step_iterator.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_STEP_ITERATOR_HPP
#define BOOST_GIL_STEP_ITERATOR_HPP

#include <boost/gil/dynamic_step.hpp>
#include <boost/gil/pixel_iterator.hpp>
#include <boost/gil/pixel_iterator_adaptor.hpp>
#include <boost/gil/utilities.hpp>

#include <boost/iterator/iterator_facade.hpp>

#include <cstddef>
#include <iterator>
#include <type_traits>

namespace boost { namespace gil {


namespace detail {


template <typename Derived,  // type of the derived class
          typename Iterator, // Models Iterator
          typename SFn>      // A policy object that can compute the distance between two iterators of type Iterator
                             // and can advance an iterator of type Iterator a given number of Iterator's units
class step_iterator_adaptor : public iterator_adaptor<Derived, Iterator, use_default, use_default, use_default, typename SFn::difference_type>
{
public:
    using parent_t = iterator_adaptor<Derived, Iterator, use_default, use_default, use_default, typename SFn::difference_type>;
    using base_difference_type = typename std::iterator_traits<Iterator>::difference_type;
    using difference_type = typename SFn::difference_type;
    using reference = typename std::iterator_traits<Iterator>::reference;

    step_iterator_adaptor() {}
    step_iterator_adaptor(const Iterator& it, SFn step_fn=SFn()) : parent_t(it), _step_fn(step_fn) {}

    difference_type step() const { return _step_fn.step(); }

protected:
    SFn _step_fn;
private:
    friend class boost::iterator_core_access;

    void increment() { _step_fn.advance(this->base_reference(),1); }
    void decrement() { _step_fn.advance(this->base_reference(),-1); }
    void advance(base_difference_type d) { _step_fn.advance(this->base_reference(),d); }
    difference_type distance_to(const step_iterator_adaptor& it) const { return _step_fn.difference(this->base_reference(),it.base_reference()); }
};

// although iterator_adaptor defines these, the default implementation computes distance and compares for zero.
// it is often faster to just apply the relation operator to the base
template <typename D,typename Iterator,typename SFn> inline
bool operator>(const step_iterator_adaptor<D,Iterator,SFn>& p1, const step_iterator_adaptor<D,Iterator,SFn>& p2) {
    return p1.step()>0 ? p1.base()> p2.base() : p1.base()< p2.base();
}

template <typename D,typename Iterator,typename SFn> inline
bool operator<(const step_iterator_adaptor<D,Iterator,SFn>& p1, const step_iterator_adaptor<D,Iterator,SFn>& p2) {
    return p1.step()>0 ? p1.base()< p2.base() : p1.base()> p2.base();
}

template <typename D,typename Iterator,typename SFn> inline
bool operator>=(const step_iterator_adaptor<D,Iterator,SFn>& p1, const step_iterator_adaptor<D,Iterator,SFn>& p2) {
    return p1.step()>0 ? p1.base()>=p2.base() : p1.base()<=p2.base();
}

template <typename D,typename Iterator,typename SFn> inline
bool operator<=(const step_iterator_adaptor<D,Iterator,SFn>& p1, const step_iterator_adaptor<D,Iterator,SFn>& p2) {
    return p1.step()>0 ? p1.base()<=p2.base() : p1.base()>=p2.base();
}

template <typename D,typename Iterator,typename SFn> inline
bool operator==(const step_iterator_adaptor<D,Iterator,SFn>& p1, const step_iterator_adaptor<D,Iterator,SFn>& p2) {
    return p1.base()==p2.base();
}

template <typename D,typename Iterator,typename SFn> inline
bool operator!=(const step_iterator_adaptor<D,Iterator,SFn>& p1, const step_iterator_adaptor<D,Iterator,SFn>& p2) {
    return p1.base()!=p2.base();
}

} // namespace detail



template <typename Iterator>
struct memunit_step_fn {
    using difference_type = std::ptrdiff_t;

    memunit_step_fn(difference_type step=memunit_step(Iterator())) : _step(step) {}

    difference_type difference(const Iterator& it1, const Iterator& it2) const { return memunit_distance(it1,it2)/_step; }
    void            advance(Iterator& it, difference_type d)             const { memunit_advance(it,d*_step); }
    difference_type step()                                               const { return _step; }

    void            set_step(std::ptrdiff_t step) { _step=step; }
private:
    BOOST_GIL_CLASS_REQUIRE(Iterator, boost::gil, MemoryBasedIteratorConcept)
    difference_type _step;
};

template <typename Iterator>
class memory_based_step_iterator : public detail::step_iterator_adaptor<memory_based_step_iterator<Iterator>,
                                                                            Iterator,
                                                                            memunit_step_fn<Iterator>>
{
    BOOST_GIL_CLASS_REQUIRE(Iterator, boost::gil, MemoryBasedIteratorConcept)
public:
    using parent_t = detail::step_iterator_adaptor<memory_based_step_iterator<Iterator>,
                                          Iterator,
                                          memunit_step_fn<Iterator>>;
    using reference = typename parent_t::reference;
    using difference_type = typename parent_t::difference_type;
    using x_iterator = Iterator;

    memory_based_step_iterator() : parent_t(Iterator()) {}
    memory_based_step_iterator(Iterator it, std::ptrdiff_t memunit_step) : parent_t(it, memunit_step_fn<Iterator>(memunit_step)) {}
    template <typename I2>
    memory_based_step_iterator(const memory_based_step_iterator<I2>& it)
        : parent_t(it.base(), memunit_step_fn<Iterator>(it.step())) {}

    reference operator[](difference_type d) const { return *(*this+d); }

    void set_step(std::ptrdiff_t memunit_step) { this->_step_fn.set_step(memunit_step); }

    x_iterator& base()              { return parent_t::base_reference(); }
    x_iterator const& base() const  { return parent_t::base_reference(); }
};

template <typename Iterator>
struct const_iterator_type<memory_based_step_iterator<Iterator>> {
    using type = memory_based_step_iterator<typename const_iterator_type<Iterator>::type>;
};

template <typename Iterator>
struct iterator_is_mutable<memory_based_step_iterator<Iterator>> : public iterator_is_mutable<Iterator> {};


//  IteratorAdaptorConcept

template <typename Iterator>
struct is_iterator_adaptor<memory_based_step_iterator<Iterator>> : std::true_type {};

template <typename Iterator>
struct iterator_adaptor_get_base<memory_based_step_iterator<Iterator>>
{
    using type = Iterator;
};

template <typename Iterator, typename NewBaseIterator>
struct iterator_adaptor_rebind<memory_based_step_iterator<Iterator>, NewBaseIterator>
{
    using type = memory_based_step_iterator<NewBaseIterator>;
};

//  PixelBasedConcept

template <typename Iterator>
struct color_space_type<memory_based_step_iterator<Iterator>> : public color_space_type<Iterator> {};

template <typename Iterator>
struct channel_mapping_type<memory_based_step_iterator<Iterator>> : public channel_mapping_type<Iterator> {};

template <typename Iterator>
struct is_planar<memory_based_step_iterator<Iterator>> : public is_planar<Iterator> {};

template <typename Iterator>
struct channel_type<memory_based_step_iterator<Iterator>> : public channel_type<Iterator> {};

//  MemoryBasedIteratorConcept
template <typename Iterator>
struct byte_to_memunit<memory_based_step_iterator<Iterator>> : public byte_to_memunit<Iterator> {};

template <typename Iterator>
inline std::ptrdiff_t memunit_step(const memory_based_step_iterator<Iterator>& p) { return p.step(); }

template <typename Iterator>
inline std::ptrdiff_t memunit_distance(const memory_based_step_iterator<Iterator>& p1,
                                    const memory_based_step_iterator<Iterator>& p2) {
    return memunit_distance(p1.base(),p2.base());
}

template <typename Iterator>
inline void memunit_advance(memory_based_step_iterator<Iterator>& p,
                         std::ptrdiff_t diff) {
    memunit_advance(p.base(), diff);
}

template <typename Iterator>
inline memory_based_step_iterator<Iterator>
memunit_advanced(const memory_based_step_iterator<Iterator>& p,
              std::ptrdiff_t diff) {
    return memory_based_step_iterator<Iterator>(memunit_advanced(p.base(), diff),p.step());
}

template <typename Iterator>
inline typename std::iterator_traits<Iterator>::reference
memunit_advanced_ref(const memory_based_step_iterator<Iterator>& p,
                  std::ptrdiff_t diff) {
    return memunit_advanced_ref(p.base(), diff);
}

//  HasDynamicXStepTypeConcept

template <typename Iterator>
struct dynamic_x_step_type<memory_based_step_iterator<Iterator>> {
    using type = memory_based_step_iterator<Iterator>;
};

// For step iterators, pass the function object to the base
template <typename Iterator, typename Deref>
struct iterator_add_deref<memory_based_step_iterator<Iterator>,Deref> {
    BOOST_GIL_CLASS_REQUIRE(Deref, boost::gil, PixelDereferenceAdaptorConcept)

    using type = memory_based_step_iterator<typename iterator_add_deref<Iterator, Deref>::type>;

    static type make(const memory_based_step_iterator<Iterator>& it, const Deref& d) { return type(iterator_add_deref<Iterator, Deref>::make(it.base(),d),it.step()); }
};


template <typename I> typename dynamic_x_step_type<I>::type make_step_iterator(const I& it, std::ptrdiff_t step);

namespace detail {

// if the iterator is a plain base iterator (non-adaptor), wraps it in memory_based_step_iterator
template <typename I>
auto make_step_iterator_impl(I const& it, std::ptrdiff_t step, std::false_type)
    -> typename dynamic_x_step_type<I>::type
{
    return memory_based_step_iterator<I>(it, step);
}

// If the iterator is compound, put the step in its base
template <typename I>
auto make_step_iterator_impl(I const& it, std::ptrdiff_t step, std::true_type)
    -> typename dynamic_x_step_type<I>::type
{
    return make_step_iterator(it.base(), step);
}

// If the iterator is memory_based_step_iterator, change the step
template <typename BaseIt>
auto make_step_iterator_impl(
    memory_based_step_iterator<BaseIt> const& it,
    std::ptrdiff_t step,
    std::true_type)
    -> memory_based_step_iterator<BaseIt>
{
    return memory_based_step_iterator<BaseIt>(it.base(), step);
}

} // namespace detail

template <typename I>  // Models MemoryBasedIteratorConcept, HasDynamicXStepTypeConcept
typename dynamic_x_step_type<I>::type make_step_iterator(const I& it, std::ptrdiff_t step) {
    return detail::make_step_iterator_impl(it, step, typename is_iterator_adaptor<I>::type());
}

}}  // namespace boost::gil

#endif