boost/libs/polygon/example/voronoi_basic_tutorial.cpp

// Boost.Polygon library voronoi_basic_tutorial.cpp file

//          Copyright Andrii Sydorchuk 2010-2012.
// Distributed under the Boost Software License, Version 1.0.
//    (See accompanying file LICENSE_1_0.txt or copy at
//          http://www.boost.org/LICENSE_1_0.txt)

// See http://www.boost.org for updates, documentation, and revision history.

#include <cstdio>
#include <vector>

#include <boost/polygon/voronoi.hpp>
using boost::polygon::voronoi_builder;
using boost::polygon::voronoi_diagram;
using boost::polygon::x;
using boost::polygon::y;
using boost::polygon::low;
using boost::polygon::high;

#include "voronoi_visual_utils.hpp"

struct Point {
  int a;
  int b;
  Point(int x, int y) : a(x), b(y) {}
};

struct Segment {
  Point p0;
  Point p1;
  Segment(int x1, int y1, int x2, int y2) : p0(x1, y1), p1(x2, y2) {}
};

namespace boost {
namespace polygon {

template <>
struct geometry_concept<Point> {
  typedef point_concept type;
};

template <>
struct point_traits<Point> {
  typedef int coordinate_type;

  static inline coordinate_type get(
      const Point& point, orientation_2d orient) {
    return (orient == HORIZONTAL) ? point.a : point.b;
  }
};

template <>
struct geometry_concept<Segment> {
  typedef segment_concept type;
};

template <>
struct segment_traits<Segment> {
  typedef int coordinate_type;
  typedef Point point_type;

  static inline point_type get(const Segment& segment, direction_1d dir) {
    return dir.to_int() ? segment.p1 : segment.p0;
  }
};
}  // polygon
}  // boost

// Traversing Voronoi edges using edge iterator.
int iterate_primary_edges1(const voronoi_diagram<double>& vd) {
  int result = 0;
  for (voronoi_diagram<double>::const_edge_iterator it = vd.edges().begin();
       it != vd.edges().end(); ++it) {
    if (it->is_primary())
      ++result;
  }
  return result;
}

// Traversing Voronoi edges using cell iterator.
int iterate_primary_edges2(const voronoi_diagram<double> &vd) {
  int result = 0;
  for (voronoi_diagram<double>::const_cell_iterator it = vd.cells().begin();
       it != vd.cells().end(); ++it) {
    const voronoi_diagram<double>::cell_type& cell = *it;
    const voronoi_diagram<double>::edge_type* edge = cell.incident_edge();
    // This is convenient way to iterate edges around Voronoi cell.
    do {
      if (edge->is_primary())
        ++result;
      edge = edge->next();
    } while (edge != cell.incident_edge());
  }
  return result;
}

// Traversing Voronoi edges using vertex iterator.
// As opposite to the above two functions this one will not iterate through
// edges without finite endpoints and will iterate only once through edges
// with single finite endpoint.
int iterate_primary_edges3(const voronoi_diagram<double> &vd) {
  int result = 0;
  for (voronoi_diagram<double>::const_vertex_iterator it =
       vd.vertices().begin(); it != vd.vertices().end(); ++it) {
    const voronoi_diagram<double>::vertex_type& vertex = *it;
    const voronoi_diagram<double>::edge_type* edge = vertex.incident_edge();
    // This is convenient way to iterate edges around Voronoi vertex.
    do {
      if (edge->is_primary())
        ++result;
      edge = edge->rot_next();
    } while (edge != vertex.incident_edge());
  }
  return result;
}

int main() {
  // Preparing Input Geometries.
  std::vector<Point> points;
  points.push_back(Point(0, 0));
  points.push_back(Point(1, 6));
  std::vector<Segment> segments;
  segments.push_back(Segment(-4, 5, 5, -1));
  segments.push_back(Segment(3, -11, 13, -1));

  // Construction of the Voronoi Diagram.
  voronoi_diagram<double> vd;
  construct_voronoi(points.begin(), points.end(),
                    segments.begin(), segments.end(),
                    &vd);

  // Traversing Voronoi Graph.
  {
    printf("Traversing Voronoi graph.\n");
    printf("Number of visited primary edges using edge iterator: %d\n",
        iterate_primary_edges1(vd));
    printf("Number of visited primary edges using cell iterator: %d\n",
        iterate_primary_edges2(vd));
    printf("Number of visited primary edges using vertex iterator: %d\n",
        iterate_primary_edges3(vd));
    printf("\n");
  }

  // Using color member of the Voronoi primitives to store the average number
  // of edges around each cell (including secondary edges).
  {
    printf("Number of edges (including secondary) around the Voronoi cells:\n");
    for (voronoi_diagram<double>::const_edge_iterator it = vd.edges().begin();
         it != vd.edges().end(); ++it) {
      std::size_t cnt = it->cell()->color();
      it->cell()->color(cnt + 1);
    }
    for (voronoi_diagram<double>::const_cell_iterator it = vd.cells().begin();
         it != vd.cells().end(); ++it) {
      printf("%lu ", it->color());
    }
    printf("\n");
    printf("\n");
  }

  // Linking Voronoi cells with input geometries.
  {
    unsigned int cell_index = 0;
    for (voronoi_diagram<double>::const_cell_iterator it = vd.cells().begin();
         it != vd.cells().end(); ++it) {
      if (it->contains_point()) {
        std::size_t index = it->source_index();
        Point p = points[index];
        printf("Cell #%ud contains a point: (%d, %d).\n",
               cell_index, x(p), y(p));
      } else {
        std::size_t index = it->source_index() - points.size();
        Point p0 = low(segments[index]);
        Point p1 = high(segments[index]);
        if (it->source_category() ==
            boost::polygon::SOURCE_CATEGORY_SEGMENT_START_POINT) {
          printf("Cell #%ud contains segment start point: (%d, %d).\n",
                 cell_index, x(p0), y(p0));
        } else if (it->source_category() ==
                   boost::polygon::SOURCE_CATEGORY_SEGMENT_END_POINT) {
          printf("Cell #%ud contains segment end point: (%d, %d).\n",
                 cell_index, x(p0), y(p0));
        } else {
          printf("Cell #%ud contains a segment: ((%d, %d), (%d, %d)). \n",
                 cell_index, x(p0), y(p0), x(p1), y(p1));
        }
      }
      ++cell_index;
    }
  }
  return 0;
}