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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 replaces a parallel loop through regular points, since more than one
// output needs to be set.
//
// 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_regular_point_transferrer_h
#define vtkm_worklet_contourtree_regular_point_transferrer_h

#include <vtkm/worklet/WorkletMapField.h>
#include <vtkm/worklet/contourtree/Mesh2D_DEM_Triangulation_Macros.h>
#include <vtkm/worklet/contourtree/Types.h>
#include <vtkm/worklet/contourtree/VertexValueComparator.h>

namespace vtkm
{
namespace worklet
{
namespace contourtree
{

// Worklet for setting initial chain maximum value
template <typename T>
class RegularPointTransferrer : public vtkm::worklet::WorkletMapField
{
public:
  struct TagType : vtkm::ListTagBase<T>
  {
  };

  using ControlSignature = void(FieldIn vertexID,           // (input) vertex ID
                                WholeArrayIn chainExtremum, // (input) chain extremum
                                WholeArrayIn values,        // (input) values array
                                WholeArrayIn valueIndex,    // (input) index into value array
                                WholeArrayInOut prunesTo,   // (i/o) where vertex is pruned to
                                WholeArrayOut outdegree);   // (output) updegree of vertex
  using ExecutionSignature = void(_1, _2, _3, _4, _5, _6);
  using InputDomain = _1;

  bool isJoinGraph;

  // Constructor
  VTKM_EXEC_CONT
  RegularPointTransferrer(bool IsJoinGraph)
    : isJoinGraph(IsJoinGraph)
  {
  }

  template <typename InFieldPortalType,
            typename InIndexPortalType,
            typename InOutFieldPortalType,
            typename OutFieldPortalType>
  VTKM_EXEC void operator()(const vtkm::Id& vertexID,
                            const InIndexPortalType& chainExtremum,
                            const InFieldPortalType& values,
                            const InIndexPortalType& valueIndex,
                            const InOutFieldPortalType& prunesTo,
                            const OutFieldPortalType& outdegree) const
  {
    VertexValueComparator<InFieldPortalType> lessThan(values);

    // ignore vertices which have already been labelled
    vtkm::Id saddleID = prunesTo.Get(vertexID);

    if (saddleID != NO_VERTEX_ASSIGNED)
      return;

    // now, if the vertex is beyond the governing saddle, we need to label it
    // and arrange to get rid of it
    saddleID = prunesTo.Get(chainExtremum.Get(vertexID));

    if (lessThan(valueIndex.Get(saddleID), valueIndex.Get(vertexID), !isJoinGraph))
    {
      // set the merge extremum to the current chain extremum
      prunesTo.Set(vertexID, chainExtremum.Get(vertexID));
      // and reset the outdegree to zero
      outdegree.Set(vertexID, 0);
    } // regular point to be pruned
  }
}; // RegularPointTransferrer
}
}
}

#endif
