sfml-fluid-simulation/Physics.cpp at main · ypatel2022/sfml-fluid-simulation · GitHub

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#include "Physics.h"
#include "Constants.h"

int IX(int x, int y);

void Physics::SetBound(int b, std::vector<float>& x)
{
	for (int i = 1; i < N - 1; i++)
	{
		x[IX(i, 0)] = b == 2 ? -x[IX(i, 1)] : x[IX(i, 1)];
		x[IX(i, N - 1)] = b == 2 ? -x[IX(i, N - 2)] : x[IX(i, N - 2)];
	}
	for (int j = 1; j < N - 1; j++)
	{
		x[IX(0, j)] = b == 1 ? -x[IX(1, j)] : x[IX(1, j)];
		x[IX(N - 1, j)] = b == 1 ? -x[IX(N - 2, j)] : x[IX(N - 2, j)];
	}

	x[IX(0, 0)] = 0.5 * (x[IX(1, 0)] + x[IX(0, 1)]);
	x[IX(0, N - 1)] = 0.5 * (x[IX(1, N - 1)] + x[IX(0, N - 2)]);
	x[IX(N - 1, 0)] = 0.5 * (x[IX(N - 2, 0)] + x[IX(N - 1, 1)]);
	x[IX(N - 1, N - 1)] = 0.5 * (x[IX(N - 2, N - 1)] + x[IX(N - 1, N - 2)]);
}

void Physics::LinearSolve(int b, std::vector<float>& x, std::vector<float>& x0, float a, float c)
{
	float cRecip = 1.0 / c;
	for (int t = 0; t < ITER; t++)
	{
		for (int j = 1; j < N - 1; j++)
		{
			for (int i = 1; i < N - 1; i++)
			{
				x[IX(i, j)] = (x0[IX(i, j)] + a * (x[IX(i + 1, j)] + x[IX(i - 1, j)] + x[IX(i, j + 1)] + x[IX(i, j - 1)])) * cRecip;
			}
		}
		Physics::SetBound(b, x);
	}
}

void Physics::Diffuse(int b, std::vector<float>& x, std::vector<float>& x0, float& diff, float dt)
{
	float a = dt * diff * (N - 2) * (N - 2);
	LinearSolve(b, x, x0, a, 1 + 6 * a);
}

void Physics::Project(std::vector<float>& velocX, std::vector<float>& velocY, std::vector<float>& p, std::vector<float>& div)
{
	for (int j = 1; j < N - 1; j++)
	{
		for (int i = 1; i < N - 1; i++)
		{
			div[IX(i, j)] = (-0.5 * (velocX[IX(i + 1, j)] -
				velocX[IX(i - 1, j)] +
				velocY[IX(i, j + 1)] -
				velocY[IX(i, j - 1)])) / N;
			p[IX(i, j)] = 0;
		}
	}

	Physics::SetBound(0, div);
	Physics::SetBound(0, p);
	Physics::LinearSolve(0, p, div, 1, 6);

	for (int j = 1; j < N - 1; j++)
	{
		for (int i = 1; i < N - 1; i++)
		{
			velocX[IX(i, j)] -= 0.5 * (p[IX(i + 1, j)] - p[IX(i - 1, j)]) * N;
			velocY[IX(i, j)] -= 0.5 * (p[IX(i, j + 1)] - p[IX(i, j - 1)]) * N;
		}
	}

	Physics::SetBound(1, velocX);
	Physics::SetBound(2, velocY);
}

void Physics::Advection(int b, std::vector<float>& d, std::vector<float>& d0, std::vector<float>& velocX, std::vector<float>& velocY, float dt)
{
	float i0, i1, j0, j1;

	float dtx = dt * (N - 2);
	float dty = dt * (N - 2);

	float s0, s1, t0, t1;
	float tmp1, tmp2, tmp3, x, y;

	float Nfloat = N - 2;
	float ifloat, jfloat;
	int i, j, k;


	for (j = 1, jfloat = 1; j < N - 1; j++, jfloat++)
	{
		for (i = 1, ifloat = 1; i < N - 1; i++, ifloat++)
		{
			tmp1 = dtx * velocX[IX(i, j)];
			tmp2 = dty * velocY[IX(i, j)];
			x = ifloat - tmp1;
			y = jfloat - tmp2;

			if (x < 0.5f)
			{
				x = 0.5f;
			}

			if (x > Nfloat + 0.5f)
			{
				x = Nfloat + 0.5f;
			}

			i0 = floorf(x);
			i1 = i0 + 1.0f;

			if (y < 0.5f)
			{
				y = 0.5f;
			}
			if (y > Nfloat + 0.5f)
			{
				y = Nfloat + 0.5f;
			}

			j0 = floorf(y);
			j1 = j0 + 1.0f;


			s1 = x - i0;
			s0 = 1.0f - s1;
			t1 = y - j0;
			t0 = 1.0f - t1;

			int i0i = i0;
			int i1i = i1;
			int j0i = j0;
			int j1i = j1;

			d[IX(i, j)] =
				s0 * (t0 * d0[IX(i0i, j0i)] + t1 * d0[IX(i0i, j1i)]) +
				s1 * (t0 * d0[IX(i1i, j0i)] + t1 * d0[IX(i1i, j1i)]);
		}
	}

	Physics::SetBound(b, d);
}