mirror of https://github.com/axmolengine/axmol.git
261 lines
7.7 KiB
C++
261 lines
7.7 KiB
C++
/*
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* Copyright (c) 2006-2011 Erin Catto http://www.box2d.org
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*
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* This software is provided 'as-is', without any express or implied
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* warranty. In no event will the authors be held liable for any damages
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* arising from the use of this software.
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* Permission is granted to anyone to use this software for any purpose,
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* including commercial applications, and to alter it and redistribute it
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* freely, subject to the following restrictions:
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* 1. The origin of this software must not be misrepresented; you must not
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* claim that you wrote the original software. If you use this software
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* in a product, an acknowledgment in the product documentation would be
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* appreciated but is not required.
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* 2. Altered source versions must be plainly marked as such, and must not be
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* misrepresented as being the original software.
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* 3. This notice may not be removed or altered from any source distribution.
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*/
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#include <Box2D/Dynamics/Joints/b2DistanceJoint.h>
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#include <Box2D/Dynamics/b2Body.h>
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#include <Box2D/Dynamics/b2TimeStep.h>
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// 1-D constrained system
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// m (v2 - v1) = lambda
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// v2 + (beta/h) * x1 + gamma * lambda = 0, gamma has units of inverse mass.
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// x2 = x1 + h * v2
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// 1-D mass-damper-spring system
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// m (v2 - v1) + h * d * v2 + h * k *
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// C = norm(p2 - p1) - L
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// u = (p2 - p1) / norm(p2 - p1)
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// Cdot = dot(u, v2 + cross(w2, r2) - v1 - cross(w1, r1))
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// J = [-u -cross(r1, u) u cross(r2, u)]
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// K = J * invM * JT
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// = invMass1 + invI1 * cross(r1, u)^2 + invMass2 + invI2 * cross(r2, u)^2
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void b2DistanceJointDef::Initialize(b2Body* b1, b2Body* b2,
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const b2Vec2& anchor1, const b2Vec2& anchor2)
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{
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bodyA = b1;
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bodyB = b2;
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localAnchorA = bodyA->GetLocalPoint(anchor1);
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localAnchorB = bodyB->GetLocalPoint(anchor2);
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b2Vec2 d = anchor2 - anchor1;
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length = d.Length();
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}
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b2DistanceJoint::b2DistanceJoint(const b2DistanceJointDef* def)
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: b2Joint(def)
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{
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m_localAnchorA = def->localAnchorA;
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m_localAnchorB = def->localAnchorB;
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m_length = def->length;
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m_frequencyHz = def->frequencyHz;
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m_dampingRatio = def->dampingRatio;
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m_impulse = 0.0f;
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m_gamma = 0.0f;
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m_bias = 0.0f;
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}
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void b2DistanceJoint::InitVelocityConstraints(const b2SolverData& data)
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{
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m_indexA = m_bodyA->m_islandIndex;
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m_indexB = m_bodyB->m_islandIndex;
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m_localCenterA = m_bodyA->m_sweep.localCenter;
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m_localCenterB = m_bodyB->m_sweep.localCenter;
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m_invMassA = m_bodyA->m_invMass;
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m_invMassB = m_bodyB->m_invMass;
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m_invIA = m_bodyA->m_invI;
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m_invIB = m_bodyB->m_invI;
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b2Vec2 cA = data.positions[m_indexA].c;
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float32 aA = data.positions[m_indexA].a;
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b2Vec2 vA = data.velocities[m_indexA].v;
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float32 wA = data.velocities[m_indexA].w;
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b2Vec2 cB = data.positions[m_indexB].c;
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float32 aB = data.positions[m_indexB].a;
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b2Vec2 vB = data.velocities[m_indexB].v;
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float32 wB = data.velocities[m_indexB].w;
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b2Rot qA(aA), qB(aB);
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m_rA = b2Mul(qA, m_localAnchorA - m_localCenterA);
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m_rB = b2Mul(qB, m_localAnchorB - m_localCenterB);
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m_u = cB + m_rB - cA - m_rA;
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// Handle singularity.
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float32 length = m_u.Length();
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if (length > b2_linearSlop)
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{
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m_u *= 1.0f / length;
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}
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else
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{
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m_u.Set(0.0f, 0.0f);
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}
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float32 crAu = b2Cross(m_rA, m_u);
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float32 crBu = b2Cross(m_rB, m_u);
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float32 invMass = m_invMassA + m_invIA * crAu * crAu + m_invMassB + m_invIB * crBu * crBu;
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// Compute the effective mass matrix.
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m_mass = invMass != 0.0f ? 1.0f / invMass : 0.0f;
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if (m_frequencyHz > 0.0f)
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{
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float32 C = length - m_length;
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// Frequency
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float32 omega = 2.0f * b2_pi * m_frequencyHz;
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// Damping coefficient
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float32 d = 2.0f * m_mass * m_dampingRatio * omega;
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// Spring stiffness
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float32 k = m_mass * omega * omega;
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// magic formulas
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float32 h = data.step.dt;
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m_gamma = h * (d + h * k);
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m_gamma = m_gamma != 0.0f ? 1.0f / m_gamma : 0.0f;
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m_bias = C * h * k * m_gamma;
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invMass += m_gamma;
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m_mass = invMass != 0.0f ? 1.0f / invMass : 0.0f;
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}
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else
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{
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m_gamma = 0.0f;
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m_bias = 0.0f;
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}
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if (data.step.warmStarting)
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{
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// Scale the impulse to support a variable time step.
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m_impulse *= data.step.dtRatio;
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b2Vec2 P = m_impulse * m_u;
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vA -= m_invMassA * P;
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wA -= m_invIA * b2Cross(m_rA, P);
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vB += m_invMassB * P;
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wB += m_invIB * b2Cross(m_rB, P);
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}
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else
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{
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m_impulse = 0.0f;
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}
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data.velocities[m_indexA].v = vA;
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data.velocities[m_indexA].w = wA;
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data.velocities[m_indexB].v = vB;
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data.velocities[m_indexB].w = wB;
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}
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void b2DistanceJoint::SolveVelocityConstraints(const b2SolverData& data)
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{
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b2Vec2 vA = data.velocities[m_indexA].v;
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float32 wA = data.velocities[m_indexA].w;
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b2Vec2 vB = data.velocities[m_indexB].v;
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float32 wB = data.velocities[m_indexB].w;
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// Cdot = dot(u, v + cross(w, r))
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b2Vec2 vpA = vA + b2Cross(wA, m_rA);
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b2Vec2 vpB = vB + b2Cross(wB, m_rB);
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float32 Cdot = b2Dot(m_u, vpB - vpA);
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float32 impulse = -m_mass * (Cdot + m_bias + m_gamma * m_impulse);
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m_impulse += impulse;
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b2Vec2 P = impulse * m_u;
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vA -= m_invMassA * P;
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wA -= m_invIA * b2Cross(m_rA, P);
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vB += m_invMassB * P;
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wB += m_invIB * b2Cross(m_rB, P);
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data.velocities[m_indexA].v = vA;
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data.velocities[m_indexA].w = wA;
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data.velocities[m_indexB].v = vB;
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data.velocities[m_indexB].w = wB;
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}
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bool b2DistanceJoint::SolvePositionConstraints(const b2SolverData& data)
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{
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if (m_frequencyHz > 0.0f)
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{
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// There is no position correction for soft distance constraints.
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return true;
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}
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b2Vec2 cA = data.positions[m_indexA].c;
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float32 aA = data.positions[m_indexA].a;
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b2Vec2 cB = data.positions[m_indexB].c;
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float32 aB = data.positions[m_indexB].a;
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b2Rot qA(aA), qB(aB);
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b2Vec2 rA = b2Mul(qA, m_localAnchorA - m_localCenterA);
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b2Vec2 rB = b2Mul(qB, m_localAnchorB - m_localCenterB);
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b2Vec2 u = cB + rB - cA - rA;
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float32 length = u.Normalize();
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float32 C = length - m_length;
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C = b2Clamp(C, -b2_maxLinearCorrection, b2_maxLinearCorrection);
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float32 impulse = -m_mass * C;
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b2Vec2 P = impulse * u;
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cA -= m_invMassA * P;
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aA -= m_invIA * b2Cross(rA, P);
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cB += m_invMassB * P;
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aB += m_invIB * b2Cross(rB, P);
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data.positions[m_indexA].c = cA;
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data.positions[m_indexA].a = aA;
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data.positions[m_indexB].c = cB;
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data.positions[m_indexB].a = aB;
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return b2Abs(C) < b2_linearSlop;
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}
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b2Vec2 b2DistanceJoint::GetAnchorA() const
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{
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return m_bodyA->GetWorldPoint(m_localAnchorA);
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}
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b2Vec2 b2DistanceJoint::GetAnchorB() const
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{
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return m_bodyB->GetWorldPoint(m_localAnchorB);
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}
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b2Vec2 b2DistanceJoint::GetReactionForce(float32 inv_dt) const
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{
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b2Vec2 F = (inv_dt * m_impulse) * m_u;
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return F;
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}
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float32 b2DistanceJoint::GetReactionTorque(float32 inv_dt) const
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{
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B2_NOT_USED(inv_dt);
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return 0.0f;
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}
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void b2DistanceJoint::Dump()
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{
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int32 indexA = m_bodyA->m_islandIndex;
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int32 indexB = m_bodyB->m_islandIndex;
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b2Log(" b2DistanceJointDef jd;\n");
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b2Log(" jd.bodyA = bodies[%d];\n", indexA);
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b2Log(" jd.bodyB = bodies[%d];\n", indexB);
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b2Log(" jd.collideConnected = bool(%d);\n", m_collideConnected);
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b2Log(" jd.localAnchorA.Set(%.15lef, %.15lef);\n", m_localAnchorA.x, m_localAnchorA.y);
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b2Log(" jd.localAnchorB.Set(%.15lef, %.15lef);\n", m_localAnchorB.x, m_localAnchorB.y);
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b2Log(" jd.length = %.15lef;\n", m_length);
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b2Log(" jd.frequencyHz = %.15lef;\n", m_frequencyHz);
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b2Log(" jd.dampingRatio = %.15lef;\n", m_dampingRatio);
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b2Log(" joints[%d] = m_world->CreateJoint(&jd);\n", m_index);
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}
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