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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 "Wm5Memory.h"
#include "Wm5OdeRungeKutta4.h"
#include "Wm5Vector2.h"
using namespace Wm5;
//----------------------------------------------------------------------------
PhysicsModule::PhysicsModule ()
:
Gravity(0.0),
Mass1(0.0),
Mass2(0.0),
Friction1(0.0),
Friction2(0.0),
mTime(0.0),
mDeltaTime(0.0),
mLength1(0.0),
mLength2(0.0),
mSolver(0)
{
mState[0] = 0.0;
mState[1] = 0.0;
mState[2] = 0.0;
mState[3] = 0.0;
mState[4] = 0.0;
mState[5] = 0.0;
mAux[0] = 0.0;
mAux[1] = 0.0;
mAux[2] = 0.0;
mAux[3] = 0.0;
mAux[4] = 0.0;
mAux[5] = 0.0;
mAux[6] = 0.0;
}
//----------------------------------------------------------------------------
PhysicsModule::~PhysicsModule ()
{
delete0(mSolver);
}
//----------------------------------------------------------------------------
void PhysicsModule::Initialize (double time, double deltaTime, double x1,
double y1, double x2, double y2, double xDot, double yDot,
double thetaDot)
{
mTime = time;
mDeltaTime = deltaTime;
// Compute length and moments.
double deltaX = x2 - x1;
double deltaY = y2 - y1;
double length = Mathd::Sqrt(deltaX*deltaX + deltaY*deltaY);
double mu0 = Mass1 + Mass2;
double invMu0 = 1.0/mu0;
double weight1 = Mass1*invMu0;
double weight2 = Mass2*invMu0;
mLength1 = weight2*length;
mLength2 = weight1*length;
double mu2 = Mass1*mLength1*mLength1 + Mass2*mLength2*mLength2;
double invMu2 = 1.0/mu2;
// state variables
mState[0] = weight1*x1 + weight2*x2;
mState[1] = xDot;
mState[2] = weight1*y1 + weight2*y2;
mState[3] = yDot;
mState[4] = Mathd::ATan2(deltaY, deltaX);
mState[5] = thetaDot;
// auxiliary variable
mAux[0] = Gravity;
mAux[1] = mLength1;
mAux[2] = mLength2;
mAux[3] = -Friction1*invMu0;
mAux[4] = -Friction2*invMu0;
mAux[5] = -Friction1*invMu2;
mAux[6] = -Friction2*invMu2;
// 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(6, mDeltaTime, OdeFunction, mAux);
}
//----------------------------------------------------------------------------
void PhysicsModule::Update ()
{
if (mSolver)
{
// Apply a single step of the ODE solver.
mSolver->Update(mTime, mState, mTime, mState);
}
}
//----------------------------------------------------------------------------
void PhysicsModule::Get (double& x1, double& y1, double& x2, double& y2) const
{
double cs = Mathd::Cos(mState[4]);
double sn = Mathd::Sin(mState[4]);
x1 = mState[0] + mLength1*cs;
y1 = mState[2] + mLength1*sn;
x2 = mState[0] - mLength2*cs;
y2 = mState[2] - mLength2*sn;
}
//----------------------------------------------------------------------------
void PhysicsModule::OdeFunction (double, const double* state, void* data,
double* output)
{
double* aux = (double*)data;
// Solve the entire system here and save the results to be returned
// in the later functions.
double cs = Mathd::Cos(state[4]);
double sn = Mathd::Sin(state[4]);
double angCos = state[5]*cs;
double angSin = state[5]*sn;
// Compute the friction vectors. The Normalize function will set a
// vector to zero if its length is smaller than Mathd::ZERO_TOLERANCE.
Vector2d F1(state[1] - aux[1]*angSin, state[3] + aux[1]*angCos);
Vector2d F2(state[1] + aux[2]*angSin, state[3] - aux[2]*angCos);
F1.Normalize();
F2.Normalize();
double xDotFunction = aux[3]*F1.X() + aux[4]*F2.X();
double yDotFunction = aux[3]*F1.Y() + aux[4]*F2.Y();
double tmp1 = aux[1]*aux[5]*(cs*F1.Y() - sn*F1.X());
double tmp2 = aux[2]*aux[6]*(sn*F2.X() - cs*F2.Y());
double thetaDotFunction = tmp1 + tmp2;
// x function
output[0] = state[1];
// dot(x) function
output[1] = xDotFunction;
// y function
output[2] = state[3];
// dot(y) function
output[3] = yDotFunction;
// theta function
output[4] = state[5];
// dot(theta) function
output[5] = thetaDotFunction;
}
//----------------------------------------------------------------------------
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