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

 /*
 * Copyright (c) 2007 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/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)
 // 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)
 
 void b2PulleyJointDef::Initialize(b2Body* bA, b2Body* bB,
                 const b2Vec2& groundA, const b2Vec2& groundB,
                 const b2Vec2& anchorA, const b2Vec2& anchorB,
                 float32 r)
 {
     bodyA = bA;
     bodyB = bB;
     groundAnchorA = groundA;
     groundAnchorB = groundB;
     localAnchorA = bodyA->GetLocalPoint(anchorA);
     localAnchorB = bodyB->GetLocalPoint(anchorB);
     b2Vec2 dA = anchorA - groundA;
     lengthA = dA.Length();
     b2Vec2 dB = anchorB - groundB;
     lengthB = dB.Length();
     ratio = r;
     b2Assert(ratio > b2_epsilon);
 }
 
 b2PulleyJoint::b2PulleyJoint(const b2PulleyJointDef* def)
 : b2Joint(def)
 {
     m_groundAnchorA = def->groundAnchorA;
     m_groundAnchorB = def->groundAnchorB;
     m_localAnchorA = def->localAnchorA;
     m_localAnchorB = def->localAnchorB;
 
     m_lengthA = def->lengthA;
     m_lengthB = def->lengthB;
 
     b2Assert(def->ratio != 0.0f);
     m_ratio = def->ratio;
 
     m_constant = def->lengthA + m_ratio * def->lengthB;
 
     m_impulse = 0.0f;
 }
 
 void b2PulleyJoint::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;
 
     b2Vec2 cA = data.positions[m_indexA].c;
     float32 aA = data.positions[m_indexA].a;
     b2Vec2 vA = data.velocities[m_indexA].v;
     float32 wA = data.velocities[m_indexA].w;
 
     b2Vec2 cB = data.positions[m_indexB].c;
     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);
 
     // Get the pulley axes.
     m_uA = cA + m_rA - m_groundAnchorA;
     m_uB = cB + m_rB - m_groundAnchorB;
 
     float32 lengthA = m_uA.Length();
     float32 lengthB = m_uB.Length();
 
     if (lengthA > 10.0f * b2_linearSlop)
     {
         m_uA *= 1.0f / lengthA;
     }
     else
     {
         m_uA.SetZero();
     }
 
     if (lengthB > 10.0f * b2_linearSlop)
     {
         m_uB *= 1.0f / lengthB;
     }
     else
     {
         m_uB.SetZero();
     }
 
     // Compute effective mass.
     float32 ruA = b2Cross(m_rA, m_uA);
     float32 ruB = b2Cross(m_rB, m_uB);
 
     float32 mA = m_invMassA + m_invIA * ruA * ruA;
     float32 mB = m_invMassB + m_invIB * ruB * ruB;
 
     m_mass = mA + m_ratio * m_ratio * mB;
 
     if (m_mass > 0.0f)
     {
         m_mass = 1.0f / m_mass;
     }
 
     if (data.step.warmStarting)
     {
         // Scale impulses to support variable time steps.
         m_impulse *= data.step.dtRatio;
 
         // Warm starting.
         b2Vec2 PA = -(m_impulse) * m_uA;
         b2Vec2 PB = (-m_ratio * m_impulse) * m_uB;
 
         vA += m_invMassA * PA;
         wA += m_invIA * b2Cross(m_rA, PA);
         vB += m_invMassB * PB;
         wB += m_invIB * b2Cross(m_rB, PB);
     }
     else
     {
         m_impulse = 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 b2PulleyJoint::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;
 
     b2Vec2 vpA = vA + b2Cross(wA, m_rA);
     b2Vec2 vpB = vB + b2Cross(wB, m_rB);
 
     float32 Cdot = -b2Dot(m_uA, vpA) - m_ratio * b2Dot(m_uB, vpB);
     float32 impulse = -m_mass * Cdot;
     m_impulse += impulse;
 
     b2Vec2 PA = -impulse * m_uA;
     b2Vec2 PB = -m_ratio * impulse * m_uB;
     vA += m_invMassA * PA;
     wA += m_invIA * b2Cross(m_rA, PA);
     vB += m_invMassB * PB;
     wB += m_invIB * b2Cross(m_rB, PB);
 
     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 b2PulleyJoint::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);
 
     b2Vec2 rA = b2Mul(qA, m_localAnchorA - m_localCenterA);
     b2Vec2 rB = b2Mul(qB, m_localAnchorB - m_localCenterB);
 
     // Get the pulley axes.
     b2Vec2 uA = cA + rA - m_groundAnchorA;
     b2Vec2 uB = cB + rB - m_groundAnchorB;
 
     float32 lengthA = uA.Length();
     float32 lengthB = uB.Length();
 
     if (lengthA > 10.0f * b2_linearSlop)
     {
         uA *= 1.0f / lengthA;
     }
     else
     {
         uA.SetZero();
     }
 
     if (lengthB > 10.0f * b2_linearSlop)
     {
         uB *= 1.0f / lengthB;
     }
     else
     {
         uB.SetZero();
     }
 
     // Compute effective mass.
     float32 ruA = b2Cross(rA, uA);
     float32 ruB = b2Cross(rB, uB);
 
     float32 mA = m_invMassA + m_invIA * ruA * ruA;
     float32 mB = m_invMassB + m_invIB * ruB * ruB;
 
     float32 mass = mA + m_ratio * m_ratio * mB;
 
     if (mass > 0.0f)
     {
         mass = 1.0f / mass;
     }
 
     float32 C = m_constant - lengthA - m_ratio * lengthB;
     float32 linearError = b2Abs(C);
 
     float32 impulse = -mass * C;
 
     b2Vec2 PA = -impulse * uA;
     b2Vec2 PB = -m_ratio * impulse * uB;
 
     cA += m_invMassA * PA;
     aA += m_invIA * b2Cross(rA, PA);
     cB += m_invMassB * PB;
     aB += m_invIB * b2Cross(rB, PB);
 
     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 linearError < b2_linearSlop;
 }
 
 b2Vec2 b2PulleyJoint::GetAnchorA() const
 {
     return m_bodyA->GetWorldPoint(m_localAnchorA);
 }
 
 b2Vec2 b2PulleyJoint::GetAnchorB() const
 {
     return m_bodyB->GetWorldPoint(m_localAnchorB);
 }
 
 b2Vec2 b2PulleyJoint::GetReactionForce(float32 inv_dt) const
 {
     b2Vec2 P = m_impulse * m_uB;
     return inv_dt * P;
 }
 
 float32 b2PulleyJoint::GetReactionTorque(float32 inv_dt) const
 {
     B2_NOT_USED(inv_dt);
     return 0.0f;
 }
 
 b2Vec2 b2PulleyJoint::GetGroundAnchorA() const
 {
     return m_groundAnchorA;
 }
 
 b2Vec2 b2PulleyJoint::GetGroundAnchorB() const
 {
     return m_groundAnchorB;
 }
 
 float32 b2PulleyJoint::GetLengthA() const
 {
     return m_lengthA;
 }
 
 float32 b2PulleyJoint::GetLengthB() const
 {
     return m_lengthB;
 }
 
 float32 b2PulleyJoint::GetRatio() const
 {
     return m_ratio;
 }
 
 float32 b2PulleyJoint::GetCurrentLengthA() const
 {
     b2Vec2 p = m_bodyA->GetWorldPoint(m_localAnchorA);
     b2Vec2 s = m_groundAnchorA;
     b2Vec2 d = p - s;
     return d.Length();
 }
 
 float32 b2PulleyJoint::GetCurrentLengthB() const
 {
     b2Vec2 p = m_bodyB->GetWorldPoint(m_localAnchorB);
     b2Vec2 s = m_groundAnchorB;
     b2Vec2 d = p - s;
     return d.Length();
 }
 
 void b2PulleyJoint::Dump()
 {
     int32 indexA = m_bodyA->m_islandIndex;
     int32 indexB = m_bodyB->m_islandIndex;
 
     b2Log("  b2PulleyJointDef 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.groundAnchorA.Set(%.15lef, %.15lef);\n", m_groundAnchorA.x, m_groundAnchorA.y);
     b2Log("  jd.groundAnchorB.Set(%.15lef, %.15lef);\n", m_groundAnchorB.x, m_groundAnchorB.y);
     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.lengthA = %.15lef;\n", m_lengthA);
     b2Log("  jd.lengthB = %.15lef;\n", m_lengthB);
     b2Log("  jd.ratio = %.15lef;\n", m_ratio);
     b2Log("  joints[%d] = m_world->CreateJoint(&jd);\n", m_index);
 }
 
 void b2PulleyJoint::ShiftOrigin(const b2Vec2& newOrigin)
 {
     m_groundAnchorA -= newOrigin;
     m_groundAnchorB -= newOrigin;
 }