private void InteractionTest(int A, int B, ref BurstSimplex simplexShape)
{
// skip the pair if their bounds don't intersect:
if (!simplexBounds[A].IntersectsAabb(simplexBounds[B]))
{
return;
}
// get the start index and size of each simplex:
int simplexStartA = simplexCounts.GetSimplexStartAndSize(A, out int simplexSizeA);
int simplexStartB = simplexCounts.GetSimplexStartAndSize(B, out int simplexSizeB);
// immediately reject simplex pairs that share particles:
for (int a = 0; a < simplexSizeA; ++a)
{
for (int b = 0; b < simplexSizeB; ++b)
{
if (simplices[simplexStartA + a] == simplices[simplexStartB + b])
{
return;
}
}
}
// get phases for each simplex:
bool restPositionsEnabled = false;
int groupA = GetSimplexPhase(simplexStartA, simplexSizeA, out Oni.ParticleFlags flagsA, ref restPositionsEnabled);
int groupB = GetSimplexPhase(simplexStartB, simplexSizeB, out Oni.ParticleFlags flagsB, ref restPositionsEnabled);
// if all particles have the same group and none have self-collision, reject the pair.
if (groupA == groupB && (flagsA & flagsB & Oni.ParticleFlags.SelfCollide) == 0)
{
return;
}
// if all simplices are fluid, check their smoothing radii:
if ((flagsA & Oni.ParticleFlags.Fluid) != 0 && (flagsB & Oni.ParticleFlags.Fluid) != 0)
{
int particleA = simplices[simplexStartA];
int particleB = simplices[simplexStartB];
// for fluid we only consider the first particle in each simplex.
float4 predictedPositionA = positions[particleA] + velocities[particleA] * dt;
float4 predictedPositionB = positions[particleB] + velocities[particleB] * dt;
// Calculate particle center distance:
float d2 = math.lengthsq(predictedPositionA - predictedPositionB);
float fluidDistance = math.max(fluidRadii[particleA], fluidRadii[particleB]);
if (d2 <= fluidDistance * fluidDistance)
{
fluidInteractionsQueue.Enqueue(new FluidInteraction {
particleA = particleA, particleB = particleB
});
}
}
else // at least one solid particle is present:
{
// swap simplices so that B is always the one-sided one.
if ((flagsA & Oni.ParticleFlags.OneSided) != 0 && groupA < groupB)
{
ObiUtils.Swap(ref A, ref B);
ObiUtils.Swap(ref simplexStartA, ref simplexStartB);
ObiUtils.Swap(ref simplexSizeA, ref simplexSizeB);
ObiUtils.Swap(ref flagsA, ref flagsB);
ObiUtils.Swap(ref groupA, ref groupB);
}
float4 simplexBary = BurstMath.BarycenterForSimplexOfSize(simplexSizeA);
float4 simplexPoint;
simplexShape.simplexStart = simplexStartB;
simplexShape.simplexSize = simplexSizeB;
simplexShape.positions = restPositions;
simplexShape.CacheData();
float simplexRadiusA = 0, simplexRadiusB = 0;
// skip the contact if there's self-intersection at rest:
if (groupA == groupB && restPositionsEnabled)
{
var restPoint = BurstLocalOptimization.Optimize <BurstSimplex>(ref simplexShape, restPositions, radii,
simplices, simplexStartA, simplexSizeA, ref simplexBary, out simplexPoint, 4, 0);
for (int j = 0; j < simplexSizeA; ++j)
{
simplexRadiusA += radii[simplices[simplexStartA + j]].x * simplexBary[j];
}
for (int j = 0; j < simplexSizeB; ++j)
{
simplexRadiusB += radii[simplices[simplexStartB + j]].x * restPoint.bary[j];
}
// compare distance along contact normal with radius.
if (math.dot(simplexPoint - restPoint.point, restPoint.normal) < simplexRadiusA + simplexRadiusB)
{
return;
}
}
simplexBary = BurstMath.BarycenterForSimplexOfSize(simplexSizeA);
simplexShape.positions = positions;
simplexShape.CacheData();
var surfacePoint = BurstLocalOptimization.Optimize <BurstSimplex>(ref simplexShape, positions, radii,
simplices, simplexStartA, simplexSizeA, ref simplexBary, out simplexPoint, optimizationIterations, optimizationTolerance);
simplexRadiusA = 0; simplexRadiusB = 0;
float4 velocityA = float4.zero, velocityB = float4.zero, normalB = float4.zero;
for (int j = 0; j < simplexSizeA; ++j)
{
int particleIndex = simplices[simplexStartA + j];
simplexRadiusA += radii[particleIndex].x * simplexBary[j];
velocityA += velocities[particleIndex] * simplexBary[j];
}
for (int j = 0; j < simplexSizeB; ++j)
{
int particleIndex = simplices[simplexStartB + j];
simplexRadiusB += radii[particleIndex].x * surfacePoint.bary[j];
velocityB += velocities[particleIndex] * surfacePoint.bary[j];
normalB += normals[particleIndex] * surfacePoint.bary[j];
}
float dAB = math.dot(simplexPoint - surfacePoint.point, surfacePoint.normal);
float vel = math.dot(velocityA - velocityB, surfacePoint.normal);
// check if the projected velocity along the contact normal will get us within collision distance.
if (vel * dt + dAB <= simplexRadiusA + simplexRadiusB + collisionMargin)
{
// adapt collision normal for one-sided simplices:
if ((flagsB & Oni.ParticleFlags.OneSided) != 0 && groupB < groupA)
{
BurstMath.OneSidedNormal(normalB, ref surfacePoint.normal);
}
contactsQueue.Enqueue(new BurstContact()
{
bodyA = A,
bodyB = B,
pointA = simplexBary,
pointB = surfacePoint.bary,
normal = surfacePoint.normal
});
}
}
}