457 lines
11 KiB
C++
457 lines
11 KiB
C++
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/*
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* Copyright (c) 2006-2007 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/b2WheelJoint.h"
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#include "Box2D/Dynamics/b2Body.h"
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#include "Box2D/Dynamics/b2TimeStep.h"
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// Linear constraint (point-to-line)
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// d = pB - pA = xB + rB - xA - rA
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// C = dot(ay, d)
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// Cdot = dot(d, cross(wA, ay)) + dot(ay, vB + cross(wB, rB) - vA - cross(wA, rA))
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// = -dot(ay, vA) - dot(cross(d + rA, ay), wA) + dot(ay, vB) + dot(cross(rB, ay), vB)
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// J = [-ay, -cross(d + rA, ay), ay, cross(rB, ay)]
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// Spring linear constraint
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// C = dot(ax, d)
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// Cdot = = -dot(ax, vA) - dot(cross(d + rA, ax), wA) + dot(ax, vB) + dot(cross(rB, ax), vB)
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// J = [-ax -cross(d+rA, ax) ax cross(rB, ax)]
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// Motor rotational constraint
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// Cdot = wB - wA
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// J = [0 0 -1 0 0 1]
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void b2WheelJointDef::Initialize(b2Body* bA, b2Body* bB, const b2Vec2& anchor, const b2Vec2& axis)
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{
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bodyA = bA;
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bodyB = bB;
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localAnchorA = bodyA->GetLocalPoint(anchor);
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localAnchorB = bodyB->GetLocalPoint(anchor);
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localAxisA = bodyA->GetLocalVector(axis);
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}
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b2WheelJoint::b2WheelJoint(const b2WheelJointDef* 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_localXAxisA = def->localAxisA;
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m_localYAxisA = b2Cross(1.0f, m_localXAxisA);
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m_mass = 0.0f;
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m_impulse = 0.0f;
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m_motorMass = 0.0f;
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m_motorImpulse = 0.0f;
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m_springMass = 0.0f;
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m_springImpulse = 0.0f;
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m_maxMotorTorque = def->maxMotorTorque;
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m_motorSpeed = def->motorSpeed;
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m_enableMotor = def->enableMotor;
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m_frequencyHz = def->frequencyHz;
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m_dampingRatio = def->dampingRatio;
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m_bias = 0.0f;
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m_gamma = 0.0f;
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m_ax.SetZero();
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m_ay.SetZero();
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}
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void b2WheelJoint::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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float32 mA = m_invMassA, mB = m_invMassB;
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float32 iA = m_invIA, iB = m_invIB;
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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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// Compute the effective masses.
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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 d = cB + rB - cA - rA;
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// Point to line constraint
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{
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m_ay = b2Mul(qA, m_localYAxisA);
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m_sAy = b2Cross(d + rA, m_ay);
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m_sBy = b2Cross(rB, m_ay);
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m_mass = mA + mB + iA * m_sAy * m_sAy + iB * m_sBy * m_sBy;
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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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}
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// Spring constraint
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m_springMass = 0.0f;
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m_bias = 0.0f;
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m_gamma = 0.0f;
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if (m_frequencyHz > 0.0f)
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{
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m_ax = b2Mul(qA, m_localXAxisA);
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m_sAx = b2Cross(d + rA, m_ax);
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m_sBx = b2Cross(rB, m_ax);
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float32 invMass = mA + mB + iA * m_sAx * m_sAx + iB * m_sBx * m_sBx;
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if (invMass > 0.0f)
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{
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m_springMass = 1.0f / invMass;
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float32 C = b2Dot(d, m_ax);
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// Frequency
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float32 omega = 2.0f * b2_pi * m_frequencyHz;
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// Damping coefficient
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float32 damp = 2.0f * m_springMass * m_dampingRatio * omega;
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// Spring stiffness
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float32 k = m_springMass * omega * omega;
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// magic formulas
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float32 h = data.step.dt;
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m_gamma = h * (damp + h * k);
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if (m_gamma > 0.0f)
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{
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m_gamma = 1.0f / m_gamma;
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}
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m_bias = C * h * k * m_gamma;
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m_springMass = invMass + m_gamma;
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if (m_springMass > 0.0f)
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{
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m_springMass = 1.0f / m_springMass;
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}
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}
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}
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else
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{
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m_springImpulse = 0.0f;
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}
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// Rotational motor
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if (m_enableMotor)
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{
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m_motorMass = iA + iB;
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if (m_motorMass > 0.0f)
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{
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m_motorMass = 1.0f / m_motorMass;
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}
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}
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else
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{
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m_motorMass = 0.0f;
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m_motorImpulse = 0.0f;
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}
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if (data.step.warmStarting)
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{
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// Account for variable time step.
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m_impulse *= data.step.dtRatio;
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m_springImpulse *= data.step.dtRatio;
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m_motorImpulse *= data.step.dtRatio;
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b2Vec2 P = m_impulse * m_ay + m_springImpulse * m_ax;
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float32 LA = m_impulse * m_sAy + m_springImpulse * m_sAx + m_motorImpulse;
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float32 LB = m_impulse * m_sBy + m_springImpulse * m_sBx + m_motorImpulse;
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vA -= m_invMassA * P;
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wA -= m_invIA * LA;
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vB += m_invMassB * P;
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wB += m_invIB * LB;
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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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m_springImpulse = 0.0f;
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m_motorImpulse = 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 b2WheelJoint::SolveVelocityConstraints(const b2SolverData& data)
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{
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float32 mA = m_invMassA, mB = m_invMassB;
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float32 iA = m_invIA, iB = m_invIB;
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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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// Solve spring constraint
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{
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float32 Cdot = b2Dot(m_ax, vB - vA) + m_sBx * wB - m_sAx * wA;
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float32 impulse = -m_springMass * (Cdot + m_bias + m_gamma * m_springImpulse);
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m_springImpulse += impulse;
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b2Vec2 P = impulse * m_ax;
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float32 LA = impulse * m_sAx;
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float32 LB = impulse * m_sBx;
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vA -= mA * P;
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wA -= iA * LA;
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vB += mB * P;
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wB += iB * LB;
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}
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// Solve rotational motor constraint
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{
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float32 Cdot = wB - wA - m_motorSpeed;
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float32 impulse = -m_motorMass * Cdot;
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float32 oldImpulse = m_motorImpulse;
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float32 maxImpulse = data.step.dt * m_maxMotorTorque;
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m_motorImpulse = b2Clamp(m_motorImpulse + impulse, -maxImpulse, maxImpulse);
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impulse = m_motorImpulse - oldImpulse;
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wA -= iA * impulse;
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wB += iB * impulse;
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}
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// Solve point to line constraint
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{
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float32 Cdot = b2Dot(m_ay, vB - vA) + m_sBy * wB - m_sAy * wA;
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float32 impulse = -m_mass * Cdot;
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m_impulse += impulse;
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b2Vec2 P = impulse * m_ay;
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float32 LA = impulse * m_sAy;
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float32 LB = impulse * m_sBy;
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vA -= mA * P;
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wA -= iA * LA;
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vB += mB * P;
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wB += iB * LB;
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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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bool b2WheelJoint::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 d = (cB - cA) + rB - rA;
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b2Vec2 ay = b2Mul(qA, m_localYAxisA);
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float32 sAy = b2Cross(d + rA, ay);
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float32 sBy = b2Cross(rB, ay);
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float32 C = b2Dot(d, ay);
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float32 k = m_invMassA + m_invMassB + m_invIA * m_sAy * m_sAy + m_invIB * m_sBy * m_sBy;
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float32 impulse;
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if (k != 0.0f)
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{
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impulse = - C / k;
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}
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else
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{
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impulse = 0.0f;
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}
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b2Vec2 P = impulse * ay;
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float32 LA = impulse * sAy;
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float32 LB = impulse * sBy;
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cA -= m_invMassA * P;
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aA -= m_invIA * LA;
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cB += m_invMassB * P;
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aB += m_invIB * LB;
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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 b2Abs(C) <= b2_linearSlop;
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}
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b2Vec2 b2WheelJoint::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 b2WheelJoint::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 b2WheelJoint::GetReactionForce(float32 inv_dt) const
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{
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return inv_dt * (m_impulse * m_ay + m_springImpulse * m_ax);
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}
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float32 b2WheelJoint::GetReactionTorque(float32 inv_dt) const
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{
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return inv_dt * m_motorImpulse;
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}
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float32 b2WheelJoint::GetJointTranslation() const
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{
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b2Body* bA = m_bodyA;
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b2Body* bB = m_bodyB;
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|
|
|
||
|
|
b2Vec2 pA = bA->GetWorldPoint(m_localAnchorA);
|
||
|
|
b2Vec2 pB = bB->GetWorldPoint(m_localAnchorB);
|
||
|
|
b2Vec2 d = pB - pA;
|
||
|
|
b2Vec2 axis = bA->GetWorldVector(m_localXAxisA);
|
||
|
|
|
||
|
|
float32 translation = b2Dot(d, axis);
|
||
|
|
return translation;
|
||
|
|
}
|
||
|
|
|
||
|
|
float32 b2WheelJoint::GetJointLinearSpeed() const
|
||
|
|
{
|
||
|
|
b2Body* bA = m_bodyA;
|
||
|
|
b2Body* bB = m_bodyB;
|
||
|
|
|
||
|
|
b2Vec2 rA = b2Mul(bA->m_xf.q, m_localAnchorA - bA->m_sweep.localCenter);
|
||
|
|
b2Vec2 rB = b2Mul(bB->m_xf.q, m_localAnchorB - bB->m_sweep.localCenter);
|
||
|
|
b2Vec2 p1 = bA->m_sweep.c + rA;
|
||
|
|
b2Vec2 p2 = bB->m_sweep.c + rB;
|
||
|
|
b2Vec2 d = p2 - p1;
|
||
|
|
b2Vec2 axis = b2Mul(bA->m_xf.q, m_localXAxisA);
|
||
|
|
|
||
|
|
b2Vec2 vA = bA->m_linearVelocity;
|
||
|
|
b2Vec2 vB = bB->m_linearVelocity;
|
||
|
|
float32 wA = bA->m_angularVelocity;
|
||
|
|
float32 wB = bB->m_angularVelocity;
|
||
|
|
|
||
|
|
float32 speed = b2Dot(d, b2Cross(wA, axis)) + b2Dot(axis, vB + b2Cross(wB, rB) - vA - b2Cross(wA, rA));
|
||
|
|
return speed;
|
||
|
|
}
|
||
|
|
|
||
|
|
float32 b2WheelJoint::GetJointAngle() const
|
||
|
|
{
|
||
|
|
b2Body* bA = m_bodyA;
|
||
|
|
b2Body* bB = m_bodyB;
|
||
|
|
return bB->m_sweep.a - bA->m_sweep.a;
|
||
|
|
}
|
||
|
|
|
||
|
|
float32 b2WheelJoint::GetJointAngularSpeed() const
|
||
|
|
{
|
||
|
|
float32 wA = m_bodyA->m_angularVelocity;
|
||
|
|
float32 wB = m_bodyB->m_angularVelocity;
|
||
|
|
return wB - wA;
|
||
|
|
}
|
||
|
|
|
||
|
|
bool b2WheelJoint::IsMotorEnabled() const
|
||
|
|
{
|
||
|
|
return m_enableMotor;
|
||
|
|
}
|
||
|
|
|
||
|
|
void b2WheelJoint::EnableMotor(bool flag)
|
||
|
|
{
|
||
|
|
if (flag != m_enableMotor)
|
||
|
|
{
|
||
|
|
m_bodyA->SetAwake(true);
|
||
|
|
m_bodyB->SetAwake(true);
|
||
|
|
m_enableMotor = flag;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
void b2WheelJoint::SetMotorSpeed(float32 speed)
|
||
|
|
{
|
||
|
|
if (speed != m_motorSpeed)
|
||
|
|
{
|
||
|
|
m_bodyA->SetAwake(true);
|
||
|
|
m_bodyB->SetAwake(true);
|
||
|
|
m_motorSpeed = speed;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
void b2WheelJoint::SetMaxMotorTorque(float32 torque)
|
||
|
|
{
|
||
|
|
if (torque != m_maxMotorTorque)
|
||
|
|
{
|
||
|
|
m_bodyA->SetAwake(true);
|
||
|
|
m_bodyB->SetAwake(true);
|
||
|
|
m_maxMotorTorque = torque;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
float32 b2WheelJoint::GetMotorTorque(float32 inv_dt) const
|
||
|
|
{
|
||
|
|
return inv_dt * m_motorImpulse;
|
||
|
|
}
|
||
|
|
|
||
|
|
void b2WheelJoint::Dump()
|
||
|
|
{
|
||
|
|
int32 indexA = m_bodyA->m_islandIndex;
|
||
|
|
int32 indexB = m_bodyB->m_islandIndex;
|
||
|
|
|
||
|
|
b2Log(" b2WheelJointDef 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.localAxisA.Set(%.15lef, %.15lef);\n", m_localXAxisA.x, m_localXAxisA.y);
|
||
|
|
b2Log(" jd.enableMotor = bool(%d);\n", m_enableMotor);
|
||
|
|
b2Log(" jd.motorSpeed = %.15lef;\n", m_motorSpeed);
|
||
|
|
b2Log(" jd.maxMotorTorque = %.15lef;\n", m_maxMotorTorque);
|
||
|
|
b2Log(" jd.frequencyHz = %.15lef;\n", m_frequencyHz);
|
||
|
|
b2Log(" jd.dampingRatio = %.15lef;\n", m_dampingRatio);
|
||
|
|
b2Log(" joints[%d] = m_world->CreateJoint(&jd);\n", m_index);
|
||
|
|
}
|