PK_ERROR_code_t  PK_FACE_ask_first_loop
(
--- received arguments ---
PK_FACE_t        face,          --- a face

--- returned arguments ---
PK_LOOP_t *const first_loop     --- the first loop (possibly PK_ENTITY_null)
)


This function returns the first loop in the given face.


If the face has no loops, for example, a whole face on a sphere, then
PK_ENTITY_null will be returned.

The first loop is not necessarily the outer perimeter of the face (should this
be meaningful).

This function should be used in conjunction with PK_LOOP_ask_next_in_face to
scan the loops of a face.