src/grid/layers.h

Multiple “layers”

This adds support for multiple “layers” i.e. a constant number nl of contiguous scalar fields.

int nl = 1;

We redefine two types of block traversals. An “outer” traversal, usable outside foreach() loops, which uses a global _layer index…

int _layer = 0;

#undef foreach_block
macro foreach_block() {
  for (_layer = 0; _layer < nl; _layer++)
    {...}
  _layer = 0;
}

… and an “inner” traversal, usable within foreach() loops, which uses the point.l index as local layer index.

#undef foreach_block_inner
macro foreach_block_inner (Point p = point) {
  for (p.l = 0; p.l < nl; p.l++)
    {...}
  p.l = 0;
}

We also redefine the “per field” (inner) traversal.

#undef foreach_blockf
macro foreach_blockf (scalar _f, Point p = point) {
  for (p.l = 0; p.l < _attribute[_f.i].block; p.l++)
    {...}
  p.l = 0;
}

The two indices are combined to access field values. In practice only one of the indices is used.

@undef _index
@def _index(a,m)
  (a.i + (_layer + point.l + m < _attribute[a.i].block ?
	  _layer + point.l + m : 0))
@

@undef val
@define val(a,k,p,m) data(k,p,m)[_index(a,m)]

foreach_layer() is just an alias for foreach_block().

#define foreach_layer() foreach_block()