specify aspect ratio filter input requirements

src/aspect_ratio_filter.cc

@@ -1,18 +1,30 @@
 #include "aspect_ratio_filter.h"
+#include "vtkDataObject.h"
 
 #include <vtkUnstructuredGrid.h>
 #include <vtkPointData.h>
 #include <vtkCellData.h>
 #include <vtkDoubleArray.h>
 #include <vtkCellIterator.h>
+#include <vtkInformation.h>
+#include <vtkInformationVector.h>
 
 
 vtkStandardNewMacro(AspectRatioFilter);
 
 
+// Ensure there is an "angles", 12 floats tuple array in the DataCell.
 int AspectRatioFilter::FillInputPortInformation(int port, vtkInformation *info) {
 	vtkUnstructuredGridAlgorithm::FillInputPortInformation(port, info);
-	// Ensure there is an "angles" array in the DataCell.
+	vtkNew<vtkInformation> anglesField;
+	anglesField->Set(vtkDataObject::FIELD_ASSOCIATION(), vtkDataObject::FIELD_ASSOCIATION_CELLS);
+	anglesField->Set(vtkDataObject::FIELD_NAME(), "angles");
+	anglesField->Set(vtkDataObject::FIELD_NUMBER_OF_COMPONENTS(), 12);
+	anglesField->Set(vtkDataObject::FIELD_ARRAY_TYPE(), VTK_DOUBLE);
+
+	vtkNew<vtkInformationVector> fields;
+	fields->Append(anglesField);
+	info->Set(vtkAlgorithm::INPUT_REQUIRED_FIELDS(), fields);
 	return 1;
 }
 

src/main.cc

@@ -14,7 +14,6 @@
 #include <vtkOpenGLProjectedTetrahedraMapper.h>
 #include <vtkUnstructuredGridReader.h>
 #include <vtkPiecewiseFunction.h>
-#include <vtkDoubleArray.h>
 
 #include <array>
 #include <vector>
@@ -60,7 +59,7 @@ int main(int argc, char **argv) {
 	/* Display angles in console. */
 	anglesFilter->Update();
 	vtkUnstructuredGrid *grid = anglesFilter->GetOutput();
-	auto *angles = vtkDoubleArray::SafeDownCast(grid->GetCellData()->GetArray("angles"));
+	auto *angles = grid->GetCellData()->GetArray("angles");
 	for (ssize_t i = 0; i < angles->GetNumberOfTuples(); i++) {
 		std::cout << "cell " << i << ": ";
 		for (ssize_t j = 0; j < angles->GetNumberOfComponents(); j++) {
@@ -76,7 +75,7 @@ int main(int argc, char **argv) {
 	/* Display aspect ratios in console. */
 	aspectRatioFilter->Update();
 	grid = aspectRatioFilter->GetOutput();
-	auto *aspectRatios = vtkDoubleArray::SafeDownCast(grid->GetCellData()->GetArray("aspect_ratio"));
+	auto *aspectRatios = grid->GetCellData()->GetArray("aspect_ratio");
 	for (ssize_t i = 0; i < aspectRatios->GetNumberOfTuples(); i++) {
 		std::cout << "cell " << i << ": "
 				  << aspectRatios->GetTuple1(i) << "\n";