/* * Copyright (c) 2007-2011 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 #include #include // Limit: // C = norm(pB - pA) - L // u = (pB - pA) / norm(pB - pA) // Cdot = dot(u, vB + cross(wB, rB) - vA - cross(wA, rA)) // J = [-u -cross(rA, u) u cross(rB, u)] // K = J * invM * JT // = invMassA + invIA * cross(rA, u)^2 + invMassB + invIB * cross(rB, u)^2 b2RopeJoint::b2RopeJoint(const b2RopeJointDef* def) : b2Joint(def) { m_localAnchorA = def->localAnchorA; m_localAnchorB = def->localAnchorB; m_maxLength = def->maxLength; m_mass = 0.0f; m_impulse = 0.0f; m_state = e_inactiveLimit; m_length = 0.0f; } void b2RopeJoint::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); m_u = cB + m_rB - cA - m_rA; m_length = m_u.Length(); float32 C = m_length - m_maxLength; if (C > 0.0f) { m_state = e_atUpperLimit; } else { m_state = e_inactiveLimit; } if (m_length > b2_linearSlop) { m_u *= 1.0f / m_length; } else { m_u.SetZero(); m_mass = 0.0f; m_impulse = 0.0f; return; } // Compute effective mass. float32 crA = b2Cross(m_rA, m_u); float32 crB = b2Cross(m_rB, m_u); float32 invMass = m_invMassA + m_invIA * crA * crA + m_invMassB + m_invIB * crB * crB; m_mass = invMass != 0.0f ? 1.0f / invMass : 0.0f; if (data.step.warmStarting) { // Scale the impulse to support a variable time step. m_impulse *= data.step.dtRatio; b2Vec2 P = m_impulse * m_u; vA -= m_invMassA * P; wA -= m_invIA * b2Cross(m_rA, P); vB += m_invMassB * P; wB += m_invIB * b2Cross(m_rB, P); } else { m_impulse = 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 b2RopeJoint::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; // Cdot = dot(u, v + cross(w, r)) b2Vec2 vpA = vA + b2Cross(wA, m_rA); b2Vec2 vpB = vB + b2Cross(wB, m_rB); float32 C = m_length - m_maxLength; float32 Cdot = b2Dot(m_u, vpB - vpA); // Predictive constraint. if (C < 0.0f) { Cdot += data.step.inv_dt * C; } float32 impulse = -m_mass * Cdot; float32 oldImpulse = m_impulse; m_impulse = b2Min(0.0f, m_impulse + impulse); impulse = m_impulse - oldImpulse; b2Vec2 P = impulse * m_u; vA -= m_invMassA * P; wA -= m_invIA * b2Cross(m_rA, P); vB += m_invMassB * P; wB += m_invIB * b2Cross(m_rB, P); 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 b2RopeJoint::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); b2Vec2 rA = b2Mul(qA, m_localAnchorA - m_localCenterA); b2Vec2 rB = b2Mul(qB, m_localAnchorB - m_localCenterB); b2Vec2 u = cB + rB - cA - rA; float32 length = u.Normalize(); float32 C = length - m_maxLength; C = b2Clamp(C, 0.0f, b2_maxLinearCorrection); float32 impulse = -m_mass * C; b2Vec2 P = impulse * u; cA -= m_invMassA * P; aA -= m_invIA * b2Cross(rA, P); cB += m_invMassB * P; aB += m_invIB * b2Cross(rB, P); 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 length - m_maxLength < b2_linearSlop; } b2Vec2 b2RopeJoint::GetAnchorA() const { return m_bodyA->GetWorldPoint(m_localAnchorA); } b2Vec2 b2RopeJoint::GetAnchorB() const { return m_bodyB->GetWorldPoint(m_localAnchorB); } b2Vec2 b2RopeJoint::GetReactionForce(float32 inv_dt) const { b2Vec2 F = (inv_dt * m_impulse) * m_u; return F; } float32 b2RopeJoint::GetReactionTorque(float32 inv_dt) const { B2_NOT_USED(inv_dt); return 0.0f; } float32 b2RopeJoint::GetMaxLength() const { return m_maxLength; } b2LimitState b2RopeJoint::GetLimitState() const { return m_state; } void b2RopeJoint::Dump() { int32 indexA = m_bodyA->m_islandIndex; int32 indexB = m_bodyB->m_islandIndex; b2Log(" b2RopeJointDef 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.maxLength = %.15lef;\n", m_maxLength); b2Log(" joints[%d] = m_world->CreateJoint(&jd);\n", m_index); }