vtk-m/vtkm/worklet/contourtree/JoinArcConnector.h

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//  This code is based on the algorithm presented in the paper:
//  “Parallel Peak Pruning for Scalable SMP Contour Tree Computation.”
//  Hamish Carr, Gunther Weber, Christopher Sewell, and James Ahrens.
//  Proceedings of the IEEE Symposium on Large Data Analysis and Visualization
//  (LDAV), October 2016, Baltimore, Maryland.

//=======================================================================================
//
// COMMENTS:
//
// This functor checks the vertex next lowest in the sort order. If it shares a maximum,
// we connect to it, otherwise we connect to the maximum's saddle.
//
// Any vector needed by the functor for lookup purposes will be passed as a parameter to
// the constructor and saved, with the actual function call being the operator ()
//
// Vectors marked I/O are intrinsically risky unless there is an algorithmic guarantee
// that the read/writes are completely independent - which for our case actually occurs
// The I/O vectors should therefore be justified in comments both here & in caller
//
//=======================================================================================

#ifndef vtkm_worklet_contourtree_join_arc_connector_h
#define vtkm_worklet_contourtree_join_arc_connector_h

#include <vtkm/worklet/WorkletMapField.h>

namespace vtkm
{
namespace worklet
{
namespace contourtree
{

// Worklet for setting initial chain maximum value
class JoinArcConnector : public vtkm::worklet::WorkletMapField
{
public:
  using ControlSignature = void(FieldIn vertex,            // (input) index into sorted edges
                                WholeArrayIn vertexSorter, // (input) sorting indices
                                WholeArrayIn extrema,      // (input) maxima
                                WholeArrayIn saddles,      // (input) saddles
                                WholeArrayOut mergeArcs);  // (output) target for write back
  using ExecutionSignature = void(_1, _2, _3, _4, _5);
  using InputDomain = _1;

  // Constructor
  VTKM_EXEC_CONT
  JoinArcConnector() {}

  template <typename InFieldPortalType, typename OutFieldPortalType>
  VTKM_EXEC void operator()(const vtkm::Id& vertex,
                            const InFieldPortalType& vertexSorter,
                            const InFieldPortalType& extrema,
                            const InFieldPortalType& saddles,
                            const OutFieldPortalType& mergeArcs) const
  {
    // work out whether we have the low element on the join arc
    bool joinToSaddle = false;
    if (vertex == 0)
    {
      joinToSaddle = true;
    }
    else
    {
      joinToSaddle =
        (extrema.Get(vertexSorter.Get(vertex)) != extrema.Get(vertexSorter.Get(vertex - 1)));
    }

    // now set the join arcs for everybody
    if (joinToSaddle)
      mergeArcs.Set(vertexSorter.Get(vertex), saddles.Get(vertexSorter.Get(vertex)));
    else
      mergeArcs.Set(vertexSorter.Get(vertex), vertexSorter.Get(vertex - 1));
  }
}; // JoinArcConnector
}
}
}

#endif