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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set sw=2 ts=8 et tw=80 : */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef mozilla_layers_AxisPhysicsMSDModel_h
#define mozilla_layers_AxisPhysicsMSDModel_h
#include "AxisPhysicsModel.h"
namespace mozilla {
namespace layers {
/**
* AxisPhysicsMSDModel encapsulates a 1-dimensional MSD (Mass-Spring-Damper)
* model. A unit mass is assumed.
*/
class AxisPhysicsMSDModel : public AxisPhysicsModel {
public:
AxisPhysicsMSDModel(double aInitialPosition, double aInitialDestination,
double aInitialVelocity, double aSpringConstant,
double aDampingRatio);
~AxisPhysicsMSDModel();
/**
* Gets the raw destination of this axis at this moment.
*/
double GetDestination() const;
/**
* Sets the raw destination of this axis at this moment.
*/
void SetDestination(double aDestination);
/**
* Returns true when the position is close to the destination and the
* velocity is low.
*/
bool IsFinished(double aSmallestVisibleIncrement);
protected:
virtual double Acceleration(const State &aState);
private:
/**
* mDestination represents the target position and the resting position of
* the simulated spring.
*/
double mDestination;
/**
* Greater values of mSpringConstant result in a stiffer / stronger spring.
*/
double mSpringConstant;
/**
* mSpringConstantSqrtTimesTwo is calculated from mSpringConstant to reduce
* calculations performed in the inner loop.
*/
double mSpringConstantSqrtXTwo;
/**
* Damping Ratio: http://en.wikipedia.org/wiki/Damping_ratio
*
* When mDampingRatio < 1.0, this is an under damped system.
* - Overshoots destination and oscillates with the amplitude gradually
* decreasing to zero.
*
* When mDampingRatio == 1.0, this is a critically damped system.
* - Reaches destination as quickly as possible without oscillating.
*
* When mDampingRatio > 1.0, this is an over damped system.
* - Reaches destination (exponentially decays) without oscillating.
*/
double mDampingRatio;
};
} // namespace layers
} // namespace mozilla
#endif
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