b2GearJoint.cpp
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00001 /*
00002 * Copyright (c) 2007-2011 Erin Catto http://www.box2d.org
00003 *
00004 * This software is provided 'as-is', without any express or implied
00005 * warranty.  In no event will the authors be held liable for any damages
00006 * arising from the use of this software.
00007 * Permission is granted to anyone to use this software for any purpose,
00008 * including commercial applications, and to alter it and redistribute it
00009 * freely, subject to the following restrictions:
00010 * 1. The origin of this software must not be misrepresented; you must not
00011 * claim that you wrote the original software. If you use this software
00012 * in a product, an acknowledgment in the product documentation would be
00013 * appreciated but is not required.
00014 * 2. Altered source versions must be plainly marked as such, and must not be
00015 * misrepresented as being the original software.
00016 * 3. This notice may not be removed or altered from any source distribution.
00017 */
00018 
00019 #include <Box2D/Dynamics/Joints/b2GearJoint.h>
00020 #include <Box2D/Dynamics/Joints/b2RevoluteJoint.h>
00021 #include <Box2D/Dynamics/Joints/b2PrismaticJoint.h>
00022 #include <Box2D/Dynamics/b2Body.h>
00023 #include <Box2D/Dynamics/b2TimeStep.h>
00024 
00025 // Gear Joint:
00026 // C0 = (coordinate1 + ratio * coordinate2)_initial
00027 // C = (coordinate1 + ratio * coordinate2) - C0 = 0
00028 // J = [J1 ratio * J2]
00029 // K = J * invM * JT
00030 //   = J1 * invM1 * J1T + ratio * ratio * J2 * invM2 * J2T
00031 //
00032 // Revolute:
00033 // coordinate = rotation
00034 // Cdot = angularVelocity
00035 // J = [0 0 1]
00036 // K = J * invM * JT = invI
00037 //
00038 // Prismatic:
00039 // coordinate = dot(p - pg, ug)
00040 // Cdot = dot(v + cross(w, r), ug)
00041 // J = [ug cross(r, ug)]
00042 // K = J * invM * JT = invMass + invI * cross(r, ug)^2
00043 
00044 b2GearJoint::b2GearJoint(const b2GearJointDef* def)
00045 : b2Joint(def)
00046 {
00047         m_joint1 = def->joint1;
00048         m_joint2 = def->joint2;
00049 
00050         m_typeA = m_joint1->GetType();
00051         m_typeB = m_joint2->GetType();
00052 
00053         b2Assert(m_typeA == e_revoluteJoint || m_typeA == e_prismaticJoint);
00054         b2Assert(m_typeB == e_revoluteJoint || m_typeB == e_prismaticJoint);
00055 
00056         float32 coordinateA, coordinateB;
00057 
00058         // TODO_ERIN there might be some problem with the joint edges in b2Joint.
00059 
00060         m_bodyC = m_joint1->GetBodyA();
00061         m_bodyA = m_joint1->GetBodyB();
00062 
00063         // Get geometry of joint1
00064         b2Transform xfA = m_bodyA->m_xf;
00065         float32 aA = m_bodyA->m_sweep.a;
00066         b2Transform xfC = m_bodyC->m_xf;
00067         float32 aC = m_bodyC->m_sweep.a;
00068 
00069         if (m_typeA == e_revoluteJoint)
00070         {
00071                 b2RevoluteJoint* revolute = (b2RevoluteJoint*)def->joint1;
00072                 m_localAnchorC = revolute->m_localAnchorA;
00073                 m_localAnchorA = revolute->m_localAnchorB;
00074                 m_referenceAngleA = revolute->m_referenceAngle;
00075                 m_localAxisC.SetZero();
00076 
00077                 coordinateA = aA - aC - m_referenceAngleA;
00078         }
00079         else
00080         {
00081                 b2PrismaticJoint* prismatic = (b2PrismaticJoint*)def->joint1;
00082                 m_localAnchorC = prismatic->m_localAnchorA;
00083                 m_localAnchorA = prismatic->m_localAnchorB;
00084                 m_referenceAngleA = prismatic->m_referenceAngle;
00085                 m_localAxisC = prismatic->m_localXAxisA;
00086 
00087                 b2Vec2 pC = m_localAnchorC;
00088                 b2Vec2 pA = b2MulT(xfC.q, b2Mul(xfA.q, m_localAnchorA) + (xfA.p - xfC.p));
00089                 coordinateA = b2Dot(pA - pC, m_localAxisC);
00090         }
00091 
00092         m_bodyD = m_joint2->GetBodyA();
00093         m_bodyB = m_joint2->GetBodyB();
00094 
00095         // Get geometry of joint2
00096         b2Transform xfB = m_bodyB->m_xf;
00097         float32 aB = m_bodyB->m_sweep.a;
00098         b2Transform xfD = m_bodyD->m_xf;
00099         float32 aD = m_bodyD->m_sweep.a;
00100 
00101         if (m_typeB == e_revoluteJoint)
00102         {
00103                 b2RevoluteJoint* revolute = (b2RevoluteJoint*)def->joint2;
00104                 m_localAnchorD = revolute->m_localAnchorA;
00105                 m_localAnchorB = revolute->m_localAnchorB;
00106                 m_referenceAngleB = revolute->m_referenceAngle;
00107                 m_localAxisD.SetZero();
00108 
00109                 coordinateB = aB - aD - m_referenceAngleB;
00110         }
00111         else
00112         {
00113                 b2PrismaticJoint* prismatic = (b2PrismaticJoint*)def->joint2;
00114                 m_localAnchorD = prismatic->m_localAnchorA;
00115                 m_localAnchorB = prismatic->m_localAnchorB;
00116                 m_referenceAngleB = prismatic->m_referenceAngle;
00117                 m_localAxisD = prismatic->m_localXAxisA;
00118 
00119                 b2Vec2 pD = m_localAnchorD;
00120                 b2Vec2 pB = b2MulT(xfD.q, b2Mul(xfB.q, m_localAnchorB) + (xfB.p - xfD.p));
00121                 coordinateB = b2Dot(pB - pD, m_localAxisD);
00122         }
00123 
00124         m_ratio = def->ratio;
00125 
00126         m_constant = coordinateA + m_ratio * coordinateB;
00127 
00128         m_impulse = 0.0f;
00129 }
00130 
00131 void b2GearJoint::InitVelocityConstraints(const b2SolverData& data)
00132 {
00133         m_indexA = m_bodyA->m_islandIndex;
00134         m_indexB = m_bodyB->m_islandIndex;
00135         m_indexC = m_bodyC->m_islandIndex;
00136         m_indexD = m_bodyD->m_islandIndex;
00137         m_lcA = m_bodyA->m_sweep.localCenter;
00138         m_lcB = m_bodyB->m_sweep.localCenter;
00139         m_lcC = m_bodyC->m_sweep.localCenter;
00140         m_lcD = m_bodyD->m_sweep.localCenter;
00141         m_mA = m_bodyA->m_invMass;
00142         m_mB = m_bodyB->m_invMass;
00143         m_mC = m_bodyC->m_invMass;
00144         m_mD = m_bodyD->m_invMass;
00145         m_iA = m_bodyA->m_invI;
00146         m_iB = m_bodyB->m_invI;
00147         m_iC = m_bodyC->m_invI;
00148         m_iD = m_bodyD->m_invI;
00149 
00150         float32 aA = data.positions[m_indexA].a;
00151         b2Vec2 vA = data.velocities[m_indexA].v;
00152         float32 wA = data.velocities[m_indexA].w;
00153 
00154         float32 aB = data.positions[m_indexB].a;
00155         b2Vec2 vB = data.velocities[m_indexB].v;
00156         float32 wB = data.velocities[m_indexB].w;
00157 
00158         float32 aC = data.positions[m_indexC].a;
00159         b2Vec2 vC = data.velocities[m_indexC].v;
00160         float32 wC = data.velocities[m_indexC].w;
00161 
00162         float32 aD = data.positions[m_indexD].a;
00163         b2Vec2 vD = data.velocities[m_indexD].v;
00164         float32 wD = data.velocities[m_indexD].w;
00165 
00166         b2Rot qA(aA), qB(aB), qC(aC), qD(aD);
00167 
00168         m_mass = 0.0f;
00169 
00170         if (m_typeA == e_revoluteJoint)
00171         {
00172                 m_JvAC.SetZero();
00173                 m_JwA = 1.0f;
00174                 m_JwC = 1.0f;
00175                 m_mass += m_iA + m_iC;
00176         }
00177         else
00178         {
00179                 b2Vec2 u = b2Mul(qC, m_localAxisC);
00180                 b2Vec2 rC = b2Mul(qC, m_localAnchorC - m_lcC);
00181                 b2Vec2 rA = b2Mul(qA, m_localAnchorA - m_lcA);
00182                 m_JvAC = u;
00183                 m_JwC = b2Cross(rC, u);
00184                 m_JwA = b2Cross(rA, u);
00185                 m_mass += m_mC + m_mA + m_iC * m_JwC * m_JwC + m_iA * m_JwA * m_JwA;
00186         }
00187 
00188         if (m_typeB == e_revoluteJoint)
00189         {
00190                 m_JvBD.SetZero();
00191                 m_JwB = m_ratio;
00192                 m_JwD = m_ratio;
00193                 m_mass += m_ratio * m_ratio * (m_iB + m_iD);
00194         }
00195         else
00196         {
00197                 b2Vec2 u = b2Mul(qD, m_localAxisD);
00198                 b2Vec2 rD = b2Mul(qD, m_localAnchorD - m_lcD);
00199                 b2Vec2 rB = b2Mul(qB, m_localAnchorB - m_lcB);
00200                 m_JvBD = m_ratio * u;
00201                 m_JwD = m_ratio * b2Cross(rD, u);
00202                 m_JwB = m_ratio * b2Cross(rB, u);
00203                 m_mass += m_ratio * m_ratio * (m_mD + m_mB) + m_iD * m_JwD * m_JwD + m_iB * m_JwB * m_JwB;
00204         }
00205 
00206         // Compute effective mass.
00207         m_mass = m_mass > 0.0f ? 1.0f / m_mass : 0.0f;
00208 
00209         if (data.step.warmStarting)
00210         {
00211                 vA += (m_mA * m_impulse) * m_JvAC;
00212                 wA += m_iA * m_impulse * m_JwA;
00213                 vB += (m_mB * m_impulse) * m_JvBD;
00214                 wB += m_iB * m_impulse * m_JwB;
00215                 vC -= (m_mC * m_impulse) * m_JvAC;
00216                 wC -= m_iC * m_impulse * m_JwC;
00217                 vD -= (m_mD * m_impulse) * m_JvBD;
00218                 wD -= m_iD * m_impulse * m_JwD;
00219         }
00220         else
00221         {
00222                 m_impulse = 0.0f;
00223         }
00224 
00225         data.velocities[m_indexA].v = vA;
00226         data.velocities[m_indexA].w = wA;
00227         data.velocities[m_indexB].v = vB;
00228         data.velocities[m_indexB].w = wB;
00229         data.velocities[m_indexC].v = vC;
00230         data.velocities[m_indexC].w = wC;
00231         data.velocities[m_indexD].v = vD;
00232         data.velocities[m_indexD].w = wD;
00233 }
00234 
00235 void b2GearJoint::SolveVelocityConstraints(const b2SolverData& data)
00236 {
00237         b2Vec2 vA = data.velocities[m_indexA].v;
00238         float32 wA = data.velocities[m_indexA].w;
00239         b2Vec2 vB = data.velocities[m_indexB].v;
00240         float32 wB = data.velocities[m_indexB].w;
00241         b2Vec2 vC = data.velocities[m_indexC].v;
00242         float32 wC = data.velocities[m_indexC].w;
00243         b2Vec2 vD = data.velocities[m_indexD].v;
00244         float32 wD = data.velocities[m_indexD].w;
00245 
00246         float32 Cdot = b2Dot(m_JvAC, vA - vC) + b2Dot(m_JvBD, vB - vD);
00247         Cdot += (m_JwA * wA - m_JwC * wC) + (m_JwB * wB - m_JwD * wD);
00248 
00249         float32 impulse = -m_mass * Cdot;
00250         m_impulse += impulse;
00251 
00252         vA += (m_mA * impulse) * m_JvAC;
00253         wA += m_iA * impulse * m_JwA;
00254         vB += (m_mB * impulse) * m_JvBD;
00255         wB += m_iB * impulse * m_JwB;
00256         vC -= (m_mC * impulse) * m_JvAC;
00257         wC -= m_iC * impulse * m_JwC;
00258         vD -= (m_mD * impulse) * m_JvBD;
00259         wD -= m_iD * impulse * m_JwD;
00260 
00261         data.velocities[m_indexA].v = vA;
00262         data.velocities[m_indexA].w = wA;
00263         data.velocities[m_indexB].v = vB;
00264         data.velocities[m_indexB].w = wB;
00265         data.velocities[m_indexC].v = vC;
00266         data.velocities[m_indexC].w = wC;
00267         data.velocities[m_indexD].v = vD;
00268         data.velocities[m_indexD].w = wD;
00269 }
00270 
00271 bool b2GearJoint::SolvePositionConstraints(const b2SolverData& data)
00272 {
00273         b2Vec2 cA = data.positions[m_indexA].c;
00274         float32 aA = data.positions[m_indexA].a;
00275         b2Vec2 cB = data.positions[m_indexB].c;
00276         float32 aB = data.positions[m_indexB].a;
00277         b2Vec2 cC = data.positions[m_indexC].c;
00278         float32 aC = data.positions[m_indexC].a;
00279         b2Vec2 cD = data.positions[m_indexD].c;
00280         float32 aD = data.positions[m_indexD].a;
00281 
00282         b2Rot qA(aA), qB(aB), qC(aC), qD(aD);
00283 
00284         float32 linearError = 0.0f;
00285 
00286         float32 coordinateA, coordinateB;
00287 
00288         b2Vec2 JvAC, JvBD;
00289         float32 JwA, JwB, JwC, JwD;
00290         float32 mass = 0.0f;
00291 
00292         if (m_typeA == e_revoluteJoint)
00293         {
00294                 JvAC.SetZero();
00295                 JwA = 1.0f;
00296                 JwC = 1.0f;
00297                 mass += m_iA + m_iC;
00298 
00299                 coordinateA = aA - aC - m_referenceAngleA;
00300         }
00301         else
00302         {
00303                 b2Vec2 u = b2Mul(qC, m_localAxisC);
00304                 b2Vec2 rC = b2Mul(qC, m_localAnchorC - m_lcC);
00305                 b2Vec2 rA = b2Mul(qA, m_localAnchorA - m_lcA);
00306                 JvAC = u;
00307                 JwC = b2Cross(rC, u);
00308                 JwA = b2Cross(rA, u);
00309                 mass += m_mC + m_mA + m_iC * JwC * JwC + m_iA * JwA * JwA;
00310 
00311                 b2Vec2 pC = m_localAnchorC - m_lcC;
00312                 b2Vec2 pA = b2MulT(qC, rA + (cA - cC));
00313                 coordinateA = b2Dot(pA - pC, m_localAxisC);
00314         }
00315 
00316         if (m_typeB == e_revoluteJoint)
00317         {
00318                 JvBD.SetZero();
00319                 JwB = m_ratio;
00320                 JwD = m_ratio;
00321                 mass += m_ratio * m_ratio * (m_iB + m_iD);
00322 
00323                 coordinateB = aB - aD - m_referenceAngleB;
00324         }
00325         else
00326         {
00327                 b2Vec2 u = b2Mul(qD, m_localAxisD);
00328                 b2Vec2 rD = b2Mul(qD, m_localAnchorD - m_lcD);
00329                 b2Vec2 rB = b2Mul(qB, m_localAnchorB - m_lcB);
00330                 JvBD = m_ratio * u;
00331                 JwD = m_ratio * b2Cross(rD, u);
00332                 JwB = m_ratio * b2Cross(rB, u);
00333                 mass += m_ratio * m_ratio * (m_mD + m_mB) + m_iD * JwD * JwD + m_iB * JwB * JwB;
00334 
00335                 b2Vec2 pD = m_localAnchorD - m_lcD;
00336                 b2Vec2 pB = b2MulT(qD, rB + (cB - cD));
00337                 coordinateB = b2Dot(pB - pD, m_localAxisD);
00338         }
00339 
00340         float32 C = (coordinateA + m_ratio * coordinateB) - m_constant;
00341 
00342         float32 impulse = 0.0f;
00343         if (mass > 0.0f)
00344         {
00345                 impulse = -C / mass;
00346         }
00347 
00348         cA += m_mA * impulse * JvAC;
00349         aA += m_iA * impulse * JwA;
00350         cB += m_mB * impulse * JvBD;
00351         aB += m_iB * impulse * JwB;
00352         cC -= m_mC * impulse * JvAC;
00353         aC -= m_iC * impulse * JwC;
00354         cD -= m_mD * impulse * JvBD;
00355         aD -= m_iD * impulse * JwD;
00356 
00357         data.positions[m_indexA].c = cA;
00358         data.positions[m_indexA].a = aA;
00359         data.positions[m_indexB].c = cB;
00360         data.positions[m_indexB].a = aB;
00361         data.positions[m_indexC].c = cC;
00362         data.positions[m_indexC].a = aC;
00363         data.positions[m_indexD].c = cD;
00364         data.positions[m_indexD].a = aD;
00365 
00366         // TODO_ERIN not implemented
00367         return linearError < b2_linearSlop;
00368 }
00369 
00370 b2Vec2 b2GearJoint::GetAnchorA() const
00371 {
00372         return m_bodyA->GetWorldPoint(m_localAnchorA);
00373 }
00374 
00375 b2Vec2 b2GearJoint::GetAnchorB() const
00376 {
00377         return m_bodyB->GetWorldPoint(m_localAnchorB);
00378 }
00379 
00380 b2Vec2 b2GearJoint::GetReactionForce(float32 inv_dt) const
00381 {
00382         b2Vec2 P = m_impulse * m_JvAC;
00383         return inv_dt * P;
00384 }
00385 
00386 float32 b2GearJoint::GetReactionTorque(float32 inv_dt) const
00387 {
00388         float32 L = m_impulse * m_JwA;
00389         return inv_dt * L;
00390 }
00391 
00392 void b2GearJoint::SetRatio(float32 ratio)
00393 {
00394         b2Assert(b2IsValid(ratio));
00395         m_ratio = ratio;
00396 }
00397 
00398 float32 b2GearJoint::GetRatio() const
00399 {
00400         return m_ratio;
00401 }
00402 
00403 void b2GearJoint::Dump()
00404 {
00405         int32 indexA = m_bodyA->m_islandIndex;
00406         int32 indexB = m_bodyB->m_islandIndex;
00407 
00408         int32 index1 = m_joint1->m_index;
00409         int32 index2 = m_joint2->m_index;
00410 
00411         b2Log("  b2GearJointDef jd;\n");
00412         b2Log("  jd.bodyA = bodies[%d];\n", indexA);
00413         b2Log("  jd.bodyB = bodies[%d];\n", indexB);
00414         b2Log("  jd.collideConnected = bool(%d);\n", m_collideConnected);
00415         b2Log("  jd.joint1 = joints[%d];\n", index1);
00416         b2Log("  jd.joint2 = joints[%d];\n", index2);
00417         b2Log("  jd.ratio = %.15lef;\n", m_ratio);
00418         b2Log("  joints[%d] = m_world->CreateJoint(&jd);\n", m_index);
00419 }


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autogenerated on Thu Jun 6 2019 22:08:34