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

 /*
 * Copyright (c) 2007-2011 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/b2RopeJoint.h>
 #include <Box2D/Dynamics/b2Body.h>
 #include <Box2D/Dynamics/b2TimeStep.h>
 
 
 // Limit:
 // C = norm(pB - pA) - L
 // u = (pB - pA) / norm(pB - pA)
 // Cdot = dot(u, vB + cross(wB, rB) - vA - cross(wA, rA))
 // J = [-u -cross(rA, u) u cross(rB, u)]
 // K = J * invM * JT
 //   = invMassA + invIA * cross(rA, u)^2 + invMassB + invIB * cross(rB, u)^2
 
 b2RopeJoint::b2RopeJoint(const b2RopeJointDef* def)
 : b2Joint(def)
 {
     m_localAnchorA = def->localAnchorA;
     m_localAnchorB = def->localAnchorB;
 
     m_maxLength = def->maxLength;
 
     m_mass = 0.0f;
     m_impulse = 0.0f;
     m_state = e_inactiveLimit;
     m_length = 0.0f;
 }
 
 void b2RopeJoint::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);
     m_u = cB + m_rB - cA - m_rA;
 
     m_length = m_u.Length();
 
     float32 C = m_length - m_maxLength;
     if (C > 0.0f)
     {
         m_state = e_atUpperLimit;
     }
     else
     {
         m_state = e_inactiveLimit;
     }
 
     if (m_length > b2_linearSlop)
     {
         m_u *= 1.0f / m_length;
     }
     else
     {
         m_u.SetZero();
         m_mass = 0.0f;
         m_impulse = 0.0f;
         return;
     }
 
     // Compute effective mass.
     float32 crA = b2Cross(m_rA, m_u);
     float32 crB = b2Cross(m_rB, m_u);
     float32 invMass = m_invMassA + m_invIA * crA * crA + m_invMassB + m_invIB * crB * crB;
 
     m_mass = invMass != 0.0f ? 1.0f / invMass : 0.0f;
 
     if (data.step.warmStarting)
     {
         // Scale the impulse to support a variable time step.
         m_impulse *= data.step.dtRatio;
 
         b2Vec2 P = m_impulse * m_u;
         vA -= m_invMassA * P;
         wA -= m_invIA * b2Cross(m_rA, P);
         vB += m_invMassB * P;
         wB += m_invIB * b2Cross(m_rB, P);
     }
     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 b2RopeJoint::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;
 
     // Cdot = dot(u, v + cross(w, r))
     b2Vec2 vpA = vA + b2Cross(wA, m_rA);
     b2Vec2 vpB = vB + b2Cross(wB, m_rB);
     float32 C = m_length - m_maxLength;
     float32 Cdot = b2Dot(m_u, vpB - vpA);
 
     // Predictive constraint.
     if (C < 0.0f)
     {
         Cdot += data.step.inv_dt * C;
     }
 
     float32 impulse = -m_mass * Cdot;
     float32 oldImpulse = m_impulse;
     m_impulse = b2Min(0.0f, m_impulse + impulse);
     impulse = m_impulse - oldImpulse;
 
     b2Vec2 P = impulse * m_u;
     vA -= m_invMassA * P;
     wA -= m_invIA * b2Cross(m_rA, P);
     vB += m_invMassB * P;
     wB += m_invIB * b2Cross(m_rB, P);
 
     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 b2RopeJoint::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);
     b2Vec2 u = cB + rB - cA - rA;
 
     float32 length = u.Normalize();
     float32 C = length - m_maxLength;
 
     C = b2Clamp(C, 0.0f, b2_maxLinearCorrection);
 
     float32 impulse = -m_mass * C;
     b2Vec2 P = impulse * u;
 
     cA -= m_invMassA * P;
     aA -= m_invIA * b2Cross(rA, P);
     cB += m_invMassB * P;
     aB += m_invIB * b2Cross(rB, P);
 
     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 length - m_maxLength < b2_linearSlop;
 }
 
 b2Vec2 b2RopeJoint::GetAnchorA() const
 {
     return m_bodyA->GetWorldPoint(m_localAnchorA);
 }
 
 b2Vec2 b2RopeJoint::GetAnchorB() const
 {
     return m_bodyB->GetWorldPoint(m_localAnchorB);
 }
 
 b2Vec2 b2RopeJoint::GetReactionForce(float32 inv_dt) const
 {
     b2Vec2 F = (inv_dt * m_impulse) * m_u;
     return F;
 }
 
 float32 b2RopeJoint::GetReactionTorque(float32 inv_dt) const
 {
     B2_NOT_USED(inv_dt);
     return 0.0f;
 }
 
 float32 b2RopeJoint::GetMaxLength() const
 {
     return m_maxLength;
 }
 
 b2LimitState b2RopeJoint::GetLimitState() const
 {
     return m_state;
 }
 
 void b2RopeJoint::Dump()
 {
     int32 indexA = m_bodyA->m_islandIndex;
     int32 indexB = m_bodyB->m_islandIndex;
 
     b2Log("  b2RopeJointDef 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.maxLength = %.15lef;\n", m_maxLength);
     b2Log("  joints[%d] = m_world->CreateJoint(&jd);\n", m_index);
 }