STYLE: Replace GetIndex() calls on iterators with ComputeIndex()

Replaced function calls of the form `iterator.GetIndex()` with
`iterator.ComputeIndex()`, for iterators derived from `ImageConstIterator`. For
those iterators, it may take a relatively expensive computation to get the index.
Using `ComputeIndex()` instead of the equivalent `GetIndex()` aims to raise
awareness of the potential performance cost of those function calls.

Author: N-Dekker

Modules/Core/Common/include/itkImageReverseConstIterator.h

@@ -207,7 +207,7 @@ class ITK_TEMPLATE_EXPORT ImageReverseConstIterator
   {
 
 
-    const IndexType ind = it.GetIndex();
+    const IndexType ind = it.ComputeIndex();
 
     m_Offset = m_Image->ComputeOffset(ind);
 

Modules/Core/Common/include/itkImageScanlineConstIterator.h

@@ -117,7 +117,7 @@ class ITK_TEMPLATE_EXPORT ImageScanlineConstIterator : public ImageConstIterator
   {
     this->ImageConstIterator<TImage>::operator=(it);
 
-    IndexType ind = this->GetIndex();
+    IndexType ind = this->ComputeIndex();
     m_SpanEndOffset = this->m_Offset + static_cast<OffsetValueType>(this->m_Region.GetSize()[0]) -
                       (ind[0] - this->m_Region.GetIndex()[0]);
     m_SpanBeginOffset = m_SpanEndOffset - static_cast<OffsetValueType>(this->m_Region.GetSize()[0]);

Modules/Filtering/DisplacementField/include/itkInvertDisplacementFieldImageFilter.hxx

@@ -194,7 +194,7 @@ InvertDisplacementFieldImageFilter<TInputImage, TOutputImage>::DynamicThreadedGe
       }
       update = ItI.Get() + update * this->m_Epsilon;
       ItI.Set(update);
-      typename DisplacementFieldType::IndexType index = ItI.GetIndex();
+      typename DisplacementFieldType::IndexType index = ItI.ComputeIndex();
       if (this->m_EnforceBoundaryCondition)
       {
         for (unsigned int d = 0; d < ImageDimension; ++d)

Modules/Filtering/DisplacementField/include/itkIterativeInverseDisplacementFieldImageFilter.hxx

@@ -98,7 +98,7 @@ IterativeInverseDisplacementFieldImageFilter<TInputImage, TOutputImage>::Generat
     while (!OutputIt.IsAtEnd())
     {
       // get the output image index
-      const OutputImageIndexType index = OutputIt.GetIndex();
+      const OutputImageIndexType index = OutputIt.ComputeIndex();
       OutputImagePointType       originalPoint;
       outputPtr->TransformIndexToPhysicalPoint(index, originalPoint);
 

Modules/Filtering/DisplacementField/include/itkTransformToDisplacementFieldFilter.hxx

@@ -192,7 +192,7 @@ TransformToDisplacementFieldFilter<TOutputImage, TParametersValueType>::Nonlinea
     while (!outIt.IsAtEndOfLine())
     {
       // Determine the index of the current output pixel
-      output->TransformIndexToPhysicalPoint(outIt.GetIndex(), outputPoint);
+      output->TransformIndexToPhysicalPoint(outIt.ComputeIndex(), outputPoint);
 
       // Compute corresponding input pixel position
       transformedPoint = transform->TransformPoint(outputPoint);
@@ -235,7 +235,7 @@ TransformToDisplacementFieldFilter<TOutputImage, TParametersValueType>::LinearTh
     // 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();
+    IndexType index = outIt.ComputeIndex();
     index[0] = largestPossibleRegion.GetIndex(0);
 
     outputPtr->TransformIndexToPhysicalPoint(index, outputPoint);
@@ -247,7 +247,7 @@ TransformToDisplacementFieldFilter<TOutputImage, TParametersValueType>::LinearTh
     inputPoint = transformPtr->TransformPoint(outputPoint);
     const typename PointType::VectorType endDisplacement = inputPoint - outputPoint;
 
-    IndexValueType scanlineIndex = outIt.GetIndex()[0];
+    IndexValueType scanlineIndex = outIt.ComputeIndex()[0];
 
     while (!outIt.IsAtEndOfLine())
     {

Modules/Filtering/ImageFeature/include/itkCannyEdgeDetectionImageFilter.hxx

@@ -294,9 +294,9 @@ CannyEdgeDetectionImageFilter<TInputImage, TOutputImage>::HysteresisThresholding
     if (value > m_UpperThreshold)
     {
       node = m_NodeStore->Borrow();
-      node->m_Value = oit.GetIndex();
+      node->m_Value = oit.ComputeIndex();
       m_NodeList->PushFront(node);
-      FollowEdge(oit.GetIndex(), multiplyImageFilterOutput);
+      FollowEdge(oit.ComputeIndex(), multiplyImageFilterOutput);
     }
 
     ++oit;

Modules/Filtering/ImageFeature/include/itkHoughTransform2DLinesImageFilter.hxx

@@ -282,8 +282,8 @@ HoughTransform2DLinesImageFilter<TInputPixelType, TOutputPixelType>::GetLines()
           // Create the line.
           LineType::LinePointListType list; // Insert two points per line.
 
-          const double radius = it_input.GetIndex()[0];
-          const double teta = ((it_input.GetIndex()[1]) * 2 * Math::pi / this->GetAngleResolution()) - Math::pi;
+          const double radius = it_input.ComputeIndex()[0];
+          const double teta = ((it_input.ComputeIndex()[1]) * 2 * Math::pi / this->GetAngleResolution()) - Math::pi;
           const double Vx = radius * std::cos(teta);
           const double Vy = radius * std::sin(teta);
           const double norm = std::sqrt(Vx * Vx + Vy * Vy);
@@ -326,8 +326,8 @@ HoughTransform2DLinesImageFilter<TInputPixelType, TOutputPixelType>::GetLines()
           {
             for (double length = 0; length < m_DiscRadius; length += 1)
             {
-              index[0] = static_cast<IndexValueType>(it_input.GetIndex()[0] + length * std::cos(angle));
-              index[1] = static_cast<IndexValueType>(it_input.GetIndex()[1] + length * std::sin(angle));
+              index[0] = static_cast<IndexValueType>(it_input.ComputeIndex()[0] + length * std::cos(angle));
+              index[1] = static_cast<IndexValueType>(it_input.ComputeIndex()[1] + length * std::sin(angle));
               if (postProcessImage->GetBufferedRegion().IsInside(index))
               {
                 postProcessImage->SetPixel(index, 0);

Modules/Filtering/ImageGradient/include/itkDifferenceOfGaussiansGradientImageFilter.hxx

@@ -76,7 +76,7 @@ DifferenceOfGaussiansGradientImageFilter<TInputImage, TDataType>::GenerateData()
   for (; !outIt.IsAtEnd(); ++outIt)
   {
     // determine the index of the output pixel
-    outputIndex = outIt.GetIndex();
+    outputIndex = outIt.ComputeIndex();
 
     // is the current index an acceptable distance from the edges
     // of the image?

Modules/Filtering/ImageGrid/include/itkBinShrinkImageFilter.hxx

@@ -155,7 +155,7 @@ BinShrinkImageFilter<TInputImage, TOutputImage>::DynamicThreadedGenerateData(
   for (ImageScanlineIterator outputIterator(outputPtr, outputRegionForThread); !outputIterator.IsAtEnd();
        outputIterator.NextLine())
   {
-    const OutputIndexType outputIndex = outputIterator.GetIndex();
+    const OutputIndexType outputIndex = outputIterator.ComputeIndex();
 
     auto                 offset = offsets.begin();
     const InputIndexType startInputIndex = outputIndex * factorSize;

Modules/Filtering/ImageGrid/include/itkExpandImageFilter.hxx

@@ -113,7 +113,7 @@ ExpandImageFilter<TInputImage, TOutputImage>::DynamicThreadedGenerateData(
   // Walk the output region, and interpolate the input image
   for (ImageScanlineIterator outIt(outputPtr, outputRegionForThread); !outIt.IsAtEnd(); outIt.NextLine())
   {
-    const typename OutputImageType::IndexType outputIndex = outIt.GetIndex();
+    const typename OutputImageType::IndexType outputIndex = outIt.ComputeIndex();
 
 
     // Determine the input pixel location associated with this output