/* Bullet Continuous Collision Detection and Physics Library Copyright (c) 2003-2006 Erwin Coumans http://continuousphysics.com/Bullet/ 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 "btHingeConstraint.h" #include "BulletDynamics/Dynamics/btRigidBody.h" #include "LinearMath/btTransformUtil.h" btHingeConstraint::btHingeConstraint(): m_enableAngularMotor(false) { } btHingeConstraint::btHingeConstraint(btRigidBody& rbA,btRigidBody& rbB, const btVector3& pivotInA,const btVector3& pivotInB, btVector3& axisInA,btVector3& axisInB) :btTypedConstraint(rbA,rbB),m_pivotInA(pivotInA),m_pivotInB(pivotInB), m_axisInA(axisInA), m_axisInB(-axisInB), m_angularOnly(false), m_enableAngularMotor(false) { } btHingeConstraint::btHingeConstraint(btRigidBody& rbA,const btVector3& pivotInA,btVector3& axisInA) :btTypedConstraint(rbA),m_pivotInA(pivotInA),m_pivotInB(rbA.getCenterOfMassTransform()(pivotInA)), m_axisInA(axisInA), //fixed axis in worldspace m_axisInB(rbA.getCenterOfMassTransform().getBasis() * -axisInA), m_angularOnly(false), m_enableAngularMotor(false) { } void btHingeConstraint::buildJacobian() { m_appliedImpulse = 0.f; btVector3 normal(0,0,0); if (!m_angularOnly) { for (int i=0;i<3;i++) { normal[i] = 1; new (&m_jac[i]) btJacobianEntry( m_rbA.getCenterOfMassTransform().getBasis().transpose(), m_rbB.getCenterOfMassTransform().getBasis().transpose(), m_rbA.getCenterOfMassTransform()*m_pivotInA - m_rbA.getCenterOfMassPosition(), m_rbB.getCenterOfMassTransform()*m_pivotInB - m_rbB.getCenterOfMassPosition(), normal, m_rbA.getInvInertiaDiagLocal(), m_rbA.getInvMass(), m_rbB.getInvInertiaDiagLocal(), m_rbB.getInvMass()); normal[i] = 0; } } //calculate two perpendicular jointAxis, orthogonal to hingeAxis //these two jointAxis require equal angular velocities for both bodies //this is unused for now, it's a todo btVector3 jointAxis0local; btVector3 jointAxis1local; btPlaneSpace1(m_axisInA,jointAxis0local,jointAxis1local); getRigidBodyA().getCenterOfMassTransform().getBasis() * m_axisInA; btVector3 jointAxis0 = getRigidBodyA().getCenterOfMassTransform().getBasis() * jointAxis0local; btVector3 jointAxis1 = getRigidBodyA().getCenterOfMassTransform().getBasis() * jointAxis1local; btVector3 hingeAxisWorld = getRigidBodyA().getCenterOfMassTransform().getBasis() * m_axisInA; new (&m_jacAng[0]) btJacobianEntry(jointAxis0, m_rbA.getCenterOfMassTransform().getBasis().transpose(), m_rbB.getCenterOfMassTransform().getBasis().transpose(), m_rbA.getInvInertiaDiagLocal(), m_rbB.getInvInertiaDiagLocal()); new (&m_jacAng[1]) btJacobianEntry(jointAxis1, m_rbA.getCenterOfMassTransform().getBasis().transpose(), m_rbB.getCenterOfMassTransform().getBasis().transpose(), m_rbA.getInvInertiaDiagLocal(), m_rbB.getInvInertiaDiagLocal()); new (&m_jacAng[2]) btJacobianEntry(hingeAxisWorld, m_rbA.getCenterOfMassTransform().getBasis().transpose(), m_rbB.getCenterOfMassTransform().getBasis().transpose(), m_rbA.getInvInertiaDiagLocal(), m_rbB.getInvInertiaDiagLocal()); } void btHingeConstraint::solveConstraint(btScalar timeStep) { btVector3 pivotAInW = m_rbA.getCenterOfMassTransform()*m_pivotInA; btVector3 pivotBInW = m_rbB.getCenterOfMassTransform()*m_pivotInB; btVector3 normal(0,0,0); btScalar tau = 0.3f; btScalar damping = 1.f; //linear part if (!m_angularOnly) { for (int i=0;i<3;i++) { normal[i] = 1; btScalar jacDiagABInv = 1.f / m_jac[i].getDiagonal(); btVector3 rel_pos1 = pivotAInW - m_rbA.getCenterOfMassPosition(); btVector3 rel_pos2 = pivotBInW - m_rbB.getCenterOfMassPosition(); btVector3 vel1 = m_rbA.getVelocityInLocalPoint(rel_pos1); btVector3 vel2 = m_rbB.getVelocityInLocalPoint(rel_pos2); btVector3 vel = vel1 - vel2; btScalar rel_vel; rel_vel = normal.dot(vel); //positional error (zeroth order error) btScalar depth = -(pivotAInW - pivotBInW).dot(normal); //this is the error projected on the normal btScalar impulse = depth*tau/timeStep * jacDiagABInv - damping * rel_vel * jacDiagABInv * damping; m_appliedImpulse += impulse; btVector3 impulse_vector = normal * impulse; m_rbA.applyImpulse(impulse_vector, pivotAInW - m_rbA.getCenterOfMassPosition()); m_rbB.applyImpulse(-impulse_vector, pivotBInW - m_rbB.getCenterOfMassPosition()); normal[i] = 0; } } { ///solve angular part // get axes in world space btVector3 axisA = getRigidBodyA().getCenterOfMassTransform().getBasis() * m_axisInA; btVector3 axisB = getRigidBodyB().getCenterOfMassTransform().getBasis() * m_axisInB; const btVector3& angVelA = getRigidBodyA().getAngularVelocity(); const btVector3& angVelB = getRigidBodyB().getAngularVelocity(); btVector3 angVelAroundHingeAxisA = axisA * axisA.dot(angVelA); btVector3 angVelAroundHingeAxisB = axisB * axisB.dot(angVelB); btVector3 angAorthog = angVelA - angVelAroundHingeAxisA; btVector3 angBorthog = angVelB - angVelAroundHingeAxisB; btVector3 velrelOrthog = angAorthog-angBorthog; { //solve orthogonal angular velocity correction float relaxation = 1.f; float len = velrelOrthog.length(); if (len > 0.00001f) { btVector3 normal = velrelOrthog.normalized(); float denom = getRigidBodyA().computeAngularImpulseDenominator(normal) + getRigidBodyB().computeAngularImpulseDenominator(normal); // scale for mass and relaxation //todo: expose this 0.9 factor to developer velrelOrthog *= (1.f/denom) * 0.9f; } //solve angular positional correction btVector3 angularError = -axisA.cross(axisB) *(1.f/timeStep); float len2 = angularError.length(); if (len2>0.00001f) { btVector3 normal2 = angularError.normalized(); float denom2 = getRigidBodyA().computeAngularImpulseDenominator(normal2) + getRigidBodyB().computeAngularImpulseDenominator(normal2); angularError *= (1.f/denom2) * relaxation; } m_rbA.applyTorqueImpulse(-velrelOrthog+angularError); m_rbB.applyTorqueImpulse(velrelOrthog-angularError); } //apply motor if (m_enableAngularMotor) { //todo: add limits too btVector3 angularLimit(0,0,0); btVector3 velrel = angVelAroundHingeAxisA - angVelAroundHingeAxisB; btScalar projRelVel = velrel.dot(axisA); btScalar desiredMotorVel = m_motorTargetVelocity; btScalar motor_relvel = desiredMotorVel - projRelVel; float denom3 = getRigidBodyA().computeAngularImpulseDenominator(axisA) + getRigidBodyB().computeAngularImpulseDenominator(axisA); btScalar unclippedMotorImpulse = (1.f/denom3) * motor_relvel;; //todo: should clip against accumulated impulse btScalar clippedMotorImpulse = unclippedMotorImpulse > m_maxMotorImpulse ? m_maxMotorImpulse : unclippedMotorImpulse; clippedMotorImpulse = clippedMotorImpulse < -m_maxMotorImpulse ? -m_maxMotorImpulse : clippedMotorImpulse; btVector3 motorImp = clippedMotorImpulse * axisA; m_rbA.applyTorqueImpulse(motorImp+angularLimit); m_rbB.applyTorqueImpulse(-motorImp-angularLimit); } } } void btHingeConstraint::updateRHS(btScalar timeStep) { }