PERF: Locally cache ComputeIndex() result in filters

Avoided calling `ImageConstIterator::ComputeIndex()` multiple times on one and
the same iterator, in one and the same iteration, by caching the computed index,
in the following filter member functions:

 - ValuedRegionalExtremaImageFilter::GenerateData
 - TransformToDisplacementFieldFilter::LinearThreadedGenerateData
 - ResampleImageFilter::LinearThreadedGenerateData
 - CannyEdgeDetectionImageFilter::HysteresisThresholding
 - HoughTransform2DLinesImageFilter::GetLines

Author: N-Dekker

Modules/Filtering/DisplacementField/include/itkTransformToDisplacementFieldFilter.hxx

@@ -230,12 +230,13 @@ TransformToDisplacementFieldFilter<TOutputImage, TParametersValueType>::LinearTh
   // Loop over the vector image, walk the output region for this thread.
   for (ImageScanlineIterator outIt(outputPtr, outputRegionForThread); !outIt.IsAtEnd(); outIt.NextLine())
   {
+    const auto computedIndex = outIt.ComputeIndex();
 
     // 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.ComputeIndex();
+    IndexType index = computedIndex;
     index[0] = largestPossibleRegion.GetIndex(0);
 
     outputPtr->TransformIndexToPhysicalPoint(index, outputPoint);
@@ -247,7 +248,7 @@ TransformToDisplacementFieldFilter<TOutputImage, TParametersValueType>::LinearTh
     inputPoint = transformPtr->TransformPoint(outputPoint);
     const typename PointType::VectorType endDisplacement = inputPoint - outputPoint;
 
-    IndexValueType scanlineIndex = outIt.ComputeIndex()[0];
+    IndexValueType scanlineIndex = computedIndex[0];
 
     while (!outIt.IsAtEndOfLine())
     {

Modules/Filtering/ImageFeature/include/itkCannyEdgeDetectionImageFilter.hxx

@@ -293,10 +293,11 @@ CannyEdgeDetectionImageFilter<TInputImage, TOutputImage>::HysteresisThresholding
 
     if (value > m_UpperThreshold)
     {
+      const auto computedIndex = oit.ComputeIndex();
       node = m_NodeStore->Borrow();
-      node->m_Value = oit.ComputeIndex();
+      node->m_Value = computedIndex;
       m_NodeList->PushFront(node);
-      FollowEdge(oit.ComputeIndex(), multiplyImageFilterOutput);
+      FollowEdge(computedIndex, multiplyImageFilterOutput);
     }
 
     ++oit;

Modules/Filtering/ImageFeature/include/itkHoughTransform2DLinesImageFilter.hxx

@@ -282,8 +282,9 @@ HoughTransform2DLinesImageFilter<TInputPixelType, TOutputPixelType>::GetLines()
           // Create the line.
           LineType::LinePointListType list; // Insert two points per line.
 
-          const double radius = it_input.ComputeIndex()[0];
-          const double teta = ((it_input.ComputeIndex()[1]) * 2 * Math::pi / this->GetAngleResolution()) - Math::pi;
+          const auto   computedIndex = it_input.ComputeIndex();
+          const double radius = computedIndex[0];
+          const double teta = (computedIndex[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 +327,8 @@ HoughTransform2DLinesImageFilter<TInputPixelType, TOutputPixelType>::GetLines()
           {
             for (double length = 0; length < m_DiscRadius; length += 1)
             {
-              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));
+              index[0] = static_cast<IndexValueType>(computedIndex[0] + length * std::cos(angle));
+              index[1] = static_cast<IndexValueType>(computedIndex[1] + length * std::sin(angle));
               if (postProcessImage->GetBufferedRegion().IsInside(index))
               {
                 postProcessImage->SetPixel(index, 0);

Modules/Filtering/ImageGrid/include/itkResampleImageFilter.hxx

@@ -466,14 +466,16 @@ ResampleImageFilter<TInputImage, TOutputImage, TInterpolatorPrecisionType, TTran
     // Determine the continuous index of the first and end pixel of output
     // scan line when mapped to the input coordinate frame.
 
-    IndexType index = outIt.ComputeIndex();
+    const auto computedIndex = outIt.ComputeIndex();
+
+    IndexType index = computedIndex;
     index[0] = firstIndexValueOfLargestPossibleRegion;
 
     const ContinuousInputIndexType startIndex = transformIndex(index);
     index[0] += firstSizeValueOfLargestPossibleRegion;
     const auto vectorFromStartIndex = transformIndex(index) - startIndex;
 
-    IndexValueType scanlineIndex = outIt.ComputeIndex()[0];
+    IndexValueType scanlineIndex = computedIndex[0];
 
 
     while (!outIt.IsAtEndOfLine())

Modules/Filtering/MathematicalMorphology/include/itkValuedRegionalExtremaImageFilter.hxx

@@ -130,8 +130,10 @@ ValuedRegionalExtremaImageFilter<TInputImage, TOutputImage, TFunction1, TFunctio
       // already visited this pixel and don't need to do so again
       if (compareOut(V, m_MarkerValue))
       {
+        const auto computedIndex = outIt.ComputeIndex();
+
         // reposition the input iterator
-        inNIt += outIt.ComputeIndex() - inNIt.GetIndex();
+        inNIt += computedIndex - inNIt.GetIndex();
 
         auto Cent = static_cast<InputImagePixelType>(V);
 
@@ -156,7 +158,7 @@ ValuedRegionalExtremaImageFilter<TInputImage, TOutputImage, TFunction1, TFunctio
             // indexes of all neighbors with value V on the stack. The
             // process terminates when the stack is empty.
 
-            outNIt += outIt.ComputeIndex() - outNIt.GetIndex();
+            outNIt += computedIndex - outNIt.GetIndex();
 
             OutputImagePixelType NVal;
             OutIndexType         idx;