itkImageBufferRange.h

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*
*  Copyright Insight Software Consortium
*
*  Licensed under the Apache License, Version 2.0 (the "License");
*  you may not use this file except in compliance with the License.
*  You may obtain a copy of the License at
*
*         http://www.apache.org/licenses/LICENSE-2.0.txt
*
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*  distributed under the License is distributed on an "AS IS" BASIS,
*  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
*  See the License for the specific language governing permissions and
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*=========================================================================*/

#ifndef itkImageBufferRange_h
#define itkImageBufferRange_h

#include <cassert>
#include <cstddef> // For ptrdiff_t.
#include <iterator> // For random_access_iterator_tag.
#include <limits>
#include <type_traits> // For conditional, is_same, and is_const.

#include "itkMacro.h" // For itkNotUsed.
#include "itkDefaultPixelAccessor.h"
#include "itkDefaultPixelAccessorFunctor.h"
#include "itkDefaultVectorPixelAccessor.h"
#include "itkDefaultVectorPixelAccessorFunctor.h"
#include "itkImageRegion.h"

namespace itk
{
namespace Experimental
{

template<typename TImage>
class ImageBufferRange final
{
private:
  using ImageType = TImage;
  using PixelType = typename TImage::PixelType;
  using InternalPixelType = typename TImage::InternalPixelType;
  using AccessorFunctorType = typename TImage::AccessorFunctorType;

  // Tells whether or not this range supports direct pixel access. If it does,
  // iterator::operator*() returns a reference to the internally stored pixel,
  // otherwise iterator::operator*() returns a proxy, which internally uses the
  // AccessorFunctor of the image to access the pixel indirectly.
  constexpr static bool SupportsDirectPixelAccess =
    std::is_same<PixelType, InternalPixelType>::value &&
    std::is_same<typename TImage::AccessorType, DefaultPixelAccessor<PixelType>>::value &&
    std::is_same<AccessorFunctorType, DefaultPixelAccessorFunctor<typename std::remove_const<TImage>::type>>::value;

  // Tells whether or not this range is using a pointer as iterator.
  constexpr static bool UsingPointerAsIterator = SupportsDirectPixelAccess;

  struct EmptyAccessorFunctor {};

  using OptionalAccessorFunctorType = typename std::conditional<SupportsDirectPixelAccess,
    EmptyAccessorFunctor, AccessorFunctorType>::type;

  // PixelProxy: internal class that aims to act like a reference to a pixel:
  // It acts either like 'PixelType &' or like 'const PixelType &', depending
  // on its boolean template argument, VIsConst.
  // The proxy retrieves the pixel value using the AccessorFunctor from the image.
  // Note: the extra TDummy argument aims to fix AppleClang 6.0.0.6000056 error
  // "explicit specialization of 'PixelProxy'"and GCC 5.4.0 error "explicit
  // specialization in non-namespace scope".
  template <bool VIsConst, typename TDummy = void> class PixelProxy {};

  // PixelProxy specialization for const pixel types:
  // acts like 'const PixelType &'
  template <typename TDummy>
  class PixelProxy<true, TDummy> final
  {
  private:
    // Reference to the internal representation of the pixel, located in the image buffer.
    const InternalPixelType& m_InternalPixel;

    // The accessor functor of the image.
    const AccessorFunctorType m_AccessorFunctor;

  public:
    // Deleted member functions:
    PixelProxy() = delete;
    PixelProxy& operator=(const PixelProxy&) = delete;

    // Explicitly-defaulted member functions:
    PixelProxy(const PixelProxy&) ITK_NOEXCEPT = default;
    ~PixelProxy() = default;

    // Constructor, called directly by operator*() of the iterator class.
    PixelProxy(
      const InternalPixelType& internalPixel,
      const AccessorFunctorType& accessorFunctor) ITK_NOEXCEPT
      :
    m_InternalPixel{ internalPixel },
    m_AccessorFunctor(accessorFunctor)
    {
    }

    // Allows implicit conversion from non-const to const proxy.
    PixelProxy(const PixelProxy<false>& pixelProxy) ITK_NOEXCEPT
      :
    m_InternalPixel{ pixelProxy.m_InternalPixel },
    m_AccessorFunctor{ pixelProxy.m_AccessorFunctor }
    {
    }

    // Conversion operator.
    operator PixelType() const ITK_NOEXCEPT
    {
      return m_AccessorFunctor.Get(m_InternalPixel);
    }
  };


  // PixelProxy specialization for non-const pixel types:
  // acts like 'PixelType &'.
  template <typename TDummy>
  class PixelProxy<false, TDummy> final
  {
  private:
    // The const proxy is a friend, to ease implementing conversion from
    // a non-const proxy to a const proxy.
    friend class PixelProxy<true>;

    // Reference to the internal representation of the pixel, located in the image buffer.
    InternalPixelType& m_InternalPixel;

    // The accessor functor of the image.
    const AccessorFunctorType m_AccessorFunctor;

  public:
    // Deleted member functions:
    PixelProxy() = delete;

    // Explicitly-defaulted member functions:
    ~PixelProxy() = default;
    PixelProxy(const PixelProxy&) ITK_NOEXCEPT = default;

    // Constructor, called directly by operator*() of the iterator class.
    explicit PixelProxy(
      InternalPixelType& internalPixel,
      const AccessorFunctorType& accessorFunctor) ITK_NOEXCEPT
      :
    m_InternalPixel{ internalPixel },
    m_AccessorFunctor(accessorFunctor)
    {
    }

    // Conversion operator.
    operator PixelType() const ITK_NOEXCEPT
    {
      return m_AccessorFunctor.Get(m_InternalPixel);
    }

    // Operator to assign a pixel value to the proxy.
    PixelProxy& operator=(const PixelType& pixelValue) ITK_NOEXCEPT
    {
      m_AccessorFunctor.Set(m_InternalPixel, pixelValue);
      return *this;
    }

    // Copy-assignment operator.
    PixelProxy& operator=(const PixelProxy& pixelProxy) ITK_NOEXCEPT
    {
      // Note that this assignment operator only copies the pixel value.
      // That is the normal behavior when a reference is assigned to another.
      const PixelType pixelValue = pixelProxy;
      *this = pixelValue;
      return *this;
    }


    friend void swap(PixelProxy lhs, PixelProxy rhs) ITK_NOEXCEPT
    {
      const auto lhsPixelValue = lhs.m_AccessorFunctor.Get(lhs.m_InternalPixel);
      const auto rhsPixelValue = rhs.m_AccessorFunctor.Get(rhs.m_InternalPixel);

      // Swap only the pixel values, not the image buffer pointers!
      lhs.m_AccessorFunctor.Set(lhs.m_InternalPixel, rhsPixelValue);
      rhs.m_AccessorFunctor.Set(rhs.m_InternalPixel, lhsPixelValue);
    }
  };


  template <bool VIsConst>
  class QualifiedIterator final
  {
  private:
    // Const and non-const iterators are friends, in order to implement the
    // constructor that allow conversion from non-const to const iterator.
    friend class QualifiedIterator<!VIsConst>;

    // ImageBufferRange is a friend, as it should be the only one that can
    // directly use the private constructor of the iterator.
    friend class ImageBufferRange;

    // Image type class that is either 'const' or non-const qualified, depending on QualifiedIterator and TImage.
    using QualifiedImageType = typename std::conditional<VIsConst, const ImageType, ImageType>::type;

    static constexpr bool IsImageTypeConst = std::is_const<QualifiedImageType>::value;

    using QualifiedInternalPixelType = typename std::conditional<IsImageTypeConst, const InternalPixelType, InternalPixelType>::type;

    // Pixel type class that is either 'const' or non-const qualified, depending on QualifiedImageType.
    using QualifiedPixelType = typename std::conditional<IsImageTypeConst, const PixelType, PixelType>::type;


    // Wraps a reference to a pixel.
    class PixelReferenceWrapper final
    {
    public:
      QualifiedPixelType& m_Pixel;

      // Wraps the pixel reference that is specified by the first argument.
      // Note: the second parameter is unused, but it is there just to support
      // the use case of iterator::operator*(), which uses either
      // PixelReferenceWrapper or PixelProxy, interchangeable, in a generic way.
      // (PixelProxy has an explicit constructor for which the second parameter
      // is its essential AccessorFunctor parameter!)
      explicit PixelReferenceWrapper(
        QualifiedPixelType& pixel,
        EmptyAccessorFunctor itkNotUsed(accessorFunctor)) ITK_NOEXCEPT
        :
      m_Pixel(pixel)
      {
      }

      // Converts implicitly to a reference to the pixel.
      operator QualifiedPixelType&() const ITK_NOEXCEPT
      {
        return m_Pixel;
      }
    };


    // QualifiedIterator data members (strictly private):

    // The accessor functor of the image.
    OptionalAccessorFunctorType m_OptionalAccessorFunctor;

    // Pointer to the current pixel.
    QualifiedInternalPixelType* m_InternalPixelPointer = nullptr;

    // Private constructor, used to create the begin and the end iterator of a range.
    // Only used by its friend class ImageBufferRange.
    QualifiedIterator(
      const OptionalAccessorFunctorType& accessorFunctor,
      QualifiedInternalPixelType* const internalPixelPointer) ITK_NOEXCEPT
      :
    // Note: Use parentheses instead of curly braces to initialize data members,
    // to avoid AppleClang 6.0.0.6000056 compilation error, "no viable conversion..."
    m_OptionalAccessorFunctor(accessorFunctor),
    m_InternalPixelPointer{ internalPixelPointer }
    {
    }

  public:
    // Types conforming the iterator requirements of the C++ standard library:
    using difference_type = std::ptrdiff_t;
    using value_type = PixelType;
    using reference = typename std::conditional< SupportsDirectPixelAccess,
      QualifiedPixelType&, PixelProxy<IsImageTypeConst>>::type;
    using pointer = QualifiedPixelType*;
    using iterator_category = std::random_access_iterator_tag;


    QualifiedIterator() = default;

    QualifiedIterator(const QualifiedIterator<false>& arg) ITK_NOEXCEPT
      :
      // Note: Use parentheses instead of curly braces to initialize data members,
      // to avoid AppleClang 6.0.0.6000056 compilation error, "no viable conversion..."
      m_OptionalAccessorFunctor(arg.m_OptionalAccessorFunctor),
      m_InternalPixelPointer{ arg.m_InternalPixelPointer }
    {
    }


    reference operator*() const ITK_NOEXCEPT
    {
      assert(m_InternalPixelPointer != nullptr);

      using PixelWrapper = typename std::conditional<SupportsDirectPixelAccess,
        PixelReferenceWrapper, reference>::type;

      return PixelWrapper{ *m_InternalPixelPointer, m_OptionalAccessorFunctor };
    }


    QualifiedIterator& operator++() ITK_NOEXCEPT
    {
      assert(m_InternalPixelPointer != nullptr);
      ++m_InternalPixelPointer;
      return *this;
    }


    QualifiedIterator operator++(int) ITK_NOEXCEPT
    {
      auto result = *this;
      ++(*this);
      return result;
    }


    QualifiedIterator& operator--() ITK_NOEXCEPT
    {
      assert(m_InternalPixelPointer != nullptr);
      --m_InternalPixelPointer;
      return *this;
    }


    QualifiedIterator operator--(int) ITK_NOEXCEPT
    {
      auto result = *this;
      --(*this);
      return result;
    }


    friend bool operator==(const QualifiedIterator& lhs, const QualifiedIterator& rhs) ITK_NOEXCEPT
    {
      return lhs.m_InternalPixelPointer == rhs.m_InternalPixelPointer;
    }


    friend bool operator!=(const QualifiedIterator& lhs, const QualifiedIterator& rhs) ITK_NOEXCEPT
    {
      // Implemented just like the corresponding std::rel_ops operator.
      return !(lhs == rhs);
    }


    friend bool operator<(const QualifiedIterator& lhs, const QualifiedIterator& rhs) ITK_NOEXCEPT
    {
      return lhs.m_InternalPixelPointer < rhs.m_InternalPixelPointer;
    }


    friend bool operator>(const QualifiedIterator& lhs, const QualifiedIterator& rhs) ITK_NOEXCEPT
    {
      // Implemented just like the corresponding std::rel_ops operator.
      return rhs < lhs;
    }


    friend bool operator<=(const QualifiedIterator& lhs, const QualifiedIterator& rhs) ITK_NOEXCEPT
    {
      // Implemented just like the corresponding std::rel_ops operator.
      return !(rhs < lhs);
    }


    friend bool operator>=(const QualifiedIterator& lhs, const QualifiedIterator& rhs) ITK_NOEXCEPT
    {
      // Implemented just like the corresponding std::rel_ops operator.
      return !(lhs < rhs);
    }


    friend QualifiedIterator& operator+=(QualifiedIterator& it, const difference_type n) ITK_NOEXCEPT
    {
      it.m_InternalPixelPointer += n;
      return it;
    }

    friend QualifiedIterator& operator-=(QualifiedIterator& it, const difference_type n) ITK_NOEXCEPT
    {
      it += (-n);
      return it;
    }

    friend difference_type operator-(const QualifiedIterator& lhs, const QualifiedIterator& rhs) ITK_NOEXCEPT
    {
      return lhs.m_InternalPixelPointer - rhs.m_InternalPixelPointer;
    }


    friend QualifiedIterator operator+(QualifiedIterator it, const difference_type n) ITK_NOEXCEPT
    {
      return it += n;
    }


    friend QualifiedIterator operator+(const difference_type n, QualifiedIterator it) ITK_NOEXCEPT
    {
      return it += n;
    }


    friend QualifiedIterator operator-(QualifiedIterator it, const difference_type n) ITK_NOEXCEPT
    {
      return it += (-n);
    }


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


    QualifiedIterator& operator=(const QualifiedIterator&) ITK_NOEXCEPT = default;
  };

  static constexpr bool IsImageTypeConst = std::is_const<TImage>::value;

  using QualifiedInternalPixelType = typename std::conditional<IsImageTypeConst, const InternalPixelType, InternalPixelType>::type;

  class AccessorFunctorInitializer final
  {
  private:
    ImageType& m_Image;
  public:
    explicit AccessorFunctorInitializer(ImageType& image) ITK_NOEXCEPT
      :
      m_Image(image)
    {
    }

    operator EmptyAccessorFunctor() const ITK_NOEXCEPT
    {
      return {};
    }

    operator AccessorFunctorType() const ITK_NOEXCEPT
    {
      AccessorFunctorType result = {};
      result.SetPixelAccessor(m_Image.GetPixelAccessor());
      result.SetBegin(m_Image.ImageType::GetBufferPointer());
      return result;
    }
  };


  // Helper class for begin() and end(), to ease proper initialization of an
  // ImageBufferRange iterator (either a 'QualifiedIterator' or a raw pixel pointer).
  class IteratorInitializer final
  {
  private:
    OptionalAccessorFunctorType m_OptionalAccessorFunctor;
    QualifiedInternalPixelType* m_InternalPixelPointer;
  public:
    explicit IteratorInitializer(
      OptionalAccessorFunctorType optionalAccessorFunctor,
      QualifiedInternalPixelType* internalPixelPointer) ITK_NOEXCEPT
      :
      m_OptionalAccessorFunctor(optionalAccessorFunctor),
      m_InternalPixelPointer(internalPixelPointer)
    {
    }

    // Converts to a 'QualifiedIterator' object.
    template <bool VIsConst>
    operator QualifiedIterator<VIsConst>() const ITK_NOEXCEPT
    {
      return QualifiedIterator<VIsConst>{m_OptionalAccessorFunctor, m_InternalPixelPointer};
    }

    // Converts to a raw pixel pointer.
    operator QualifiedInternalPixelType*() const ITK_NOEXCEPT
    {
      return m_InternalPixelPointer;
    }
  };


  // ImageBufferRange data members (strictly private):

  // The accessor functor of the image.
  OptionalAccessorFunctorType m_OptionalAccessorFunctor;

  // Pointer to the buffer of the image.
  QualifiedInternalPixelType* m_ImageBufferPointer = nullptr;

  // Image size.
  SizeValueType m_NumberOfPixels = 0;

public:
  using const_iterator = typename std::conditional<UsingPointerAsIterator,
    const InternalPixelType*, QualifiedIterator<true>>::type;
  using iterator = typename std::conditional<UsingPointerAsIterator,
    QualifiedInternalPixelType*, QualifiedIterator<IsImageTypeConst>>::type;
  using reverse_iterator = std::reverse_iterator<iterator>;
  using const_reverse_iterator = std::reverse_iterator<const_iterator>;


  ImageBufferRange() = default;


  explicit ImageBufferRange(ImageType& image)
    :
  // Note: Use parentheses instead of curly braces to initialize data members,
  // to avoid AppleClang 6.0.0.6000056 compile errors, "no viable conversion..."
  m_OptionalAccessorFunctor(AccessorFunctorInitializer{ image }),
  m_ImageBufferPointer{ image.ImageType::GetBufferPointer() },
  m_NumberOfPixels{ image.ImageType::GetBufferedRegion().GetNumberOfPixels() }
  {
  }


  iterator begin() const ITK_NOEXCEPT
  {
    return IteratorInitializer{ m_OptionalAccessorFunctor, m_ImageBufferPointer };
  }

  iterator end() const ITK_NOEXCEPT
  {
    return IteratorInitializer{ m_OptionalAccessorFunctor, m_ImageBufferPointer + m_NumberOfPixels, };
  }

  const_iterator cbegin() const ITK_NOEXCEPT
  {
    return this->begin();
  }

  const_iterator cend() const ITK_NOEXCEPT
  {
    return this->end();
  }

  reverse_iterator rbegin() const ITK_NOEXCEPT
  {
    return reverse_iterator(this->end());
  }

  reverse_iterator rend() const ITK_NOEXCEPT
  {
    return reverse_iterator(this->begin());
  }

  const_reverse_iterator crbegin() const ITK_NOEXCEPT
  {
    return this->rbegin();
  }

  const_reverse_iterator crend() const ITK_NOEXCEPT
  {
    return this->rend();
  }


  std::size_t size() const ITK_NOEXCEPT
  {
    return m_NumberOfPixels;
  }


  bool empty() const ITK_NOEXCEPT
  {
    return m_NumberOfPixels == 0;
  }


  typename QualifiedIterator<false>::reference operator[](const std::size_t n) const ITK_NOEXCEPT
  {
    assert(n < this->size());
    assert(n <= static_cast<std::size_t>(std::numeric_limits<std::ptrdiff_t>::max()));

    return this->begin()[static_cast<std::ptrdiff_t>(n)];
  }
};

template<typename TImage>
ImageBufferRange<TImage> MakeImageBufferRange(TImage* const image)
{
  if (image == nullptr)
  {
    return {};
  }
  else
  {
    return ImageBufferRange<TImage>{*image};
  }
}

} // namespace Experimental
} // namespace itk

#endif