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axmol/Box2D/Dynamics/Joints/b2RevoluteJoint.cpp

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/*
* Copyright (c) 2006-2011 Erin Catto http://www.box2d.org
*
* This software is provided 'as-is', without any express or implied
* warranty. In no event will the authors be held liable for any damages
* arising from the use of this software.
* Permission is granted to anyone to use this software for any purpose,
* including commercial applications, and to alter it and redistribute it
* freely, subject to the following restrictions:
* 1. The origin of this software must not be misrepresented; you must not
* claim that you wrote the original software. If you use this software
* in a product, an acknowledgment in the product documentation would be
* appreciated but is not required.
* 2. Altered source versions must be plainly marked as such, and must not be
* misrepresented as being the original software.
* 3. This notice may not be removed or altered from any source distribution.
*/
#include <Box2D/Dynamics/Joints/b2RevoluteJoint.h>
#include <Box2D/Dynamics/b2Body.h>
#include <Box2D/Dynamics/b2TimeStep.h>
// Point-to-point constraint
// C = p2 - p1
// Cdot = v2 - v1
// = v2 + cross(w2, r2) - v1 - cross(w1, r1)
// J = [-I -r1_skew I r2_skew ]
// Identity used:
// w k % (rx i + ry j) = w * (-ry i + rx j)
// Motor constraint
// Cdot = w2 - w1
// J = [0 0 -1 0 0 1]
// K = invI1 + invI2
void b2RevoluteJointDef::Initialize(b2Body* bA, b2Body* bB, const b2Vec2& anchor)
{
bodyA = bA;
bodyB = bB;
localAnchorA = bodyA->GetLocalPoint(anchor);
localAnchorB = bodyB->GetLocalPoint(anchor);
referenceAngle = bodyB->GetAngle() - bodyA->GetAngle();
}
b2RevoluteJoint::b2RevoluteJoint(const b2RevoluteJointDef* def)
: b2Joint(def)
{
m_localAnchorA = def->localAnchorA;
m_localAnchorB = def->localAnchorB;
m_referenceAngle = def->referenceAngle;
m_impulse.SetZero();
m_motorImpulse = 0.0f;
m_lowerAngle = def->lowerAngle;
m_upperAngle = def->upperAngle;
m_maxMotorTorque = def->maxMotorTorque;
m_motorSpeed = def->motorSpeed;
m_enableLimit = def->enableLimit;
m_enableMotor = def->enableMotor;
m_limitState = e_inactiveLimit;
}
void b2RevoluteJoint::InitVelocityConstraints(const b2SolverData& data)
{
m_indexA = m_bodyA->m_islandIndex;
m_indexB = m_bodyB->m_islandIndex;
m_localCenterA = m_bodyA->m_sweep.localCenter;
m_localCenterB = 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;
b2Vec2 cA = data.positions[m_indexA].c;
float32 aA = data.positions[m_indexA].a;
b2Vec2 vA = data.velocities[m_indexA].v;
float32 wA = data.velocities[m_indexA].w;
b2Vec2 cB = data.positions[m_indexB].c;
float32 aB = data.positions[m_indexB].a;
b2Vec2 vB = data.velocities[m_indexB].v;
float32 wB = data.velocities[m_indexB].w;
b2Rot qA(aA), qB(aB);
m_rA = b2Mul(qA, m_localAnchorA - m_localCenterA);
m_rB = b2Mul(qB, m_localAnchorB - m_localCenterB);
// J = [-I -r1_skew I r2_skew]
// [ 0 -1 0 1]
// r_skew = [-ry; rx]
// Matlab
// K = [ mA+r1y^2*iA+mB+r2y^2*iB, -r1y*iA*r1x-r2y*iB*r2x, -r1y*iA-r2y*iB]
// [ -r1y*iA*r1x-r2y*iB*r2x, mA+r1x^2*iA+mB+r2x^2*iB, r1x*iA+r2x*iB]
// [ -r1y*iA-r2y*iB, r1x*iA+r2x*iB, iA+iB]
float32 mA = m_invMassA, mB = m_invMassB;
float32 iA = m_invIA, iB = m_invIB;
bool fixedRotation = (iA + iB == 0.0f);
m_mass.ex.x = mA + mB + m_rA.y * m_rA.y * iA + m_rB.y * m_rB.y * iB;
m_mass.ey.x = -m_rA.y * m_rA.x * iA - m_rB.y * m_rB.x * iB;
m_mass.ez.x = -m_rA.y * iA - m_rB.y * iB;
m_mass.ex.y = m_mass.ey.x;
m_mass.ey.y = mA + mB + m_rA.x * m_rA.x * iA + m_rB.x * m_rB.x * iB;
m_mass.ez.y = m_rA.x * iA + m_rB.x * iB;
m_mass.ex.z = m_mass.ez.x;
m_mass.ey.z = m_mass.ez.y;
m_mass.ez.z = iA + iB;
m_motorMass = iA + iB;
if (m_motorMass > 0.0f)
{
m_motorMass = 1.0f / m_motorMass;
}
if (m_enableMotor == false || fixedRotation)
{
m_motorImpulse = 0.0f;
}
if (m_enableLimit && fixedRotation == false)
{
float32 jointAngle = aB - aA - m_referenceAngle;
if (b2Abs(m_upperAngle - m_lowerAngle) < 2.0f * b2_angularSlop)
{
m_limitState = e_equalLimits;
}
else if (jointAngle <= m_lowerAngle)
{
if (m_limitState != e_atLowerLimit)
{
m_impulse.z = 0.0f;
}
m_limitState = e_atLowerLimit;
}
else if (jointAngle >= m_upperAngle)
{
if (m_limitState != e_atUpperLimit)
{
m_impulse.z = 0.0f;
}
m_limitState = e_atUpperLimit;
}
else
{
m_limitState = e_inactiveLimit;
m_impulse.z = 0.0f;
}
}
else
{
m_limitState = e_inactiveLimit;
}
if (data.step.warmStarting)
{
// Scale impulses to support a variable time step.
m_impulse *= data.step.dtRatio;
m_motorImpulse *= data.step.dtRatio;
b2Vec2 P(m_impulse.x, m_impulse.y);
vA -= mA * P;
wA -= iA * (b2Cross(m_rA, P) + m_motorImpulse + m_impulse.z);
vB += mB * P;
wB += iB * (b2Cross(m_rB, P) + m_motorImpulse + m_impulse.z);
}
else
{
m_impulse.SetZero();
m_motorImpulse = 0.0f;
}
data.velocities[m_indexA].v = vA;
data.velocities[m_indexA].w = wA;
data.velocities[m_indexB].v = vB;
data.velocities[m_indexB].w = wB;
}
void b2RevoluteJoint::SolveVelocityConstraints(const b2SolverData& data)
{
b2Vec2 vA = data.velocities[m_indexA].v;
float32 wA = data.velocities[m_indexA].w;
b2Vec2 vB = data.velocities[m_indexB].v;
float32 wB = data.velocities[m_indexB].w;
float32 mA = m_invMassA, mB = m_invMassB;
float32 iA = m_invIA, iB = m_invIB;
bool fixedRotation = (iA + iB == 0.0f);
// Solve motor constraint.
if (m_enableMotor && m_limitState != e_equalLimits && fixedRotation == false)
{
float32 Cdot = wB - wA - m_motorSpeed;
float32 impulse = -m_motorMass * Cdot;
float32 oldImpulse = m_motorImpulse;
float32 maxImpulse = data.step.dt * m_maxMotorTorque;
m_motorImpulse = b2Clamp(m_motorImpulse + impulse, -maxImpulse, maxImpulse);
impulse = m_motorImpulse - oldImpulse;
wA -= iA * impulse;
wB += iB * impulse;
}
// Solve limit constraint.
if (m_enableLimit && m_limitState != e_inactiveLimit && fixedRotation == false)
{
b2Vec2 Cdot1 = vB + b2Cross(wB, m_rB) - vA - b2Cross(wA, m_rA);
float32 Cdot2 = wB - wA;
b2Vec3 Cdot(Cdot1.x, Cdot1.y, Cdot2);
b2Vec3 impulse = -m_mass.Solve33(Cdot);
if (m_limitState == e_equalLimits)
{
m_impulse += impulse;
}
else if (m_limitState == e_atLowerLimit)
{
float32 newImpulse = m_impulse.z + impulse.z;
if (newImpulse < 0.0f)
{
b2Vec2 rhs = -Cdot1 + m_impulse.z * b2Vec2(m_mass.ez.x, m_mass.ez.y);
b2Vec2 reduced = m_mass.Solve22(rhs);
impulse.x = reduced.x;
impulse.y = reduced.y;
impulse.z = -m_impulse.z;
m_impulse.x += reduced.x;
m_impulse.y += reduced.y;
m_impulse.z = 0.0f;
}
else
{
m_impulse += impulse;
}
}
else if (m_limitState == e_atUpperLimit)
{
float32 newImpulse = m_impulse.z + impulse.z;
if (newImpulse > 0.0f)
{
b2Vec2 rhs = -Cdot1 + m_impulse.z * b2Vec2(m_mass.ez.x, m_mass.ez.y);
b2Vec2 reduced = m_mass.Solve22(rhs);
impulse.x = reduced.x;
impulse.y = reduced.y;
impulse.z = -m_impulse.z;
m_impulse.x += reduced.x;
m_impulse.y += reduced.y;
m_impulse.z = 0.0f;
}
else
{
m_impulse += impulse;
}
}
b2Vec2 P(impulse.x, impulse.y);
vA -= mA * P;
wA -= iA * (b2Cross(m_rA, P) + impulse.z);
vB += mB * P;
wB += iB * (b2Cross(m_rB, P) + impulse.z);
}
else
{
// Solve point-to-point constraint
b2Vec2 Cdot = vB + b2Cross(wB, m_rB) - vA - b2Cross(wA, m_rA);
b2Vec2 impulse = m_mass.Solve22(-Cdot);
m_impulse.x += impulse.x;
m_impulse.y += impulse.y;
vA -= mA * impulse;
wA -= iA * b2Cross(m_rA, impulse);
vB += mB * impulse;
wB += iB * b2Cross(m_rB, impulse);
}
data.velocities[m_indexA].v = vA;
data.velocities[m_indexA].w = wA;
data.velocities[m_indexB].v = vB;
data.velocities[m_indexB].w = wB;
}
bool b2RevoluteJoint::SolvePositionConstraints(const b2SolverData& data)
{
b2Vec2 cA = data.positions[m_indexA].c;
float32 aA = data.positions[m_indexA].a;
b2Vec2 cB = data.positions[m_indexB].c;
float32 aB = data.positions[m_indexB].a;
b2Rot qA(aA), qB(aB);
float32 angularError = 0.0f;
float32 positionError = 0.0f;
bool fixedRotation = (m_invIA + m_invIB == 0.0f);
// Solve angular limit constraint.
if (m_enableLimit && m_limitState != e_inactiveLimit && fixedRotation == false)
{
float32 angle = aB - aA - m_referenceAngle;
float32 limitImpulse = 0.0f;
if (m_limitState == e_equalLimits)
{
// Prevent large angular corrections
float32 C = b2Clamp(angle - m_lowerAngle, -b2_maxAngularCorrection, b2_maxAngularCorrection);
limitImpulse = -m_motorMass * C;
angularError = b2Abs(C);
}
else if (m_limitState == e_atLowerLimit)
{
float32 C = angle - m_lowerAngle;
angularError = -C;
// Prevent large angular corrections and allow some slop.
C = b2Clamp(C + b2_angularSlop, -b2_maxAngularCorrection, 0.0f);
limitImpulse = -m_motorMass * C;
}
else if (m_limitState == e_atUpperLimit)
{
float32 C = angle - m_upperAngle;
angularError = C;
// Prevent large angular corrections and allow some slop.
C = b2Clamp(C - b2_angularSlop, 0.0f, b2_maxAngularCorrection);
limitImpulse = -m_motorMass * C;
}
aA -= m_invIA * limitImpulse;
aB += m_invIB * limitImpulse;
}
// Solve point-to-point constraint.
{
qA.Set(aA);
qB.Set(aB);
b2Vec2 rA = b2Mul(qA, m_localAnchorA - m_localCenterA);
b2Vec2 rB = b2Mul(qB, m_localAnchorB - m_localCenterB);
b2Vec2 C = cB + rB - cA - rA;
positionError = C.Length();
float32 mA = m_invMassA, mB = m_invMassB;
float32 iA = m_invIA, iB = m_invIB;
b2Mat22 K;
K.ex.x = mA + mB + iA * rA.y * rA.y + iB * rB.y * rB.y;
K.ex.y = -iA * rA.x * rA.y - iB * rB.x * rB.y;
K.ey.x = K.ex.y;
K.ey.y = mA + mB + iA * rA.x * rA.x + iB * rB.x * rB.x;
b2Vec2 impulse = -K.Solve(C);
cA -= mA * impulse;
aA -= iA * b2Cross(rA, impulse);
cB += mB * impulse;
aB += iB * b2Cross(rB, impulse);
}
data.positions[m_indexA].c = cA;
data.positions[m_indexA].a = aA;
data.positions[m_indexB].c = cB;
data.positions[m_indexB].a = aB;
return positionError <= b2_linearSlop && angularError <= b2_angularSlop;
}
b2Vec2 b2RevoluteJoint::GetAnchorA() const
{
return m_bodyA->GetWorldPoint(m_localAnchorA);
}
b2Vec2 b2RevoluteJoint::GetAnchorB() const
{
return m_bodyB->GetWorldPoint(m_localAnchorB);
}
b2Vec2 b2RevoluteJoint::GetReactionForce(float32 inv_dt) const
{
b2Vec2 P(m_impulse.x, m_impulse.y);
return inv_dt * P;
}
float32 b2RevoluteJoint::GetReactionTorque(float32 inv_dt) const
{
return inv_dt * m_impulse.z;
}
float32 b2RevoluteJoint::GetJointAngle() const
{
b2Body* bA = m_bodyA;
b2Body* bB = m_bodyB;
return bB->m_sweep.a - bA->m_sweep.a - m_referenceAngle;
}
float32 b2RevoluteJoint::GetJointSpeed() const
{
b2Body* bA = m_bodyA;
b2Body* bB = m_bodyB;
return bB->m_angularVelocity - bA->m_angularVelocity;
}
bool b2RevoluteJoint::IsMotorEnabled() const
{
return m_enableMotor;
}
void b2RevoluteJoint::EnableMotor(bool flag)
{
m_bodyA->SetAwake(true);
m_bodyB->SetAwake(true);
m_enableMotor = flag;
}
float32 b2RevoluteJoint::GetMotorTorque(float32 inv_dt) const
{
return inv_dt * m_motorImpulse;
}
void b2RevoluteJoint::SetMotorSpeed(float32 speed)
{
m_bodyA->SetAwake(true);
m_bodyB->SetAwake(true);
m_motorSpeed = speed;
}
void b2RevoluteJoint::SetMaxMotorTorque(float32 torque)
{
m_bodyA->SetAwake(true);
m_bodyB->SetAwake(true);
m_maxMotorTorque = torque;
}
bool b2RevoluteJoint::IsLimitEnabled() const
{
return m_enableLimit;
}
void b2RevoluteJoint::EnableLimit(bool flag)
{
if (flag != m_enableLimit)
{
m_bodyA->SetAwake(true);
m_bodyB->SetAwake(true);
m_enableLimit = flag;
m_impulse.z = 0.0f;
}
}
float32 b2RevoluteJoint::GetLowerLimit() const
{
return m_lowerAngle;
}
float32 b2RevoluteJoint::GetUpperLimit() const
{
return m_upperAngle;
}
void b2RevoluteJoint::SetLimits(float32 lower, float32 upper)
{
b2Assert(lower <= upper);
if (lower != m_lowerAngle || upper != m_upperAngle)
{
m_bodyA->SetAwake(true);
m_bodyB->SetAwake(true);
m_impulse.z = 0.0f;
m_lowerAngle = lower;
m_upperAngle = upper;
}
}
void b2RevoluteJoint::Dump()
{
int32 indexA = m_bodyA->m_islandIndex;
int32 indexB = m_bodyB->m_islandIndex;
b2Log(" b2RevoluteJointDef 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.referenceAngle = %.15lef;\n", m_referenceAngle);
b2Log(" jd.enableLimit = bool(%d);\n", m_enableLimit);
b2Log(" jd.lowerAngle = %.15lef;\n", m_lowerAngle);
b2Log(" jd.upperAngle = %.15lef;\n", m_upperAngle);
b2Log(" jd.enableMotor = bool(%d);\n", m_enableMotor);
b2Log(" jd.motorSpeed = %.15lef;\n", m_motorSpeed);
b2Log(" jd.maxMotorTorque = %.15lef;\n", m_maxMotorTorque);
b2Log(" joints[%d] = m_world->CreateJoint(&jd);\n", m_index);
}
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