Fix streaming in vtkImageMarchingCubes

This filter wasn't streaming because the input's whole extent was
updated before vtkImageMarchingCubes::RequestData() was called.
In order for streaming to work properly, the input data must not
be updated before RequestData() updates it.  To state this in
another way, setting a memory limit for the input has no effect
if the whole input is filled before vtkImageMarchingCubes even
executes.

To properly test this filter, the test was modified to use a
streaming reader (vtkImageReader2 instead of vtkVolume16Reader),
and the InputMemoryLimit was reduced.

Filters/General/vtkImageMarchingCubes.cxx

@@ -70,6 +70,21 @@ int vtkImageMarchingCubesGetTypeSize(T*)
   return sizeof(T);
 }
 
+//----------------------------------------------------------------------------
+int vtkImageMarchingCubes::RequestUpdateExtent(
+  vtkInformation* vtkNotUsed(request),
+  vtkInformationVector** inputVector,
+  vtkInformationVector* vtkNotUsed(outputVector))
+{
+  // start with an empty UPDATE_EXTENT to ensure proper streaming
+  // (the UPDATE_EXTENT will be set properly in RequestData()).
+  int extent[6] = { 0, -1, 0, -1, 0, -1 };
+  vtkInformation* inInfo = inputVector[0]->GetInformationObject(0);
+  inInfo->Set(vtkStreamingDemandDrivenPipeline::UPDATE_EXTENT(),
+              extent, 6);
+  return 1;
+}
+
 //----------------------------------------------------------------------------
 int vtkImageMarchingCubes::RequestData(
   vtkInformation *vtkNotUsed(request),
@@ -123,6 +138,7 @@ int vtkImageMarchingCubes::RequestData(
       return 1;
   }
 
+  // Get the WHOLE_EXTENT and divide it into chunks
   int extent[6];
   inInfo->Get(vtkStreamingDemandDrivenPipeline::WHOLE_EXTENT(), extent);
   // multiply by the area of each slice

Filters/General/vtkImageMarchingCubes.h

@@ -146,7 +146,10 @@ protected:
   int LocatorMinX;
   int LocatorMinY;
 
-  int RequestData(vtkInformation *, vtkInformationVector **, vtkInformationVector *) override;
+  int RequestData(vtkInformation *, vtkInformationVector **,
+                  vtkInformationVector *) override;
+  int RequestUpdateExtent(vtkInformation *, vtkInformationVector **,
+                          vtkInformationVector *) override;
   int FillInputPortInformation(int port, vtkInformation *info) override;
 
   void March(vtkImageData *inData, int chunkMin, int chunkMax,

Filters/Modeling/Testing/Python/TestImageMarchingCubes.py

@@ -22,19 +22,17 @@ iren.SetRenderWindow(renWin)
 
 # create pipeline
 #
-v16 = vtk.vtkVolume16Reader()
-v16.SetDataDimensions(64, 64)
-v16.GetOutput().SetOrigin(0.0, 0.0, 0.0)
-v16.SetDataByteOrderToLittleEndian()
-v16.SetFilePrefix(VTK_DATA_ROOT + "/Data/headsq/quarter")
-v16.SetImageRange(1, 93)
-v16.SetDataSpacing(3.2, 3.2, 1.5)
-v16.Update()
+reader = vtk.vtkImageReader2()
+reader.SetDataScalarTypeToUnsignedShort()
+reader.SetFilePrefix(VTK_DATA_ROOT + "/Data/headsq/quarter")
+reader.SetDataExtent(0, 63, 0, 63, 1, 93)
+reader.SetDataSpacing(3.2, 3.2, 1.5)
+reader.SetDataOrigin(0.0, 0.0, 0.0)
 
 iso = vtk.vtkImageMarchingCubes()
-iso.SetInputConnection(v16.GetOutputPort())
+iso.SetInputConnection(reader.GetOutputPort())
 iso.SetValue(0, 1150)
-iso.SetInputMemoryLimit(1000)
+iso.SetInputMemoryLimit(100)
 
 isoMapper = vtk.vtkPolyDataMapper()
 isoMapper.SetInputConnection(iso.GetOutputPort())
@@ -45,7 +43,7 @@ isoActor.SetMapper(isoMapper)
 isoActor.GetProperty().SetColor(GetRGBColor('antique_white'))
 
 outline = vtk.vtkOutlineFilter()
-outline.SetInputConnection(v16.GetOutputPort())
+outline.SetInputConnection(reader.GetOutputPort())
 
 outlineMapper = vtk.vtkPolyDataMapper()
 outlineMapper.SetInputConnection(outline.GetOutputPort())