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// Geometric Tools, LLC
// Copyright (c) 1998-2014
// Distributed under the Boost Software License, Version 1.0.
// http://www.boost.org/LICENSE_1_0.txt
// http://www.geometrictools.com/License/Boost/LICENSE_1_0.txt
//
// File Version: 5.0.0 (2010/01/01)
#include "PhysicsModule.h"
#include "Wm5Math.h"
#include "Wm5Memory.h"
#include "Wm5OdeRungeKutta4.h"
//----------------------------------------------------------------------------
PhysicsModule::PhysicsModule ()
:
Gravity(0.0),
Mass1(0.0),
Mass2(0.0),
Length1(0.0),
Length2(0.0),
JointX(0.0),
JointY(0.0),
mTime(0.0),
mDeltaTime(0.0),
mSolver(0)
{
mState[0] = 0.0;
mState[1] = 0.0;
mState[2] = 0.0;
mState[3] = 0.0;
mAux[0] = 0.0;
mAux[1] = 0.0;
mAux[2] = 0.0;
mAux[3] = 0.0;
}
//----------------------------------------------------------------------------
PhysicsModule::~PhysicsModule ()
{
delete0(mSolver);
}
//----------------------------------------------------------------------------
void PhysicsModule::Initialize (double time, double deltaTime, double theta1,
double theta2, double theta1Dot, double theta2Dot)
{
mTime = time;
mDeltaTime = deltaTime;
// state variables
mState[0] = theta1;
mState[1] = theta1Dot;
mState[2] = theta2;
mState[3] = theta2Dot;
// auxiliary variables
mAux[0] = Gravity;
mAux[1] = Length1;
mAux[2] = Length2;
mAux[3] = Mass2/(Mass1 + Mass2);
// RK4 differential equation solver. Since mSolver is a base class
// pointer, you can instead create a solver of whatever class you prefer.
delete0(mSolver);
mSolver = new0 OdeRungeKutta4d(4, mDeltaTime, OdeFunction, mAux);
}
//----------------------------------------------------------------------------
void PhysicsModule::GetPositions (double& x1, double& y1, double& x2,
double& y2) const
{
x1 = JointX + Length1*Mathd::Sin(mState[0]);
y1 = JointY - Length1*Mathd::Cos(mState[0]);
x2 = x1 + Length2*Mathd::Sin(mState[2]);
y2 = y1 - Length2*Mathd::Cos(mState[2]);
}
//----------------------------------------------------------------------------
void PhysicsModule::Update ()
{
// Apply a single step of the ODE solver.
if (mSolver)
{
mSolver->Update(mTime, mState, mTime, mState);
}
}
//----------------------------------------------------------------------------
void PhysicsModule::OdeFunction (double, const double* state,
void* data, double* output)
{
double* aux = (double*)data;
double angleD = state[0] - state[2];
double csD = Mathd::Cos(angleD);
double snD = Mathd::Sin(angleD);
double invDet = 1.0/(aux[1]*aux[2]*(1.0 - aux[3]*csD*csD));
double sn0 = Mathd::Sin(state[0]);
double sn2 = Mathd::Sin(state[2]);
double b1 = -aux[0]*sn0 - aux[3]*aux[2]*snD*state[3]*state[3];
double b2 = -aux[0]*sn2 + aux[1]*snD*state[1]*state[1];
double theta1DotFunction = (b1 - aux[3]*csD*b2)*aux[2]*invDet;
double theta2DotFunction = (b2 - csD*b1)*aux[1]*invDet;
// theta1 function
output[0] = state[1];
// dot(theta1) function
output[1] = theta1DotFunction;
// theta2 function
output[2] = state[3];
// dot(theta2) function
output[3] = theta2DotFunction;
}
//----------------------------------------------------------------------------
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