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Boost Polygon Library: Point Concept

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Point Concept

The point concept tag is point_concept

To register a user defined type as a model of point concept, specialize the geometry concept meta-function for that type.  In the example below CPoint is registered as a model of point  concept.

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

The semantic of a point is that it has an x and y coordinate.  A std::pair, boost::tuple or boost::array could all be made models of point by simply providing indirect access to their elements through traits, however, these objects cannot be made a model of both point and interval in the same compilation unit, for obvious reason that duplicate specialization of the geometry_concept struct is illegal, but also because it would make overloading generic function by concept ambiguous if a type modeled more than one concept.

Below is shown the default point traits.  Specialization of these traits is required for types that don't conform to the default behavior.

template
struct point_traits {
     typedef typename T::coordinate_type coordinate_type;

     static inline coordinate_type get(const T& point, orientation_2d orient) {
          return point.get(orient);
     }
};

template
struct point_mutable_traits {
     static inline void set(T& point, orientation_2d orient, typename point_traits::coordinate_type value) {
          point.set(orient, value);
     }
     static inline T construct(typename point_traits::coordinate_type x_value, typename point_traits::coordinate_type y_value) {
          return T(x_value, y_value);
     }
};

Example code custom_point.cpp demonstrates how to map a user defined point class to the library point_concept

Functions

template
coordinate_type get(const T& point, orientation_2d)		 Expects a model of point.  Returns the x or y coordinate of the point, depending on the orientation_2d value.
 
template
void set(T& point, orientation_2d, coordinate_type)		 Expects a model of point.   Sets the x or y coordinate of the point to the coordinate, depending on the orientation_2d  value.
template
T construct(coordinate_type x, coordinate_type y)		 Construct an object that is a model of point given x and y coordinate values.
template
T1& assign(T1& left, const T2& right)		 Copies data from right object that models point into left object that models point.
template
bool equivalence(const T& point1, const T2& point2)		 Given two objects that model point, compares and returns true if their x and y values are respectively equal to each other.
template
coordinate_type x(const point_type& point)		 Returns the x coordinate of an object that models point.
template
coordinate_type y(const point_type& point)		 Returns the y coordinate of an object that models point.
template
void x(point_type& point, coordinate_type )		 Sets the x coordinate of the object that models point to the coordinate value. 
template
void y(point_type& point, coordinate_type )		 Sets the y coordinate of the object that models point to the coordinate value. 
template
point_type& scale_up(point_type& point,
                        unsigned_area_type factor)		 Multiplies x and y coordinate of an object that models point by unsigned factor.
template
point_type& scale_down(point_type& point,
                          unsigned_area_type factor)		 Divides x and y coordinate of an object that models point by unsigned factor.
template
point_type& scale(point_type& point,
                  const scaling_type& factor) 		Calls the scale member function of scaling type on the x and y value of an object that models point and sets the point to the scaled values.
template
point_type& transform(point_type& point,
                      const transform_type& transform) 		Calls the transform member function of transform type on the x and y value of an object that models point and sets the point to the transformed values.
template
point_type& move(point_type& point, orientation_2d
                 coordinate_difference displacement)		 Adds displacement value to the coordinate of an object that models point indicated by the orientation_2d.
template
T1& convolve(T1& a, const T2& b)		 Adds x coordinate of b to x coordinate of a and adds y coordinate of b to y coordinate of a.
template
T1& deconvolve(T1& a, const T2& b)		 Subtracts x coordinate of b from x coordinate of a and subtracts y coordinate of b from y coordinate of a.
template
coordinate_distance euclidean_distance(const T1&,
                                       const T2&)		 Returns the distance from an object that models point to a second object that models point.
template
coordinate_difference euclidean_distance(const T&,
           orientation_2d, coordinate_type)		 Returns the distance from an object that models point to a coordinate in the given orientation_2d.
template
coordinate_difference manhattan_distance(const T1&,
                                       const T2&)		 Returns the distance in x plus the distance in y from an object that models point to a second object that models point.
template
coordinate_difference distance_squared(const T1&,
                                       const T2&)		 Returns the square of the distance in x plus the square of the distance in y from an object that models point to a second object that models point.

Point Data

The library provides a model of point concept declared template point_data where T is the coordinate type.

This data type is used internally when a point is needed and is available to the library user who finds it convenient to use a library point data type instead of providing their own.  The data type is implemented to be convenient to use with the library traits.

Example code point_usage.cpp demonstrates using the library provided point data type and functions

Members

geometry_type point_concept
coordinate_type T
point_data() Default constructs the two coordinate values of the point.
point_data(T x, T y) Constructs an interval with two coordinates.
point_data(const point_data* that) Copy construct
point_data& operator=(const point_data& that) Assignment operator.
template  
point_data& operator=(const T2& that) const		 Assign from an object that is a model of point.
template
bool operator==(const T2& that) const		 Compare equality to an object that is a model of point.
template
bool operator!=(const T2& that) const		 Compare inequality to an object that is a model of point.
template
bool operator<(const T2& that) const		 Compares y coordinates then x coordinates to break ties.
template
bool operator<=(const T2& that) const		 Compares y coordinates then x coordinates to break ties.
template
bool operator>(const T2& that) const		 Compares low coordinates then high coordinates to break ties.
template
bool operator>=(const T2& that) const		 Compares low coordinates then high coordinates to break ties.
T get(orientation_2d orient) const Get the coordinate in the given orientation.
T x() const Get the coordinate in the horizontal orientation.
T y() const Get the coordinate in the vertical orientation.
void set(orientation_2d orient, T value) Sets the coordinate in the given orientation to the value.
void x(T value) Sets the coordinate in the horizontal orientation to the value.
void y(T value) Sets the coordinate in the vertical orientation to the value.
 
Copyright: Copyright © Intel Corporation 2008-2010.
License: 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)