sandbox/popinet/cache.c

Traversing a subset of the mesh

The goal is to build an array/list/cache of cells which can then be used to traverse only a subset of the entire mesh.

int main()
{

We first setup the mesh and shift the origin.

  init_grid (32);
  origin (-0.5, -0.5);

We will use the pre-defined structure Cache and associated functions. Note that for the moment these are defined in /src/grid/tree.h i.e. this will only work on bi/quad/octrees. All fields of a are initially zero.

  Cache a = {0};

We then traverse the entire mesh and add the cells which are inside a circle to the cache. point is the index of the current cell. The last argument is an optional integer associated with the cell.

  foreach()
    if (x*x + y*y < sq(0.25))
      cache_append (&a, point, 0);

We “optimize” the size of the cache i.e. shrink the dynamic array of indices if necessary.

  cache_shrink (&a);

We can then simply traverse the cells contained in cache a like this:

  foreach_cache (a)
    fprintf (stderr, "%g %g\n", x, y);

We output the mesh to make the figure below.

  output_cells (stdout);

Finally, we free the cache.

  free (a.p);
}

set size ratio -1
unset key
plot 'out' w l, 'log'

Cells and cached cells (script)