CGAL 5.4.4  2D Straight Skeleton and Polygon Offsetting

#include <CGAL/Trisegment_2.h>
A straight skeleton event is the simultaneous collision of three offseted oriented straight line segments e0*
,e1*
,e2*
(e*
denotes an offseted edge).
This record stores the segments corresponding to the INPUT edges (e0,e1,e2)
whose offsets intersect at the event along with their collinearity.
If the event is an edgeevent, then e0*>e1*>e2*
must be consecutive right before the event so that after the event e0*
and e2*
become consecutive. Thus, there are offset vertices (e0*,e1*)
and (e1*,e2*)
in the offset polygon which do not necessarily exist in the original polygon.
If the event is a splitevent, e0*>e1*
must be consecutive right before the event so that after the event e0*>right(e2*)
and left(e2*)>e1*
become consecutive. Thus, there is an offset vertex (e0*,e1*)
in the offset polygon which does not necessarily exist in the original polygon.
The offset vertices (e0*,e1*)
and (e1*,e2*)
are called the left and right seeds for the event. A seed is a contour node if the vertex is already present in the input polygon, otherwise is a skeleton node. If a seed is a skeleton node it is produced by a previous event so it is itself defined as a trisegment, thus, a trisegment is actually a node in a binary tree.
Since trisegments are tree nodes they must always be handled via the nested smart pointer type Self_ptr
.
K_  must be a model of Kernel 
Segment_  must be a model of Kernel::Segment_2 
Construct_ss_trisegment_2
(see the concept StraightSkeletonBuilderTraits_2
).PolygonOffsetBuilderTraits_2
Public Types  
typedef boost::intrusive_ptr< Trisegment_2< K_, Segment_ > >  Self_ptr 
Public Member Functions  
const Segment_ &  e0 () const 
returns e0 .  
const Segment_ &  e1 () const 
returns e1 .  
const Segment_ &  e2 () const 
returns e2 .  