HOLLBY ( body, offset, check, pierce, faces, dists, tol, mxflts, oldfas,
=========================================================================
newfas, badtag, state, ifail )
==============================
Hollows a solid body
Receives:
KI_tag_body *body --- body to be hollowed
<KI_dbl> *offset --- default offset
KI_cod_logical *check --- level of checking required
<KI_tag_list_face> *pierce --- faces not to be offset
<KI_tag_list_face> *faces --- faces offset by other amounts
<KI_tag_list_dbl> *dists --- list of other offset distances
<KI_dbl_distance> *tol --- maximum applied tolerance
<KI_int_nitems> *mxflts --- maximum number of entities in badtag
Returns:
<KI_tag_list_entity> *oldfas --- list of original faces offset
<KI_tag_list_entity> *newfas --- list of corresponding new faces
<KI_tag_list_entity> *badtag --- entities which caused problems
KI_cod_rtof *state --- state of body after hollow
KI_cod_error *ifail --- failure code
Specific errors:
KI_cant_hollow failed to hollow body
KI_boolean_failure boolean failed
KI_not_unique boolean resulted in more than one body
KI_unsuitable_entity could not duplicate body
body is not a solid body
Mixed body
KI_bad_tolerance proposed tolerance is too small
KI_bad_value non-default offset too small
default offset too small
KI_not_in_same_body Offset face is not in supplied body
Pierced face is not in supplied body
KI_duplicate_list_item face is in both pierced and faces
KI_list_wrong_length list of faces and dists not same length
too many faces in lists pierced and faces
too many faces for non-default offset
too many pierced faces
KI_list_too_short no dists supplied for faces
Description:
The 'body' is hollowed. The 'offset' argument gives the default offset of the
hollowing - the thickness of the skin of the resulting body. A positive
'offset' will offset the body outwards (i.e. in the direction of the face
normals) and a negative value inwards.
Faces which are to be offset by amounts other than the default can be
specified in the 'faces' argument with the specific offset for this face
supplied in the corresponding position in the 'dists' list. Notice that using
these arguments allows a 'mixed' hollow to be defined with some faces being
offset inwards and some outwards.
Faces which are not to be offset at all are defined in the 'pierce' list.
If no faces are pierced the result of hollowing a body will be to generate a
body containing a void. Pierced faces remain only as a section through the
hollowed body. For instance, hollowing a cylindrical solid with one end face
pierced will result in a tube with one open and one closed end.
Under some circumstances the function may need to replace exact geometry by
tolerant geometry. For instance, a four-edge vertex in general will offset
to two three-edge vertices and a connecting edge. If this new edge is smaller
than the supplied tolerance then the vertex becomes tolerant and no new edge
is introduced. In all situations where approximation is required the new
geometry will have a tolerance less than or equal to the tolerance supplied
through the 'tol' argument.
Many circumstances can give rise to changes in topology. Amongst them are :
1) Dealing with geometry which fails to offset. It it is known that the
offset surface of a face would be self-intersecting an attempt is made
to either remove the offset face or split it into faces with good
regions of the failing surface. For example, a blend may be removed
from an edge. The investigation of self-intersection is not exhaustive,
however, and it can occur that instances are not trapped. If a face is
split then this will cause the corresponding element in the 'oldfas'
or 'newfas' list to itself become a list. If the split face is on the
outside of the hollowed body then the first element of the list will
be the original face which has been split to create the other elements.
2) Dealing with configurations which can be repaired. For instance,
an edge can offset to a point or a face can become absorbed into
the body.
The extent to which checking is applied to the body is specified by the
'check' argument. If 'check' is true then face-face checks are done on
the body in addition to default checks. For most applications setting
'check' false will give an adequate level of checking.
The tag of a face in the original body will remain on the exterior of the
resulting body and will retain the same sense.
Each face to be offset will have a partner created in the final body which is
an offset of the original face. The pairs of original and new faces are
returned in the 'oldfas' and 'newfas' arguments. Both 'oldfas' and 'newfas'
can contain null tags. This will occur when faces are removed for the reasons
given above. Both 'oldfas' and 'newfas' can also contain lists of faces.
The error reporting scheme comprises the four arguments 'badtag', 'state',
'mxflts' and 'ifail'. A non-zero 'ifail' is reserved for reporting unsuitable
arguments to the function, failures in the internal boolean operation and
system errors.
Algorithmic failures where the items causing the failure can be identified
result in a zero 'ifail' and more specific information being returned in the
'state' argument and 'badtag'. For example, if new geometry cannot be found for
an edge 'state' RTOFEM will be returned and the tag of the edge whose curve
could not be found in 'badtag'. The user may set an upper limit on the number
of faults found in 'mxflts'; if 'mxflts' is zero then no limit is applied.
'state' refers to the validity of the item after modification and not to its
original validity and after such a failure 'body' may be corrupt and a
rollback should be performed. For this reason tags of new paired and unpaired
topology cannot be returned in 'badtag' and the tags will refer to topology in
the original body supplied. In the case of new unpaired edges and vertices,
tags will refer to adjacent faces in the original body. For example if a new
unpaired edge cannot be modified a 'state' RTOFEM is returned and 'badtag' and
will contain the tag of a list of the two faces whose offsets are to be used
to find the new curve. 'badtag' is a list of items which failed for the reason
indicated in the 'state' argument.
Possible values of 'state' and the contents of elements of 'badtag' are :
Token | Tag in | Meaning
| badtag list|
-------|------------|------------------------------------------------------
RTOFOK | null | Body is OK
RTOFSO | face | Surface failed to offset or face could not be deleted
RTOFVM | vertex | Failed to find new geometry for vertex
| list faces | Failed to find geometry for new unpaired vertex
RTOFEM | edge | Failed to find new geometry for edge
| list faces | Failed to find geometry for new unpaired edge
RTOFVT | edge | Edge should have disappeared
| list faces | New unpaired edge should have disappeared
RTOFFA | face | Face failed checks
RTOFSX | list faces | Pair of faces where face-face inconsistency found
Notice that a successful execution of the hollowing operation is indicated by:
'ifail' returning KI_no_errors and 'state' returning RTOFOK
This function is not supported for general bodies.
