tgBulletCompressionSpring.h

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/*
 * Copyright © 2012, United States Government, as represented by the
 * Administrator of the National Aeronautics and Space Administration.
 * All rights reserved.
 * 
 * The NASA Tensegrity Robotics Toolkit (NTRT) v1 platform is licensed
 * under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * http://www.apache.org/licenses/LICENSE-2.0.
 * 
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
*/

#ifndef SRC_CORE_TG_BULLET_COMPRESSION_SPRING_H_
#define SRC_CORE_TG_BULLET_COMPRESSION_SPRING_H_

// The Bullet Physics library
#include "LinearMath/btVector3.h"
// The C++ Standard Library
#include <vector>

// Forward references
// Note that even though this object is not a tgSpringCable,
// we're still using tgSpringCableAnchor as a convenience.
// This works because there actually don't seem to be any references
// to tgSpringCable in tgSpringCableAnchor or tgBulletSpringCableAnchor.
class btRigidBody;
class tgSpringCableAnchor;
class tgBulletSpringCableAnchor;

class tgBulletCompressionSpring
{
public: 
    tgBulletCompressionSpring( const std::vector<tgBulletSpringCableAnchor*>& anchors,
                        bool isFreeEndAttached,
                double coefK,
                double coefD,
                double restLength);
    
    virtual ~tgBulletCompressionSpring();

    virtual void step(double dt);
    
    virtual const double getCurrentAnchorDistance() const;

    virtual const double getCurrentSpringLength() const;

    virtual const btVector3 getAnchorDirectionUnitVector() const;

    virtual const btVector3 getSpringEndpoint() const;

    
    virtual const double getSpringForce() const;
    
    virtual const double getCoefK() const
    {
        return m_coefK;
    }
    
    virtual const double getCoefD() const
    {
        return m_coefD;
    }
    
    virtual const double getVelocity() const
    {
        return m_velocity;
    }
    
    virtual const double getDampingForce() const
    {
        return m_dampingForce;
    }

    virtual const double getRestLength() const
    {
        return m_restLength;
    }

    virtual const bool isFreeEndAttached() const
    {
        return m_isFreeEndAttached;
    }
    
    virtual const std::vector<const tgSpringCableAnchor*> getAnchors() const;

    
protected:
    
   std::vector<tgBulletSpringCableAnchor*> m_anchors;
    
    tgBulletSpringCableAnchor * const anchor1;

    tgBulletSpringCableAnchor * const anchor2;

    double m_dampingForce;
    
    double m_velocity;

    bool m_isFreeEndAttached;

    const double m_coefK;

    const double m_coefD;
    
    double m_restLength;
 
    double m_prevLength;
    
    virtual void calculateAndApplyForce(double dt);

private: 
    bool invariant(void) const;
};

#endif  // SRC_CORE_TG_BULLET_SPRING_CABLE_H_