private void DoubleDensityRelaxation()
{
float q;
for (int i = 0; i < Particles.Count; i++)
{
Particle particle = Particles[i];
particle.Density = 0;
particle.NearDensity = 0;
_tempParticles = Particles.GetNearby(particle);
int len2 = _tempParticles.Count;
if (len2 > MaxNeighbors)
{
len2 = MaxNeighbors;
}
for (int j = 0; j < len2; j++)
{
Particle tempParticle = _tempParticles[j];
Vector2.DistanceSquared(ref particle.Position, ref tempParticle.Position, out q);
if (q < InfluenceRadiusSquared && q != 0)
{
q = (float)Math.Sqrt(q);
q /= InfluenceRadius;
float qq = ((1 - q) * (1 - q));
particle.Density += qq;
particle.NearDensity += qq * (1 - q);
}
}
particle.Pressure = (Stiffness * (particle.Density - DensityRest));
particle.NearPressure = (StiffnessNear * particle.NearDensity);
_dx = Vector2.Zero;
for (int j = 0; j < len2; j++)
{
Particle tempParticle = _tempParticles[j];
Vector2.DistanceSquared(ref particle.Position, ref tempParticle.Position, out q);
if ((q < InfluenceRadiusSquared) && (q != 0))
{
q = (float)Math.Sqrt(q);
Vector2.Subtract(ref tempParticle.Position, ref particle.Position, out _rij);
Vector2.Divide(ref _rij, q, out _rij);
q /= InfluenceRadius;
float D = (_deltaTime2 * (particle.Pressure * (1 - q) + particle.NearPressure * (1 - q) * (1 - q)));
Vector2.Multiply(ref _rij, (D * 0.5f), out _rij);
tempParticle.Position = new Vector2(tempParticle.Position.X + _rij.X, tempParticle.Position.Y + _rij.Y);
Vector2.Subtract(ref _dx, ref _rij, out _dx);
}
}
particle.Position = particle.Position + _dx;
}
}
private void ApplyViscosity(FluidParticle p, float timeStep)
{
for (int i = 0; i < p.Neighbours.Count; ++i)
{
FluidParticle neighbour = p.Neighbours[i];
if (p.Index >= neighbour.Index)
{
continue;
}
float q;
Vector2.DistanceSquared(ref p.Position, ref neighbour.Position, out q);
if (q > _influenceRadiusSquared)
{
continue;
}
Vector2 direction;
Vector2.Subtract(ref neighbour.Position, ref p.Position, out direction);
if (direction.LengthSquared() < float.Epsilon)
{
continue;
}
direction.Normalize();
Vector2 deltaVelocity;
Vector2.Subtract(ref p.Velocity, ref neighbour.Velocity, out deltaVelocity);
float u;
Vector2.Dot(ref deltaVelocity, ref direction, out u);
if (u > 0.0f)
{
q = 1.0f - (float)Math.Sqrt(q) / Definition.InfluenceRadius;
float impulseFactor = 0.5f * timeStep * q * (u * (Definition.ViscositySigma + Definition.ViscosityBeta * u));
Vector2 impulse;
Vector2.Multiply(ref direction, -impulseFactor, out impulse);
p.ApplyImpulse(ref impulse);
Vector2.Multiply(ref direction, impulseFactor, out impulse);
neighbour.ApplyImpulse(ref impulse);
}
}
}
private void ApplyViscosity(float deltaTime)
{
float u, q;
for (int i = 0; i < Particles.Count; i++)
{
Particle particle = Particles[i];
_tempParticles = Particles.GetNearby(particle);
int len2 = _tempParticles.Count;
if (len2 > MaxNeighbors)
{
len2 = MaxNeighbors;
}
for (int j = 0; j < len2; j++)
{
Particle tempParticle = _tempParticles[j];
Vector2.DistanceSquared(ref particle.Position, ref tempParticle.Position, out q);
if ((q < InfluenceRadiusSquared) && (q != 0))
{
q = (float)Math.Sqrt(q);
Vector2.Subtract(ref tempParticle.Position, ref particle.Position, out _rij);
Vector2.Divide(ref _rij, q, out _rij);
Vector2.Subtract(ref particle.Velocity, ref tempParticle.Velocity, out _tempVect);
Vector2.Dot(ref _tempVect, ref _rij, out u);
if (u <= 0.0f)
{
continue;
}
q /= InfluenceRadius;
float I = (deltaTime * (1 - q) * (ViscositySigma * u + ViscosityBeta * u * u));
Vector2.Multiply(ref _rij, (I * 0.5f), out _rij);
Vector2.Subtract(ref particle.Velocity, ref _rij, out _tempVect);
particle.Velocity = _tempVect;
_tempVect = tempParticle.Velocity;
_tempVect += _rij;
tempParticle.Velocity = _tempVect;
}
}
}
}
//private void DoubleDensityRelaxation1(FluidParticle p, float timeStep)
//{
// _density = 0;
// _densityNear = 0;
// _len2 = p.Neighbours.Count;
// if (_len2 > MaxNeighbors)
// _len2 = MaxNeighbors;
// for (_j = 0; _j < _len2; _j++)
// {
// _q = Vector2.DistanceSquared(p.Position, p.Neighbours[_j].Position);
// _distanceCache[_j] = _q;
// if (_q < _influenceRadiusSquared && _q != 0)
// {
// _q = (float)Math.Sqrt(_q);
// _q /= Definition.InfluenceRadius;
// _qq = ((1 - _q) * (1 - _q));
// _density += _qq;
// _densityNear += _qq * (1 - _q);
// }
// }
// _pressure = Definition.Stiffness * (_density - Definition.DensityRest);
// _pressureNear = Definition.StiffnessNear * _densityNear;
// _dx = Vector2.Zero;
// for (_j = 0; _j < _len2; _j++)
// {
// _q = _distanceCache[_j];
// if (_q < _influenceRadiusSquared && _q != 0)
// {
// _q = (float)Math.Sqrt(_q);
// _rij = p.Neighbours[_j].Position;
// _rij -= p.Position;
// _rij *= 1 / _q;
// _q /= _influenceRadiusSquared;
// _d = ((timeStep * timeStep) * (_pressure * (1 - _q) + _pressureNear * (1 - _q) * (1 - _q)));
// _rij *= _d * 0.5f;
// p.Neighbours[_j].Position += _rij;
// _dx -= _rij;
// }
// }
// p.Position += _dx;
//}
private void DoubleDensityRelaxation(FluidParticle particle, float deltaTime2)
{
_density = 0.0f;
_densityNear = 0.0f;
int neightborCount = particle.Neighbours.Count;
if (neightborCount > MaxNeighbors)
{
neightborCount = MaxNeighbors;
}
for (int i = 0; i < neightborCount; ++i)
{
FluidParticle neighbour = particle.Neighbours[i];
if (particle.Index == neighbour.Index)
{
continue;
}
float q;
Vector2.DistanceSquared(ref particle.Position, ref neighbour.Position, out q);
_distanceCache[i] = q;
if (q > _influenceRadiusSquared)
{
continue;
}
q = 1.0f - (float)Math.Sqrt(q) / Definition.InfluenceRadius;
float densityDelta = q * q;
_density += densityDelta;
_densityNear += densityDelta * q;
}
_pressure = Definition.Stiffness * (_density - Definition.DensityRest);
_pressureNear = Definition.StiffnessNear * _densityNear;
// For gameplay purposes
particle.Density = _density + _densityNear;
particle.Pressure = _pressure + _pressureNear;
Vector2 delta = Vector2.Zero;
for (int i = 0; i < neightborCount; ++i)
{
FluidParticle neighbour = particle.Neighbours[i];
if (particle.Index == neighbour.Index)
{
continue;
}
float q = _distanceCache[i];
if (q > _influenceRadiusSquared)
{
continue;
}
q = 1.0f - (float)Math.Sqrt(q) / Definition.InfluenceRadius;
float dispFactor = deltaTime2 * (q * (_pressure + _pressureNear * q));
Vector2 direction;
Vector2.Subtract(ref neighbour.Position, ref particle.Position, out direction);
if (direction.LengthSquared() < float.Epsilon)
{
continue;
}
direction.Normalize();
Vector2 disp;
Vector2.Multiply(ref direction, dispFactor, out disp);
Vector2.Add(ref neighbour.Position, ref disp, out neighbour.Position);
Vector2.Multiply(ref direction, -dispFactor, out disp);
Vector2.Add(ref delta, ref disp, out delta);
}
Vector2.Add(ref particle.Position, ref delta, out particle.Position);
}
public static Vector2 Multiply(Vector2 vector, float scale)
{
var result = MonoGameVector2.Multiply(vector.MonoGameVector, scale);
return(new Vector2(result));
}
