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/b2WeldJoint.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)
 
 // Angle constraint
 // C = angle2 - angle1 - referenceAngle
 // Cdot = w2 - w1
 // J = [0 0 -1 0 0 1]
 // K = invI1 + invI2
 
 void b2WeldJointDef::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();
 }
 
 b2WeldJoint::b2WeldJoint(const b2WeldJointDef* def)
 : b2Joint(def)
 {
     m_localAnchorA = def->localAnchorA;
     m_localAnchorB = def->localAnchorB;
     m_referenceAngle = def->referenceAngle;
     m_frequencyHz = def->frequencyHz;
     m_dampingRatio = def->dampingRatio;
 
     m_impulse.SetZero();
 }
 
 void b2WeldJoint::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;
 
     b2Mat33 K;
     K.ex.x = mA + mB + m_rA.y * m_rA.y * iA + m_rB.y * m_rB.y * iB;
     K.ey.x = -m_rA.y * m_rA.x * iA - m_rB.y * m_rB.x * iB;
     K.ez.x = -m_rA.y * iA - m_rB.y * iB;
     K.ex.y = K.ey.x;
     K.ey.y = mA + mB + m_rA.x * m_rA.x * iA + m_rB.x * m_rB.x * iB;
     K.ez.y = m_rA.x * iA + m_rB.x * iB;
     K.ex.z = K.ez.x;
     K.ey.z = K.ez.y;
     K.ez.z = iA + iB;
 
     if (m_frequencyHz > 0.0f)
     {
         K.GetInverse22(&m_mass);
 
         float32 invM = iA + iB;
         float32 m = invM > 0.0f ? 1.0f / invM : 0.0f;
 
         float32 C = aB - aA - m_referenceAngle;
 
         // Frequency
         float32 omega = 2.0f * b2_pi * m_frequencyHz;
 
         // Damping coefficient
         float32 d = 2.0f * m * m_dampingRatio * omega;
 
         // Spring stiffness
         float32 k = m * omega * omega;
 
         // magic formulas
         float32 h = data.step.dt;
         m_gamma = h * (d + h * k);
         m_gamma = m_gamma != 0.0f ? 1.0f / m_gamma : 0.0f;
         m_bias = C * h * k * m_gamma;
 
         invM += m_gamma;
         m_mass.ez.z = invM != 0.0f ? 1.0f / invM : 0.0f;
     }
     else if (K.ez.z == 0.0f)
     {
         K.GetInverse22(&m_mass);
         m_gamma = 0.0f;
         m_bias = 0.0f;
     }
     else
     {
         K.GetSymInverse33(&m_mass);
         m_gamma = 0.0f;
         m_bias = 0.0f;
     }
 
     if (data.step.warmStarting)
     {
         // Scale impulses to support a variable time step.
         m_impulse *= data.step.dtRatio;
 
         b2Vec2 P(m_impulse.x, m_impulse.y);
 
         vA -= mA * P;
         wA -= iA * (b2Cross(m_rA, P) + m_impulse.z);
 
         vB += mB * P;
         wB += iB * (b2Cross(m_rB, P) + m_impulse.z);
     }
     else
     {
         m_impulse.SetZero();
     }
 
     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 b2WeldJoint::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;
 
     if (m_frequencyHz > 0.0f)
     {
         float32 Cdot2 = wB - wA;
 
         float32 impulse2 = -m_mass.ez.z * (Cdot2 + m_bias + m_gamma * m_impulse.z);
         m_impulse.z += impulse2;
 
         wA -= iA * impulse2;
         wB += iB * impulse2;
 
         b2Vec2 Cdot1 = vB + b2Cross(wB, m_rB) - vA - b2Cross(wA, m_rA);
 
         b2Vec2 impulse1 = -b2Mul22(m_mass, Cdot1);
         m_impulse.x += impulse1.x;
         m_impulse.y += impulse1.y;
 
         b2Vec2 P = impulse1;
 
         vA -= mA * P;
         wA -= iA * b2Cross(m_rA, P);
 
         vB += mB * P;
         wB += iB * b2Cross(m_rB, P);
     }
     else
     {
         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 = -b2Mul(m_mass, Cdot);
         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);
     }
 
     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 b2WeldJoint::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 mA = m_invMassA, mB = m_invMassB;
     float32 iA = m_invIA, iB = m_invIB;
 
     b2Vec2 rA = b2Mul(qA, m_localAnchorA - m_localCenterA);
     b2Vec2 rB = b2Mul(qB, m_localAnchorB - m_localCenterB);
 
     float32 positionError, angularError;
 
     b2Mat33 K;
     K.ex.x = mA + mB + rA.y * rA.y * iA + rB.y * rB.y * iB;
     K.ey.x = -rA.y * rA.x * iA - rB.y * rB.x * iB;
     K.ez.x = -rA.y * iA - rB.y * iB;
     K.ex.y = K.ey.x;
     K.ey.y = mA + mB + rA.x * rA.x * iA + rB.x * rB.x * iB;
     K.ez.y = rA.x * iA + rB.x * iB;
     K.ex.z = K.ez.x;
     K.ey.z = K.ez.y;
     K.ez.z = iA + iB;
 
     if (m_frequencyHz > 0.0f)
     {
         b2Vec2 C1 =  cB + rB - cA - rA;
 
         positionError = C1.Length();
         angularError = 0.0f;
 
         b2Vec2 P = -K.Solve22(C1);
 
         cA -= mA * P;
         aA -= iA * b2Cross(rA, P);
 
         cB += mB * P;
         aB += iB * b2Cross(rB, P);
     }
     else
     {
         b2Vec2 C1 =  cB + rB - cA - rA;
         float32 C2 = aB - aA - m_referenceAngle;
 
         positionError = C1.Length();
         angularError = b2Abs(C2);
 
         b2Vec3 C(C1.x, C1.y, C2);
     
         b2Vec3 impulse;
         if (K.ez.z > 0.0f)
         {
             impulse = -K.Solve33(C);
         }
         else
         {
             b2Vec2 impulse2 = -K.Solve22(C1);
             impulse.Set(impulse2.x, impulse2.y, 0.0f);
         }
 
         b2Vec2 P(impulse.x, impulse.y);
 
         cA -= mA * P;
         aA -= iA * (b2Cross(rA, P) + impulse.z);
 
         cB += mB * P;
         aB += iB * (b2Cross(rB, P) + impulse.z);
     }
 
     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 b2WeldJoint::GetAnchorA() const
 {
     return m_bodyA->GetWorldPoint(m_localAnchorA);
 }
 
 b2Vec2 b2WeldJoint::GetAnchorB() const
 {
     return m_bodyB->GetWorldPoint(m_localAnchorB);
 }
 
 b2Vec2 b2WeldJoint::GetReactionForce(float32 inv_dt) const
 {
     b2Vec2 P(m_impulse.x, m_impulse.y);
     return inv_dt * P;
 }
 
 float32 b2WeldJoint::GetReactionTorque(float32 inv_dt) const
 {
     return inv_dt * m_impulse.z;
 }
 
 void b2WeldJoint::Dump()
 {
     int32 indexA = m_bodyA->m_islandIndex;
     int32 indexB = m_bodyB->m_islandIndex;
 
     b2Log("  b2WeldJointDef 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.frequencyHz = %.15lef;\n", m_frequencyHz);
     b2Log("  jd.dampingRatio = %.15lef;\n", m_dampingRatio);
     b2Log("  joints[%d] = m_world->CreateJoint(&jd);\n", m_index);
 }