NAME

cxPyrActiveNext - flag as active/inactive the elements at the next lower pyramid layer

C SPECIFICATION

#include <cx/Pyramid.h>

char *cxPyrActiveNext(cxPyramid *pyr, long curLayer, long dstLayer, char *flg)

FORTRAN SPECIFICATION

integer function cxPyrActiveNext( pyr, curLayer, dstLayer, flg )
integer pyr
integer curLayer
integer dstLayer
character*1 flg(*)

PARAMETERS

pyr: Input pyramid structure for which computations are to be performed.
curLayer: Input layer of currently active elements (1-based value).
dstLayer: Input layer of next active elements (1-based value).
flg: Input byte array indicating which elements are currently active in layer curLayer.

FUNCTION RETURN VALUE

Returns a pointer to a byte array indicating (with non-zero value) which elements are active in layer dstLayer, given that the flg elements are active in layer curLayer. Returns a NULL if its input is malformed, if an allocation error occurs, or if the destination layer is in a compressed region. Returns a list of active vertices if dstLayer is zero, even in the presence of compression.

DESCRIPTION

cxPyrActiveNext accepts a byte vector of indicators showing which elements are active in the pyramid pyr at a given layer, and from this information computes which subordinate elements are active at the lower layer dstLayer. If dstLayer is greater than curLayer, the routine returns an indicator vector of all elements that can be reached from the top of the input pyramid.

Position i of the returned byte array holds a 0 if element i of the layer is inactive, a 1 if the element is active and contained within only one parent element, or a 2 if the element is active and contained within more than one parent element.

cxPyrActiveNext is useful in circumstances where a subset of the elements at a given level are to be manipulated, and the caller wishes to identify the subordinate elements to manipulate at a lower level. This is the approved way of determining the pyramid elements which should be manipulated or displayed in any pyramid-based module (the alternative method of displaying all elements available at a given level is not correct).

The returned indicator array is considered to be owned by the caller of cxPyrActiveNext and should be freed (with free(3C)) after use.