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libs/gil/example/interleaved_ptr.hpp

//
// 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_EXAMPLE_INTERLEAVED_PTR_HPP
#define BOOST_GIL_EXAMPLE_INTERLEAVED_PTR_HPP

#include <boost/gil.hpp>
#include <boost/mp11.hpp>

#include <type_traits>

#include "interleaved_ref.hpp"

// Example on how to create a pixel iterator

namespace boost { namespace gil {

// A model of an interleaved pixel iterator. Contains an iterator to the first channel of the current pixel
//
// Models:
//     MutablePixelIteratorConcept
//        PixelIteratorConcept
//           boost_concepts::RandomAccessTraversalConcept
//           PixelBasedConcept
//     HomogeneousPixelBasedConcept
//        PixelBasedConcept
//     ByteAdvanceableConcept
//     HasDynamicXStepTypeConcept

template <typename ChannelPtr,  // Models Channel Iterator (examples: unsigned char* or const unsigned char*)
          typename Layout>      // A layout (includes the color space and channel ordering)
struct interleaved_ptr : boost::iterator_facade
    <
        interleaved_ptr<ChannelPtr, Layout>,
        pixel<typename std::iterator_traits<ChannelPtr>::value_type, Layout>,
        boost::random_access_traversal_tag,
        interleaved_ref<typename std::iterator_traits<ChannelPtr>::reference, Layout> const
    >
{
private:
    using parent_t = boost::iterator_facade
        <
            interleaved_ptr<ChannelPtr, Layout>,
            pixel<typename std::iterator_traits<ChannelPtr>::value_type, Layout>,
            boost::random_access_traversal_tag,
            interleaved_ref
            <
                typename std::iterator_traits<ChannelPtr>::reference,
                Layout
            > const
        >;

    using channel_t = typename std::iterator_traits<ChannelPtr>::value_type;

public:
    using reference = typename parent_t::reference;
    using difference_type = typename parent_t::difference_type;

    interleaved_ptr() {}
    interleaved_ptr(const interleaved_ptr& ptr) : _channels(ptr._channels) {}
    template <typename CP> interleaved_ptr(const interleaved_ptr<CP,Layout>& ptr) : _channels(ptr._channels) {}

    interleaved_ptr(const ChannelPtr& channels) : _channels(channels) {}

    // Construct from a pointer to the reference type. Not required by concepts but important
    interleaved_ptr(reference* pix) : _channels(&((*pix)[0])) {}
    interleaved_ptr& operator=(reference* pix) { _channels=&((*pix)[0]); return *this; }

    /// For some reason operator[] provided by boost::iterator_facade returns a custom class that is convertible to reference
    /// We require our own reference because it is registered in iterator_traits
    reference operator[](difference_type d) const { return memunit_advanced_ref(*this,d*sizeof(channel_t));}

    // Put this for every iterator whose reference is a proxy type
    reference operator->()                  const { return **this; }

    // Channels accessor (not required by any concept)
    const ChannelPtr& channels()            const { return _channels; }
          ChannelPtr& channels()                  { return _channels; }

    // Not required by concepts but useful
    static const std::size_t num_channels = mp11::mp_size<typename Layout::color_space_t>::value;
private:
    ChannelPtr _channels;
    friend class boost::iterator_core_access;
    template <typename CP, typename L> friend struct interleaved_ptr;

    void increment()            { _channels+=num_channels; }
    void decrement()            { _channels-=num_channels; }
    void advance(std::ptrdiff_t d)   { _channels+=num_channels*d; }

    std::ptrdiff_t distance_to(const interleaved_ptr& it) const { return (it._channels-_channels)/num_channels; }
    bool equal(const interleaved_ptr& it) const { return _channels==it._channels; }

    reference dereference() const { return reference(_channels); }
};

/////////////////////////////
//  PixelIteratorConcept
/////////////////////////////

// To get from the channel pointer a channel pointer to const, we have to go through the channel traits, which take a model of channel
// So we can get a model of channel from the channel pointer via iterator_traits. Notice that we take the iterator_traits::reference and not
// iterator_traits::value_type. This is because sometimes multiple reference and pointer types share the same value type. An example of this is
// GIL's planar reference and iterator ("planar_pixel_reference" and "planar_pixel_iterator") which share the class "pixel" as the value_type. The
// class "pixel" is also the value type for interleaved pixel references. Here we are dealing with channels, not pixels, but the principles still apply.
template <typename ChannelPtr, typename Layout>
struct const_iterator_type<interleaved_ptr<ChannelPtr,Layout>> {
private:
    using channel_ref_t = typename std::iterator_traits<ChannelPtr>::reference;
    using channel_const_ptr_t = typename channel_traits<channel_ref_t>::const_pointer;
public:
    using type = interleaved_ptr<channel_const_ptr_t, Layout>;
};

template <typename ChannelPtr, typename Layout>
struct iterator_is_mutable<interleaved_ptr<ChannelPtr,Layout>> : std::true_type {};
template <typename Channel, typename Layout>
struct iterator_is_mutable<interleaved_ptr<const Channel*,Layout>> : std::false_type {};

template <typename ChannelPtr, typename Layout>
struct is_iterator_adaptor<interleaved_ptr<ChannelPtr,Layout>> : std::false_type {};

/////////////////////////////
//  PixelBasedConcept
/////////////////////////////

template <typename ChannelPtr, typename Layout>
struct color_space_type<interleaved_ptr<ChannelPtr,Layout>>
{
    using type = typename Layout::color_space_t;
};

template <typename ChannelPtr, typename Layout>
struct channel_mapping_type<interleaved_ptr<ChannelPtr,Layout>>
{
    using type = typename Layout::channel_mapping_t;
};

template <typename ChannelPtr, typename Layout>
struct is_planar<interleaved_ptr<ChannelPtr,Layout>> : std::false_type {};

/////////////////////////////
//  HomogeneousPixelBasedConcept
/////////////////////////////

template <typename ChannelPtr, typename Layout>
struct channel_type<interleaved_ptr<ChannelPtr, Layout>>
{
    using type = typename std::iterator_traits<ChannelPtr>::value_type;
};

/////////////////////////////
//  ByteAdvanceableConcept
/////////////////////////////

template <typename ChannelPtr, typename Layout>
inline std::ptrdiff_t memunit_step(const interleaved_ptr<ChannelPtr,Layout>&) {
    return sizeof(typename std::iterator_traits<ChannelPtr>::value_type)*   // size of each channel in bytes
           interleaved_ptr<ChannelPtr,Layout>::num_channels;                // times the number of channels
}

template <typename ChannelPtr, typename Layout>
inline std::ptrdiff_t memunit_distance(const interleaved_ptr<ChannelPtr,Layout>& p1, const interleaved_ptr<ChannelPtr,Layout>& p2) {
    return memunit_distance(p1.channels(),p2.channels());
}

template <typename ChannelPtr, typename Layout>
inline void memunit_advance(interleaved_ptr<ChannelPtr,Layout>& p, std::ptrdiff_t diff) {
    memunit_advance(p.channels(), diff);
}

template <typename ChannelPtr, typename Layout>
inline interleaved_ptr<ChannelPtr,Layout> memunit_advanced(const interleaved_ptr<ChannelPtr,Layout>& p, std::ptrdiff_t diff) {
    interleaved_ptr<ChannelPtr,Layout> ret=p;
    memunit_advance(ret, diff);
    return ret;
}

template <typename ChannelPtr, typename Layout>
inline typename interleaved_ptr<ChannelPtr,Layout>::reference memunit_advanced_ref(const interleaved_ptr<ChannelPtr,Layout>& p, std::ptrdiff_t diff) {
    interleaved_ptr<ChannelPtr,Layout> ret=p;
    memunit_advance(ret, diff);
    return *ret;
}

/////////////////////////////
//  HasDynamicXStepTypeConcept
/////////////////////////////

template <typename ChannelPtr, typename Layout>
struct dynamic_x_step_type<interleaved_ptr<ChannelPtr, Layout>>
{
    using type = memory_based_step_iterator<interleaved_ptr<ChannelPtr, Layout>>;
};
} }  // namespace boost::gil

#endif