Hi Robert and all,
Attached modification works around a division by zero. NOTE: it does
*not* fix potential overflow still lurking there if the wind_accel is
a small vector (which it probably can be, if I have run into it being
zero...)
--
Csaba
#include <osgParticle/FluidProgram>
osgParticle::FluidProgram::FluidProgram():
Program()
{
setFluidToAir();
}
osgParticle::FluidProgram::FluidProgram(const FluidProgram& copy, const osg::CopyOp& copyop):
Program(copy, copyop),
_acceleration(copy._acceleration),
_viscosity(copy._viscosity),
_density(copy._density),
_wind(copy._wind),
_viscosityCoefficient(copy._viscosityCoefficient),
_densityCoefficient(copy._densityCoefficient)
{
}
void osgParticle::FluidProgram::execute(double dt)
{
const float four_over_three = 4.0f/3.0f;
ParticleSystem* ps = getParticleSystem();
int n = ps->numParticles();
for (int i=0; i<n; ++i)
{
Particle* particle = ps->getParticle(i);
if (particle->isAlive())
{
float radius = particle->getRadius();
float Area = osg::PI*radius*radius;
float Volume = Area*radius*four_over_three;
// compute force due to gravity + boyancy of displacing the fluid that the particle is emersed in.
osg::Vec3 accel_gravity = _acceleration * ((particle->getMass() - _density*Volume) * particle->getMassInv());
// compute force due to friction
osg::Vec3 velBefore = particle->getVelocity();
osg::Vec3 relative_wind = particle->getVelocity()-_wind;
osg::Vec3 wind_force = - relative_wind * Area * (_viscosityCoefficient + _densityCoefficient*relative_wind.length());
osg::Vec3 wind_accel = wind_force * particle->getMassInv();
double compenstated_dt = dt;
double wind_accel_length2 = wind_accel.length2();
if (wind_accel_length2 != 0)
{
double critical_dt2 = relative_wind.length2()/wind_accel_length2;
if (critical_dt2 < dt*dt)
{
// osg::notify(osg::NOTICE)<<"** Could be critical: dt="<<dt<<" critical_dt="<<sqrtf(critical_dt2)<<std::endl;
compenstated_dt = sqrtf(critical_dt2)*0.8f;
}
}
particle->addVelocity(accel_gravity*dt + wind_accel*compenstated_dt);
}
}
}
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