PretensionController.cpp

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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.
*/

// This module
#include "PretensionController.h"
// This library
#include "core/tgLinearString.h"
// The C++ Standard Library
#include <cassert>
#include <stdexcept>
#include <vector>

PretensionController::PretensionController(double tensionPct) :
    m_tension(tensionPct) 
{
    if (tensionPct < 0.0)
    {
        throw std::invalid_argument("Negative pretension");
    }
}

void PretensionController::onStep(tgLinearString& subject, double dt)
{
    if (dt <= 0.0)
    {
        throw std::invalid_argument("dt is not positive");
    }
    else
    {
                                double startLength = subject.getStartLength();
                                subject.setRestLength( (1 - m_tension) * startLength, dt);
    }
}