From ceb157d634d7e4801781c92ea8e04b27621845ec Mon Sep 17 00:00:00 2001
From: Niels Dekker <N.Dekker@lumc.nl>
Date: Thu, 6 Aug 2020 10:14:49 +0200
Subject: [PATCH] BUG: Fix issue #1950, ImageMaskSpatialObject access outside
 image buffer

Fixed issue #1950, "ImageMaskSpatialObject tries to access pixels
outside the image buffer (segfault)".

In the original code, `TransformPhysicalPointToContinuousIndex` did
estimate whether the specified point was inside the image buffer, but
then `GetInterpolator()->EvaluateAtContinuousIndex(index)` did in some
cases still try to access a pixel outside the image buffer.

This fix avoids using an interpolator. It only accesses a pixel when its
index is inside the buffered region.

The use of an interpolator appears less relevant for an image mask than
for other spatial objects, as for each mask pixel value, it is usually
only interesting to know whether it is zero or non-zero.

Added ImageMaskSpatialObject.CornerPointIsNotInsideMaskOfZeroValues unit
test.
---
 .../include/itkImageMaskSpatialObject.hxx      | 18 +++++-------------
 .../test/itkImageMaskSpatialObjectGTest.cxx    | 17 +++++++++++++++++
 2 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/Modules/Core/SpatialObjects/include/itkImageMaskSpatialObject.hxx b/Modules/Core/SpatialObjects/include/itkImageMaskSpatialObject.hxx
index 85a2cbdfbe5..94b0148675a 100644
--- a/Modules/Core/SpatialObjects/include/itkImageMaskSpatialObject.hxx
+++ b/Modules/Core/SpatialObjects/include/itkImageMaskSpatialObject.hxx
@@ -40,20 +40,12 @@ template <unsigned int TDimension, typename TPixel>
 bool
 ImageMaskSpatialObject<TDimension, TPixel>::IsInsideInObjectSpace(const PointType & point) const
 {
-  typename Superclass::InterpolatorType::ContinuousIndexType index;
-  if (this->GetImage()->TransformPhysicalPointToContinuousIndex(point, index))
-  {
-    using InterpolatorOutputType = typename InterpolatorType::OutputType;
-    bool insideMask = (Math::NotExactlyEquals(DefaultConvertPixelTraits<InterpolatorOutputType>::GetScalarValue(
-                                                this->GetInterpolator()->EvaluateAtContinuousIndex(index)),
-                                              NumericTraits<PixelType>::ZeroValue()));
-    if (insideMask)
-    {
-      return true;
-    }
-  }
+  const ImageType * const image = this->GetImage();
+
+  const IndexType index = image->TransformPhysicalPointToIndex(point);
 
-  return false;
+  return image->GetBufferedRegion().IsInside(index) &&
+         Math::NotExactlyEquals(image->GetPixel(index), NumericTraits<PixelType>::ZeroValue());
 }
 
 
diff --git a/Modules/Core/SpatialObjects/test/itkImageMaskSpatialObjectGTest.cxx b/Modules/Core/SpatialObjects/test/itkImageMaskSpatialObjectGTest.cxx
index b04a86cba50..d6715fd855e 100644
--- a/Modules/Core/SpatialObjects/test/itkImageMaskSpatialObjectGTest.cxx
+++ b/Modules/Core/SpatialObjects/test/itkImageMaskSpatialObjectGTest.cxx
@@ -306,3 +306,20 @@ TEST(ImageMaskSpatialObject, IsInsideIndependentOfDistantPixels)
 
 
 #endif
+
+
+// Tests that IsInsideInObjectSpace returns false for a corner point, when the
+// mask image is filled with zero values. This test would sometimes fail on
+// ITK v5.0.1 and v5.1.0
+TEST(ImageMaskSpatialObject, CornerPointIsNotInsideMaskOfZeroValues)
+{
+  // Create a mask image, and fill the image with zero vales.
+  const auto image = itk::Image<unsigned char>::New();
+  image->SetRegions(itk::Size<>{ { 2, 2 } });
+  image->Allocate(true);
+
+  const auto imageMaskSpatialObject = itk::ImageMaskSpatialObject<2>::New();
+  imageMaskSpatialObject->SetImage(image);
+  const double cornerPoint[] = { 1.5, 1.5 };
+  ASSERT_FALSE(imageMaskSpatialObject->IsInsideInObjectSpace(cornerPoint));
+}