text: /*=========================================================================
   *
   *  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
   *
   *  Unless required by applicable law or agreed to in writing, software
   *  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.
   *
   *=========================================================================*/
  #ifndef itkTransformToDisplacementFieldFilter_hxx
  #define itkTransformToDisplacementFieldFilter_hxx
  
  #include "itkTransformToDisplacementFieldFilter.h"
  
  #include "itkIdentityTransform.h"
  #include "itkProgressReporter.h"
  #include "itkImageRegionIteratorWithIndex.h"
  #include "itkImageScanlineIterator.h"
  
  namespace itk
  {
  
  template< typename TOutputImage, typename TParametersValueType>
  TransformToDisplacementFieldFilter< TOutputImage, TParametersValueType>
  ::TransformToDisplacementFieldFilter():
    m_UseReferenceImage( false )
  {
    this->m_OutputSpacing.Fill(1.0);
    this->m_OutputOrigin.Fill(0.0);
    this->m_OutputDirection.SetIdentity();
  
    this->m_Size.Fill(0);
    this->m_OutputStartIndex.Fill(0);
  
    this->SetNumberOfRequiredInputs( 1 );
    this->SetPrimaryInputName( "Transform" );
  
    //  #1 "ReferenceImage" optional
    Self::AddOptionalInputName("ReferenceImage",1);
    this->DynamicMultiThreadingOn();
  }
  
  
  template< typename TOutputImage, typename TParametersValueType>
  void
  TransformToDisplacementFieldFilter< TOutputImage, TParametersValueType>
  ::PrintSelf(std::ostream & os, Indent indent) const
  {
    Superclass::PrintSelf(os, indent);
  
    os << indent << "Size: " << this->m_Size << std::endl;
    os << indent << "OutputStartIndex: " << this->m_OutputStartIndex << std::endl;
    os << indent << "OutputSpacing: " << this->m_OutputSpacing << std::endl;
    os << indent << "OutputOrigin: " << this->m_OutputOrigin << std::endl;
    os << indent << "OutputDirection: " << this->m_OutputDirection << std::endl;
    os << indent << "UseReferenceImage: ";
    if( this->m_UseReferenceImage )
      {
      os << "On" << std::endl;
      }
    else
      {
      os << "Off" << std::endl;
      }
  }
  
  
  template< typename TOutputImage, typename TParametersValueType>
  void
  TransformToDisplacementFieldFilter< TOutputImage, TParametersValueType>
  ::SetOutputSpacing(const SpacePrecisionType *spacing)
  {
    SpacingType ss(spacing);
    this->SetOutputSpacing(ss);
  }
  
  
  template< typename TOutputImage, typename TParametersValueType>
  void
  TransformToDisplacementFieldFilter< TOutputImage, TParametersValueType>
  ::SetOutputOrigin(const SpacePrecisionType *origin)
  {
    OriginType pp(origin);
    this->SetOutputOrigin(pp);
  }
  
  template< typename TOutputImage, typename TParametersValueType>
  void
  TransformToDisplacementFieldFilter< TOutputImage, TParametersValueType>
  ::SetInput( const TransformInputType * input )
  {
    if( input != itkDynamicCastInDebugMode< TransformInputType * >( this->ProcessObject::GetPrimaryInput() ) )
      {
      // Process object is not const-correct so the const_cast is required here
      this->ProcessObject::SetNthInput( 0, const_cast< TransformInputType * >( input ) );
      this->Modified();
      }
  }
  
  template< typename TOutputImage, typename TParametersValueType>
  const typename TransformToDisplacementFieldFilter< TOutputImage, TParametersValueType>::TransformInputType *
  TransformToDisplacementFieldFilter< TOutputImage, TParametersValueType>
  ::GetInput() const
  {
    return itkDynamicCastInDebugMode< const TransformInputType * >( this->GetPrimaryInput() );
  }
  
  
  template< typename TOutputImage, typename TParametersValueType>
  void
  TransformToDisplacementFieldFilter< TOutputImage, TParametersValueType>
  ::GenerateOutputInformation()
  {
    OutputImageType * output = this->GetOutput();
    if ( !output )
      {
      return;
      }
  
    const ReferenceImageBaseType *referenceImage = this->GetReferenceImage();
  
    // Set the size of the output region
    if ( m_UseReferenceImage && referenceImage )
      {
      output->SetLargestPossibleRegion(
        referenceImage->GetLargestPossibleRegion() );
      }
    else
      {
      typename TOutputImage::RegionType outputLargestPossibleRegion;
      outputLargestPossibleRegion.SetSize(m_Size);
      outputLargestPossibleRegion.SetIndex(m_OutputStartIndex);
      output->SetLargestPossibleRegion(outputLargestPossibleRegion);
      }
  
    // Set spacing and origin
    if ( m_UseReferenceImage && referenceImage )
      {
      output->SetSpacing( referenceImage->GetSpacing() );
      output->SetOrigin( referenceImage->GetOrigin() );
      output->SetDirection( referenceImage->GetDirection() );
      }
    else
      {
      output->SetSpacing(m_OutputSpacing);
      output->SetOrigin(m_OutputOrigin);
      output->SetDirection(m_OutputDirection);
      }
  }
  
  
  template< typename TOutputImage, typename TParametersValueType>
  void
  TransformToDisplacementFieldFilter< TOutputImage, TParametersValueType>
  ::DynamicThreadedGenerateData( const OutputImageRegionType & outputRegionForThread )
  {
    const TransformType * transform = this->GetInput()->Get();
    // Check whether we can use a fast path for resampling. Fast path
    // can be used if the transformation is linear. Transform respond
    // to the IsLinear() call.
    if ( transform->IsLinear() )
      {
      this->LinearThreadedGenerateData(outputRegionForThread);
      return;
      }
  
    // Otherwise, we use the normal method where the transform is called
    // for computing the transformation of every point.
    this->NonlinearThreadedGenerateData(outputRegionForThread);
  }
  
  
  template< typename TOutputImage, typename TParametersValueType>
  void
  TransformToDisplacementFieldFilter< TOutputImage, TParametersValueType>
  ::NonlinearThreadedGenerateData( const OutputImageRegionType & outputRegionForThread )
  {
    // Get the output pointer
    OutputImageType * output = this->GetOutput();
    const TransformType * transform = this->GetInput()->Get();
  
    // Create an iterator that will walk the output region for this thread.
    using OutputIteratorType = ImageScanlineIterator< TOutputImage >;
    OutputIteratorType outIt( output, outputRegionForThread );
  
    // Define a few variables that will be used to translate from an input pixel
    // to an output pixel
    PointType outputPoint;         // Coordinates of output pixel
    PointType transformedPoint;    // Coordinates of transformed pixel
    PixelType displacement;         // the difference
  
    // Walk the output region
    outIt.GoToBegin();
    while ( !outIt.IsAtEnd() )
      {
      while ( !outIt.IsAtEndOfLine() )
        {
        // Determine the index of the current output pixel
        output->TransformIndexToPhysicalPoint( outIt.GetIndex(), outputPoint );
  
        // Compute corresponding input pixel position
        transformedPoint = transform->TransformPoint( outputPoint );
  
        displacement = transformedPoint - outputPoint;
        outIt.Set( displacement );
        ++outIt;
        }
      outIt.NextLine();
      }
  }
  
  
  template< typename TOutputImage, typename TParametersValueType>
  void
  TransformToDisplacementFieldFilter< TOutputImage, TParametersValueType>
  ::LinearThreadedGenerateData( const OutputImageRegionType & outputRegionForThread )
  {
    // Get the output pointer
    OutputImageType * outputPtr = this->GetOutput();
    const TransformType * transformPtr = this->GetInput()->Get();
  
    const OutputImageRegionType &largestPossibleRegion = outputPtr->GetLargestPossibleRegion();
  
    // Create an iterator that will walk the output region for this thread.
    using OutputIteratorType = ImageScanlineIterator< TOutputImage >;
    OutputIteratorType outIt( outputPtr, outputRegionForThread );
  
    // Define a few indices that will be used to translate from an input pixel
    // to an output pixel
    PointType outputPoint;         // Coordinates of current output pixel
    PointType inputPoint;
  
  
    // loop over the vector image
    while ( !outIt.IsAtEnd() )
      {
  
      // Compare with the ResampleImageFilter
      // The region may be split along the fast scan-line direction, so
      // the computation is done for the beginning and end of the largest
      // possible region to improve consistent numerics.
      IndexType index  = outIt.GetIndex();
      index[0] = largestPossibleRegion.GetIndex(0);
  
      outputPtr->TransformIndexToPhysicalPoint(index, outputPoint);
      inputPoint = transformPtr->TransformPoint(outputPoint);
      const typename PointType::VectorType startDisplacement = inputPoint - outputPoint;
  
      index[0] += largestPossibleRegion.GetSize(0);
      outputPtr->TransformIndexToPhysicalPoint(index, outputPoint);
      inputPoint = transformPtr->TransformPoint(outputPoint);
      const typename PointType::VectorType endDisplacement = inputPoint - outputPoint;
  
      IndexValueType scanlineIndex = outIt.GetIndex()[0];
  
      while ( !outIt.IsAtEndOfLine() )
        {
        // Perform linear interpolation between startIndex and endIndex
        const double alpha = (scanlineIndex - largestPossibleRegion.GetIndex(0) ) / double(largestPossibleRegion.GetSize(0));
        const double oneMinusAlpha = 1.0 - alpha;
  
        PixelType displacement;
        for (unsigned int i = 0; i < ImageDimension; ++i)
          {
          displacement[i] = oneMinusAlpha*startDisplacement[i] + alpha*endDisplacement[i];
          }
  
  
        outIt.Set( displacement );
        ++outIt;
        ++scanlineIndex;
        }
  
      outIt.NextLine();
      }
  }
  
  } // end namespace itk
  
  #endif
  