/*

* Copyright (c) 2009 Nokia Corporation and/or its subsidiary(-ies).

* All rights reserved.

* This component and the accompanying materials are made available

* under the terms of "Eclipse Public License v1.0"

* which accompanies this distribution, and is available

* at the URL "http://www.eclipse.org/legal/epl-v10.html".

*

* Initial Contributors:

* Nokia Corporation - initial contribution.

*

* Contributors:

*

* Description:    

*

*/

// INCLUDE FILES

#include "HgVgSpring.h"

#include "HgVgConstants.h"

#include <e32math.h>

using namespace HgVgConstants;

THgVgSpring::THgVgSpring(TReal aSpringK, TReal aSpringDamping, 

                TReal aSpringMaxVelocity, TReal aPositionSnap,

                TReal aVelocitySnap) : 

iPrevX(0), 

iPrevY(0),

iX(0), 

iY(0),

iEndX(0), 

iEndY(0),

iVelX(0), 

iVelY(0),

iAccumulator(0),

iSpringK(aSpringK),

iSpringDamping(aSpringDamping),

iMaxSpringVelocity(aSpringMaxVelocity),

iPositionSnap(aPositionSnap),

iVelocitySnap(aVelocitySnap)

    {

    }

void THgVgSpring::SetConstants(TReal aSpringK, TReal aSpringDamping, 

    TReal aSpringMaxVelocity, TReal aPositionSnap,

    TReal aVelocitySnap)

    {

    iSpringK = aSpringK;

    iSpringDamping = aSpringDamping;

    iMaxSpringVelocity = aSpringMaxVelocity;

    iPositionSnap = aPositionSnap;

    iVelocitySnap = aVelocitySnap;

    }

void THgVgSpring::Reset(TReal aX, TReal aY)

    {

    iEndX = aX;

    iEndY = aY;

    Reset();

    }

void THgVgSpring::Reset()

    {

    iPrevX = iX = iEndX;

    iPrevY = iY = iEndY;

    iAccumulator = 0;

    iVelX = 0;

    iVelY = 0;

    }

void THgVgSpring::SetXY(TReal aX, TReal aY)

    {

    iPrevX = iX = aX;

    iPrevY = iY = aY;

    }

void THgVgSpring::SetEnd(TReal aX, TReal aY)

    {

    iEndX = aX;

    iEndY = aY;

    }

void THgVgSpring::SetVelocity(TReal aVx, TReal aVy)

    {

    iVelX = aVx;

    iVelY = aVy;

    }

TBool THgVgSpring::IntegratePhysics(TReal aDeltaTime, TBool aEndCondition)

    {

    iAccumulator += aDeltaTime;    

    while (iAccumulator >= KTimeStep)

        {

        iPrevX = iX;

        iPrevY = iY;

        // calculate spring force F = -kx - bv

        TReal Fx = -(iX - iEndX) * iSpringK - iVelX * iSpringDamping;

        TReal Fy = -(iY - iEndY) * iSpringK - iVelY * iSpringDamping;

        // do euler integration

        iVelX += Fx * KTimeStep;

        iVelY += Fy * KTimeStep;

        // limit velocity to certain max

        if (Abs(iVelX) > iMaxSpringVelocity)

            iVelX = (iVelX < 0) ? -iMaxSpringVelocity : iMaxSpringVelocity;

        if (Abs(iVelY) > iMaxSpringVelocity)

            iVelY = (iVelY < 0) ? -iMaxSpringVelocity : iMaxSpringVelocity;

        // do euler integration

        iX += iVelX * KTimeStep;

        iY += iVelY * KTimeStep;

        // decrease accumulator

        iAccumulator -= KTimeStep;

        // snap to item if close enough and speed is small enough

        if (Abs(iX - iEndX) < iPositionSnap && Abs(iVelX) < iVelocitySnap &&

                Abs(iY - iEndY) < iPositionSnap && Abs(iVelY) < iVelocitySnap && aEndCondition)

            {

            Reset();

            return ETrue;

            }

        }

    return EFalse;

    }

TReal THgVgSpring::GetX() const

    {

    return iX;

    }

TReal THgVgSpring::GetY() const

    {

    return iY;

    }

TReal THgVgSpring::EndX() const

    {

    return iEndX;

    }

TReal THgVgSpring::EndY() const

    {

    return iEndY;

    }

TReal THgVgSpring::VelX() const

    {

    return iVelX;

    }

TReal THgVgSpring::VelY() const

    {

    return iVelY;

    }

TReal THgVgSpring::GetInterpolatedX() const

    {

    TReal a = iAccumulator / KTimeStep;

    return iX * (1.0 - a) + iPrevX * a;    

    }

TReal THgVgSpring::GetInterpolatedY() const

    {

    TReal a = iAccumulator / KTimeStep;

    return iY * (1.0 - a) + iPrevY * a;

    }

// End of File