CGAL 2维布尔运算

研究了几天nef_2，终于明白了一点，写下来记录一下

本文主要讨论nef布尔运算后Explorer的情况

#include <CGAL/Gmpq.h>
#include <CGAL/Lazy_exact_nt.h>
#include <CGAL/Simple_cartesian.h>
#include <CGAL/Bounded_kernel.h>
#include <CGAL/Nef_polyhedron_2.h>

typedef CGAL::Lazy_exact_nt<CGAL::Gmpq> FT;
typedef CGAL::Simple_cartesian<FT> Kernel;
typedef CGAL::Bounded_kernel<Kernel> Extended_kernel;
typedef CGAL::Nef_polyhedron_2<Extended_kernel> Nef_polyhedron;
typedef Nef_polyhedron::Point Point;

typedef Nef_polyhedron::Explorer Explorer;
typedef Explorer::Face_const_iterator Face_const_iterator;
typedef Explorer::Hole_const_iterator Hole_const_iterator;
typedef Explorer::Halfedge_around_face_const_circulator Halfedge_around_face_const_circulator;
typedef Explorer::Vertex_const_handle Vertex_const_handle;
typedef Explorer::Point_const_iterator Point_const_iterator;
typedef Explorer::Isolated_vertex_const_iterator Isolated_vertex_const_iterator;

头文件和预定义，没什么好说的，下面开始三角形和线段的定义

Point r1[3] = { Point(20, 15), Point(25, 5), Point(30, 15) };
　 Point s0[2] = { Point(20, 10), Point(25, 16) };

std::list<std::pair<Point*, Point*> > polylines, polylines1;
    polylines.push_back(std::make_pair(r1 + 0, r1 + 3));
    polylines1.push_back(std::make_pair(s0 + 0, s0 + 2));

　　Nef_polyhedron RST0(polylines.begin(), polylines.end(), Nef_polyhedron::POLYGONS);//定义多边形
    Nef_polyhedron RST1(polylines1.begin(), polylines1.end(), Nef_polyhedron::POLYLINES);//多段线

//相交运算

Nef_polyhedron RST = RST1.intersection(RST0);

//使用探测器

Explorer explorer = RST.explorer();

//遍历点

std::cout << "Point" << std::endl;
    for (Point_const_iterator pntPos = explorer.points_begin(); pntPos != explorer.points_end(); ++pntPos)
    {
        std::cout << pntPos->x() << "," << pntPos->y() << std::endl;
    }

//半边

std::cout << "halfedges" << std::endl;
    for (Explorer::Halfedge_const_iterator posEdge = explorer.halfedges_begin(); posEdge != explorer.halfedges_end(); ++posEdge)
    {
        Vertex_const_handle vh = explorer.target(posEdge);
        std::cout << explorer.point(vh) << " [" << explorer.point(vh).x() << " | " << explorer.point(vh).y() << "],  ";
    }

//开始面的遍历

//第一个面是无限大的面，没有外轮廓，只包含洞

Face_const_iterator posFace = explorer.faces_begin();
    for (Hole_const_iterator hit = explorer.holes_begin(posFace); hit != explorer.holes_end(posFace); hit++)
    {
        std::cout << " A hole" << std::endl;

//半边循环
        Halfedge_around_face_const_circulator hafc(hit), done(hafc);
        do
        {
            Vertex_const_handle vh = explorer.target(hafc);
            std::cout << explorer.point(vh) << " [" << explorer.point(vh).x() << " | " << explorer.point(vh).y() << "],  ";
            hafc++;
        } while (hafc != done);
    }

//其他面，有外轮廓，包含洞

for (++posFace; posFace != explorer.faces_end(); ++posFace)
    {
        
        Halfedge_around_face_const_circulator hafc = explorer.face_cycle(posFace), done(hafc);
        do
        {
            Vertex_const_handle vh = explorer.target(hafc);
            std::cout << explorer.point(vh) << " [" << explorer.point(vh).x()<< " | " << explorer.point(vh).y() << "],  ";
            hafc++;
        } while (hafc != done);
    }