private static void SetBoundary(uint N, BoundaryCollisionType b, float[] x)
{
for (uint i = 1; i <= N; i++)
{
x[GetIndex(N, 0, i)] = b == BoundaryCollisionType.XDirection ? -x[GetIndex(N, 1, i)] : x[GetIndex(N, 1, i)];
x[GetIndex(N, N + 1, i)] = b == BoundaryCollisionType.XDirection ? -x[GetIndex(N, N, i)] : x[GetIndex(N, N, i)];
x[GetIndex(N, i, 0)] = b == BoundaryCollisionType.YDirection ? -x[GetIndex(N, i, 1)] : x[GetIndex(N, i, 1)];
x[GetIndex(N, i, N + 1)] = b == BoundaryCollisionType.YDirection ? -x[GetIndex(N, i, N)] : x[GetIndex(N, i, N)];
}
x[GetIndex(N, 0, 0)] = 0.5f * (x[GetIndex(N, 1, 0)] + x[GetIndex(N, 0, 1)]);
x[GetIndex(N, 0, N + 1)] = 0.5f * (x[GetIndex(N, 1, N + 1)] + x[GetIndex(N, 0, N)]);
x[GetIndex(N, N + 1, 0)] = 0.5f * (x[GetIndex(N, N, 0)] + x[GetIndex(N, N + 1, 1)]);
x[GetIndex(N, N + 1, N + 1)] = 0.5f * (x[GetIndex(N, N, N + 1)] + x[GetIndex(N, N + 1, N)]);
}
private static void Advect(uint N, float dt, float[] dest, float[] destPre, float[] u, float[] v, BoundaryCollisionType b)
{
float a = dt * N;
for (uint i = 1; i <= N; ++i)
{
for (uint j = 1; j <= N; ++j)
{
uint centerIndex = GetIndex(N, i, j);
float x = i - a * u[centerIndex];
float y = j - a * v[centerIndex];
if (x < 0.5f)
{
x = 0.5f;
}
if (x > N + 0.5f)
{
x = N + 0.5f;
}
uint i0 = (uint)x; uint i1 = i0 + 1;
if (y < 0.5f)
{
y = 0.5f;
}
if (y > N + 0.5f)
{
y = N + 0.5f;
}
uint j0 = (uint)y; uint j1 = j0 + 1;
float s1 = x - i0; float s0 = 1 - s1; float t1 = y - j0; float t0 = 1 - t1;
dest[centerIndex] =
s0 * (
t0 * destPre[GetIndex(N, i0, j0)] +
t1 * destPre[GetIndex(N, i0, j1)]
) +
s1 * (
t0 * destPre[GetIndex(N, i1, j0)] +
t1 * destPre[GetIndex(N, i1, j1)]
);
}
}
SetBoundary(N, b, dest);
}
private static void Diffuse(uint N, float[] cur, float[] pre, float dt, float diffusionVelocity, BoundaryCollisionType b)
{
float a = diffusionVelocity * dt * N * N;
for (uint k = 0; k < 20; ++k)
{
for (uint i = 1; i <= N; ++i)
{
for (uint j = 1; j <= N; ++j)
{
uint centerIndex = GetIndex(N, i, j);
cur[centerIndex] =
(
pre[centerIndex] + a *
(
cur[GetIndex(N, i + 1, j)] + cur[GetIndex(N, i, j + 1)] + cur[GetIndex(N, i - 1, j)] + cur[GetIndex(N, i, j - 1)]
)
)
/ (1 + 4 * a);
}
}
SetBoundary(N, b, cur);
}
}
