PERF: Locally cache ComputeIndex() result in Watershed Segmenter

N-Dekker · N-Dekker · commit c60439c4a142 · 2026-02-15T17:56:58.000+01:00
Avoided calling `ImageConstIterator::ComputeIndex()` multiple times on one and
the same iterator, in one and the same iteration, by caching the computed index,
in `watershed::Segmenter::GradientDescent`
diff --git a/Modules/Segmentation/Watersheds/include/itkWatershedSegmenter.hxx b/Modules/Segmentation/Watersheds/include/itkWatershedSegmenter.hxx
@@ -820,8 +820,9 @@ Segmenter<TInputImage>::GradientDescent(InputImageTypePointer img, ImageRegionTy
   {
     if (it.Get() == NULL_LABEL)
     {
-      valueIt.SetLocation(it.ComputeIndex());
-      labelIt.SetLocation(it.ComputeIndex());
+      const auto computeIndex = it.ComputeIndex();
+      valueIt.SetLocation(computeIndex);
+      labelIt.SetLocation(computeIndex);
       IdentifierType newLabel = NULL_LABEL; // Follow the path of steep-
       while (newLabel == NULL_LABEL)        // est descent until a label
       {

Original file line number	Diff line number	Diff line change
`@@ -820,8 +820,9 @@ Segmenter<TInputImage>::GradientDescent(InputImageTypePointer img, ImageRegionTy`
`820`	`820`	`{`
`821`	`821`	`if (it.Get() == NULL_LABEL)`
`822`	`822`	`{`
`823`		`- valueIt.SetLocation(it.ComputeIndex());`
`824`		`- labelIt.SetLocation(it.ComputeIndex());`
	`823`	`+ const auto computeIndex = it.ComputeIndex();`
	`824`	`+ valueIt.SetLocation(computeIndex);`
	`825`	`+ labelIt.SetLocation(computeIndex);`
`825`	`826`	`IdentifierType newLabel = NULL_LABEL; // Follow the path of steep-`
`826`	`827`	`while (newLabel == NULL_LABEL) // est descent until a label`
`827`	`828`	`{`