b2RevoluteJoint.cpp
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- /*
- * Copyright (c) 2006-2007 Erin Catto http://www.gphysics.com
- *
- * 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* b1, b2Body* b2, const b2Vec2& anchor)
- {
- bodyA = b1;
- bodyB = b2;
- localAnchorA = bodyA->GetLocalPoint(anchor);
- localAnchorB = bodyB->GetLocalPoint(anchor);
- referenceAngle = bodyB->GetAngle() - bodyA->GetAngle();
- }
- b2RevoluteJoint::b2RevoluteJoint(const b2RevoluteJointDef* def)
- : b2Joint(def)
- {
- m_localAnchor1 = def->localAnchorA;
- m_localAnchor2 = 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 b2TimeStep& step)
- {
- b2Body* b1 = m_bodyA;
- b2Body* b2 = m_bodyB;
- if (m_enableMotor || m_enableLimit)
- {
- // You cannot create a rotation limit between bodies that
- // both have fixed rotation.
- b2Assert(b1->m_invI > 0.0f || b2->m_invI > 0.0f);
- }
- // Compute the effective mass matrix.
- b2Vec2 r1 = b2Mul(b1->GetTransform().R, m_localAnchor1 - b1->GetLocalCenter());
- b2Vec2 r2 = b2Mul(b2->GetTransform().R, m_localAnchor2 - b2->GetLocalCenter());
- // J = [-I -r1_skew I r2_skew]
- // [ 0 -1 0 1]
- // r_skew = [-ry; rx]
- // Matlab
- // K = [ m1+r1y^2*i1+m2+r2y^2*i2, -r1y*i1*r1x-r2y*i2*r2x, -r1y*i1-r2y*i2]
- // [ -r1y*i1*r1x-r2y*i2*r2x, m1+r1x^2*i1+m2+r2x^2*i2, r1x*i1+r2x*i2]
- // [ -r1y*i1-r2y*i2, r1x*i1+r2x*i2, i1+i2]
- float32 m1 = b1->m_invMass, m2 = b2->m_invMass;
- float32 i1 = b1->m_invI, i2 = b2->m_invI;
- m_mass.col1.x = m1 + m2 + r1.y * r1.y * i1 + r2.y * r2.y * i2;
- m_mass.col2.x = -r1.y * r1.x * i1 - r2.y * r2.x * i2;
- m_mass.col3.x = -r1.y * i1 - r2.y * i2;
- m_mass.col1.y = m_mass.col2.x;
- m_mass.col2.y = m1 + m2 + r1.x * r1.x * i1 + r2.x * r2.x * i2;
- m_mass.col3.y = r1.x * i1 + r2.x * i2;
- m_mass.col1.z = m_mass.col3.x;
- m_mass.col2.z = m_mass.col3.y;
- m_mass.col3.z = i1 + i2;
- m_motorMass = i1 + i2;
- if (m_motorMass > 0.0f)
- {
- m_motorMass = 1.0f / m_motorMass;
- }
- if (m_enableMotor == false)
- {
- m_motorImpulse = 0.0f;
- }
- if (m_enableLimit)
- {
- float32 jointAngle = b2->m_sweep.a - b1->m_sweep.a - 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 (step.warmStarting)
- {
- // Scale impulses to support a variable time step.
- m_impulse *= step.dtRatio;
- m_motorImpulse *= step.dtRatio;
- b2Vec2 P(m_impulse.x, m_impulse.y);
- b1->m_linearVelocity -= m1 * P;
- b1->m_angularVelocity -= i1 * (b2Cross(r1, P) + m_motorImpulse + m_impulse.z);
- b2->m_linearVelocity += m2 * P;
- b2->m_angularVelocity += i2 * (b2Cross(r2, P) + m_motorImpulse + m_impulse.z);
- }
- else
- {
- m_impulse.SetZero();
- m_motorImpulse = 0.0f;
- }
- }
- void b2RevoluteJoint::SolveVelocityConstraints(const b2TimeStep& step)
- {
- b2Body* b1 = m_bodyA;
- b2Body* b2 = m_bodyB;
- b2Vec2 v1 = b1->m_linearVelocity;
- float32 w1 = b1->m_angularVelocity;
- b2Vec2 v2 = b2->m_linearVelocity;
- float32 w2 = b2->m_angularVelocity;
- float32 m1 = b1->m_invMass, m2 = b2->m_invMass;
- float32 i1 = b1->m_invI, i2 = b2->m_invI;
- // Solve motor constraint.
- if (m_enableMotor && m_limitState != e_equalLimits)
- {
- float32 Cdot = w2 - w1 - m_motorSpeed;
- float32 impulse = m_motorMass * (-Cdot);
- float32 oldImpulse = m_motorImpulse;
- float32 maxImpulse = step.dt * m_maxMotorTorque;
- m_motorImpulse = b2Clamp(m_motorImpulse + impulse, -maxImpulse, maxImpulse);
- impulse = m_motorImpulse - oldImpulse;
- w1 -= i1 * impulse;
- w2 += i2 * impulse;
- }
- // Solve limit constraint.
- if (m_enableLimit && m_limitState != e_inactiveLimit)
- {
- b2Vec2 r1 = b2Mul(b1->GetTransform().R, m_localAnchor1 - b1->GetLocalCenter());
- b2Vec2 r2 = b2Mul(b2->GetTransform().R, m_localAnchor2 - b2->GetLocalCenter());
- // Solve point-to-point constraint
- b2Vec2 Cdot1 = v2 + b2Cross(w2, r2) - v1 - b2Cross(w1, r1);
- float32 Cdot2 = w2 - w1;
- 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 reduced = m_mass.Solve22(-Cdot1);
- 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 if (m_limitState == e_atUpperLimit)
- {
- float32 newImpulse = m_impulse.z + impulse.z;
- if (newImpulse > 0.0f)
- {
- b2Vec2 reduced = m_mass.Solve22(-Cdot1);
- 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;
- }
- }
- b2Vec2 P(impulse.x, impulse.y);
- v1 -= m1 * P;
- w1 -= i1 * (b2Cross(r1, P) + impulse.z);
- v2 += m2 * P;
- w2 += i2 * (b2Cross(r2, P) + impulse.z);
- }
- else
- {
- b2Vec2 r1 = b2Mul(b1->GetTransform().R, m_localAnchor1 - b1->GetLocalCenter());
- b2Vec2 r2 = b2Mul(b2->GetTransform().R, m_localAnchor2 - b2->GetLocalCenter());
- // Solve point-to-point constraint
- b2Vec2 Cdot = v2 + b2Cross(w2, r2) - v1 - b2Cross(w1, r1);
- b2Vec2 impulse = m_mass.Solve22(-Cdot);
- m_impulse.x += impulse.x;
- m_impulse.y += impulse.y;
- v1 -= m1 * impulse;
- w1 -= i1 * b2Cross(r1, impulse);
- v2 += m2 * impulse;
- w2 += i2 * b2Cross(r2, impulse);
- }
- b1->m_linearVelocity = v1;
- b1->m_angularVelocity = w1;
- b2->m_linearVelocity = v2;
- b2->m_angularVelocity = w2;
- }
- bool b2RevoluteJoint::SolvePositionConstraints(float32 baumgarte)
- {
- // TODO_ERIN block solve with limit.
- B2_NOT_USED(baumgarte);
- b2Body* b1 = m_bodyA;
- b2Body* b2 = m_bodyB;
- float32 angularError = 0.0f;
- float32 positionError = 0.0f;
- // Solve angular limit constraint.
- if (m_enableLimit && m_limitState != e_inactiveLimit)
- {
- float32 angle = b2->m_sweep.a - b1->m_sweep.a - 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;
- }
- b1->m_sweep.a -= b1->m_invI * limitImpulse;
- b2->m_sweep.a += b2->m_invI * limitImpulse;
- b1->SynchronizeTransform();
- b2->SynchronizeTransform();
- }
- // Solve point-to-point constraint.
- {
- b2Vec2 r1 = b2Mul(b1->GetTransform().R, m_localAnchor1 - b1->GetLocalCenter());
- b2Vec2 r2 = b2Mul(b2->GetTransform().R, m_localAnchor2 - b2->GetLocalCenter());
- b2Vec2 C = b2->m_sweep.c + r2 - b1->m_sweep.c - r1;
- positionError = C.Length();
- float32 invMass1 = b1->m_invMass, invMass2 = b2->m_invMass;
- float32 invI1 = b1->m_invI, invI2 = b2->m_invI;
- // Handle large detachment.
- const float32 k_allowedStretch = 10.0f * b2_linearSlop;
- if (C.LengthSquared() > k_allowedStretch * k_allowedStretch)
- {
- // Use a particle solution (no rotation).
- b2Vec2 u = C; u.Normalize();
- float32 m = invMass1 + invMass2;
- if (m > 0.0f)
- {
- m = 1.0f / m;
- }
- b2Vec2 impulse = m * (-C);
- const float32 k_beta = 0.5f;
- b1->m_sweep.c -= k_beta * invMass1 * impulse;
- b2->m_sweep.c += k_beta * invMass2 * impulse;
- C = b2->m_sweep.c + r2 - b1->m_sweep.c - r1;
- }
- b2Mat22 K1;
- K1.col1.x = invMass1 + invMass2; K1.col2.x = 0.0f;
- K1.col1.y = 0.0f; K1.col2.y = invMass1 + invMass2;
- b2Mat22 K2;
- K2.col1.x = invI1 * r1.y * r1.y; K2.col2.x = -invI1 * r1.x * r1.y;
- K2.col1.y = -invI1 * r1.x * r1.y; K2.col2.y = invI1 * r1.x * r1.x;
- b2Mat22 K3;
- K3.col1.x = invI2 * r2.y * r2.y; K3.col2.x = -invI2 * r2.x * r2.y;
- K3.col1.y = -invI2 * r2.x * r2.y; K3.col2.y = invI2 * r2.x * r2.x;
- b2Mat22 K = K1 + K2 + K3;
- b2Vec2 impulse = K.Solve(-C);
- b1->m_sweep.c -= b1->m_invMass * impulse;
- b1->m_sweep.a -= b1->m_invI * b2Cross(r1, impulse);
- b2->m_sweep.c += b2->m_invMass * impulse;
- b2->m_sweep.a += b2->m_invI * b2Cross(r2, impulse);
- b1->SynchronizeTransform();
- b2->SynchronizeTransform();
- }
-
- return positionError <= b2_linearSlop && angularError <= b2_angularSlop;
- }
- b2Vec2 b2RevoluteJoint::GetAnchorA() const
- {
- return m_bodyA->GetWorldPoint(m_localAnchor1);
- }
- b2Vec2 b2RevoluteJoint::GetAnchorB() const
- {
- return m_bodyB->GetWorldPoint(m_localAnchor2);
- }
- 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* b1 = m_bodyA;
- b2Body* b2 = m_bodyB;
- return b2->m_sweep.a - b1->m_sweep.a - m_referenceAngle;
- }
- float32 b2RevoluteJoint::GetJointSpeed() const
- {
- b2Body* b1 = m_bodyA;
- b2Body* b2 = m_bodyB;
- return b2->m_angularVelocity - b1->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() const
- {
- return 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)
- {
- m_bodyA->SetAwake(true);
- m_bodyB->SetAwake(true);
- m_enableLimit = flag;
- }
- float32 b2RevoluteJoint::GetLowerLimit() const
- {
- return m_lowerAngle;
- }
- float32 b2RevoluteJoint::GetUpperLimit() const
- {
- return m_upperAngle;
- }
- void b2RevoluteJoint::SetLimits(float32 lower, float32 upper)
- {
- b2Assert(lower <= upper);
- m_bodyA->SetAwake(true);
- m_bodyB->SetAwake(true);
- m_lowerAngle = lower;
- m_upperAngle = upper;
- }