349 lines
8.6 KiB
C++
349 lines
8.6 KiB
C++
/*
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* Copyright (c) 2007 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/b2PulleyJoint.h"
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#include "Box2D/Dynamics/b2Body.h"
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#include "Box2D/Dynamics/b2TimeStep.h"
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// Pulley:
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// length1 = norm(p1 - s1)
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// length2 = norm(p2 - s2)
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// C0 = (length1 + ratio * length2)_initial
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// C = C0 - (length1 + ratio * length2)
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// u1 = (p1 - s1) / norm(p1 - s1)
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// u2 = (p2 - s2) / norm(p2 - s2)
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// Cdot = -dot(u1, v1 + cross(w1, r1)) - ratio * dot(u2, v2 + cross(w2, r2))
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// J = -[u1 cross(r1, u1) ratio * u2 ratio * cross(r2, u2)]
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// K = J * invM * JT
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// = invMass1 + invI1 * cross(r1, u1)^2 + ratio^2 * (invMass2 + invI2 * cross(r2, u2)^2)
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void b2PulleyJointDef::Initialize(b2Body* bA, b2Body* bB,
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const b2Vec2& groundA, const b2Vec2& groundB,
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const b2Vec2& anchorA, const b2Vec2& anchorB,
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float32 r)
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{
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bodyA = bA;
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bodyB = bB;
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groundAnchorA = groundA;
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groundAnchorB = groundB;
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localAnchorA = bodyA->GetLocalPoint(anchorA);
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localAnchorB = bodyB->GetLocalPoint(anchorB);
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b2Vec2 dA = anchorA - groundA;
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lengthA = dA.Length();
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b2Vec2 dB = anchorB - groundB;
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lengthB = dB.Length();
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ratio = r;
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b2Assert(ratio > b2_epsilon);
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}
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b2PulleyJoint::b2PulleyJoint(const b2PulleyJointDef* def)
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: b2Joint(def)
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{
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m_groundAnchorA = def->groundAnchorA;
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m_groundAnchorB = def->groundAnchorB;
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m_localAnchorA = def->localAnchorA;
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m_localAnchorB = def->localAnchorB;
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m_lengthA = def->lengthA;
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m_lengthB = def->lengthB;
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b2Assert(def->ratio != 0.0f);
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m_ratio = def->ratio;
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m_constant = def->lengthA + m_ratio * def->lengthB;
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m_impulse = 0.0f;
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}
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void b2PulleyJoint::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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// Get the pulley axes.
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m_uA = cA + m_rA - m_groundAnchorA;
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m_uB = cB + m_rB - m_groundAnchorB;
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float32 lengthA = m_uA.Length();
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float32 lengthB = m_uB.Length();
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if (lengthA > 10.0f * b2_linearSlop)
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{
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m_uA *= 1.0f / lengthA;
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}
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else
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{
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m_uA.SetZero();
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}
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if (lengthB > 10.0f * b2_linearSlop)
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{
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m_uB *= 1.0f / lengthB;
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}
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else
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{
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m_uB.SetZero();
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}
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// Compute effective mass.
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float32 ruA = b2Cross(m_rA, m_uA);
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float32 ruB = b2Cross(m_rB, m_uB);
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float32 mA = m_invMassA + m_invIA * ruA * ruA;
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float32 mB = m_invMassB + m_invIB * ruB * ruB;
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m_mass = mA + m_ratio * m_ratio * mB;
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if (m_mass > 0.0f)
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{
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m_mass = 1.0f / m_mass;
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}
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if (data.step.warmStarting)
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{
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// Scale impulses to support variable time steps.
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m_impulse *= data.step.dtRatio;
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// Warm starting.
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b2Vec2 PA = -(m_impulse) * m_uA;
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b2Vec2 PB = (-m_ratio * m_impulse) * m_uB;
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vA += m_invMassA * PA;
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wA += m_invIA * b2Cross(m_rA, PA);
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vB += m_invMassB * PB;
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wB += m_invIB * b2Cross(m_rB, PB);
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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 b2PulleyJoint::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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b2Vec2 vpA = vA + b2Cross(wA, m_rA);
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b2Vec2 vpB = vB + b2Cross(wB, m_rB);
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float32 Cdot = -b2Dot(m_uA, vpA) - m_ratio * b2Dot(m_uB, vpB);
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float32 impulse = -m_mass * Cdot;
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m_impulse += impulse;
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b2Vec2 PA = -impulse * m_uA;
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b2Vec2 PB = -m_ratio * impulse * m_uB;
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vA += m_invMassA * PA;
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wA += m_invIA * b2Cross(m_rA, PA);
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vB += m_invMassB * PB;
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wB += m_invIB * b2Cross(m_rB, PB);
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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 b2PulleyJoint::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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// Get the pulley axes.
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b2Vec2 uA = cA + rA - m_groundAnchorA;
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b2Vec2 uB = cB + rB - m_groundAnchorB;
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float32 lengthA = uA.Length();
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float32 lengthB = uB.Length();
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if (lengthA > 10.0f * b2_linearSlop)
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{
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uA *= 1.0f / lengthA;
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}
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else
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{
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uA.SetZero();
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}
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if (lengthB > 10.0f * b2_linearSlop)
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{
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uB *= 1.0f / lengthB;
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}
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else
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{
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uB.SetZero();
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}
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// Compute effective mass.
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float32 ruA = b2Cross(rA, uA);
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float32 ruB = b2Cross(rB, uB);
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float32 mA = m_invMassA + m_invIA * ruA * ruA;
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float32 mB = m_invMassB + m_invIB * ruB * ruB;
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float32 mass = mA + m_ratio * m_ratio * mB;
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if (mass > 0.0f)
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{
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mass = 1.0f / mass;
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}
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float32 C = m_constant - lengthA - m_ratio * lengthB;
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float32 linearError = b2Abs(C);
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float32 impulse = -mass * C;
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b2Vec2 PA = -impulse * uA;
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b2Vec2 PB = -m_ratio * impulse * uB;
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cA += m_invMassA * PA;
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aA += m_invIA * b2Cross(rA, PA);
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cB += m_invMassB * PB;
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aB += m_invIB * b2Cross(rB, PB);
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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 linearError < b2_linearSlop;
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}
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b2Vec2 b2PulleyJoint::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 b2PulleyJoint::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 b2PulleyJoint::GetReactionForce(float32 inv_dt) const
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{
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b2Vec2 P = m_impulse * m_uB;
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return inv_dt * P;
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}
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float32 b2PulleyJoint::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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b2Vec2 b2PulleyJoint::GetGroundAnchorA() const
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{
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return m_groundAnchorA;
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}
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b2Vec2 b2PulleyJoint::GetGroundAnchorB() const
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{
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return m_groundAnchorB;
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}
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float32 b2PulleyJoint::GetLengthA() const
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{
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return m_lengthA;
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}
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float32 b2PulleyJoint::GetLengthB() const
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{
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return m_lengthB;
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}
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float32 b2PulleyJoint::GetRatio() const
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{
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return m_ratio;
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}
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float32 b2PulleyJoint::GetCurrentLengthA() const
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{
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b2Vec2 p = m_bodyA->GetWorldPoint(m_localAnchorA);
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b2Vec2 s = m_groundAnchorA;
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b2Vec2 d = p - s;
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return d.Length();
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}
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float32 b2PulleyJoint::GetCurrentLengthB() const
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{
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b2Vec2 p = m_bodyB->GetWorldPoint(m_localAnchorB);
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b2Vec2 s = m_groundAnchorB;
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b2Vec2 d = p - s;
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return d.Length();
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}
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void b2PulleyJoint::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(" b2PulleyJointDef 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.groundAnchorA.Set(%.15lef, %.15lef);\n", m_groundAnchorA.x, m_groundAnchorA.y);
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b2Log(" jd.groundAnchorB.Set(%.15lef, %.15lef);\n", m_groundAnchorB.x, m_groundAnchorB.y);
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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.lengthA = %.15lef;\n", m_lengthA);
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b2Log(" jd.lengthB = %.15lef;\n", m_lengthB);
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b2Log(" jd.ratio = %.15lef;\n", m_ratio);
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b2Log(" joints[%d] = m_world->CreateJoint(&jd);\n", m_index);
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}
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void b2PulleyJoint::ShiftOrigin(const b2Vec2& newOrigin)
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{
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m_groundAnchorA -= newOrigin;
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m_groundAnchorB -= newOrigin;
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}
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