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00019 #include <Box2D/Dynamics/Joints/b2DistanceJoint.h>
00020 #include <Box2D/Dynamics/b2Body.h>
00021 #include <Box2D/Dynamics/b2TimeStep.h>
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00038 void b2DistanceJointDef::Initialize(b2Body* b1, b2Body* b2,
00039 const b2Vec2& anchor1, const b2Vec2& anchor2)
00040 {
00041 bodyA = b1;
00042 bodyB = b2;
00043 localAnchorA = bodyA->GetLocalPoint(anchor1);
00044 localAnchorB = bodyB->GetLocalPoint(anchor2);
00045 b2Vec2 d = anchor2 - anchor1;
00046 length = d.Length();
00047 }
00048
00049 b2DistanceJoint::b2DistanceJoint(const b2DistanceJointDef* def)
00050 : b2Joint(def)
00051 {
00052 m_localAnchorA = def->localAnchorA;
00053 m_localAnchorB = def->localAnchorB;
00054 m_length = def->length;
00055 m_frequencyHz = def->frequencyHz;
00056 m_dampingRatio = def->dampingRatio;
00057 m_impulse = 0.0f;
00058 m_gamma = 0.0f;
00059 m_bias = 0.0f;
00060 }
00061
00062 void b2DistanceJoint::InitVelocityConstraints(const b2SolverData& data)
00063 {
00064 m_indexA = m_bodyA->m_islandIndex;
00065 m_indexB = m_bodyB->m_islandIndex;
00066 m_localCenterA = m_bodyA->m_sweep.localCenter;
00067 m_localCenterB = m_bodyB->m_sweep.localCenter;
00068 m_invMassA = m_bodyA->m_invMass;
00069 m_invMassB = m_bodyB->m_invMass;
00070 m_invIA = m_bodyA->m_invI;
00071 m_invIB = m_bodyB->m_invI;
00072
00073 b2Vec2 cA = data.positions[m_indexA].c;
00074 float32 aA = data.positions[m_indexA].a;
00075 b2Vec2 vA = data.velocities[m_indexA].v;
00076 float32 wA = data.velocities[m_indexA].w;
00077
00078 b2Vec2 cB = data.positions[m_indexB].c;
00079 float32 aB = data.positions[m_indexB].a;
00080 b2Vec2 vB = data.velocities[m_indexB].v;
00081 float32 wB = data.velocities[m_indexB].w;
00082
00083 b2Rot qA(aA), qB(aB);
00084
00085 m_rA = b2Mul(qA, m_localAnchorA - m_localCenterA);
00086 m_rB = b2Mul(qB, m_localAnchorB - m_localCenterB);
00087 m_u = cB + m_rB - cA - m_rA;
00088
00089
00090 float32 length = m_u.Length();
00091 if (length > b2_linearSlop)
00092 {
00093 m_u *= 1.0f / length;
00094 }
00095 else
00096 {
00097 m_u.Set(0.0f, 0.0f);
00098 }
00099
00100 float32 crAu = b2Cross(m_rA, m_u);
00101 float32 crBu = b2Cross(m_rB, m_u);
00102 float32 invMass = m_invMassA + m_invIA * crAu * crAu + m_invMassB + m_invIB * crBu * crBu;
00103
00104
00105 m_mass = invMass != 0.0f ? 1.0f / invMass : 0.0f;
00106
00107 if (m_frequencyHz > 0.0f)
00108 {
00109 float32 C = length - m_length;
00110
00111
00112 float32 omega = 2.0f * b2_pi * m_frequencyHz;
00113
00114
00115 float32 d = 2.0f * m_mass * m_dampingRatio * omega;
00116
00117
00118 float32 k = m_mass * omega * omega;
00119
00120
00121 float32 h = data.step.dt;
00122 m_gamma = h * (d + h * k);
00123 m_gamma = m_gamma != 0.0f ? 1.0f / m_gamma : 0.0f;
00124 m_bias = C * h * k * m_gamma;
00125
00126 invMass += m_gamma;
00127 m_mass = invMass != 0.0f ? 1.0f / invMass : 0.0f;
00128 }
00129 else
00130 {
00131 m_gamma = 0.0f;
00132 m_bias = 0.0f;
00133 }
00134
00135 if (data.step.warmStarting)
00136 {
00137
00138 m_impulse *= data.step.dtRatio;
00139
00140 b2Vec2 P = m_impulse * m_u;
00141 vA -= m_invMassA * P;
00142 wA -= m_invIA * b2Cross(m_rA, P);
00143 vB += m_invMassB * P;
00144 wB += m_invIB * b2Cross(m_rB, P);
00145 }
00146 else
00147 {
00148 m_impulse = 0.0f;
00149 }
00150
00151 data.velocities[m_indexA].v = vA;
00152 data.velocities[m_indexA].w = wA;
00153 data.velocities[m_indexB].v = vB;
00154 data.velocities[m_indexB].w = wB;
00155 }
00156
00157 void b2DistanceJoint::SolveVelocityConstraints(const b2SolverData& data)
00158 {
00159 b2Vec2 vA = data.velocities[m_indexA].v;
00160 float32 wA = data.velocities[m_indexA].w;
00161 b2Vec2 vB = data.velocities[m_indexB].v;
00162 float32 wB = data.velocities[m_indexB].w;
00163
00164
00165 b2Vec2 vpA = vA + b2Cross(wA, m_rA);
00166 b2Vec2 vpB = vB + b2Cross(wB, m_rB);
00167 float32 Cdot = b2Dot(m_u, vpB - vpA);
00168
00169 float32 impulse = -m_mass * (Cdot + m_bias + m_gamma * m_impulse);
00170 m_impulse += impulse;
00171
00172 b2Vec2 P = impulse * m_u;
00173 vA -= m_invMassA * P;
00174 wA -= m_invIA * b2Cross(m_rA, P);
00175 vB += m_invMassB * P;
00176 wB += m_invIB * b2Cross(m_rB, P);
00177
00178 data.velocities[m_indexA].v = vA;
00179 data.velocities[m_indexA].w = wA;
00180 data.velocities[m_indexB].v = vB;
00181 data.velocities[m_indexB].w = wB;
00182 }
00183
00184 bool b2DistanceJoint::SolvePositionConstraints(const b2SolverData& data)
00185 {
00186 if (m_frequencyHz > 0.0f)
00187 {
00188
00189 return true;
00190 }
00191
00192 b2Vec2 cA = data.positions[m_indexA].c;
00193 float32 aA = data.positions[m_indexA].a;
00194 b2Vec2 cB = data.positions[m_indexB].c;
00195 float32 aB = data.positions[m_indexB].a;
00196
00197 b2Rot qA(aA), qB(aB);
00198
00199 b2Vec2 rA = b2Mul(qA, m_localAnchorA - m_localCenterA);
00200 b2Vec2 rB = b2Mul(qB, m_localAnchorB - m_localCenterB);
00201 b2Vec2 u = cB + rB - cA - rA;
00202
00203 float32 length = u.Normalize();
00204 float32 C = length - m_length;
00205 C = b2Clamp(C, -b2_maxLinearCorrection, b2_maxLinearCorrection);
00206
00207 float32 impulse = -m_mass * C;
00208 b2Vec2 P = impulse * u;
00209
00210 cA -= m_invMassA * P;
00211 aA -= m_invIA * b2Cross(rA, P);
00212 cB += m_invMassB * P;
00213 aB += m_invIB * b2Cross(rB, P);
00214
00215 data.positions[m_indexA].c = cA;
00216 data.positions[m_indexA].a = aA;
00217 data.positions[m_indexB].c = cB;
00218 data.positions[m_indexB].a = aB;
00219
00220 return b2Abs(C) < b2_linearSlop;
00221 }
00222
00223 b2Vec2 b2DistanceJoint::GetAnchorA() const
00224 {
00225 return m_bodyA->GetWorldPoint(m_localAnchorA);
00226 }
00227
00228 b2Vec2 b2DistanceJoint::GetAnchorB() const
00229 {
00230 return m_bodyB->GetWorldPoint(m_localAnchorB);
00231 }
00232
00233 b2Vec2 b2DistanceJoint::GetReactionForce(float32 inv_dt) const
00234 {
00235 b2Vec2 F = (inv_dt * m_impulse) * m_u;
00236 return F;
00237 }
00238
00239 float32 b2DistanceJoint::GetReactionTorque(float32 inv_dt) const
00240 {
00241 B2_NOT_USED(inv_dt);
00242 return 0.0f;
00243 }
00244
00245 void b2DistanceJoint::Dump()
00246 {
00247 int32 indexA = m_bodyA->m_islandIndex;
00248 int32 indexB = m_bodyB->m_islandIndex;
00249
00250 b2Log(" b2DistanceJointDef jd;\n");
00251 b2Log(" jd.bodyA = bodies[%d];\n", indexA);
00252 b2Log(" jd.bodyB = bodies[%d];\n", indexB);
00253 b2Log(" jd.collideConnected = bool(%d);\n", m_collideConnected);
00254 b2Log(" jd.localAnchorA.Set(%.15lef, %.15lef);\n", m_localAnchorA.x, m_localAnchorA.y);
00255 b2Log(" jd.localAnchorB.Set(%.15lef, %.15lef);\n", m_localAnchorB.x, m_localAnchorB.y);
00256 b2Log(" jd.length = %.15lef;\n", m_length);
00257 b2Log(" jd.frequencyHz = %.15lef;\n", m_frequencyHz);
00258 b2Log(" jd.dampingRatio = %.15lef;\n", m_dampingRatio);
00259 b2Log(" joints[%d] = m_world->CreateJoint(&jd);\n", m_index);
00260 }