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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<CPoint> { typedef point_concept type; };

The semantic of a point is that it has an x and y coordinate.  A std::pair<int, int>, boost::tuple<int, int> or boost::array<int, 2> 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 <typename T>
struct point_traits {
     typedef typename T::coordinate_type coordinate_type;

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

template <typename T>
struct point_mutable_traits {
     typedef typename T::coordinate_type coordinate_type;

     static void set(T& point, orientation_2d orient, typename point_traits<T>::coordinate_type value) {
          point.set(orient, value);
     }
     static T construct(typename point_traits<T>::coordinate_type x_value,
                        typename point_traits<T>::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

Point Data

The library provides a model of point concept declared template<typename T> 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

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