Add a minimum ghost level option to D3.

Filters/Parallel/Testing/Cxx/DistributedData.cxx

@@ -200,6 +200,35 @@ void MyProcess::Execute()
 
   prm->InitializeOffScreen();   // Mesa GL only
 
+  // Test the minimum ghost cell settings:
+  bool ghostCellSuccess = true;
+  {
+    dd->UseMinimalMemoryOn();
+    dd->SetBoundaryModeToAssignToOneRegion();
+
+    dd->SetMinimumGhostLevel(0);
+    dd->Update();
+    int ncells = static_cast<vtkUnstructuredGrid*>(dd->GetOutput())->GetNumberOfCells();
+    if (me == 0 && ncells != 79)
+    {
+      std::cerr << "Invalid number of cells for ghost level 0: " << ncells << "\n";
+      ghostCellSuccess = false;
+    }
+
+    dd->SetMinimumGhostLevel(2);
+    dd->Update();
+    ncells = static_cast<vtkUnstructuredGrid*>(dd->GetOutput())->GetNumberOfCells();
+    if (me == 0 && ncells != 160)
+    {
+      std::cerr << "Invalid number of cells for ghost level 2: " << ncells << "\n";
+      ghostCellSuccess = false;
+    }
+
+    dd->SetMinimumGhostLevel(0);
+    dd->UseMinimalMemoryOff();
+    dd->SetBoundaryModeToSplitBoundaryCells();  // clipping
+  }
+
   // We must update the whole pipeline here, otherwise node 0
   // goes into GetActiveCamera which updates the pipeline, putting
   // it into vtkDistributedDataFilter::Execute() which then hangs.
@@ -236,6 +265,11 @@ void MyProcess::Execute()
     this->ReturnValue =
       vtkRegressionTester::Test(this->Argc,this->Argv,renWin, 10);
 
+    if (this->ReturnValue == vtkTesting::PASSED && !ghostCellSuccess)
+    {
+      this->ReturnValue = vtkTesting::FAILED;
+    }
+
     if (ncells != 152)
     {
       this->ReturnValue = vtkTesting::FAILED;

Filters/ParallelMPI/vtkDistributedDataFilter.cxx

@@ -170,6 +170,7 @@ vtkDistributedDataFilter::vtkDistributedDataFilter()
   this->NumConvexSubRegions = 0;
   this->ConvexSubRegionBounds = nullptr;
 
+  this->MinimumGhostLevel = 0;
   this->GhostLevel = 0;
 
   this->RetainKdtree = 1;
@@ -497,6 +498,7 @@ int vtkDistributedDataFilter::RequestData(
 
   this->GhostLevel = outInfo->Get(
     vtkStreamingDemandDrivenPipeline::UPDATE_NUMBER_OF_GHOST_LEVELS());
+  this->GhostLevel = std::max(this->GhostLevel, this->MinimumGhostLevel);
 
   // get the input and output
   vtkDataSet *inputDS = vtkDataSet::GetData(inputVector[0], 0);

Filters/ParallelMPI/vtkDistributedDataFilter.h

@@ -220,6 +220,12 @@ public:
   vtkGetMacro(UseMinimalMemory, int);
   vtkSetMacro(UseMinimalMemory, int);
 
+  /**
+   * The minimum number of ghost levels to add to each processor's output. If
+   * the pipeline also requests ghost levels, the larger value will be used.
+   */
+  vtkGetMacro(MinimumGhostLevel, int)
+  vtkSetMacro(MinimumGhostLevel, int)
 
   /**
    * Turn on collection of timing data
@@ -610,6 +616,10 @@ private:
   int NumConvexSubRegions;
   double *ConvexSubRegionBounds;
 
+  // User-adjustable minimum number of ghost levels.
+  int MinimumGhostLevel;
+
+  // Actual number of ghost levels used during execution.
   int GhostLevel;
 
   int RetainKdtree;