242 lines
6.2 KiB
C++
242 lines
6.2 KiB
C++
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/*
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* Copyright (c) 2007-2011 Erin Catto http://www.box2d.org
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*
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* This software is provided 'as-is', without any express or implied
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* warranty. In no event will the authors be held liable for any damages
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* arising from the use of this software.
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* Permission is granted to anyone to use this software for any purpose,
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* including commercial applications, and to alter it and redistribute it
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* freely, subject to the following restrictions:
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* 1. The origin of this software must not be misrepresented; you must not
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* claim that you wrote the original software. If you use this software
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* in a product, an acknowledgment in the product documentation would be
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* appreciated but is not required.
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* 2. Altered source versions must be plainly marked as such, and must not be
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* misrepresented as being the original software.
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* 3. This notice may not be removed or altered from any source distribution.
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*/
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#include "Box2D/Dynamics/Joints/b2RopeJoint.h"
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#include "Box2D/Dynamics/b2Body.h"
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#include "Box2D/Dynamics/b2TimeStep.h"
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// Limit:
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// C = norm(pB - pA) - L
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// u = (pB - pA) / norm(pB - pA)
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// Cdot = dot(u, vB + cross(wB, rB) - vA - cross(wA, rA))
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// J = [-u -cross(rA, u) u cross(rB, u)]
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// K = J * invM * JT
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// = invMassA + invIA * cross(rA, u)^2 + invMassB + invIB * cross(rB, u)^2
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b2RopeJoint::b2RopeJoint(const b2RopeJointDef* def)
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: b2Joint(def)
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{
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m_localAnchorA = def->localAnchorA;
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m_localAnchorB = def->localAnchorB;
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m_maxLength = def->maxLength;
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m_mass = 0.0f;
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m_impulse = 0.0f;
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m_state = e_inactiveLimit;
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m_length = 0.0f;
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}
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void b2RopeJoint::InitVelocityConstraints(const b2SolverData& data)
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{
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m_indexA = m_bodyA->m_islandIndex;
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m_indexB = m_bodyB->m_islandIndex;
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m_localCenterA = m_bodyA->m_sweep.localCenter;
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m_localCenterB = m_bodyB->m_sweep.localCenter;
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m_invMassA = m_bodyA->m_invMass;
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m_invMassB = m_bodyB->m_invMass;
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m_invIA = m_bodyA->m_invI;
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m_invIB = m_bodyB->m_invI;
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b2Vec2 cA = data.positions[m_indexA].c;
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float32 aA = data.positions[m_indexA].a;
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b2Vec2 vA = data.velocities[m_indexA].v;
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float32 wA = data.velocities[m_indexA].w;
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b2Vec2 cB = data.positions[m_indexB].c;
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float32 aB = data.positions[m_indexB].a;
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b2Vec2 vB = data.velocities[m_indexB].v;
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float32 wB = data.velocities[m_indexB].w;
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b2Rot qA(aA), qB(aB);
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m_rA = b2Mul(qA, m_localAnchorA - m_localCenterA);
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m_rB = b2Mul(qB, m_localAnchorB - m_localCenterB);
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m_u = cB + m_rB - cA - m_rA;
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m_length = m_u.Length();
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float32 C = m_length - m_maxLength;
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if (C > 0.0f)
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{
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m_state = e_atUpperLimit;
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}
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else
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{
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m_state = e_inactiveLimit;
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}
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if (m_length > b2_linearSlop)
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{
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m_u *= 1.0f / m_length;
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}
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else
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{
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m_u.SetZero();
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m_mass = 0.0f;
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m_impulse = 0.0f;
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return;
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}
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// Compute effective mass.
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float32 crA = b2Cross(m_rA, m_u);
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float32 crB = b2Cross(m_rB, m_u);
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float32 invMass = m_invMassA + m_invIA * crA * crA + m_invMassB + m_invIB * crB * crB;
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m_mass = invMass != 0.0f ? 1.0f / invMass : 0.0f;
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if (data.step.warmStarting)
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{
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// Scale the impulse to support a variable time step.
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m_impulse *= data.step.dtRatio;
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b2Vec2 P = m_impulse * m_u;
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vA -= m_invMassA * P;
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wA -= m_invIA * b2Cross(m_rA, P);
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vB += m_invMassB * P;
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wB += m_invIB * b2Cross(m_rB, P);
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}
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else
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{
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m_impulse = 0.0f;
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}
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data.velocities[m_indexA].v = vA;
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data.velocities[m_indexA].w = wA;
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data.velocities[m_indexB].v = vB;
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data.velocities[m_indexB].w = wB;
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}
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void b2RopeJoint::SolveVelocityConstraints(const b2SolverData& data)
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{
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b2Vec2 vA = data.velocities[m_indexA].v;
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float32 wA = data.velocities[m_indexA].w;
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b2Vec2 vB = data.velocities[m_indexB].v;
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float32 wB = data.velocities[m_indexB].w;
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// Cdot = dot(u, v + cross(w, r))
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b2Vec2 vpA = vA + b2Cross(wA, m_rA);
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b2Vec2 vpB = vB + b2Cross(wB, m_rB);
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float32 C = m_length - m_maxLength;
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float32 Cdot = b2Dot(m_u, vpB - vpA);
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// Predictive constraint.
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if (C < 0.0f)
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{
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Cdot += data.step.inv_dt * C;
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}
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float32 impulse = -m_mass * Cdot;
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float32 oldImpulse = m_impulse;
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m_impulse = b2Min(0.0f, m_impulse + impulse);
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impulse = m_impulse - oldImpulse;
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b2Vec2 P = impulse * m_u;
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vA -= m_invMassA * P;
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wA -= m_invIA * b2Cross(m_rA, P);
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vB += m_invMassB * P;
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wB += m_invIB * b2Cross(m_rB, P);
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data.velocities[m_indexA].v = vA;
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data.velocities[m_indexA].w = wA;
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data.velocities[m_indexB].v = vB;
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data.velocities[m_indexB].w = wB;
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}
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bool b2RopeJoint::SolvePositionConstraints(const b2SolverData& data)
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{
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b2Vec2 cA = data.positions[m_indexA].c;
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float32 aA = data.positions[m_indexA].a;
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b2Vec2 cB = data.positions[m_indexB].c;
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float32 aB = data.positions[m_indexB].a;
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b2Rot qA(aA), qB(aB);
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b2Vec2 rA = b2Mul(qA, m_localAnchorA - m_localCenterA);
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b2Vec2 rB = b2Mul(qB, m_localAnchorB - m_localCenterB);
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b2Vec2 u = cB + rB - cA - rA;
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float32 length = u.Normalize();
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float32 C = length - m_maxLength;
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C = b2Clamp(C, 0.0f, b2_maxLinearCorrection);
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float32 impulse = -m_mass * C;
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b2Vec2 P = impulse * u;
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cA -= m_invMassA * P;
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aA -= m_invIA * b2Cross(rA, P);
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cB += m_invMassB * P;
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aB += m_invIB * b2Cross(rB, P);
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data.positions[m_indexA].c = cA;
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data.positions[m_indexA].a = aA;
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data.positions[m_indexB].c = cB;
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data.positions[m_indexB].a = aB;
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return length - m_maxLength < b2_linearSlop;
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}
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b2Vec2 b2RopeJoint::GetAnchorA() const
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{
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return m_bodyA->GetWorldPoint(m_localAnchorA);
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}
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b2Vec2 b2RopeJoint::GetAnchorB() const
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{
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return m_bodyB->GetWorldPoint(m_localAnchorB);
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}
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b2Vec2 b2RopeJoint::GetReactionForce(float32 inv_dt) const
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{
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b2Vec2 F = (inv_dt * m_impulse) * m_u;
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return F;
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}
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float32 b2RopeJoint::GetReactionTorque(float32 inv_dt) const
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{
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B2_NOT_USED(inv_dt);
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return 0.0f;
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}
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float32 b2RopeJoint::GetMaxLength() const
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{
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return m_maxLength;
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}
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b2LimitState b2RopeJoint::GetLimitState() const
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{
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return m_state;
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}
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void b2RopeJoint::Dump()
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{
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int32 indexA = m_bodyA->m_islandIndex;
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int32 indexB = m_bodyB->m_islandIndex;
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b2Log(" b2RopeJointDef jd;\n");
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b2Log(" jd.bodyA = bodies[%d];\n", indexA);
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b2Log(" jd.bodyB = bodies[%d];\n", indexB);
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b2Log(" jd.collideConnected = bool(%d);\n", m_collideConnected);
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b2Log(" jd.localAnchorA.Set(%.15lef, %.15lef);\n", m_localAnchorA.x, m_localAnchorA.y);
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b2Log(" jd.localAnchorB.Set(%.15lef, %.15lef);\n", m_localAnchorB.x, m_localAnchorB.y);
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b2Log(" jd.maxLength = %.15lef;\n", m_maxLength);
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b2Log(" joints[%d] = m_world->CreateJoint(&jd);\n", m_index);
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}
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