//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 Add(Vector2 left, Vector2 right)
{
var result = MonoGameVector2.Add(left.MonoGameVector, right.MonoGameVector);
return(new Vector2(result));
}