Pressure solve for velocity projection

gistfile1.cpp

  for (int k=0; k<20; k++) {
    for (int i=1; i<N+1; i++) {
      for (int j=1; j<N+1; j++) {
        if (!m_has_fluid(i, j)) continue;

        int adj_fluid_cells = 0;
        scalar p = pressure(i, j);
        pressure(i, j) = div(i, j);

        if (!m_has_solid(i-1, j)) {
          pressure(i, j) += pressure(i-1, j) - p;
          adj_fluid_cells++;
        }

        if (!m_has_solid(i+1, j)) {
          pressure(i, j) += pressure(i+1, j) - p;
          adj_fluid_cells++;
        }

        if (!m_has_solid(i, j-1)) {
          pressure(i, j) += pressure(i, j-1) - p;
          adj_fluid_cells++;
        }

        if (!m_has_solid(i, j+1)) {
          pressure(i, j) += pressure(i, j+1) - p;
          adj_fluid_cells++;
        }

        pressure(i, j) /= adj_fluid_cells;
      }
    }

    for (int i=0; i<N+2; i++) {
      pressure(i, 0) = pressure(i, 1);
      pressure(i, N+1) = pressure(i, N);
      pressure(0, i) = pressure(1, i);
      pressure(N+1, i) = pressure(N, i);
    }

    pressure(0, 0) = pressure(0, 1);
    pressure(0, N+1) = pressure(1, N);
    pressure(N+1, 0) = pressure(N, 1);
    pressure(N+1, N+1) = pressure(N, N);

  }