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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 is applied to all remaining active vertices. The remaining maximum is the
// chain maximum of all vertices, and is set to prune to NO_VERTEX_ASSIGNED (the global
// root). All others are set to prune to it.
//
// 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_trunk_builder_h
#define vtkm_worklet_contourtree_trunk_builder_h

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

namespace vtkm
{
namespace worklet
{
namespace contourtree
{

// Worklet for setting initial chain maximum value
class TrunkBuilder : public vtkm::worklet::WorkletMapField
{
public:
  using ControlSignature = void(FieldIn vertexID,           // (input) index into active vertices
                                WholeArrayIn chainExtremum, // (input) chain extemum for vertices
                                WholeArrayOut prunesTo);    // (output) where a vertex prunes to
  using ExecutionSignature = void(_1, _2, _3);
  using InputDomain = _1;

  // Constructor
  VTKM_EXEC_CONT
  TrunkBuilder() {}

  template <typename InFieldPortalType, typename OutFieldPortalType>
  VTKM_EXEC void operator()(const vtkm::Id& vertexID,
                            const InFieldPortalType& chainExtremum,
                            const OutFieldPortalType& prunesTo) const
  {
    // the chain max of everyone prunes to the global minimum
    vtkm::Id chainExt = chainExtremum.Get(vertexID);
    if (vertexID == chainExt)
      prunesTo.Set(vertexID, NO_VERTEX_ASSIGNED);
    else
      prunesTo.Set(vertexID, chainExt);
  }
}; // TrunkBuilder
}
}
}

#endif
