Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

Click here to view the latest version of this page.

boost/polygon/detail/voronoi_structures.hpp

// Boost.Polygon library detail/voronoi_structures.hpp header 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.

#ifndef BOOST_POLYGON_DETAIL_VORONOI_STRUCTURES
#define BOOST_POLYGON_DETAIL_VORONOI_STRUCTURES

#include <list>
#include <queue>
#include <vector>

#include "boost/polygon/voronoi_geometry_type.hpp"

namespace boost {
namespace polygon {
namespace detail {
// Cartesian 2D point data structure.
template <typename T>
class point_2d {
 public:
  typedef T coordinate_type;

  point_2d() {}

  point_2d(coordinate_type x, coordinate_type y) :
      x_(x),
      y_(y) {}

  bool operator==(const point_2d& that) const {
    return (this->x_ == that.x()) && (this->y_ == that.y());
  }

  bool operator!=(const point_2d& that) const {
    return (this->x_ != that.x()) || (this->y_ != that.y());
  }

  coordinate_type x() const {
    return x_;
  }

  coordinate_type y() const {
    return y_;
  }

  point_2d& x(coordinate_type x) {
    x_ = x;
    return *this;
  }

  point_2d& y(coordinate_type y) {
    y_ = y;
    return *this;
  }

 private:
  coordinate_type x_;
  coordinate_type y_;
};

// Site event type.
// Occurs when the sweepline sweeps over one of the initial sites:
//   1) point site
//   2) start-point of the segment site
//   3) endpoint of the segment site
// Implicit segment direction is defined: the start-point of
// the segment compares less than its endpoint.
// Each input segment is divided onto two site events:
//   1) One going from the start-point to the endpoint
//      (is_inverse() = false)
//   2) Another going from the endpoint to the start-point
//      (is_inverse() = true)
// In beach line data structure segment sites of the first
// type precede sites of the second type for the same segment.
// Members:
//   point0_ - point site or segment's start-point
//   point1_ - segment's endpoint if site is a segment
//   sorted_index_ - the last bit encodes information if the site is inverse;
//     the other bits encode site event index among the sorted site events
//   initial_index_ - site index among the initial input set
// Note: for all sites is_inverse_ flag is equal to false by default.
template <typename T>
class site_event {
 public:
  typedef T coordinate_type;
  typedef point_2d<T> point_type;

  site_event() :
      point0_(0, 0),
      point1_(0, 0),
      sorted_index_(0),
      flags_(0) {}

  site_event(coordinate_type x, coordinate_type y) :
      point0_(x, y),
      point1_(x, y),
      sorted_index_(0),
      flags_(0) {}

  explicit site_event(const point_type& point) :
      point0_(point),
      point1_(point),
      sorted_index_(0),
      flags_(0) {}

  site_event(coordinate_type x1, coordinate_type y1,
             coordinate_type x2, coordinate_type y2):
      point0_(x1, y1),
      point1_(x2, y2),
      sorted_index_(0),
      flags_(0) {}

  site_event(const point_type& point1, const point_type& point2) :
      point0_(point1),
      point1_(point2),
      sorted_index_(0),
      flags_(0) {}

  bool operator==(const site_event& that) const {
    return (this->point0_ == that.point0_) &&
           (this->point1_ == that.point1_);
  }

  bool operator!=(const site_event& that) const {
    return (this->point0_ != that.point0_) ||
           (this->point1_ != that.point1_);
  }

  coordinate_type x() const {
    return point0_.x();
  }

  coordinate_type y() const {
    return point0_.y();
  }

  coordinate_type x0() const {
    return point0_.x();
  }

  coordinate_type y0() const {
    return point0_.y();
  }

  coordinate_type x1() const {
    return point1_.x();
  }

  coordinate_type y1() const {
    return point1_.y();
  }

  const point_type& point0() const {
    return point0_;
  }

  const point_type& point1() const {
    return point1_;
  }

  std::size_t sorted_index() const {
    return sorted_index_;
  }

  site_event& sorted_index(std::size_t index) {
    sorted_index_ = index;
    return *this;
  }

  std::size_t initial_index() const {
    return initial_index_;
  }

  site_event& initial_index(std::size_t index) {
    initial_index_ = index;
    return *this;
  }

  bool is_inverse() const {
    return (flags_ & IS_INVERSE) ? true : false;
  }

  site_event& inverse() {
    std::swap(point0_, point1_);
    flags_ ^= IS_INVERSE;
    return *this;
  }

  SourceCategory source_category() const {
    return static_cast<SourceCategory>(flags_ & SOURCE_CATEGORY_BITMASK);
  }

  site_event& source_category(SourceCategory source_category) {
    flags_ |= source_category;
    return *this;
  }

  bool is_point() const {
    return (point0_.x() == point1_.x()) && (point0_.y() == point1_.y());
  }

  bool is_segment() const {
    return (point0_.x() != point1_.x()) || (point0_.y() != point1_.y());
  }

 private:
  enum Bits {
    IS_INVERSE = 0x20  // 32
  };

  point_type point0_;
  point_type point1_;
  std::size_t sorted_index_;
  std::size_t initial_index_;
  std::size_t flags_;
};

// Circle event type.
// Occurs when the sweepline sweeps over the rightmost point of the Voronoi
// circle (with the center at the intersection point of the bisectors).
// Circle event is made of the two consecutive nodes in the beach line data
// structure. In case another node was inserted during algorithm execution
// between the given two nodes circle event becomes inactive.
// Variables:
//   center_x_ - center x-coordinate;
//   center_y_ - center y-coordinate;
//   lower_x_ - leftmost x-coordinate;
//   is_active_ - states whether circle event is still active.
// NOTE: lower_y coordinate is always equal to center_y.
template <typename T>
class circle_event {
 public:
  typedef T coordinate_type;

  circle_event() : is_active_(true) {}

  circle_event(coordinate_type c_x,
               coordinate_type c_y,
               coordinate_type lower_x) :
      center_x_(c_x),
      center_y_(c_y),
      lower_x_(lower_x),
      is_active_(true) {}

  coordinate_type x() const {
    return center_x_;
  }

  circle_event& x(coordinate_type center_x) {
    center_x_ = center_x;
    return *this;
  }

  coordinate_type y() const {
    return center_y_;
  }

  circle_event& y(coordinate_type center_y) {
    center_y_ = center_y;
    return *this;
  }

  coordinate_type lower_x() const {
    return lower_x_;
  }

  circle_event& lower_x(coordinate_type lower_x) {
    lower_x_ = lower_x;
    return *this;
  }

  coordinate_type lower_y() const {
    return center_y_;
  }

  bool is_active() const {
    return is_active_;
  }

  circle_event& deactivate() {
    is_active_ = false;
    return *this;
  }

 private:
  coordinate_type center_x_;
  coordinate_type center_y_;
  coordinate_type lower_x_;
  bool is_active_;
};

// Event queue data structure, holds circle events.
// During algorithm run, some of the circle events disappear (become
// inactive). Priority queue data structure doesn't support
// iterators (there is no direct ability to modify its elements).
// Instead list is used to store all the circle events and priority queue
// of the iterators to the list elements is used to keep the correct circle
// events ordering.
template <typename T, typename Predicate>
class ordered_queue {
 public:
  ordered_queue() {}

  bool empty() const {
    return c_.empty();
  }

  const T &top() const {
    return *c_.top();
  }

  void pop() {
    list_iterator_type it = c_.top();
    c_.pop();
    c_list_.erase(it);
  }

  T &push(const T &e) {
    c_list_.push_front(e);
    c_.push(c_list_.begin());
    return c_list_.front();
  }

  void clear() {
    while (!c_.empty())
        c_.pop();
    c_list_.clear();
  }

 private:
  typedef typename std::list<T>::iterator list_iterator_type;

  struct comparison {
    bool operator() (const list_iterator_type &it1,
                     const list_iterator_type &it2) const {
      return cmp_(*it1, *it2);
    }
    Predicate cmp_;
  };

  std::priority_queue< list_iterator_type,
                       std::vector<list_iterator_type>,
                       comparison > c_;
  std::list<T> c_list_;

  // Disallow copy constructor and operator=
  ordered_queue(const ordered_queue&);
  void operator=(const ordered_queue&);
};

// Represents a bisector node made by two arcs that correspond to the left
// and right sites. Arc is defined as a curve with points equidistant from
// the site and from the sweepline. If the site is a point then arc is
// a parabola, otherwise it's a line segment. A segment site event will
// produce different bisectors based on its direction.
// In general case two sites will create two opposite bisectors. That's
// why the order of the sites is important to define the unique bisector.
// The one site is considered to be newer than the other one if it was
// processed by the algorithm later (has greater index).
template <typename Site>
class beach_line_node_key {
 public:
  typedef Site site_type;

  // Constructs degenerate bisector, used to search an arc that is above
  // the given site. The input to the constructor is the new site point.
  explicit beach_line_node_key(const site_type &new_site) :
      left_site_(new_site),
      right_site_(new_site) {}

  // Constructs a new bisector. The input to the constructor is the two
  // sites that create the bisector. The order of sites is important.
  beach_line_node_key(const site_type &left_site,
                      const site_type &right_site) :
      left_site_(left_site),
      right_site_(right_site) {}

  const site_type &left_site() const {
    return left_site_;
  }

  site_type &left_site() {
    return left_site_;
  }

  beach_line_node_key& left_site(const site_type &site) {
    left_site_ = site;
    return *this;
  }

  const site_type &right_site() const {
    return right_site_;
  }

  site_type &right_site() {
    return right_site_;
  }

  beach_line_node_key& right_site(const site_type &site) {
    right_site_ = site;
    return *this;
  }

 private:
  site_type left_site_;
  site_type right_site_;
};

// Represents edge data structure from the Voronoi output, that is
// associated as a value with beach line bisector in the beach
// line. Contains pointer to the circle event in the circle event
// queue if the edge corresponds to the right bisector of the circle event.
template <typename Edge, typename Circle>
class beach_line_node_data {
 public:
  explicit beach_line_node_data(Edge* new_edge) :
      circle_event_(NULL),
      edge_(new_edge) {}

  Circle* circle_event() const {
    return circle_event_;
  }

  beach_line_node_data& circle_event(Circle* circle_event) {
    circle_event_ = circle_event;
    return *this;
  }

  Edge* edge() const {
    return edge_;
  }

  beach_line_node_data& edge(Edge* new_edge) {
    edge_ = new_edge;
    return *this;
  }

 private:
  Circle* circle_event_;
  Edge* edge_;
};
}  // detail
}  // polygon
}  // boost

#endif  // BOOST_POLYGON_DETAIL_VORONOI_STRUCTURES