vtkMergeArrays: fix missing temporal information

(cherry picked from commit 768d2ef0)

Documentation/release/dev/fix-merge-arrays-for-temporal-data.md

+# Fix MergeArrays filter for temporal datas
+
+MergeArrays now ensure to forward time informations from the input to the output.

Filters/General/vtkMergeArrays.cxx

@@ -14,6 +14,10 @@
 #include "vtkObjectFactory.h"
 #include "vtkPointData.h"
 #include "vtkSmartPointer.h"
+#include "vtkStreamingDemandDrivenPipeline.h"
+
+#include <set>
+#include <vector>
 
 VTK_ABI_NAMESPACE_BEGIN
 vtkStandardNewMacro(vtkMergeArrays);
@@ -111,6 +115,62 @@ int vtkMergeArrays::FillInputPortInformation(int vtkNotUsed(port), vtkInformatio
   return 1;
 }
 
+//------------------------------------------------------------------------------
+int vtkMergeArrays::RequestInformation(vtkInformation* vtkNotUsed(request),
+  vtkInformationVector** inputVector, vtkInformationVector* outputVector)
+{
+  int numberOfInputs = inputVector[0]->GetNumberOfInformationObjects();
+  if (numberOfInputs < 2)
+  {
+    vtkErrorMacro(<< "This filter needs at least 2 inputs.");
+    return 0;
+  }
+
+  vtkInformation* outInfo = outputVector->GetInformationObject(0);
+
+  // Aggregates time values
+  std::set<double> allTimeSteps;
+  for (int idx = 0; idx < numberOfInputs; ++idx)
+  {
+    vtkInformation* inInfo = inputVector[0]->GetInformationObject(idx);
+    if (!inInfo)
+    {
+      continue;
+    }
+
+    if (!inInfo->Has(vtkStreamingDemandDrivenPipeline::TIME_STEPS()))
+    {
+      continue;
+    }
+
+    int numberOfTimeSteps = inInfo->Length(vtkStreamingDemandDrivenPipeline::TIME_STEPS());
+    double* values = inInfo->Get(vtkStreamingDemandDrivenPipeline::TIME_STEPS());
+
+    for (int step = 0; step < numberOfTimeSteps; step++)
+    {
+      allTimeSteps.insert(values[step]);
+    }
+  }
+
+  if (allTimeSteps.empty())
+  {
+    // Not having any timesteps is fine, just return.
+    return 1;
+  }
+
+  // Forward these timesteps to the output
+  std::vector<double> allTimeStepsVec(allTimeSteps.begin(), allTimeSteps.end());
+  outInfo->Set(vtkStreamingDemandDrivenPipeline::TIME_STEPS(), allTimeStepsVec.data(),
+    static_cast<int>(allTimeStepsVec.size()));
+
+  double timeRange[2];
+  timeRange[0] = allTimeStepsVec.front();
+  timeRange[1] = allTimeStepsVec.back();
+  outInfo->Set(vtkStreamingDemandDrivenPipeline::TIME_RANGE(), timeRange, 2);
+
+  return 1;
+}
+
 //------------------------------------------------------------------------------
 int vtkMergeArrays::RequestData(vtkInformation* vtkNotUsed(request),
   vtkInformationVector** inputVector, vtkInformationVector* outputVector)

Filters/General/vtkMergeArrays.h

@@ -66,9 +66,17 @@ protected:
   virtual int MergeDataObjectFields(vtkDataObject* input, int inputIndex, vtkDataObject* output);
   ///@}
 
-  // see algorithm for more info
+  /**
+   * Make sure that this filter can take a dynamic number of input.
+   */
   int FillInputPortInformation(int port, vtkInformation* info) override;
 
+  /**
+   * Gets the metadata from input informations and aggregates time information to the output.
+   */
+  int RequestInformation(vtkInformation* request, vtkInformationVector** inputVector,
+    vtkInformationVector* outputVector) override;
+
   int RequestData(vtkInformation*, vtkInformationVector**, vtkInformationVector*) override;
 
 private: