text: //
  // Copyright 2005-2007 Adobe Systems Incorporated
  //
  // 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
  //
  #ifndef BOOST_GIL_PIXEL_HPP
  #define BOOST_GIL_PIXEL_HPP
  
  #include <boost/gil/channel.hpp>
  #include <boost/gil/color_base.hpp>
  #include <boost/gil/color_base_algorithm.hpp>
  #include <boost/gil/concepts.hpp>
  #include <boost/gil/metafunctions.hpp>
  #include <boost/gil/utilities.hpp>
  
  #include <boost/core/ignore_unused.hpp>
  #include <boost/mpl/bool.hpp>
  #include <boost/mpl/front.hpp>
  #include <boost/type_traits.hpp>
  
  #include <functional>
  #include <type_traits>
  
  namespace boost { namespace gil {
  
  // Forward-declare gray_t
  struct gray_color_t;
  using gray_t = mpl::vector1<gray_color_t>;
  template <typename PixelBased> struct color_space_type;
  template <typename PixelBased> struct channel_mapping_type;
  template <typename PixelBased> struct channel_type;
  template <typename PixelBased> struct is_planar;
  
  template <typename PixelBased> struct color_space_type<const PixelBased> : public color_space_type<PixelBased> {};
  template <typename PixelBased> struct channel_mapping_type<const PixelBased> : public channel_mapping_type<PixelBased> {};
  template <typename PixelBased> struct channel_type<const PixelBased> : public channel_type<PixelBased> {};
  
  template <typename PixelBased> struct is_planar : mpl::false_ {};
  template <typename PixelBased> struct is_planar<const PixelBased> : public is_planar<PixelBased> {};
  
  
  template <typename T> struct is_pixel : public mpl::false_{};
  template <typename T> struct is_pixel<const T> : public is_pixel<T> {};
  
  /// \ingroup PixelBasedAlgorithm
  /// \brief Returns the number of channels of a pixel-based GIL construct
  template <typename PixelBased>
  struct num_channels : public mpl::size<typename color_space_type<PixelBased>::type> {};
  
  /**
  \addtogroup PixelBasedAlgorithm
  
  Example:
  \code
  static_assert(num_channels<rgb8_view_t>::value == 3, "");
  static_assert(num_channels<cmyk16_planar_ptr_t>::value == 4, "");
  
  static_assert(is_planar<rgb16_planar_image_t>::value));
  static_assert(is_same<color_space_type<rgb8_planar_ref_t>::type, rgb_t>::value, "");
  static_assert(is_same<channel_mapping_type<cmyk8_pixel_t>::type,
                               channel_mapping_type<rgba8_pixel_t>::type>::value, "");
  static_assert(is_same<channel_type<bgr8_pixel_t>::type, uint8_t>::value, "");
  \endcode
  */
  
  /// \defgroup ColorBaseModelPixel pixel
  /// \ingroup ColorBaseModel
  /// \brief A homogeneous color base whose element is a channel value. Models HomogeneousColorBaseValueConcept
  
  /// \defgroup PixelModelPixel pixel
  /// \ingroup PixelModel
  /// \brief A homogeneous pixel value. Models HomogeneousPixelValueConcept
  
  /// \ingroup PixelModelPixel ColorBaseModelPixel PixelBasedModel
  /// \brief Represents a pixel value (a container of channels). Models: HomogeneousColorBaseValueConcept, PixelValueConcept, HomogeneousPixelBasedConcept
  ///
  /// A pixel is a set of channels defining the color at a given point in an image. Conceptually, a pixel is little more than a color base whose elements
  /// model \p ChannelConcept. The class \p pixel defines a simple, homogeneous pixel value. It is used to store
  /// the value of a color. The built-in C++ references to \p pixel, \p pixel& and \p const \p pixel& are used to represent a reference to a pixel
  /// inside an interleaved image view (a view in which all channels are together in memory). Similarly, built-in pointer types \p pixel* and \p const \p pixel*
  /// are used as the standard iterator over a row of interleaved homogeneous pixels.
  ///
  /// Since \p pixel inherits the properties of color base, assigning, equality comparison and copy-construcion are allowed between compatible pixels.
  /// This means that an 8-bit RGB pixel may be assigned to an 8-bit BGR pixel, or to an 8-bit planar reference. The channels are properly paired semantically.
  ///
  /// The single-channel (grayscale) instantiation of the class pixel, (i.e. \p pixel<T,gray_layout_t>) is also convertible to/from a channel value.
  /// This allows grayscale pixels to be used in simpler expressions like *gray_pix1 = *gray_pix2  instead of more complicated at_c<0>(gray_pix1) = at_c<0>(gray_pix2)
  /// or get_color<gray_color_t>(gray_pix1) = get_color<gray_color_t>(gray_pix2)
  
  template <typename ChannelValue, typename Layout> // = mpl::range_c<int,0,ColorSpace::size> >
  struct pixel : public detail::homogeneous_color_base<ChannelValue,Layout,mpl::size<typename Layout::color_space_t>::value> {
  private:
      using channel_t = ChannelValue;
      using parent_t = detail::homogeneous_color_base<ChannelValue,Layout,mpl::size<typename Layout::color_space_t>::value>;
  public:
      using value_type = pixel<ChannelValue, Layout>;
      using reference = value_type&;
      using const_reference = value_type const&;
      static constexpr bool is_mutable = channel_traits<channel_t>::is_mutable;
  
      pixel(){}
      explicit pixel(channel_t v) : parent_t(v) {}  // sets all channels to v
      pixel(channel_t v0, channel_t v1)                                                         : parent_t(v0,v1) {}
      pixel(channel_t v0, channel_t v1, channel_t v2)                                           : parent_t(v0,v1,v2) {}
      pixel(channel_t v0, channel_t v1, channel_t v2, channel_t v3)                             : parent_t(v0,v1,v2,v3) {}
      pixel(channel_t v0, channel_t v1, channel_t v2, channel_t v3, channel_t v4)               : parent_t(v0,v1,v2,v3,v4) {}
      pixel(channel_t v0, channel_t v1, channel_t v2, channel_t v3, channel_t v4, channel_t v5) : parent_t(v0,v1,v2,v3,v4,v5) {}
  
      pixel(const pixel& p) : parent_t(p) {}
      pixel&                       operator=(const pixel& p)       { static_copy(p,*this); return *this; }
  
      // Construct from another compatible pixel type
      template <typename Pixel>
      pixel(Pixel const& p,
          typename std::enable_if<is_pixel<Pixel>::value>::type* /*dummy*/ = nullptr)
          : parent_t(p)
      {
          check_compatible<Pixel>();
      }
  
      template <typename P> pixel& operator=(const P& p)           { assign(p, mpl::bool_<is_pixel<P>::value>()); return *this; }
      template <typename P> bool   operator==(const P& p)    const { return equal(p, mpl::bool_<is_pixel<P>::value>()); }
  
      template <typename P> bool   operator!=(const P& p)    const { return !(*this==p); }
  
      // homogeneous pixels have operator[]
      typename channel_traits<channel_t>::reference       operator[](std::size_t i)       { return dynamic_at_c(*this,i); }
      typename channel_traits<channel_t>::const_reference operator[](std::size_t i) const { return dynamic_at_c(*this,i); }
  private:
      template <typename Pixel> void assign(const Pixel& p, mpl::true_)       { check_compatible<Pixel>(); static_copy(p,*this); }
      template <typename Pixel> bool  equal(const Pixel& p, mpl::true_) const { check_compatible<Pixel>(); return static_equal(*this,p); }
  
      template <typename Pixel> void check_compatible() const { gil_function_requires<PixelsCompatibleConcept<Pixel,pixel> >(); }
  
  // Support for assignment/equality comparison of a channel with a grayscale pixel
  
  private:
      static void check_gray()
      {
          static_assert(is_same<typename Layout::color_space_t, gray_t>::value, "");
      }
      template <typename Channel> void assign(const Channel& chan, mpl::false_)       { check_gray(); gil::at_c<0>(*this)=chan; }
      template <typename Channel> bool equal (const Channel& chan, mpl::false_) const { check_gray(); return gil::at_c<0>(*this)==chan; }
  public:
      pixel&  operator= (channel_t chan)       { check_gray(); gil::at_c<0>(*this)=chan; return *this; }
      bool    operator==(channel_t chan) const { check_gray(); return gil::at_c<0>(*this)==chan; }
  };
  
  /////////////////////////////
  //  ColorBasedConcept
  /////////////////////////////
  
  template <typename ChannelValue, typename Layout, int K>
  struct kth_element_type<pixel<ChannelValue,Layout>, K> {
      using type = ChannelValue;
  };
  
  template <typename ChannelValue, typename Layout, int K>
  struct kth_element_reference_type<pixel<ChannelValue,Layout>, K> {
      using type = typename channel_traits<ChannelValue>::reference;
  };
  
  template <typename ChannelValue, typename Layout, int K>
  struct kth_element_reference_type<const pixel<ChannelValue,Layout>, K> {
      using type = typename channel_traits<ChannelValue>::const_reference;
  };
  
  template <typename ChannelValue, typename Layout, int K>
  struct kth_element_const_reference_type<pixel<ChannelValue,Layout>, K> {
      using type = typename channel_traits<ChannelValue>::const_reference;
  };
  
  /////////////////////////////
  //  PixelConcept
  /////////////////////////////
  
  template <typename ChannelValue, typename Layout>
  struct is_pixel<pixel<ChannelValue,Layout> > : public mpl::true_{};
  
  /////////////////////////////
  //  HomogeneousPixelBasedConcept
  /////////////////////////////
  
  template <typename ChannelValue, typename Layout>
  struct color_space_type<pixel<ChannelValue,Layout> > {
      using type = typename Layout::color_space_t;
  };
  
  template <typename ChannelValue, typename Layout>
  struct channel_mapping_type<pixel<ChannelValue,Layout> > {
      using type = typename Layout::channel_mapping_t;
  };
  
  template <typename ChannelValue, typename Layout>
  struct is_planar<pixel<ChannelValue,Layout> > : public mpl::false_ {};
  
  template <typename ChannelValue, typename Layout>
  struct channel_type<pixel<ChannelValue,Layout> > {
      using type = ChannelValue;
  };
  
  }}  // namespace boost::gil
  
  namespace boost {
      template <typename ChannelValue, typename Layout>
      struct has_trivial_constructor<gil::pixel<ChannelValue,Layout> > : public has_trivial_constructor<ChannelValue> {};
  }
  
  #endif
  