com.almasb.fxgl.physics.box2d.dynamics.joints.GearJoint Maven / Gradle / Ivy
/*
* FXGL - JavaFX Game Library. The MIT License (MIT).
* Copyright (c) AlmasB ([email protected]).
* See LICENSE for details.
*/
/**
* Created at 11:34:45 AM Jan 23, 2011
*/
package com.almasb.fxgl.physics.box2d.dynamics.joints;
import com.almasb.fxgl.core.math.Vec2;
import com.almasb.fxgl.physics.box2d.common.JBoxSettings;
import com.almasb.fxgl.physics.box2d.common.Rotation;
import com.almasb.fxgl.physics.box2d.common.Transform;
import com.almasb.fxgl.physics.box2d.dynamics.Body;
import com.almasb.fxgl.physics.box2d.dynamics.SolverData;
import com.almasb.fxgl.physics.box2d.pooling.IWorldPool;
//Gear Joint:
//C0 = (coordinate1 + ratio * coordinate2)_initial
//C = (coordinate1 + ratio * coordinate2) - C0 = 0
//J = [J1 ratio * J2]
//K = J * invM * JT
//= J1 * invM1 * J1T + ratio * ratio * J2 * invM2 * J2T
//
//Revolute:
//coordinate = rotation
//Cdot = angularVelocity
//J = [0 0 1]
//K = J * invM * JT = invI
//
//Prismatic:
//coordinate = dot(p - pg, ug)
//Cdot = dot(v + cross(w, r), ug)
//J = [ug cross(r, ug)]
//K = J * invM * JT = invMass + invI * cross(r, ug)^2
/**
* A gear joint is used to connect two joints together. Either joint can be a revolute or prismatic
* joint. You specify a gear ratio to bind the motions together: coordinate1 + ratio * coordinate2 =
* constant The ratio can be negative or positive. If one joint is a revolute joint and the other
* joint is a prismatic joint, then the ratio will have units of length or units of 1/length.
*
* @warning The revolute and prismatic joints must be attached to fixed bodies (which must be body1
* on those joints).
* @warning You have to manually destroy the gear joint if joint1 or joint2 is destroyed.
* @author Daniel Murphy
*/
public class GearJoint extends Joint {
private final Joint m_joint1;
private final Joint m_joint2;
private final JointType m_typeA;
private final JointType m_typeB;
// Body A is connected to body C
// Body B is connected to body D
private final Body m_bodyC;
private final Body m_bodyD;
// Solver shared
private final Vec2 m_localAnchorA = new Vec2();
private final Vec2 m_localAnchorB = new Vec2();
private final Vec2 m_localAnchorC = new Vec2();
private final Vec2 m_localAnchorD = new Vec2();
private final Vec2 m_localAxisC = new Vec2();
private final Vec2 m_localAxisD = new Vec2();
private float m_referenceAngleA;
private float m_referenceAngleB;
private float m_constant;
private float m_ratio;
private float m_impulse;
// Solver temp
private int m_indexA, m_indexB, m_indexC, m_indexD;
private final Vec2 m_lcA = new Vec2(), m_lcB = new Vec2(), m_lcC = new Vec2(),
m_lcD = new Vec2();
private float m_mA, m_mB, m_mC, m_mD;
private float m_iA, m_iB, m_iC, m_iD;
private final Vec2 m_JvAC = new Vec2(), m_JvBD = new Vec2();
private float m_JwA, m_JwB, m_JwC, m_JwD;
private float m_mass;
protected GearJoint(IWorldPool argWorldPool, GearJointDef def) {
super(argWorldPool, def);
m_joint1 = def.joint1;
m_joint2 = def.joint2;
m_typeA = m_joint1.getType();
m_typeB = m_joint2.getType();
assert m_typeA == JointType.REVOLUTE || m_typeA == JointType.PRISMATIC;
assert m_typeB == JointType.REVOLUTE || m_typeB == JointType.PRISMATIC;
float coordinateA, coordinateB;
// TODO_ERIN there might be some problem with the joint edges in Joint.
m_bodyC = m_joint1.getBodyA();
m_bodyA = m_joint1.getBodyB();
// Get geometry of joint1
Transform xfA = m_bodyA.m_xf;
float aA = m_bodyA.m_sweep.a;
Transform xfC = m_bodyC.m_xf;
float aC = m_bodyC.m_sweep.a;
if (m_typeA == JointType.REVOLUTE) {
RevoluteJoint revolute = (RevoluteJoint) def.joint1;
m_localAnchorC.set(revolute.m_localAnchorA);
m_localAnchorA.set(revolute.m_localAnchorB);
m_referenceAngleA = revolute.m_referenceAngle;
m_localAxisC.setZero();
coordinateA = aA - aC - m_referenceAngleA;
} else {
Vec2 pA = pool.popVec2();
Vec2 temp = pool.popVec2();
PrismaticJoint prismatic = (PrismaticJoint) def.joint1;
m_localAnchorC.set(prismatic.m_localAnchorA);
m_localAnchorA.set(prismatic.m_localAnchorB);
m_referenceAngleA = prismatic.m_referenceAngle;
m_localAxisC.set(prismatic.m_localXAxisA);
Vec2 pC = m_localAnchorC;
Rotation.mulToOutUnsafe(xfA.q, m_localAnchorA, temp);
temp.addLocal(xfA.p).subLocal(xfC.p);
Rotation.mulTransUnsafe(xfC.q, temp, pA);
coordinateA = Vec2.dot(pA.subLocal(pC), m_localAxisC);
pool.pushVec2(2);
}
m_bodyD = m_joint2.getBodyA();
m_bodyB = m_joint2.getBodyB();
// Get geometry of joint2
Transform xfB = m_bodyB.m_xf;
float aB = m_bodyB.m_sweep.a;
Transform xfD = m_bodyD.m_xf;
float aD = m_bodyD.m_sweep.a;
if (m_typeB == JointType.REVOLUTE) {
RevoluteJoint revolute = (RevoluteJoint) def.joint2;
m_localAnchorD.set(revolute.m_localAnchorA);
m_localAnchorB.set(revolute.m_localAnchorB);
m_referenceAngleB = revolute.m_referenceAngle;
m_localAxisD.setZero();
coordinateB = aB - aD - m_referenceAngleB;
} else {
Vec2 pB = pool.popVec2();
Vec2 temp = pool.popVec2();
PrismaticJoint prismatic = (PrismaticJoint) def.joint2;
m_localAnchorD.set(prismatic.m_localAnchorA);
m_localAnchorB.set(prismatic.m_localAnchorB);
m_referenceAngleB = prismatic.m_referenceAngle;
m_localAxisD.set(prismatic.m_localXAxisA);
Vec2 pD = m_localAnchorD;
Rotation.mulToOutUnsafe(xfB.q, m_localAnchorB, temp);
temp.addLocal(xfB.p).subLocal(xfD.p);
Rotation.mulTransUnsafe(xfD.q, temp, pB);
coordinateB = Vec2.dot(pB.subLocal(pD), m_localAxisD);
pool.pushVec2(2);
}
m_ratio = def.ratio;
m_constant = coordinateA + m_ratio * coordinateB;
m_impulse = 0.0f;
}
@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_JvAC).mulLocal(m_impulse);
argOut.mulLocal(inv_dt);
}
@Override
public float getReactionTorque(float inv_dt) {
float L = m_impulse * m_JwA;
return inv_dt * L;
}
public void setRatio(float argRatio) {
m_ratio = argRatio;
}
public float getRatio() {
return m_ratio;
}
@Override
public void initVelocityConstraints(SolverData data) {
m_indexA = m_bodyA.m_islandIndex;
m_indexB = m_bodyB.m_islandIndex;
m_indexC = m_bodyC.m_islandIndex;
m_indexD = m_bodyD.m_islandIndex;
m_lcA.set(m_bodyA.m_sweep.localCenter);
m_lcB.set(m_bodyB.m_sweep.localCenter);
m_lcC.set(m_bodyC.m_sweep.localCenter);
m_lcD.set(m_bodyD.m_sweep.localCenter);
m_mA = m_bodyA.m_invMass;
m_mB = m_bodyB.m_invMass;
m_mC = m_bodyC.m_invMass;
m_mD = m_bodyD.m_invMass;
m_iA = m_bodyA.m_invI;
m_iB = m_bodyB.m_invI;
m_iC = m_bodyC.m_invI;
m_iD = m_bodyD.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;
// Vec2 cC = data.positions[m_indexC].c;
float aC = data.positions[m_indexC].a;
Vec2 vC = data.velocities[m_indexC].v;
float wC = data.velocities[m_indexC].w;
// Vec2 cD = data.positions[m_indexD].c;
float aD = data.positions[m_indexD].a;
Vec2 vD = data.velocities[m_indexD].v;
float wD = data.velocities[m_indexD].w;
Rotation qA = pool.popRot(), qB = pool.popRot(), qC = pool.popRot(), qD = pool.popRot();
qA.set(aA);
qB.set(aB);
qC.set(aC);
qD.set(aD);
m_mass = 0.0f;
Vec2 temp = pool.popVec2();
if (m_typeA == JointType.REVOLUTE) {
m_JvAC.setZero();
m_JwA = 1.0f;
m_JwC = 1.0f;
m_mass += m_iA + m_iC;
} else {
Vec2 rC = pool.popVec2();
Vec2 rA = pool.popVec2();
Rotation.mulToOutUnsafe(qC, m_localAxisC, m_JvAC);
Rotation.mulToOutUnsafe(qC, temp.set(m_localAnchorC).subLocal(m_lcC), rC);
Rotation.mulToOutUnsafe(qA, temp.set(m_localAnchorA).subLocal(m_lcA), rA);
m_JwC = Vec2.cross(rC, m_JvAC);
m_JwA = Vec2.cross(rA, m_JvAC);
m_mass += m_mC + m_mA + m_iC * m_JwC * m_JwC + m_iA * m_JwA * m_JwA;
pool.pushVec2(2);
}
if (m_typeB == JointType.REVOLUTE) {
m_JvBD.setZero();
m_JwB = m_ratio;
m_JwD = m_ratio;
m_mass += m_ratio * m_ratio * (m_iB + m_iD);
} else {
Vec2 u = pool.popVec2();
Vec2 rD = pool.popVec2();
Vec2 rB = pool.popVec2();
Rotation.mulToOutUnsafe(qD, m_localAxisD, u);
Rotation.mulToOutUnsafe(qD, temp.set(m_localAnchorD).subLocal(m_lcD), rD);
Rotation.mulToOutUnsafe(qB, temp.set(m_localAnchorB).subLocal(m_lcB), rB);
m_JvBD.set(u).mulLocal(m_ratio);
m_JwD = m_ratio * Vec2.cross(rD, u);
m_JwB = m_ratio * Vec2.cross(rB, u);
m_mass += m_ratio * m_ratio * (m_mD + m_mB) + m_iD * m_JwD * m_JwD + m_iB * m_JwB * m_JwB;
pool.pushVec2(3);
}
// Compute effective mass.
m_mass = m_mass > 0.0f ? 1.0f / m_mass : 0.0f;
if (data.step.warmStarting) {
vA.x += (m_mA * m_impulse) * m_JvAC.x;
vA.y += (m_mA * m_impulse) * m_JvAC.y;
wA += m_iA * m_impulse * m_JwA;
vB.x += (m_mB * m_impulse) * m_JvBD.x;
vB.y += (m_mB * m_impulse) * m_JvBD.y;
wB += m_iB * m_impulse * m_JwB;
vC.x -= (m_mC * m_impulse) * m_JvAC.x;
vC.y -= (m_mC * m_impulse) * m_JvAC.y;
wC -= m_iC * m_impulse * m_JwC;
vD.x -= (m_mD * m_impulse) * m_JvBD.x;
vD.y -= (m_mD * m_impulse) * m_JvBD.y;
wD -= m_iD * m_impulse * m_JwD;
} else {
m_impulse = 0.0f;
}
pool.pushVec2(1);
pool.pushRot(4);
// data.velocities[m_indexA].v = vA;
data.velocities[m_indexA].w = wA;
// data.velocities[m_indexB].v = vB;
data.velocities[m_indexB].w = wB;
// data.velocities[m_indexC].v = vC;
data.velocities[m_indexC].w = wC;
// data.velocities[m_indexD].v = vD;
data.velocities[m_indexD].w = wD;
}
@Override
public void solveVelocityConstraints(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;
Vec2 vC = data.velocities[m_indexC].v;
float wC = data.velocities[m_indexC].w;
Vec2 vD = data.velocities[m_indexD].v;
float wD = data.velocities[m_indexD].w;
Vec2 temp1 = pool.popVec2();
Vec2 temp2 = pool.popVec2();
float Cdot =
Vec2.dot(m_JvAC, temp1.set(vA).subLocal(vC)) + Vec2.dot(m_JvBD, temp2.set(vB).subLocal(vD));
Cdot += (m_JwA * wA - m_JwC * wC) + (m_JwB * wB - m_JwD * wD);
pool.pushVec2(2);
float impulse = -m_mass * Cdot;
m_impulse += impulse;
vA.x += (m_mA * impulse) * m_JvAC.x;
vA.y += (m_mA * impulse) * m_JvAC.y;
wA += m_iA * impulse * m_JwA;
vB.x += (m_mB * impulse) * m_JvBD.x;
vB.y += (m_mB * impulse) * m_JvBD.y;
wB += m_iB * impulse * m_JwB;
vC.x -= (m_mC * impulse) * m_JvAC.x;
vC.y -= (m_mC * impulse) * m_JvAC.y;
wC -= m_iC * impulse * m_JwC;
vD.x -= (m_mD * impulse) * m_JvBD.x;
vD.y -= (m_mD * impulse) * m_JvBD.y;
wD -= m_iD * impulse * m_JwD;
// data.velocities[m_indexA].v = vA;
data.velocities[m_indexA].w = wA;
// data.velocities[m_indexB].v = vB;
data.velocities[m_indexB].w = wB;
// data.velocities[m_indexC].v = vC;
data.velocities[m_indexC].w = wC;
// data.velocities[m_indexD].v = vD;
data.velocities[m_indexD].w = wD;
}
public Joint getJoint1() {
return m_joint1;
}
public Joint getJoint2() {
return m_joint2;
}
@Override
public boolean solvePositionConstraints(SolverData data) {
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;
Vec2 cC = data.positions[m_indexC].c;
float aC = data.positions[m_indexC].a;
Vec2 cD = data.positions[m_indexD].c;
float aD = data.positions[m_indexD].a;
Rotation qA = pool.popRot();
Rotation qB = pool.popRot();
Rotation qC = pool.popRot();
Rotation qD = pool.popRot();
qA.set(aA);
qB.set(aB);
qC.set(aC);
qD.set(aD);
float linearError = 0.0f;
float coordinateA, coordinateB;
Vec2 temp = pool.popVec2();
Vec2 JvAC = pool.popVec2();
Vec2 JvBD = pool.popVec2();
float JwA, JwB, JwC, JwD;
float mass = 0.0f;
if (m_typeA == JointType.REVOLUTE) {
JvAC.setZero();
JwA = 1.0f;
JwC = 1.0f;
mass += m_iA + m_iC;
coordinateA = aA - aC - m_referenceAngleA;
} else {
Vec2 rC = pool.popVec2();
Vec2 rA = pool.popVec2();
Vec2 pC = pool.popVec2();
Vec2 pA = pool.popVec2();
Rotation.mulToOutUnsafe(qC, m_localAxisC, JvAC);
Rotation.mulToOutUnsafe(qC, temp.set(m_localAnchorC).subLocal(m_lcC), rC);
Rotation.mulToOutUnsafe(qA, temp.set(m_localAnchorA).subLocal(m_lcA), rA);
JwC = Vec2.cross(rC, JvAC);
JwA = Vec2.cross(rA, JvAC);
mass += m_mC + m_mA + m_iC * JwC * JwC + m_iA * JwA * JwA;
pC.set(m_localAnchorC).subLocal(m_lcC);
Rotation.mulTransUnsafe(qC, temp.set(rA).addLocal(cA).subLocal(cC), pA);
coordinateA = Vec2.dot(pA.subLocal(pC), m_localAxisC);
pool.pushVec2(4);
}
if (m_typeB == JointType.REVOLUTE) {
JvBD.setZero();
JwB = m_ratio;
JwD = m_ratio;
mass += m_ratio * m_ratio * (m_iB + m_iD);
coordinateB = aB - aD - m_referenceAngleB;
} else {
Vec2 u = pool.popVec2();
Vec2 rD = pool.popVec2();
Vec2 rB = pool.popVec2();
Vec2 pD = pool.popVec2();
Vec2 pB = pool.popVec2();
Rotation.mulToOutUnsafe(qD, m_localAxisD, u);
Rotation.mulToOutUnsafe(qD, temp.set(m_localAnchorD).subLocal(m_lcD), rD);
Rotation.mulToOutUnsafe(qB, temp.set(m_localAnchorB).subLocal(m_lcB), rB);
JvBD.set(u).mulLocal(m_ratio);
JwD = Vec2.cross(rD, u);
JwB = Vec2.cross(rB, u);
mass += m_ratio * m_ratio * (m_mD + m_mB) + m_iD * JwD * JwD + m_iB * JwB * JwB;
pD.set(m_localAnchorD).subLocal(m_lcD);
Rotation.mulTransUnsafe(qD, temp.set(rB).addLocal(cB).subLocal(cD), pB);
coordinateB = Vec2.dot(pB.subLocal(pD), m_localAxisD);
pool.pushVec2(5);
}
float C = coordinateA + m_ratio * coordinateB - m_constant;
float impulse = 0.0f;
if (mass > 0.0f) {
impulse = -C / mass;
}
pool.pushVec2(3);
pool.pushRot(4);
cA.x += (m_mA * impulse) * JvAC.x;
cA.y += (m_mA * impulse) * JvAC.y;
aA += m_iA * impulse * JwA;
cB.x += (m_mB * impulse) * JvBD.x;
cB.y += (m_mB * impulse) * JvBD.y;
aB += m_iB * impulse * JwB;
cC.x -= (m_mC * impulse) * JvAC.x;
cC.y -= (m_mC * impulse) * JvAC.y;
aC -= m_iC * impulse * JwC;
cD.x -= (m_mD * impulse) * JvBD.x;
cD.y -= (m_mD * impulse) * JvBD.y;
aD -= m_iD * impulse * JwD;
// data.positions[m_indexA].c = cA;
data.positions[m_indexA].a = aA;
// data.positions[m_indexB].c = cB;
data.positions[m_indexB].a = aB;
// data.positions[m_indexC].c = cC;
data.positions[m_indexC].a = aC;
// data.positions[m_indexD].c = cD;
data.positions[m_indexD].a = aD;
// TODO_ERIN not implemented
return linearError < JBoxSettings.linearSlop;
}
}
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