itkImageRegionReverseConstIterator.h

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 *
 *  Copyright NumFOCUS
 *
 *  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
 *
 *         https://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
 *  limitations under the License.
 *
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#ifndef itkImageRegionReverseConstIterator_h
#define itkImageRegionReverseConstIterator_h
 
#include "itkImageReverseConstIterator.h"
#include "itkImageRegionIterator.h"
#include <type_traits> // For remove_const_t.
 
namespace itk
{
template <typename TImage>
class ITK_TEMPLATE_EXPORT ImageRegionReverseConstIterator : public ImageReverseConstIterator<TImage>
{
public:
  using Self = ImageRegionReverseConstIterator;
  using Superclass = ImageReverseConstIterator<TImage>;

  using typename Superclass::IndexType;

  using typename Superclass::SizeType;

  using typename Superclass::OffsetType;

  using typename Superclass::RegionType;

  using typename Superclass::ImageType;

  using typename Superclass::PixelContainer;
  using PixelContainerPointer = typename PixelContainer::Pointer;

  using typename Superclass::InternalPixelType;

  using typename Superclass::PixelType;

  using typename Superclass::AccessorType;

  itkOverrideGetNameOfClassMacro(ImageRegionReverseConstIterator);

  ImageRegionReverseConstIterator()
    : Superclass()
  {}

  ImageRegionReverseConstIterator(const TImage * ptr, const RegionType & region)
    : Superclass(ptr, region)
    , m_SpanBeginOffset(this->m_BeginOffset)
    , m_SpanEndOffset(this->m_BeginOffset - static_cast<OffsetValueType>(this->m_Region.GetSize()[0]))
  {}

  ImageRegionReverseConstIterator(const ImageConstIterator<TImage> & it)
    : Superclass(it)
  {
    this->InitializeSpans();
  }

  ImageRegionReverseConstIterator(const ImageReverseConstIterator<TImage> & it)
    : Superclass(it)
  {
    this->InitializeSpans();
  }

  ImageRegionReverseConstIterator(const ImageRegionIterator<TImage> & it)
    : Superclass(it)
  {
    this->InitializeSpans();
  }

  void
  GoToBegin()
  {
    Superclass::GoToBegin();
 
    // reset the span offsets
    m_SpanBeginOffset = this->m_BeginOffset;
    m_SpanEndOffset = this->m_BeginOffset - static_cast<OffsetValueType>(this->m_Region.GetSize()[0]);
  }

  void
  GoToEnd()
  {
    Superclass::GoToEnd();
 
    // reset the span offsets
    m_SpanEndOffset = this->m_EndOffset;
    m_SpanBeginOffset = m_SpanEndOffset + static_cast<OffsetValueType>(this->m_Region.GetSize()[0]);
  }

  void
  SetIndex(const IndexType & ind) override
  {
    Superclass::SetIndex(ind);
    this->InitializeSpans();
  }

  Self &
  operator++()
  {
    if (--this->m_Offset <= m_SpanEndOffset)
    {
      // We have past the beginning of the span (row), need to wrap around.
 
      // First move forward one pixel, because we are going to use a different
      // algorithm to compute the next pixel
      this->m_Offset++;
 
      // Get the index of the first pixel on the span (row)
      typename ImageConstIterator<TImage>::IndexType ind =
        this->m_Image->ComputeIndex(static_cast<OffsetValueType>(this->m_Offset));
 
      const typename ImageConstIterator<TImage>::IndexType & startIndex = this->m_Region.GetIndex();
      const typename ImageConstIterator<TImage>::SizeType &  size = this->m_Region.GetSize();
 
      // Decrement along a row, then wrap at the beginning of the region row.
 
      // Check to see if we are past the first pixel in the region
      // Note that --ind[0] moves to the previous pixel along the row.
      bool done = (--ind[0] == startIndex[0] - 1);
      for (unsigned int i = 1; done && i < this->ImageIteratorDimension; ++i)
      {
        done = (ind[i] == startIndex[i]);
      }
 
      // if the iterator is outside the region (but not past region begin) then
      // we need to wrap around the region
      unsigned int dim = 0;
      if (!done)
      {
        while ((dim < this->ImageIteratorDimension - 1) && (ind[dim] < startIndex[dim]))
        {
          ind[dim] = startIndex[dim] + static_cast<OffsetValueType>(size[dim]) - 1;
          ind[++dim]--;
        }
      }
      this->m_Offset = this->m_Image->ComputeOffset(ind);
      m_SpanBeginOffset = this->m_Offset;
      m_SpanEndOffset = m_SpanBeginOffset - static_cast<OffsetValueType>(size[0]);
    }
    return *this;
  }

  Self &
  operator--()
  {
    if (++this->m_Offset >= m_SpanBeginOffset)
    {
      // We have reached the end of the span (row), need to wrap around.
 
      // First back up one pixel, because we are going to use a different
      // algorithm to compute the next pixel
      --this->m_Offset;
 
      // Get the index of the last pixel on the span (row)
      typename ImageConstIterator<TImage>::IndexType ind =
        this->m_Image->ComputeIndex(static_cast<OffsetValueType>(this->m_Offset));
 
      const typename ImageIterator<TImage>::IndexType & startIndex = this->m_Region.GetIndex();
      const typename ImageIterator<TImage>::SizeType &  size = this->m_Region.GetSize();
 
      // Increment along a row, then wrap at the end of the region row.
      // Check to see if we are past the last pixel in the region
      // Note that ++ind[0] moves to the next pixel along the row.
      bool done = (++ind[0] == startIndex[0] + static_cast<OffsetValueType>(size[0]));
      for (unsigned int i = 1; done && i < this->ImageIteratorDimension; ++i)
      {
        done = (ind[i] == startIndex[i] + static_cast<OffsetValueType>(size[i]) - 1);
      }
 
      // if the iterator is outside the region (but not past region end) then
      // we need to wrap around the region
      unsigned int dim = 0;
      if (!done)
      {
        while ((dim < this->ImageIteratorDimension - 1) &&
               (ind[dim] > startIndex[dim] + static_cast<OffsetValueType>(size[dim]) - 1))
        {
          ind[dim] = startIndex[dim];
          ind[++dim]++;
        }
      }
      this->m_Offset = this->m_Image->ComputeOffset(ind);
      m_SpanBeginOffset = this->m_Offset;
      m_SpanEndOffset = this->m_Offset - static_cast<OffsetValueType>(size[0]);
    }
    return *this;
  }
 
protected:
  SizeValueType m_SpanBeginOffset{}; // offset to last pixel in the row
  SizeValueType m_SpanEndOffset{};   // offset to one pixel before the row
 
private:
  void
  InitializeSpans()
  {
    const IndexType ind = this->GetIndex();
    const auto      rowSize = static_cast<OffsetValueType>(this->m_Region.GetSize()[0]);
    m_SpanBeginOffset = this->m_Offset + rowSize - 1 - (ind[0] - this->m_Region.GetIndex()[0]);
    m_SpanEndOffset = m_SpanBeginOffset - rowSize;
  }
};
 
// Deduction guide for class template argument deduction (CTAD).
template <typename TImage>
ImageRegionReverseConstIterator(SmartPointer<TImage>, const typename TImage::RegionType &)
  -> ImageRegionReverseConstIterator<std::remove_const_t<TImage>>;
 
} // end namespace itk
 
#endif