/*******************************************************************************
* Copyright (c) 2013, Daniel Murphy
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without modification,
* are permitted provided that the following conditions are met:
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
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*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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******************************************************************************/
/**
* Created at 12:12:02 PM Jan 23, 2011
*/
package org.jbox2d.dynamics.joints;
import org.jbox2d.common.MathUtils;
import org.jbox2d.common.Rot;
import org.jbox2d.common.Settings;
import org.jbox2d.common.Vec2;
import org.jbox2d.dynamics.SolverData;
import org.jbox2d.pooling.IWorldPool;
/**
* The pulley joint is connected to two bodies and two fixed ground points. The pulley supports a
* ratio such that: length1 + ratio * length2 <= constant Yes, the force transmitted is scaled by
* the ratio. Warning: the pulley joint can get a bit squirrelly by itself. They often work better
* when combined with prismatic joints. You should also cover the the anchor points with static
* shapes to prevent one side from going to zero length.
*
* @author Daniel Murphy
*/
public class PulleyJoint extends Joint {
public static final float MIN_PULLEY_LENGTH = 2.0f;
private final Vec2 m_groundAnchorA = new Vec2();
private final Vec2 m_groundAnchorB = new Vec2();
private float m_lengthA;
private float m_lengthB;
// Solver shared
private final Vec2 m_localAnchorA = new Vec2();
private final Vec2 m_localAnchorB = new Vec2();
private float m_constant;
private float m_ratio;
private float m_impulse;
// Solver temp
private int m_indexA;
private int m_indexB;
private final Vec2 m_uA = new Vec2();
private final Vec2 m_uB = new Vec2();
private final Vec2 m_rA = new Vec2();
private final Vec2 m_rB = new Vec2();
private final Vec2 m_localCenterA = new Vec2();
private final Vec2 m_localCenterB = new Vec2();
private float m_invMassA;
private float m_invMassB;
private float m_invIA;
private float m_invIB;
private float m_mass;
protected PulleyJoint(IWorldPool argWorldPool, PulleyJointDef def) {
super(argWorldPool, def);
m_groundAnchorA.set(def.groundAnchorA);
m_groundAnchorB.set(def.groundAnchorB);
m_localAnchorA.set(def.localAnchorA);
m_localAnchorB.set(def.localAnchorB);
assert (def.ratio != 0.0f);
m_ratio = def.ratio;
m_lengthA = def.lengthA;
m_lengthB = def.lengthB;
m_constant = def.lengthA + m_ratio * def.lengthB;
m_impulse = 0.0f;
}
public float getLengthA() {
return m_lengthA;
}
public float getLengthB() {
return m_lengthB;
}
public float getCurrentLengthA() {
final Vec2 p = pool.popVec2();
m_bodyA.getWorldPointToOut(m_localAnchorA, p);
p.subLocal(m_groundAnchorA);
float length = p.length();
pool.pushVec2(1);
return length;
}
public float getCurrentLengthB() {
final Vec2 p = pool.popVec2();
m_bodyB.getWorldPointToOut(m_localAnchorB, p);
p.subLocal(m_groundAnchorB);
float length = p.length();
pool.pushVec2(1);
return length;
}
public Vec2 getLocalAnchorA() {
return m_localAnchorA;
}
public Vec2 getLocalAnchorB() {
return m_localAnchorB;
}
@Override
public void getAnchorA(Vec2 argOut) {
m_bodyA.getWorldPointToOut(m_localAnchorA, argOut);
}
@Override
public void getAnchorB(Vec2 argOut) {
m_bodyB.getWorldPointToOut(m_localAnchorB, argOut);
}
@Override
public void getReactionForce(float inv_dt, Vec2 argOut) {
argOut.set(m_uB).mulLocal(m_impulse).mulLocal(inv_dt);
}
@Override
public float getReactionTorque(float inv_dt) {
return 0f;
}
public Vec2 getGroundAnchorA() {
return m_groundAnchorA;
}
public Vec2 getGroundAnchorB() {
return m_groundAnchorB;
}
public float getLength1() {
final Vec2 p = pool.popVec2();
m_bodyA.getWorldPointToOut(m_localAnchorA, p);
p.subLocal(m_groundAnchorA);
float len = p.length();
pool.pushVec2(1);
return len;
}
public float getLength2() {
final Vec2 p = pool.popVec2();
m_bodyB.getWorldPointToOut(m_localAnchorB, p);
p.subLocal(m_groundAnchorB);
float len = p.length();
pool.pushVec2(1);
return len;
}
public float getRatio() {
return m_ratio;
}
@Override
public void initVelocityConstraints(final SolverData data) {
m_indexA = m_bodyA.m_islandIndex;
m_indexB = m_bodyB.m_islandIndex;
m_localCenterA.set(m_bodyA.m_sweep.localCenter);
m_localCenterB.set(m_bodyB.m_sweep.localCenter);
m_invMassA = m_bodyA.m_invMass;
m_invMassB = m_bodyB.m_invMass;
m_invIA = m_bodyA.m_invI;
m_invIB = m_bodyB.m_invI;
Vec2 cA = data.positions[m_indexA].c;
float aA = data.positions[m_indexA].a;
Vec2 vA = data.velocities[m_indexA].v;
float wA = data.velocities[m_indexA].w;
Vec2 cB = data.positions[m_indexB].c;
float aB = data.positions[m_indexB].a;
Vec2 vB = data.velocities[m_indexB].v;
float wB = data.velocities[m_indexB].w;
final Rot qA = pool.popRot();
final Rot qB = pool.popRot();
final Vec2 temp = pool.popVec2();
qA.set(aA);
qB.set(aB);
// Compute the effective masses.
Rot.mulToOutUnsafe(qA, temp.set(m_localAnchorA).subLocal(m_localCenterA), m_rA);
Rot.mulToOutUnsafe(qB, temp.set(m_localAnchorB).subLocal(m_localCenterB), m_rB);
m_uA.set(cA).addLocal(m_rA).subLocal(m_groundAnchorA);
m_uB.set(cB).addLocal(m_rB).subLocal(m_groundAnchorB);
float lengthA = m_uA.length();
float lengthB = m_uB.length();
if (lengthA > 10f * Settings.linearSlop) {
m_uA.mulLocal(1.0f / lengthA);
} else {
m_uA.setZero();
}
if (lengthB > 10f * Settings.linearSlop) {
m_uB.mulLocal(1.0f / lengthB);
} else {
m_uB.setZero();
}
// Compute effective mass.
float ruA = Vec2.cross(m_rA, m_uA);
float ruB = Vec2.cross(m_rB, m_uB);
float mA = m_invMassA + m_invIA * ruA * ruA;
float mB = m_invMassB + m_invIB * ruB * ruB;
m_mass = mA + m_ratio * m_ratio * mB;
if (m_mass > 0.0f) {
m_mass = 1.0f / m_mass;
}
if (data.step.warmStarting) {
// Scale impulses to support variable time steps.
m_impulse *= data.step.dtRatio;
// Warm starting.
final Vec2 PA = pool.popVec2();
final Vec2 PB = pool.popVec2();
PA.set(m_uA).mulLocal(-m_impulse);
PB.set(m_uB).mulLocal(-m_ratio * m_impulse);
vA.x += m_invMassA * PA.x;
vA.y += m_invMassA * PA.y;
wA += m_invIA * Vec2.cross(m_rA, PA);
vB.x += m_invMassB * PB.x;
vB.y += m_invMassB * PB.y;
wB += m_invIB * Vec2.cross(m_rB, PB);
pool.pushVec2(2);
} else {
m_impulse = 0.0f;
}
// data.velocities[m_indexA].v.set(vA);
data.velocities[m_indexA].w = wA;
// data.velocities[m_indexB].v.set(vB);
data.velocities[m_indexB].w = wB;
pool.pushVec2(1);
pool.pushRot(2);
}
@Override
public void solveVelocityConstraints(final SolverData data) {
Vec2 vA = data.velocities[m_indexA].v;
float wA = data.velocities[m_indexA].w;
Vec2 vB = data.velocities[m_indexB].v;
float wB = data.velocities[m_indexB].w;
final Vec2 vpA = pool.popVec2();
final Vec2 vpB = pool.popVec2();
final Vec2 PA = pool.popVec2();
final Vec2 PB = pool.popVec2();
Vec2.crossToOutUnsafe(wA, m_rA, vpA);
vpA.addLocal(vA);
Vec2.crossToOutUnsafe(wB, m_rB, vpB);
vpB.addLocal(vB);
float Cdot = -Vec2.dot(m_uA, vpA) - m_ratio * Vec2.dot(m_uB, vpB);
float impulse = -m_mass * Cdot;
m_impulse += impulse;
PA.set(m_uA).mulLocal(-impulse);
PB.set(m_uB).mulLocal(-m_ratio * impulse);
vA.x += m_invMassA * PA.x;
vA.y += m_invMassA * PA.y;
wA += m_invIA * Vec2.cross(m_rA, PA);
vB.x += m_invMassB * PB.x;
vB.y += m_invMassB * PB.y;
wB += m_invIB * Vec2.cross(m_rB, PB);
// data.velocities[m_indexA].v.set(vA);
data.velocities[m_indexA].w = wA;
// data.velocities[m_indexB].v.set(vB);
data.velocities[m_indexB].w = wB;
pool.pushVec2(4);
}
@Override
public boolean solvePositionConstraints(final SolverData data) {
final Rot qA = pool.popRot();
final Rot qB = pool.popRot();
final Vec2 rA = pool.popVec2();
final Vec2 rB = pool.popVec2();
final Vec2 uA = pool.popVec2();
final Vec2 uB = pool.popVec2();
final Vec2 temp = pool.popVec2();
final Vec2 PA = pool.popVec2();
final Vec2 PB = pool.popVec2();
Vec2 cA = data.positions[m_indexA].c;
float aA = data.positions[m_indexA].a;
Vec2 cB = data.positions[m_indexB].c;
float aB = data.positions[m_indexB].a;
qA.set(aA);
qB.set(aB);
Rot.mulToOutUnsafe(qA, temp.set(m_localAnchorA).subLocal(m_localCenterA), rA);
Rot.mulToOutUnsafe(qB, temp.set(m_localAnchorB).subLocal(m_localCenterB), rB);
uA.set(cA).addLocal(rA).subLocal(m_groundAnchorA);
uB.set(cB).addLocal(rB).subLocal(m_groundAnchorB);
float lengthA = uA.length();
float lengthB = uB.length();
if (lengthA > 10.0f * Settings.linearSlop) {
uA.mulLocal(1.0f / lengthA);
} else {
uA.setZero();
}
if (lengthB > 10.0f * Settings.linearSlop) {
uB.mulLocal(1.0f / lengthB);
} else {
uB.setZero();
}
// Compute effective mass.
float ruA = Vec2.cross(rA, uA);
float ruB = Vec2.cross(rB, uB);
float mA = m_invMassA + m_invIA * ruA * ruA;
float mB = m_invMassB + m_invIB * ruB * ruB;
float mass = mA + m_ratio * m_ratio * mB;
if (mass > 0.0f) {
mass = 1.0f / mass;
}
float C = m_constant - lengthA - m_ratio * lengthB;
float linearError = MathUtils.abs(C);
float impulse = -mass * C;
PA.set(uA).mulLocal(-impulse);
PB.set(uB).mulLocal(-m_ratio * impulse);
cA.x += m_invMassA * PA.x;
cA.y += m_invMassA * PA.y;
aA += m_invIA * Vec2.cross(rA, PA);
cB.x += m_invMassB * PB.x;
cB.y += m_invMassB * PB.y;
aB += m_invIB * Vec2.cross(rB, PB);
// data.positions[m_indexA].c.set(cA);
data.positions[m_indexA].a = aA;
// data.positions[m_indexB].c.set(cB);
data.positions[m_indexB].a = aB;
pool.pushRot(2);
pool.pushVec2(7);
return linearError < Settings.linearSlop;
}
}