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Bullet Continuous Collision Detection and Physics Library, http://bulletphysics.org
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Copyright (C) 2006, 2007 Sony Computer Entertainment Inc.
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This software is provided 'as-is', without any express or implied warranty.
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In no event will the authors be held liable for any damages 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 freely,
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subject to the following restrictions:
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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.
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2. Altered source versions must be plainly marked as such, and must not be 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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#include "btGeneric6DofSpringConstraint.h"
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#include "BulletDynamics/Dynamics/btRigidBody.h"
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#include "LinearMath/btTransformUtil.h"
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btGeneric6DofSpringConstraint::btGeneric6DofSpringConstraint(btRigidBody& rbA, btRigidBody& rbB, const btTransform& frameInA, const btTransform& frameInB ,bool useLinearReferenceFrameA)
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: btGeneric6DofConstraint(rbA, rbB, frameInA, frameInB, useLinearReferenceFrameA)
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m_objectType = D6_SPRING_CONSTRAINT_TYPE;
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for(int i = 0; i < 6; i++)
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m_springEnabled[i] = false;
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m_equilibriumPoint[i] = btScalar(0.f);
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m_springStiffness[i] = btScalar(0.f);
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m_springDamping[i] = btScalar(1.f);
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void btGeneric6DofSpringConstraint::enableSpring(int index, bool onOff)
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btAssert((index >= 0) && (index < 6));
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m_springEnabled[index] = onOff;
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m_linearLimits.m_enableMotor[index] = onOff;
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m_angularLimits[index - 3].m_enableMotor = onOff;
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void btGeneric6DofSpringConstraint::setStiffness(int index, btScalar stiffness)
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btAssert((index >= 0) && (index < 6));
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m_springStiffness[index] = stiffness;
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void btGeneric6DofSpringConstraint::setDamping(int index, btScalar damping)
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btAssert((index >= 0) && (index < 6));
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m_springDamping[index] = damping;
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void btGeneric6DofSpringConstraint::setEquilibriumPoint()
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calculateTransforms();
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for( i = 0; i < 3; i++)
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m_equilibriumPoint[i] = m_calculatedLinearDiff[i];
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for(i = 0; i < 3; i++)
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m_equilibriumPoint[i + 3] = m_calculatedAxisAngleDiff[i];
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void btGeneric6DofSpringConstraint::setEquilibriumPoint(int index)
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btAssert((index >= 0) && (index < 6));
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calculateTransforms();
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m_equilibriumPoint[index] = m_calculatedLinearDiff[index];
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m_equilibriumPoint[index] = m_calculatedAxisAngleDiff[index - 3];
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void btGeneric6DofSpringConstraint::setEquilibriumPoint(int index, btScalar val)
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btAssert((index >= 0) && (index < 6));
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m_equilibriumPoint[index] = val;
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void btGeneric6DofSpringConstraint::internalUpdateSprings(btConstraintInfo2* info)
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// it is assumed that calculateTransforms() have been called before this call
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btVector3 relVel = m_rbB.getLinearVelocity() - m_rbA.getLinearVelocity();
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for(i = 0; i < 3; i++)
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if(m_springEnabled[i])
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// get current position of constraint
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btScalar currPos = m_calculatedLinearDiff[i];
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// calculate difference
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btScalar delta = currPos - m_equilibriumPoint[i];
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// spring force is (delta * m_stiffness) according to Hooke's Law
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btScalar force = delta * m_springStiffness[i];
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btScalar velFactor = info->fps * m_springDamping[i] / btScalar(info->m_numIterations);
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m_linearLimits.m_targetVelocity[i] = velFactor * force;
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m_linearLimits.m_maxMotorForce[i] = btFabs(force) / info->fps;
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for(i = 0; i < 3; i++)
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if(m_springEnabled[i + 3])
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// get current position of constraint
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btScalar currPos = m_calculatedAxisAngleDiff[i];
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// calculate difference
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btScalar delta = currPos - m_equilibriumPoint[i+3];
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// spring force is (-delta * m_stiffness) according to Hooke's Law
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btScalar force = -delta * m_springStiffness[i+3];
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btScalar velFactor = info->fps * m_springDamping[i+3] / btScalar(info->m_numIterations);
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m_angularLimits[i].m_targetVelocity = velFactor * force;
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m_angularLimits[i].m_maxMotorForce = btFabs(force) / info->fps;
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void btGeneric6DofSpringConstraint::getInfo2(btConstraintInfo2* info)
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// this will be called by constraint solver at the constraint setup stage
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// set current motor parameters
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internalUpdateSprings(info);
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// do the rest of job for constraint setup
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btGeneric6DofConstraint::getInfo2(info);
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void btGeneric6DofSpringConstraint::setAxis(const btVector3& axis1,const btVector3& axis2)
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btVector3 zAxis = axis1.normalized();
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btVector3 yAxis = axis2.normalized();
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btVector3 xAxis = yAxis.cross(zAxis); // we want right coordinate system
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btTransform frameInW;
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frameInW.setIdentity();
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frameInW.getBasis().setValue( xAxis[0], yAxis[0], zAxis[0],
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xAxis[1], yAxis[1], zAxis[1],
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xAxis[2], yAxis[2], zAxis[2]);
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// now get constraint frame in local coordinate systems
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m_frameInA = m_rbA.getCenterOfMassTransform().inverse() * frameInW;
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m_frameInB = m_rbB.getCenterOfMassTransform().inverse() * frameInW;
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calculateTransforms();