struct PK_blend_fix_propagate_s
    {
    PK_LOGICAL_t     propagate;            --- whether to propagate
                                           --- (PK_LOGICAL_true)
    double           tolerance;            --- propagation angular tolerance
                                           --- (pi/36)
    PK_BODY_blend_propagate_f_t function;  --- user propagation function (NULL)
    PK_POINTER_t     data;                 --- user data for callback function
                                           --- (NULL)
    };
typedef struct PK_blend_fix_propagate_s PK_blend_fix_propagate_t;



This structure records information specifying the amount
of propagation which shall be performed during a blending operation.


This structure contains a collection of switches which will determine
the level of propagation performed during a blending operation.
These control which edges will be propagated to during a blend operation
propagate       prevents any propagation if PK_LOGICAL_false.
                  The default value is PK_LOGICAL_true.
tolerance       controls the maximum angle (in radians) past which we
                  will propagate. The default value is pi/36.
function        is a user callback function called on any edge onto which
                  the operation is going to propagate.
                  The default value is NULL
data            is a pointer to the user data for that function.
                  The default value is NULL
If propagation is prevented, either by setting 'propagate' to false or by the
user function returning false for an edge, PK_body_fix_blends will return
PK_blend_fault_edge_c and the tag of the edge onto which it would otherwise
have propagated.