2 // Copyright 2005-2007 Adobe Systems Incorporated
4 // Distributed under the Boost Software License, Version 1.0
5 // See accompanying file LICENSE_1_0.txt or copy at
6 // http://www.boost.org/LICENSE_1_0.txt
8 #ifndef BOOST_GIL_STEP_ITERATOR_HPP
9 #define BOOST_GIL_STEP_ITERATOR_HPP
11 #include <boost/gil/dynamic_step.hpp>
12 #include <boost/gil/pixel_iterator.hpp>
13 #include <boost/gil/pixel_iterator_adaptor.hpp>
14 #include <boost/gil/utilities.hpp>
16 #include <boost/iterator/iterator_facade.hpp>
20 #include <type_traits>
22 namespace boost { namespace gil {
24 /// \defgroup PixelIteratorModelStepPtr step iterators
25 /// \ingroup PixelIteratorModel
26 /// \brief Iterators that allow for specifying the step between two adjacent values
30 /// \ingroup PixelIteratorModelStepPtr
31 /// \brief An adaptor over an existing iterator that changes the step unit
33 /// (i.e. distance(it,it+1)) by a given predicate. Instead of calling base's
34 /// operators ++, --, +=, -=, etc. the adaptor is using the passed policy object SFn
35 /// for advancing and for computing the distance between iterators.
37 template <typename Derived, // type of the derived class
38 typename Iterator, // Models Iterator
39 typename SFn> // A policy object that can compute the distance between two iterators of type Iterator
40 // and can advance an iterator of type Iterator a given number of Iterator's units
41 class step_iterator_adaptor : public iterator_adaptor<Derived, Iterator, use_default, use_default, use_default, typename SFn::difference_type>
44 using parent_t = iterator_adaptor<Derived, Iterator, use_default, use_default, use_default, typename SFn::difference_type>;
45 using base_difference_type = typename std::iterator_traits<Iterator>::difference_type;
46 using difference_type = typename SFn::difference_type;
47 using reference = typename std::iterator_traits<Iterator>::reference;
49 step_iterator_adaptor() {}
50 step_iterator_adaptor(const Iterator& it, SFn step_fn=SFn()) : parent_t(it), _step_fn(step_fn) {}
52 difference_type step() const { return _step_fn.step(); }
57 friend class boost::iterator_core_access;
59 void increment() { _step_fn.advance(this->base_reference(),1); }
60 void decrement() { _step_fn.advance(this->base_reference(),-1); }
61 void advance(base_difference_type d) { _step_fn.advance(this->base_reference(),d); }
62 difference_type distance_to(const step_iterator_adaptor& it) const { return _step_fn.difference(this->base_reference(),it.base_reference()); }
65 // although iterator_adaptor defines these, the default implementation computes distance and compares for zero.
66 // it is often faster to just apply the relation operator to the base
67 template <typename D,typename Iterator,typename SFn> inline
68 bool operator>(const step_iterator_adaptor<D,Iterator,SFn>& p1, const step_iterator_adaptor<D,Iterator,SFn>& p2) {
69 return p1.step()>0 ? p1.base()> p2.base() : p1.base()< p2.base();
72 template <typename D,typename Iterator,typename SFn> inline
73 bool operator<(const step_iterator_adaptor<D,Iterator,SFn>& p1, const step_iterator_adaptor<D,Iterator,SFn>& p2) {
74 return p1.step()>0 ? p1.base()< p2.base() : p1.base()> p2.base();
77 template <typename D,typename Iterator,typename SFn> inline
78 bool operator>=(const step_iterator_adaptor<D,Iterator,SFn>& p1, const step_iterator_adaptor<D,Iterator,SFn>& p2) {
79 return p1.step()>0 ? p1.base()>=p2.base() : p1.base()<=p2.base();
82 template <typename D,typename Iterator,typename SFn> inline
83 bool operator<=(const step_iterator_adaptor<D,Iterator,SFn>& p1, const step_iterator_adaptor<D,Iterator,SFn>& p2) {
84 return p1.step()>0 ? p1.base()<=p2.base() : p1.base()>=p2.base();
87 template <typename D,typename Iterator,typename SFn> inline
88 bool operator==(const step_iterator_adaptor<D,Iterator,SFn>& p1, const step_iterator_adaptor<D,Iterator,SFn>& p2) {
89 return p1.base()==p2.base();
92 template <typename D,typename Iterator,typename SFn> inline
93 bool operator!=(const step_iterator_adaptor<D,Iterator,SFn>& p1, const step_iterator_adaptor<D,Iterator,SFn>& p2) {
94 return p1.base()!=p2.base();
99 ////////////////////////////////////////////////////////////////////////////////////////
100 /// MEMORY-BASED STEP ITERATOR
101 ////////////////////////////////////////////////////////////////////////////////////////
103 /// \class memory_based_step_iterator
104 /// \ingroup PixelIteratorModelStepPtr PixelBasedModel
105 /// \brief Iterator with dynamically specified step in memory units (bytes or bits). Models StepIteratorConcept, IteratorAdaptorConcept, MemoryBasedIteratorConcept, PixelIteratorConcept, HasDynamicXStepTypeConcept
107 /// A refinement of step_iterator_adaptor that uses a dynamic parameter for the step
108 /// which is specified in memory units, such as bytes or bits
110 /// Pixel step iterators are used to provide iteration over non-adjacent pixels.
111 /// Common use is a vertical traversal, where the step is the row stride.
113 /// Another application is as a sub-channel view. For example, a red intensity image over
114 /// interleaved RGB data would use a step iterator adaptor with step sizeof(channel_t)*3
115 /// In the latter example the step size could be fixed at compile time for efficiency.
116 /// Compile-time fixed step can be implemented by providing a step function object that takes the step as a template
117 ////////////////////////////////////////////////////////////////////////////////////////
119 /// \ingroup PixelIteratorModelStepPtr
120 /// \brief function object that returns the memory unit distance between two iterators and advances a given iterator a given number of mem units (bytes or bits)
121 template <typename Iterator>
122 struct memunit_step_fn {
123 using difference_type = std::ptrdiff_t;
125 memunit_step_fn(difference_type step=memunit_step(Iterator())) : _step(step) {}
127 difference_type difference(const Iterator& it1, const Iterator& it2) const { return memunit_distance(it1,it2)/_step; }
128 void advance(Iterator& it, difference_type d) const { memunit_advance(it,d*_step); }
129 difference_type step() const { return _step; }
131 void set_step(std::ptrdiff_t step) { _step=step; }
133 GIL_CLASS_REQUIRE(Iterator, boost::gil, MemoryBasedIteratorConcept)
134 difference_type _step;
137 template <typename Iterator>
138 class memory_based_step_iterator : public detail::step_iterator_adaptor<memory_based_step_iterator<Iterator>,
140 memunit_step_fn<Iterator>>
142 GIL_CLASS_REQUIRE(Iterator, boost::gil, MemoryBasedIteratorConcept)
144 using parent_t = detail::step_iterator_adaptor<memory_based_step_iterator<Iterator>,
146 memunit_step_fn<Iterator>>;
147 using reference = typename parent_t::reference;
148 using difference_type = typename parent_t::difference_type;
149 using x_iterator = Iterator;
151 memory_based_step_iterator() : parent_t(Iterator()) {}
152 memory_based_step_iterator(Iterator it, std::ptrdiff_t memunit_step) : parent_t(it, memunit_step_fn<Iterator>(memunit_step)) {}
153 template <typename I2>
154 memory_based_step_iterator(const memory_based_step_iterator<I2>& it)
155 : parent_t(it.base(), memunit_step_fn<Iterator>(it.step())) {}
157 /// For some reason operator[] provided by iterator_adaptor returns a custom class that is convertible to reference
158 /// We require our own reference because it is registered in iterator_traits
159 reference operator[](difference_type d) const { return *(*this+d); }
161 void set_step(std::ptrdiff_t memunit_step) { this->_step_fn.set_step(memunit_step); }
163 x_iterator& base() { return parent_t::base_reference(); }
164 x_iterator const& base() const { return parent_t::base_reference(); }
167 template <typename Iterator>
168 struct const_iterator_type<memory_based_step_iterator<Iterator>> {
169 using type = memory_based_step_iterator<typename const_iterator_type<Iterator>::type>;
172 template <typename Iterator>
173 struct iterator_is_mutable<memory_based_step_iterator<Iterator>> : public iterator_is_mutable<Iterator> {};
176 /////////////////////////////
177 // IteratorAdaptorConcept
178 /////////////////////////////
180 template <typename Iterator>
181 struct is_iterator_adaptor<memory_based_step_iterator<Iterator>> : std::true_type {};
183 template <typename Iterator>
184 struct iterator_adaptor_get_base<memory_based_step_iterator<Iterator>>
186 using type = Iterator;
189 template <typename Iterator, typename NewBaseIterator>
190 struct iterator_adaptor_rebind<memory_based_step_iterator<Iterator>, NewBaseIterator>
192 using type = memory_based_step_iterator<NewBaseIterator>;
195 /////////////////////////////
197 /////////////////////////////
199 template <typename Iterator>
200 struct color_space_type<memory_based_step_iterator<Iterator>> : public color_space_type<Iterator> {};
202 template <typename Iterator>
203 struct channel_mapping_type<memory_based_step_iterator<Iterator>> : public channel_mapping_type<Iterator> {};
205 template <typename Iterator>
206 struct is_planar<memory_based_step_iterator<Iterator>> : public is_planar<Iterator> {};
208 template <typename Iterator>
209 struct channel_type<memory_based_step_iterator<Iterator>> : public channel_type<Iterator> {};
211 /////////////////////////////
212 // MemoryBasedIteratorConcept
213 /////////////////////////////
214 template <typename Iterator>
215 struct byte_to_memunit<memory_based_step_iterator<Iterator>> : public byte_to_memunit<Iterator> {};
217 template <typename Iterator>
218 inline std::ptrdiff_t memunit_step(const memory_based_step_iterator<Iterator>& p) { return p.step(); }
220 template <typename Iterator>
221 inline std::ptrdiff_t memunit_distance(const memory_based_step_iterator<Iterator>& p1,
222 const memory_based_step_iterator<Iterator>& p2) {
223 return memunit_distance(p1.base(),p2.base());
226 template <typename Iterator>
227 inline void memunit_advance(memory_based_step_iterator<Iterator>& p,
228 std::ptrdiff_t diff) {
229 memunit_advance(p.base(), diff);
232 template <typename Iterator>
233 inline memory_based_step_iterator<Iterator>
234 memunit_advanced(const memory_based_step_iterator<Iterator>& p,
235 std::ptrdiff_t diff) {
236 return memory_based_step_iterator<Iterator>(memunit_advanced(p.base(), diff),p.step());
239 template <typename Iterator>
240 inline typename std::iterator_traits<Iterator>::reference
241 memunit_advanced_ref(const memory_based_step_iterator<Iterator>& p,
242 std::ptrdiff_t diff) {
243 return memunit_advanced_ref(p.base(), diff);
246 /////////////////////////////
247 // HasDynamicXStepTypeConcept
248 /////////////////////////////
250 template <typename Iterator>
251 struct dynamic_x_step_type<memory_based_step_iterator<Iterator>> {
252 using type = memory_based_step_iterator<Iterator>;
255 // For step iterators, pass the function object to the base
256 template <typename Iterator, typename Deref>
257 struct iterator_add_deref<memory_based_step_iterator<Iterator>,Deref> {
258 GIL_CLASS_REQUIRE(Deref, boost::gil, PixelDereferenceAdaptorConcept)
260 using type = memory_based_step_iterator<typename iterator_add_deref<Iterator, Deref>::type>;
262 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()); }
265 ////////////////////////////////////////////////////////////////////////////////////////
266 /// make_step_iterator
267 ////////////////////////////////////////////////////////////////////////////////////////
269 template <typename I> typename dynamic_x_step_type<I>::type make_step_iterator(const I& it, std::ptrdiff_t step);
273 // if the iterator is a plain base iterator (non-adaptor), wraps it in memory_based_step_iterator
274 template <typename I>
275 auto make_step_iterator_impl(I const& it, std::ptrdiff_t step, std::false_type)
276 -> typename dynamic_x_step_type<I>::type
278 return memory_based_step_iterator<I>(it, step);
281 // If the iterator is compound, put the step in its base
282 template <typename I>
283 auto make_step_iterator_impl(I const& it, std::ptrdiff_t step, std::true_type)
284 -> typename dynamic_x_step_type<I>::type
286 return make_step_iterator(it.base(), step);
289 // If the iterator is memory_based_step_iterator, change the step
290 template <typename BaseIt>
291 auto make_step_iterator_impl(
292 memory_based_step_iterator<BaseIt> const& it,
295 -> memory_based_step_iterator<BaseIt>
297 return memory_based_step_iterator<BaseIt>(it.base(), step);
300 } // namespace detail
302 /// \brief Constructs a step iterator from a base iterator and a step.
304 /// To construct a step iterator from a given iterator Iterator and a given step, if Iterator does not
305 /// already have a dynamic step, we wrap it in a memory_based_step_iterator. Otherwise we
306 /// do a compile-time traversal of the chain of iterator adaptors to locate the step iterator
307 /// and then set it step to the new one.
309 /// The step iterator of Iterator is not always memory_based_step_iterator<Iterator>. For example, Iterator may
310 /// already be a memory_based_step_iterator, in which case it will be inefficient to stack them;
311 /// we can obtain the same result by multiplying their steps. Note that for Iterator to be a
312 /// step iterator it does not necessarily have to have the form memory_based_step_iterator<J>.
313 /// The step iterator can be wrapped inside another iterator. Also, it may not have the
314 /// type memory_based_step_iterator, but it could be a user-provided type.
315 template <typename I> // Models MemoryBasedIteratorConcept, HasDynamicXStepTypeConcept
316 typename dynamic_x_step_type<I>::type make_step_iterator(const I& it, std::ptrdiff_t step) {
317 return detail::make_step_iterator_impl(it, step, typename is_iterator_adaptor<I>::type());
320 }} // namespace boost::gil