1 /*

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

     3 * All rights reserved.

     4 * This component and the accompanying materials are made available

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

     6 * which accompanies this distribution, and is available

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

     8 *

     9 * Initial Contributors:

    10 * Nokia Corporation - initial contribution.

    11 *

    12 * Contributors:

    13 *

    14 * Description:    

    15 *

    16 */

    17 

    18 // INCLUDE FILES

    19 

    20 #include "HgVgSpring.h"

    21 #include "HgVgConstants.h"

    22 

    23 #include <e32math.h>

    24 

    25 using namespace HgVgConstants;

    26 

    27 

    28 THgVgSpring::THgVgSpring(TReal aSpringK, TReal aSpringDamping, 

    29                 TReal aSpringMaxVelocity, TReal aPositionSnap,

    30                 TReal aVelocitySnap) : 

    31 iPrevX(0), 

    32 iPrevY(0),

    33 iX(0), 

    34 iY(0),

    35 iEndX(0), 

    36 iEndY(0),

    37 iVelX(0), 

    38 iVelY(0),

    39 iAccumulator(0),

    40 iSpringK(aSpringK),

    41 iSpringDamping(aSpringDamping),

    42 iMaxSpringVelocity(aSpringMaxVelocity),

    43 iPositionSnap(aPositionSnap),

    44 iVelocitySnap(aVelocitySnap),

    45 iStartX(0),

    46 iStartY(0)

    47     {

    48     

    49     }

    50 

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

    52     TReal aSpringMaxVelocity, TReal aPositionSnap,

    53     TReal aVelocitySnap)

    54     {

    55     iSpringK = aSpringK;

    56     iSpringDamping = aSpringDamping;

    57     iMaxSpringVelocity = aSpringMaxVelocity;

    58     iPositionSnap = aPositionSnap;

    59     iVelocitySnap = aVelocitySnap;

    60     }

    61 

    62 

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

    64     {

    65     iEndX = aX;

    66     iEndY = aY;

    67     Reset();

    68     }

    69 

    70 void THgVgSpring::Reset()

    71     {

    72     iPrevX = iX = iStartX = iEndX;

    73     iPrevY = iY = iStartY = iEndY;

    74     iAccumulator = 0;

    75     iVelX = 0;

    76     iVelY = 0;

    77     }

    78 

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

    80     {

    81     iStartX = iPrevX = iX = aX;

    82     iStartY = iPrevY = iY = aY;

    83     }

    84 

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

    86     {

    87     iStartX = iEndX;

    88     iStartY = iEndY;

    89     iEndX = aX;

    90     iEndY = aY;

    91     }

    92 

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

    94     {

    95     iVelX = aVx;

    96     iVelY = aVy;

    97     }

    98 

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

   100     {

   101     iAccumulator += aDeltaTime;    

   102     while (iAccumulator >= KTimeStep)

   103         {

   104         iPrevX = iX;

   105         iPrevY = iY;

   106 

   107         // calculate spring force F = -kx - bv

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

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

   110         

   111         // do euler integration

   112         iVelX += Fx * KTimeStep;

   113         iVelY += Fy * KTimeStep;

   114                 

   115         // limit velocity to certain max

   116         if (Abs(iVelX) > iMaxSpringVelocity)

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

   118         

   119         if (Abs(iVelY) > iMaxSpringVelocity)

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

   121 

   122         // do euler integration

   123         iX += iVelX * KTimeStep;

   124         iY += iVelY * KTimeStep;

   125         

   126         // decrease accumulator

   127         iAccumulator -= KTimeStep;

   128 

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

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

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

   132             {

   133             Reset();

   134             return ETrue;

   135             }

   136                 

   137         }

   138     

   139     return EFalse;

   140     }

   141 

   142 TReal THgVgSpring::GetX() const

   143     {

   144     return iX;

   145     }

   146 

   147 TReal THgVgSpring::GetY() const

   148     {

   149     return iY;

   150     }

   151 

   152 TReal THgVgSpring::EndX() const

   153     {

   154     return iEndX;

   155     }

   156 

   157 TReal THgVgSpring::EndY() const

   158     {

   159     return iEndY;

   160     }

   161 

   162 TReal THgVgSpring::VelX() const

   163     {

   164     return iVelX;

   165     }

   166 

   167 TReal THgVgSpring::VelY() const

   168     {

   169     return iVelY;

   170     }

   171 

   172 TReal THgVgSpring::GetInterpolatedX() const

   173     {

   174     TReal a = iAccumulator / KTimeStep;

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

   176     }

   177 

   178 TReal THgVgSpring::GetInterpolatedY() const

   179     {

   180     TReal a = iAccumulator / KTimeStep;

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

   182     }

   183 

   184 TReal THgVgSpring::StartX() const

   185     {

   186     return iStartX;

   187     }

   188 

   189 TReal THgVgSpring::StartY() const

   190     {

   191     return iStartY;

   192     }

   193 

   194 

   195 // End of File