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     {

    46     

    47     }

    48 

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

    50     TReal aSpringMaxVelocity, TReal aPositionSnap,

    51     TReal aVelocitySnap)

    52     {

    53     iSpringK = aSpringK;

    54     iSpringDamping = aSpringDamping;

    55     iMaxSpringVelocity = aSpringMaxVelocity;

    56     iPositionSnap = aPositionSnap;

    57     iVelocitySnap = aVelocitySnap;

    58     }

    59 

    60 

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

    62     {

    63     iEndX = aX;

    64     iEndY = aY;

    65     Reset();

    66     }

    67 

    68 void THgVgSpring::Reset()

    69     {

    70     iPrevX = iX = iEndX;

    71     iPrevY = iY = iEndY;

    72     iAccumulator = 0;

    73     iVelX = 0;

    74     iVelY = 0;

    75     }

    76 

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

    78     {

    79     iPrevX = iX = aX;

    80     iPrevY = iY = aY;

    81     }

    82 

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

    84     {

    85     iEndX = aX;

    86     iEndY = aY;

    87     }

    88 

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

    90     {

    91     iVelX = aVx;

    92     iVelY = aVy;

    93     }

    94 

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

    96     {

    97     iAccumulator += aDeltaTime;    

    98     while (iAccumulator >= KTimeStep)

    99         {

   100         iPrevX = iX;

   101         iPrevY = iY;

   102 

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

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

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

   106         

   107         // do euler integration

   108         iVelX += Fx * KTimeStep;

   109         iVelY += Fy * KTimeStep;

   110                 

   111         // limit velocity to certain max

   112         if (Abs(iVelX) > iMaxSpringVelocity)

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

   114         

   115         if (Abs(iVelY) > iMaxSpringVelocity)

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

   117 

   118         // do euler integration

   119         iX += iVelX * KTimeStep;

   120         iY += iVelY * KTimeStep;

   121         

   122         // decrease accumulator

   123         iAccumulator -= KTimeStep;

   124 

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

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

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

   128             {

   129             Reset();

   130             return ETrue;

   131             }

   132                 

   133         }

   134     

   135     return EFalse;

   136     }

   137 

   138 TReal THgVgSpring::GetX() const

   139     {

   140     return iX;

   141     }

   142 

   143 TReal THgVgSpring::GetY() const

   144     {

   145     return iY;

   146     }

   147 

   148 TReal THgVgSpring::EndX() const

   149     {

   150     return iEndX;

   151     }

   152 

   153 TReal THgVgSpring::EndY() const

   154     {

   155     return iEndY;

   156     }

   157 

   158 TReal THgVgSpring::VelX() const

   159     {

   160     return iVelX;

   161     }

   162 

   163 TReal THgVgSpring::VelY() const

   164     {

   165     return iVelY;

   166     }

   167 

   168 TReal THgVgSpring::GetInterpolatedX() const

   169     {

   170     TReal a = iAccumulator / KTimeStep;

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

   172     }

   173 

   174 TReal THgVgSpring::GetInterpolatedY() const

   175     {

   176     TReal a = iAccumulator / KTimeStep;

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

   178     }

   179 

   180 

   181 // End of File