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(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;
}
}
}
}
public static Vector2 Divide(Vector2 vector, float scale)
{
var result = MonoGameVector2.Divide(vector.MonoGameVector, scale);
return(new Vector2(result));
}