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Diffstat (limited to 'Source/external/Box2D/Dynamics/Joints/b2FrictionJoint.cpp')
| -rw-r--r-- | Source/external/Box2D/Dynamics/Joints/b2FrictionJoint.cpp | 251 |
1 files changed, 251 insertions, 0 deletions
diff --git a/Source/external/Box2D/Dynamics/Joints/b2FrictionJoint.cpp b/Source/external/Box2D/Dynamics/Joints/b2FrictionJoint.cpp new file mode 100644 index 0000000..cb122eb --- /dev/null +++ b/Source/external/Box2D/Dynamics/Joints/b2FrictionJoint.cpp @@ -0,0 +1,251 @@ +/* +* 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/b2FrictionJoint.h" +#include "Box2D/Dynamics/b2Body.h" +#include "Box2D/Dynamics/b2TimeStep.h" + +// Point-to-point constraint +// 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) + +// Angle constraint +// Cdot = w2 - w1 +// J = [0 0 -1 0 0 1] +// K = invI1 + invI2 + +void b2FrictionJointDef::Initialize(b2Body* bA, b2Body* bB, const b2Vec2& anchor) +{ + bodyA = bA; + bodyB = bB; + localAnchorA = bodyA->GetLocalPoint(anchor); + localAnchorB = bodyB->GetLocalPoint(anchor); +} + +b2FrictionJoint::b2FrictionJoint(const b2FrictionJointDef* def) +: b2Joint(def) +{ + m_localAnchorA = def->localAnchorA; + m_localAnchorB = def->localAnchorB; + + m_linearImpulse.SetZero(); + m_angularImpulse = 0.0f; + + m_maxForce = def->maxForce; + m_maxTorque = def->maxTorque; +} + +void b2FrictionJoint::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; + + float32 aA = data.positions[m_indexA].a; + b2Vec2 vA = data.velocities[m_indexA].v; + float32 wA = data.velocities[m_indexA].w; + + 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); + + // Compute the effective mass matrix. + 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; + + b2Mat22 K; + K.ex.x = mA + mB + iA * m_rA.y * m_rA.y + iB * m_rB.y * m_rB.y; + K.ex.y = -iA * m_rA.x * m_rA.y - iB * m_rB.x * m_rB.y; + K.ey.x = K.ex.y; + K.ey.y = mA + mB + iA * m_rA.x * m_rA.x + iB * m_rB.x * m_rB.x; + + m_linearMass = K.GetInverse(); + + m_angularMass = iA + iB; + if (m_angularMass > 0.0f) + { + m_angularMass = 1.0f / m_angularMass; + } + + if (data.step.warmStarting) + { + // Scale impulses to support a variable time step. + m_linearImpulse *= data.step.dtRatio; + m_angularImpulse *= data.step.dtRatio; + + b2Vec2 P(m_linearImpulse.x, m_linearImpulse.y); + vA -= mA * P; + wA -= iA * (b2Cross(m_rA, P) + m_angularImpulse); + vB += mB * P; + wB += iB * (b2Cross(m_rB, P) + m_angularImpulse); + } + else + { + m_linearImpulse.SetZero(); + m_angularImpulse = 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 b2FrictionJoint::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; + + float32 h = data.step.dt; + + // Solve angular friction + { + float32 Cdot = wB - wA; + float32 impulse = -m_angularMass * Cdot; + + float32 oldImpulse = m_angularImpulse; + float32 maxImpulse = h * m_maxTorque; + m_angularImpulse = b2Clamp(m_angularImpulse + impulse, -maxImpulse, maxImpulse); + impulse = m_angularImpulse - oldImpulse; + + wA -= iA * impulse; + wB += iB * impulse; + } + + // Solve linear friction + { + b2Vec2 Cdot = vB + b2Cross(wB, m_rB) - vA - b2Cross(wA, m_rA); + + b2Vec2 impulse = -b2Mul(m_linearMass, Cdot); + b2Vec2 oldImpulse = m_linearImpulse; + m_linearImpulse += impulse; + + float32 maxImpulse = h * m_maxForce; + + if (m_linearImpulse.LengthSquared() > maxImpulse * maxImpulse) + { + m_linearImpulse.Normalize(); + m_linearImpulse *= maxImpulse; + } + + impulse = m_linearImpulse - oldImpulse; + + 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 b2FrictionJoint::SolvePositionConstraints(const b2SolverData& data) +{ + B2_NOT_USED(data); + + return true; +} + +b2Vec2 b2FrictionJoint::GetAnchorA() const +{ + return m_bodyA->GetWorldPoint(m_localAnchorA); +} + +b2Vec2 b2FrictionJoint::GetAnchorB() const +{ + return m_bodyB->GetWorldPoint(m_localAnchorB); +} + +b2Vec2 b2FrictionJoint::GetReactionForce(float32 inv_dt) const +{ + return inv_dt * m_linearImpulse; +} + +float32 b2FrictionJoint::GetReactionTorque(float32 inv_dt) const +{ + return inv_dt * m_angularImpulse; +} + +void b2FrictionJoint::SetMaxForce(float32 force) +{ + b2Assert(b2IsValid(force) && force >= 0.0f); + m_maxForce = force; +} + +float32 b2FrictionJoint::GetMaxForce() const +{ + return m_maxForce; +} + +void b2FrictionJoint::SetMaxTorque(float32 torque) +{ + b2Assert(b2IsValid(torque) && torque >= 0.0f); + m_maxTorque = torque; +} + +float32 b2FrictionJoint::GetMaxTorque() const +{ + return m_maxTorque; +} + +void b2FrictionJoint::Dump() +{ + int32 indexA = m_bodyA->m_islandIndex; + int32 indexB = m_bodyB->m_islandIndex; + + b2Log(" b2FrictionJointDef 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.maxForce = %.15lef;\n", m_maxForce); + b2Log(" jd.maxTorque = %.15lef;\n", m_maxTorque); + b2Log(" joints[%d] = m_world->CreateJoint(&jd);\n", m_index); +} |