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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"
//----------------------------------------------------------------------------
PhysicsModule::PhysicsModule (int numParticles, float step,
const Vector3f& gravity, const Vector3f& wind, float windChangeAmplitude,
float viscosity)
:
MassSpringCurve3f(numParticles, step),
EnableWind(false),
EnableWindChange(false),
mGravity(gravity),
mWind(wind),
mWindChangeAmplitude(windChangeAmplitude),
mViscosity(viscosity)
{
}
//----------------------------------------------------------------------------
Vector3f PhysicsModule::ExternalAcceleration (int i, float, const Vector3f*,
const Vector3f* velocities)
{
// Acceleration due to gravity.
Vector3f acceleration = mGravity;
// Acceleration due to wind.
if (EnableWind)
{
if (EnableWindChange)
{
// Generate random direction close to last one.
Vector3f U, V, W = mWind;
float length = W.Normalize();
Vector3f::GenerateComplementBasis(U, V, W);
float uDelta = mWindChangeAmplitude*Mathf::SymmetricRandom();
float vDelta = mWindChangeAmplitude*Mathf::SymmetricRandom();
W += uDelta*U + vDelta*V;
W.Normalize();
mWind = length*W;
}
acceleration += mWind;
}
// Add in a friction term. Otherwise the system tends to be "stiff"
// (in the numerical stability sense) and leads to oscillatory behavior.
acceleration -= mViscosity*velocities[i];
return acceleration;
}
//----------------------------------------------------------------------------
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