     }
     else
     {
         m_u2.SetZero();
     }
 
     qreal C = m_constant - length1 - m_ratio * length2;
     if (C > 0.0f)
     {
         m_state = e_inactiveLimit;
         m_impulse = 0.0f;
     }
     else
     {
         m_state = e_atUpperLimit;
     }
 
     if (length1 < m_maxLength1)
     {
         m_limitState1 = e_inactiveLimit;
         m_limitImpulse1 = 0.0f;
     }
     else
     {
         m_limitState1 = e_atUpperLimit;
     }
 
     if (length2 < m_maxLength2)
     {
         m_limitState2 = e_inactiveLimit;
         m_limitImpulse2 = 0.0f;
     }
     else
     {
         m_limitState2 = e_atUpperLimit;
     }
 
     // Compute effective mass.
     qreal cr1u1 = b2Cross(r1, m_u1);
     qreal cr2u2 = b2Cross(r2, m_u2);
 
     m_limitMass1 = b1->m_invMass + b1->m_invI * cr1u1 * cr1u1;
     m_limitMass2 = b2->m_invMass + b2->m_invI * cr2u2 * cr2u2;
     m_pulleyMass = m_limitMass1 + m_ratio * m_ratio * m_limitMass2;
     b2Assert(m_limitMass1 > b2_epsilon);
     b2Assert(m_limitMass2 > b2_epsilon);
     b2Assert(m_pulleyMass > b2_epsilon);
     m_limitMass1 = 1.0f / m_limitMass1;
     m_limitMass2 = 1.0f / m_limitMass2;
     m_pulleyMass = 1.0f / m_pulleyMass;
 
     if (step.warmStarting)
     {
         // Scale impulses to support variable time steps.
         m_impulse *= step.dtRatio;
         m_limitImpulse1 *= step.dtRatio;
         m_limitImpulse2 *= step.dtRatio;
 
         // Warm starting.
         b2Vec2 P1 = -(m_impulse + m_limitImpulse1) * m_u1;
         b2Vec2 P2 = (-m_ratio * m_impulse - m_limitImpulse2) * m_u2;
         b1->m_linearVelocity += b1->m_invMass * P1;
         b1->m_angularVelocity += b1->m_invI * b2Cross(r1, P1);
         b2->m_linearVelocity += b2->m_invMass * P2;
         b2->m_angularVelocity += b2->m_invI * b2Cross(r2, P2);
     }
     else
     {
         m_impulse = 0.0f;
         m_limitImpulse1 = 0.0f;
         m_limitImpulse2 = 0.0f;
     }
 }
 
 void b2PulleyJoint::SolveVelocityConstraints(const b2TimeStep& step)
 {
     B2_NOT_USED(step);
 
     b2Body* b1 = m_bodyA;
     b2Body* b2 = m_bodyB;
 
     b2Vec2 r1 = b2Mul(b1->GetTransform().R, m_localAnchor1 - b1->GetLocalCenter());
     b2Vec2 r2 = b2Mul(b2->GetTransform().R, m_localAnchor2 - b2->GetLocalCenter());
 
     if (m_state == e_atUpperLimit)
     {
         b2Vec2 v1 = b1->m_linearVelocity + b2Cross(b1->m_angularVelocity, r1);
         b2Vec2 v2 = b2->m_linearVelocity + b2Cross(b2->m_angularVelocity, r2);
 
         qreal Cdot = -b2Dot(m_u1, v1) - m_ratio * b2Dot(m_u2, v2);
         qreal impulse = m_pulleyMass * (-Cdot);
         qreal oldImpulse = m_impulse;
         m_impulse = b2Max(0.0f, m_impulse + impulse);
         impulse = m_impulse - oldImpulse;
 
         b2Vec2 P1 = -impulse * m_u1;
         b2Vec2 P2 = -m_ratio * impulse * m_u2;
         b1->m_linearVelocity += b1->m_invMass * P1;
         b1->m_angularVelocity += b1->m_invI * b2Cross(r1, P1);
         b2->m_linearVelocity += b2->m_invMass * P2;
         b2->m_angularVelocity += b2->m_invI * b2Cross(r2, P2);
     }
 
     if (m_limitState1 == e_atUpperLimit)
     {
         b2Vec2 v1 = b1->m_linearVelocity + b2Cross(b1->m_angularVelocity, r1);
 
         qreal Cdot = -b2Dot(m_u1, v1);
         qreal impulse = -m_limitMass1 * Cdot;
         qreal oldImpulse = m_limitImpulse1;
         m_limitImpulse1 = b2Max(0.0f, m_limitImpulse1 + impulse);
         impulse = m_limitImpulse1 - oldImpulse;
 
         b2Vec2 P1 = -impulse * m_u1;
         b1->m_linearVelocity += b1->m_invMass * P1;
         b1->m_angularVelocity += b1->m_invI * b2Cross(r1, P1);
     }
 
     if (m_limitState2 == e_atUpperLimit)
     {
         b2Vec2 v2 = b2->m_linearVelocity + b2Cross(b2->m_angularVelocity, r2);
 
         qreal Cdot = -b2Dot(m_u2, v2);
         qreal impulse = -m_limitMass2 * Cdot;
         qreal oldImpulse = m_limitImpulse2;
         m_limitImpulse2 = b2Max(0.0f, m_limitImpulse2 + impulse);
         impulse = m_limitImpulse2 - oldImpulse;
 
         b2Vec2 P2 = -impulse * m_u2;
         b2->m_linearVelocity += b2->m_invMass * P2;
         b2->m_angularVelocity += b2->m_invI * b2Cross(r2, P2);
     }
 }
 
 bool b2PulleyJoint::SolvePositionConstraints(qreal baumgarte)
 {
     B2_NOT_USED(baumgarte);
 
     b2Body* b1 = m_bodyA;
     b2Body* b2 = m_bodyB;
 
     b2Vec2 s1 = m_groundAnchor1;
     b2Vec2 s2 = m_groundAnchor2;
 
     qreal linearError = 0.0f;
 
     if (m_state == e_atUpperLimit)
     {
         b2Vec2 r1 = b2Mul(b1->GetTransform().R, m_localAnchor1 - b1->GetLocalCenter());
         b2Vec2 r2 = b2Mul(b2->GetTransform().R, m_localAnchor2 - b2->GetLocalCenter());
 
         b2Vec2 p1 = b1->m_sweep.c + r1;
         b2Vec2 p2 = b2->m_sweep.c + r2;
 
         // Get the pulley axes.
         m_u1 = p1 - s1;
         m_u2 = p2 - s2;
 
         qreal length1 = m_u1.Length();
         qreal length2 = m_u2.Length();
 
         if (length1 > b2_linearSlop)
         {
             m_u1 *= 1.0f / length1;
         }
         else
         {
             m_u1.SetZero();
         }
 
         if (length2 > b2_linearSlop)
         {
             m_u2 *= 1.0f / length2;
         }
         else
         {
             m_u2.SetZero();
         }
 
         qreal C = m_constant - length1 - m_ratio * length2;
         linearError = b2Max(linearError, -C);
 
         C = b2Clamp(C + b2_linearSlop, -b2_maxLinearCorrection, 0.0f);
         qreal impulse = -m_pulleyMass * C;
 
         b2Vec2 P1 = -impulse * m_u1;
         b2Vec2 P2 = -m_ratio * impulse * m_u2;
 
         b1->m_sweep.c += b1->m_invMass * P1;
         b1->m_sweep.a += b1->m_invI * b2Cross(r1, P1);
         b2->m_sweep.c += b2->m_invMass * P2;
         b2->m_sweep.a += b2->m_invI * b2Cross(r2, P2);
 
         b1->SynchronizeTransform();
         b2->SynchronizeTransform();
     }
 
     if (m_limitState1 == e_atUpperLimit)
     {
         b2Vec2 r1 = b2Mul(b1->GetTransform().R, m_localAnchor1 - b1->GetLocalCenter());
         b2Vec2 p1 = b1->m_sweep.c + r1;
 
         m_u1 = p1 - s1;
         qreal length1 = m_u1.Length();
 
         if (length1 > b2_linearSlop)
         {
             m_u1 *= 1.0f / length1;
         }
         else
         {
             m_u1.SetZero();
         }
 
         qreal C = m_maxLength1 - length1;
         linearError = b2Max(linearError, -C);
         C = b2Clamp(C + b2_linearSlop, -b2_maxLinearCorrection, 0.0f);
         qreal impulse = -m_limitMass1 * C;
 
         b2Vec2 P1 = -impulse * m_u1;
         b1->m_sweep.c += b1->m_invMass * P1;
         b1->m_sweep.a += b1->m_invI * b2Cross(r1, P1);
 
         b1->SynchronizeTransform();
     }
 
     if (m_limitState2 == e_atUpperLimit)
     {
         b2Vec2 r2 = b2Mul(b2->GetTransform().R, m_localAnchor2 - b2->GetLocalCenter());
         b2Vec2 p2 = b2->m_sweep.c + r2;
 
         m_u2 = p2 - s2;
         qreal length2 = m_u2.Length();
 
         if (length2 > b2_linearSlop)
         {
             m_u2 *= 1.0f / length2;
         }
         else
         {
             m_u2.SetZero();
         }
 
         qreal C = m_maxLength2 - length2;
         linearError = b2Max(linearError, -C);
         C = b2Clamp(C + b2_linearSlop, -b2_maxLinearCorrection, 0.0f);
         qreal impulse = -m_limitMass2 * C;
 
         b2Vec2 P2 = -impulse * m_u2;
         b2->m_sweep.c += b2->m_invMass * P2;
         b2->m_sweep.a += b2->m_invI * b2Cross(r2, P2);
 
         b2->SynchronizeTransform();
     }
 
     return linearError < b2_linearSlop;
 }
 
 b2Vec2 b2PulleyJoint::GetAnchorA() const
 {
     return m_bodyA->GetWorldPoint(m_localAnchor1);
 }
 
 b2Vec2 b2PulleyJoint::GetAnchorB() const
 {
     return m_bodyB->GetWorldPoint(m_localAnchor2);
 }
 
 b2Vec2 b2PulleyJoint::GetReactionForce(qreal inv_dt) const
 {
     b2Vec2 P = m_impulse * m_u2;
     return inv_dt * P;
 }
 
 qreal b2PulleyJoint::GetReactionTorque(qreal inv_dt) const
 {
     B2_NOT_USED(inv_dt);
     return 0.0f;
 }
 
 b2Vec2 b2PulleyJoint::GetGroundAnchorA() const
 {
     return m_groundAnchor1;
 }
 
 b2Vec2 b2PulleyJoint::GetGroundAnchorB() const
 {
     return m_groundAnchor2;
 }
 
 qreal b2PulleyJoint::GetLength1() const
 {
     b2Vec2 p = m_bodyA->GetWorldPoint(m_localAnchor1);
     b2Vec2 s = m_groundAnchor1;
     b2Vec2 d = p - s;
     return d.Length();
 }
 
 qreal b2PulleyJoint::GetLength2() const
 {
     b2Vec2 p = m_bodyB->GetWorldPoint(m_localAnchor2);
     b2Vec2 s = m_groundAnchor2;
     b2Vec2 d = p - s;
     return d.Length();
 }
 
 qreal b2PulleyJoint::GetRatio() const
 {
     return m_ratio;
 }