Ensure that field data is copied to output of vtkExtractBlocks

Add an actual test of vtkExtractBlock to TestExtractBlock. Previously,
the test only exercised vtkExtractSelection with a vtkSelection of
blocks.

Filters/Extraction/Testing/Cxx/TestExtractBlock.cxx

@@ -12,9 +12,13 @@
      PURPOSE.  See the above copyright notice for more information.
 
 =========================================================================*/
-// This tests an extraction of a block from vtkSelection
+// This tests an extraction of a block using first vtkExtractBlock then
+// a block selection from a vtkSelection and vtkExtractSelection
 
+#include <vtkExtractBlock.h>
 #include <vtkExtractSelection.h>
+#include <vtkFieldData.h>
+#include <vtkIntArray.h>
 #include <vtkMultiBlockDataSet.h>
 #include <vtkNew.h>
 #include <vtkSelectionSource.h>
@@ -37,6 +41,39 @@ int TestExtractBlock(int vtkNotUsed(argc), char* vtkNotUsed(argv)[])
   mb0->SetBlock(0, GetSphere(0, 0, -2));
   mb0->SetBlock(1, GetSphere(0, 0, 2));
 
+  // Add a field data to the multiblock dataset
+  vtkNew<vtkIntArray> fieldData;
+  std::string globalIdName("GlobalID");
+  fieldData->SetName(globalIdName.c_str());
+  fieldData->SetNumberOfComponents(1);
+  fieldData->SetNumberOfTuples(1);
+  fieldData->SetValue(0, 5);
+  mb0->GetFieldData()->AddArray(fieldData);
+
+  // Test vtkExtractBlock
+  vtkNew<vtkExtractBlock> extractBlock;
+  extractBlock->AddIndex(2);
+  extractBlock->SetPruneOutput(1);
+  extractBlock->SetInputData(mb0);
+  extractBlock->Update();
+
+  auto output = vtkMultiBlockDataSet::SafeDownCast(extractBlock->GetOutput());
+  if (output->GetBlock(0) == nullptr)
+  {
+    std::cerr << "Invalid block extracted by vtkExtractBlock. Should be block 0." << std::endl;
+    std::cerr << *output << std::endl;
+    return EXIT_FAILURE;
+  }
+  vtkIntArray* outputFDArray =
+    vtkIntArray::SafeDownCast(output->GetFieldData()->GetArray(globalIdName.c_str()));
+  if (outputFDArray == nullptr || outputFDArray->GetValue(0) != 5)
+  {
+    std::cerr << "Field data not copied to output. Should be." << std::endl;
+    std::cerr << *output << std::endl;
+    return EXIT_FAILURE;
+  }
+
+  // Now test a block selection
   vtkNew<vtkSelectionSource> selectionSource;
   selectionSource->SetContentType(vtkSelectionNode::BLOCKS);
   selectionSource->AddBlock(2);
@@ -46,13 +83,19 @@ int TestExtractBlock(int vtkNotUsed(argc), char* vtkNotUsed(argv)[])
   extract->SetSelectionConnection(selectionSource->GetOutputPort());
   extract->Update();
 
-  auto output = vtkMultiBlockDataSet::SafeDownCast(extract->GetOutput());
+  output = vtkMultiBlockDataSet::SafeDownCast(extract->GetOutput());
   if (output->GetBlock(0) != nullptr || output->GetBlock(1) == nullptr)
   {
     std::cerr << "Invalid block extracted. Should be block 1." << std::endl;
     std::cerr << *output << std::endl;
     return EXIT_FAILURE;
   }
+  outputFDArray = vtkIntArray::SafeDownCast(output->GetFieldData()->GetArray(globalIdName.c_str()));
+  if (outputFDArray == nullptr || outputFDArray->GetValue(0) != 5)
+  {
+    std::cerr << "Field data not copied to output. Should be." << std::endl;
+    return EXIT_FAILURE;
+  }
 
   // now extract non-leaf block.
   selectionSource->RemoveAllBlocks();

Filters/Extraction/vtkExtractBlock.cxx

@@ -16,6 +16,7 @@
 
 #include "vtkDataObjectTreeIterator.h"
 #include "vtkDataSet.h"
+#include "vtkFieldData.h"
 #include "vtkInformation.h"
 #include "vtkInformationIntegerKey.h"
 #include "vtkInformationVector.h"
@@ -197,6 +198,10 @@ bool vtkExtractBlock::Prune(vtkMultiPieceDataSet* mpiece)
 {
   // * Remove any children on mpiece that don't have DONT_PRUNE set.
   vtkMultiPieceDataSet* clone = vtkMultiPieceDataSet::New();
+
+  // Copy global field data, otherwise it will be lost
+  clone->GetFieldData()->ShallowCopy(mpiece->GetFieldData());
+
   unsigned int index = 0;
   unsigned int numChildren = mpiece->GetNumberOfPieces();
   for (unsigned int cc = 0; cc < numChildren; cc++)
@@ -219,6 +224,10 @@ bool vtkExtractBlock::Prune(vtkMultiPieceDataSet* mpiece)
 bool vtkExtractBlock::Prune(vtkMultiBlockDataSet* mblock)
 {
   vtkMultiBlockDataSet* clone = vtkMultiBlockDataSet::New();
+
+  // Copy global field data, otherwise it will be lost
+  clone->GetFieldData()->ShallowCopy(mblock->GetFieldData());
+
   unsigned int index = 0;
   unsigned int numChildren = mblock->GetNumberOfBlocks();
   for (unsigned int cc = 0; cc < numChildren; cc++)