Removing virtuals v1

-- Remove virtuals from Integrators, Fields, Particles
-- Remaining virtuals are in the CellInterpolationHelpers

vtkm/filter/Lagrangian.hxx

@@ -25,9 +25,9 @@
 #include <vtkm/worklet/WorkletMapField.h>
 #include <vtkm/worklet/particleadvection/Field.h>
 #include <vtkm/worklet/particleadvection/GridEvaluators.h>
-#include <vtkm/worklet/particleadvection/IntegratorBase.h>
 #include <vtkm/worklet/particleadvection/Particles.h>
 #include <vtkm/worklet/particleadvection/RK4Integrator.h>
+#include <vtkm/worklet/particleadvection/Stepper.h>
 
 #include <cstring>
 #include <sstream>
@@ -279,12 +279,14 @@ inline VTKM_CONT vtkm::cont::DataSet Lagrangian::DoExecute(
   using FieldType = vtkm::worklet::particleadvection::VelocityField<FieldHandle>;
   using GridEvalType = vtkm::worklet::particleadvection::GridEvaluator<FieldType>;
   using RK4Type = vtkm::worklet::particleadvection::RK4Integrator<GridEvalType>;
+  using Stepper = vtkm::worklet::particleadvection::Stepper<RK4Type, GridEvalType>;
+
   vtkm::worklet::ParticleAdvection particleadvection;
   vtkm::worklet::ParticleAdvectionResult<vtkm::Particle> res;
 
   FieldType velocities(field);
   GridEvalType gridEval(coords, cells, velocities);
-  RK4Type rk4(gridEval, static_cast<vtkm::Float32>(this->stepSize));
+  Stepper rk4(gridEval, static_cast<vtkm::Float32>(this->stepSize));
 
   res = particleadvection.Run(rk4, basisParticleArray, 1); // Taking a single step
   auto particles = res.Particles;

vtkm/filter/LagrangianStructures.h

@@ -17,7 +17,7 @@
 
 #include <vtkm/worklet/ParticleAdvection.h>
 #include <vtkm/worklet/particleadvection/GridEvaluators.h>
-#include <vtkm/worklet/particleadvection/IntegratorBase.h>
+#include <vtkm/worklet/particleadvection/Stepper.h>
 
 namespace vtkm
 {

vtkm/filter/LagrangianStructures.hxx

@@ -16,9 +16,9 @@
 #include <vtkm/cont/Invoker.h>
 #include <vtkm/worklet/particleadvection/Field.h>
 #include <vtkm/worklet/particleadvection/GridEvaluators.h>
-#include <vtkm/worklet/particleadvection/IntegratorBase.h>
 #include <vtkm/worklet/particleadvection/Particles.h>
 #include <vtkm/worklet/particleadvection/RK4Integrator.h>
+#include <vtkm/worklet/particleadvection/Stepper.h>
 
 #include <vtkm/worklet/LagrangianStructures.h>
 
@@ -86,7 +86,8 @@ inline VTKM_CONT vtkm::cont::DataSet LagrangianStructures::DoExecute(
   using FieldHandle = vtkm::cont::ArrayHandle<vtkm::Vec<T, 3>, StorageType>;
   using FieldType = vtkm::worklet::particleadvection::VelocityField<FieldHandle>;
   using GridEvaluator = vtkm::worklet::particleadvection::GridEvaluator<FieldType>;
-  using Integrator = vtkm::worklet::particleadvection::RK4Integrator<GridEvaluator>;
+  using IntegratorType = vtkm::worklet::particleadvection::RK4Integrator<GridEvaluator>;
+  using Stepper = vtkm::worklet::particleadvection::Stepper<IntegratorType, GridEvaluator>;
 
   vtkm::FloatDefault stepSize = this->GetStepSize();
   vtkm::Id numberOfSteps = this->GetNumberOfSteps();
@@ -138,7 +139,7 @@ inline VTKM_CONT vtkm::cont::DataSet LagrangianStructures::DoExecute(
 
     FieldType velocities(field);
     GridEvaluator evaluator(input.GetCoordinateSystem(), input.GetCellSet(), velocities);
-    Integrator integrator(evaluator, stepSize);
+    Stepper integrator(evaluator, stepSize);
     vtkm::worklet::ParticleAdvection particles;
     vtkm::worklet::ParticleAdvectionResult<vtkm::Particle> advectionResult;
     vtkm::cont::ArrayHandle<vtkm::Particle> advectionPoints;

vtkm/filter/Pathline.h

@@ -14,7 +14,7 @@
 #include <vtkm/filter/FilterDataSetWithField.h>
 #include <vtkm/worklet/ParticleAdvection.h>
 #include <vtkm/worklet/particleadvection/GridEvaluators.h>
-#include <vtkm/worklet/particleadvection/IntegratorBase.h>
+#include <vtkm/worklet/particleadvection/Stepper.h>
 
 namespace vtkm
 {

vtkm/filter/StreamSurface.h

@@ -15,7 +15,7 @@
 #include <vtkm/worklet/ParticleAdvection.h>
 #include <vtkm/worklet/StreamSurface.h>
 #include <vtkm/worklet/particleadvection/GridEvaluators.h>
-#include <vtkm/worklet/particleadvection/IntegratorBase.h>
+#include <vtkm/worklet/particleadvection/Stepper.h>
 
 namespace vtkm
 {

vtkm/filter/StreamSurface.hxx

@@ -21,6 +21,7 @@
 #include <vtkm/worklet/particleadvection/GridEvaluators.h>
 #include <vtkm/worklet/particleadvection/Particles.h>
 #include <vtkm/worklet/particleadvection/RK4Integrator.h>
+#include <vtkm/worklet/particleadvection/Stepper.h>
 
 namespace vtkm
 {
@@ -57,11 +58,12 @@ inline VTKM_CONT vtkm::cont::DataSet StreamSurface::DoExecute(
   using FieldType = vtkm::worklet::particleadvection::VelocityField<FieldHandle>;
   using GridEvalType = vtkm::worklet::particleadvection::GridEvaluator<FieldType>;
   using RK4Type = vtkm::worklet::particleadvection::RK4Integrator<GridEvalType>;
+  using Stepper = vtkm::worklet::particleadvection::Stepper<RK4Type, GridEvalType>;
 
   //compute streamlines
   FieldType velocities(field);
   GridEvalType eval(coords, cells, velocities);
-  RK4Type rk4(eval, this->StepSize);
+  Stepper rk4(eval, this->StepSize);
 
   vtkm::worklet::Streamline streamline;
 

vtkm/filter/particleadvection/DataSetIntegrator.h

@@ -15,6 +15,7 @@
 #include <vtkm/cont/DataSet.h>
 #include <vtkm/worklet/ParticleAdvection.h>
 #include <vtkm/worklet/particleadvection/RK4Integrator.h>
+#include <vtkm/worklet/particleadvection/Stepper.h>
 #include <vtkm/worklet/particleadvection/TemporalGridEvaluators.h>
 
 #include <memory>
@@ -51,17 +52,18 @@ public:
   {
     auto copyFlag = (this->CopySeedArray ? vtkm::CopyFlag::On : vtkm::CopyFlag::Off);
     auto seedArray = vtkm::cont::make_ArrayHandle(v, copyFlag);
-    RK4Type rk4(*this->Eval, stepSize);
+    Stepper rk4(*this->Eval, stepSize);
     this->DoAdvect(seedArray, rk4, maxSteps, result);
   }
 
 protected:
   using RK4Type = vtkm::worklet::particleadvection::RK4Integrator<GridEvalType>;
+  using Stepper = vtkm::worklet::particleadvection::Stepper<RK4Type, GridEvalType>;
   using FieldHandleType = vtkm::cont::ArrayHandle<vtkm::Vec3f>;
 
   template <typename ResultType>
   inline void DoAdvect(vtkm::cont::ArrayHandle<vtkm::Particle>& seeds,
-                       const RK4Type& rk4,
+                       const Stepper& rk4,
                        vtkm::Id maxSteps,
                        ResultType& result) const;
 

vtkm/filter/particleadvection/DataSetIntegrator.hxx

@@ -23,7 +23,10 @@ using GridEvalType = vtkm::worklet::particleadvection::GridEvaluator<
 using TemporalGridEvalType = vtkm::worklet::particleadvection::TemporalGridEvaluator<
   vtkm::worklet::particleadvection::VelocityField<vtkm::cont::ArrayHandle<vtkm::Vec3f>>>;
 using RK4Type = vtkm::worklet::particleadvection::RK4Integrator<GridEvalType>;
+using Stepper = vtkm::worklet::particleadvection::Stepper<RK4Type, GridEvalType>;
 using TemporalRK4Type = vtkm::worklet::particleadvection::RK4Integrator<TemporalGridEvalType>;
+using TemporalStepper =
+  vtkm::worklet::particleadvection::Stepper<TemporalRK4Type, TemporalGridEvalType>;
 
 //-----
 // Specialization for ParticleAdvection worklet
@@ -31,7 +34,7 @@ template <>
 template <>
 inline void DataSetIntegratorBase<GridEvalType>::DoAdvect(
   vtkm::cont::ArrayHandle<vtkm::Particle>& seeds,
-  const RK4Type& rk4,
+  const Stepper& rk4,
   vtkm::Id maxSteps,
   vtkm::worklet::ParticleAdvectionResult<vtkm::Particle>& result) const
 {
@@ -45,7 +48,7 @@ template <>
 template <>
 inline void DataSetIntegratorBase<GridEvalType>::DoAdvect(
   vtkm::cont::ArrayHandle<vtkm::Particle>& seeds,
-  const RK4Type& rk4,
+  const Stepper& rk4,
   vtkm::Id maxSteps,
   vtkm::worklet::StreamlineResult<vtkm::Particle>& result) const
 {
@@ -59,7 +62,7 @@ template <>
 template <>
 inline void DataSetIntegratorBase<TemporalGridEvalType>::DoAdvect(
   vtkm::cont::ArrayHandle<vtkm::Particle>& seeds,
-  const TemporalRK4Type& rk4,
+  const TemporalStepper& rk4,
   vtkm::Id maxSteps,
   vtkm::worklet::StreamlineResult<vtkm::Particle>& result) const
 {

vtkm/worklet/particleadvection/CMakeLists.txt

@@ -14,7 +14,7 @@ set(headers
   Field.h
   GridEvaluators.h
   GridEvaluatorStatus.h
-  IntegratorBase.h
+  Stepper.h
   IntegratorStatus.h
   Particles.h
   ParticleAdvectionWorklets.h

vtkm/worklet/particleadvection/EulerIntegrator.h

@@ -13,8 +13,6 @@
 #ifndef vtk_m_worklet_particleadvection_EulerIntegrator_h
 #define vtk_m_worklet_particleadvection_EulerIntegrator_h
 
-#include <vtkm/worklet/particleadvection/IntegratorBase.h>
-
 namespace vtkm
 {
 namespace worklet
@@ -22,73 +20,56 @@ namespace worklet
 namespace particleadvection
 {
 
-template <typename FieldEvaluateType>
-class EulerIntegrator : public IntegratorBase
+template <typename EvaluatorType>
+class ExecEulerIntegrator
 {
+public:
+  VTKM_EXEC_CONT
+  ExecEulerIntegrator(const EvaluatorType& evaluator)
+    : Evaluator(evaluator)
+  {
+  }
+
+  template <typename Particle>
+  VTKM_EXEC IntegratorStatus CheckStep(Particle& particle,
+                                       vtkm::FloatDefault stepLength,
+                                       vtkm::Vec3f& velocity) const
+  {
+    auto time = particle.Time;
+    auto inpos = particle.Pos;
+    vtkm::VecVariable<vtkm::Vec3f, 2> vectors;
+    GridEvaluatorStatus status = this->Evaluator.Evaluate(inpos, time, vectors);
+    if (status.CheckOk())
+      velocity = particle.Velocity(vectors, stepLength);
+    return IntegratorStatus(status);
+  }
+
+private:
+  EvaluatorType Evaluator;
+};
+
+template <typename EvaluatorType>
+class EulerIntegrator
+{
+private:
+  EvaluatorType Evaluator;
+
 public:
   EulerIntegrator() = default;
 
   VTKM_CONT
-  EulerIntegrator(const FieldEvaluateType& evaluator, const vtkm::FloatDefault stepLength)
-    : IntegratorBase(stepLength)
-    , Evaluator(evaluator)
+  EulerIntegrator(const EvaluatorType& evaluator)
+    : Evaluator(evaluator)
   {
   }
 
-  template <typename Device>
-  class ExecObject
-    : public IntegratorBase::ExecObjectBaseImpl<
-        vtkm::cont::internal::ExecutionObjectType<FieldEvaluateType, Device>,
-        typename EulerIntegrator::template ExecObject<Device>>
+  VTKM_CONT auto PrepareForExecution(vtkm::cont::DeviceAdapterId device,
+                                     vtkm::cont::Token& token) const
+    -> ExecEulerIntegrator<decltype(this->Evaluator.PrepareForExecution(device, token))>
   {
-    VTKM_IS_DEVICE_ADAPTER_TAG(Device);
-
-    using FieldEvaluateExecType =
-      vtkm::cont::internal::ExecutionObjectType<FieldEvaluateType, Device>;
-    using Superclass =
-      IntegratorBase::ExecObjectBaseImpl<FieldEvaluateExecType,
-                                         typename EulerIntegrator::template ExecObject<Device>>;
-
-  public:
-    VTKM_EXEC_CONT
-    ExecObject(const FieldEvaluateExecType& evaluator,
-               vtkm::FloatDefault stepLength,
-               vtkm::FloatDefault tolerance)
-      : Superclass(evaluator, stepLength, tolerance)
-    {
-    }
-
-    VTKM_EXEC
-    IntegratorStatus CheckStep(vtkm::Particle* particle,
-                               vtkm::FloatDefault stepLength,
-                               vtkm::Vec3f& velocity) const
-    {
-      auto time = particle->Time;
-      auto inpos = particle->Pos;
-      vtkm::VecVariable<vtkm::Vec3f, 2> vectors;
-      GridEvaluatorStatus status = this->Evaluator.Evaluate(inpos, time, vectors);
-      if (status.CheckOk())
-        velocity = particle->Velocity(vectors, stepLength);
-      return IntegratorStatus(status);
-    }
-  };
-
-private:
-  FieldEvaluateType Evaluator;
-
-protected:
-  VTKM_CONT virtual void PrepareForExecutionImpl(
-    vtkm::cont::DeviceAdapterId device,
-    vtkm::cont::VirtualObjectHandle<IntegratorBase::ExecObject>& execObjectHandle,
-    vtkm::cont::Token& token) const override
-  {
-    vtkm::cont::TryExecuteOnDevice(device,
-                                   detail::IntegratorPrepareForExecutionFunctor<ExecObject>(),
-                                   execObjectHandle,
-                                   this->Evaluator,
-                                   this->StepLength,
-                                   this->Tolerance,
-                                   token);
+    auto evaluator = this->Evaluator.PrepareForExecution(device, token);
+    using ExecEvaluatorType = decltype(evaluator);
+    return ExecEulerIntegrator<ExecEvaluatorType>(evaluator);
   }
 }; //EulerIntegrator
 

vtkm/worklet/particleadvection/Field.h

@@ -26,22 +26,8 @@ namespace worklet
 namespace particleadvection
 {
 
-class ExecutionField : public vtkm::VirtualObjectBase
-{
-public:
-  VTKM_EXEC_CONT
-  virtual ~ExecutionField() noexcept override {}
-
-  VTKM_EXEC
-  virtual void GetValue(const vtkm::VecVariable<vtkm::Id, 8>& indices,
-                        const vtkm::Id vertices,
-                        const vtkm::Vec3f& parametric,
-                        const vtkm::UInt8 cellShape,
-                        vtkm::VecVariable<vtkm::Vec3f, 2>& value) const = 0;
-};
-
 template <typename FieldArrayType>
-class ExecutionVelocityField : public vtkm::worklet::particleadvection::ExecutionField
+class ExecutionVelocityField
 {
 public:
   using FieldPortalType = typename FieldArrayType::ReadPortalType;
@@ -73,7 +59,7 @@ private:
 };
 
 template <typename FieldArrayType>
-class ExecutionElectroMagneticField : public vtkm::worklet::particleadvection::ExecutionField
+class ExecutionElectroMagneticField
 {
 public:
   using FieldPortalType = typename FieldArrayType::ReadPortalType;
@@ -112,22 +98,15 @@ private:
   FieldPortalType MagneticValues;
 };
 
-class Field : public vtkm::cont::ExecutionObjectBase
+template <typename FieldArrayType>
+class VelocityField : public vtkm::cont::ExecutionObjectBase
 {
 public:
-  using HandleType = vtkm::cont::VirtualObjectHandle<ExecutionField>;
-
-  virtual ~Field() = default;
+  using ExecutionType = ExecutionVelocityField<FieldArrayType>;
 
   VTKM_CONT
-  virtual const ExecutionField* PrepareForExecution(vtkm::cont::DeviceAdapterId deviceId,
-                                                    vtkm::cont::Token& token) const = 0;
-};
+  VelocityField() = default;
 
-template <typename FieldArrayType>
-class VelocityField : public vtkm::worklet::particleadvection::Field
-{
-public:
   VTKM_CONT
   VelocityField(const FieldArrayType& fieldValues)
     : FieldValues(fieldValues)
@@ -135,24 +114,25 @@ public:
   }
 
   VTKM_CONT
-  const ExecutionField* PrepareForExecution(vtkm::cont::DeviceAdapterId device,
-                                            vtkm::cont::Token& token) const override
+  const ExecutionType PrepareForExecution(vtkm::cont::DeviceAdapterId device,
+                                          vtkm::cont::Token& token) const
   {
-    using ExecutionType = ExecutionVelocityField<FieldArrayType>;
-    ExecutionType* execObject = new ExecutionType(this->FieldValues, device, token);
-    this->ExecHandle.Reset(execObject);
-    return this->ExecHandle.PrepareForExecution(device, token);
+    return ExecutionType(this->FieldValues, device, token);
   }
 
 private:
   FieldArrayType FieldValues;
-  mutable HandleType ExecHandle;
 };
 
 template <typename FieldArrayType>
-class ElectroMagneticField : public vtkm::worklet::particleadvection::Field
+class ElectroMagneticField : public vtkm::cont::ExecutionObjectBase
 {
 public:
+  using ExecutionType = ExecutionElectroMagneticField<FieldArrayType>;
+
+  VTKM_CONT
+  ElectroMagneticField() = default;
+
   VTKM_CONT
   ElectroMagneticField(const FieldArrayType& electricField, const FieldArrayType& magneticField)
     : ElectricField(electricField)
@@ -161,20 +141,15 @@ public:
   }
 
   VTKM_CONT
-  const ExecutionField* PrepareForExecution(vtkm::cont::DeviceAdapterId device,
-                                            vtkm::cont::Token& token) const override
+  const ExecutionType PrepareForExecution(vtkm::cont::DeviceAdapterId device,
+                                          vtkm::cont::Token& token) const
   {
-    using ExecutionType = ExecutionElectroMagneticField<FieldArrayType>;
-    ExecutionType* execObject =
-      new ExecutionType(this->ElectricField, this->MagneticField, device, token);
-    this->ExecHandle.Reset(execObject);
-    return this->ExecHandle.PrepareForExecution(device, token);
+    return ExecutionType(this->ElectricField, this->MagneticField, device, token);
   }
 
 private:
   FieldArrayType ElectricField;
   FieldArrayType MagneticField;
-  mutable HandleType ExecHandle;
 };
 
 } // namespace particleadvection

vtkm/worklet/particleadvection/GridEvaluatorStatus.h

@@ -22,9 +22,6 @@
 #include <vtkm/cont/DataSet.h>
 #include <vtkm/cont/DeviceAdapter.h>
 
-#include <vtkm/worklet/particleadvection/CellInterpolationHelper.h>
-#include <vtkm/worklet/particleadvection/IntegratorBase.h>
-
 namespace vtkm
 {
 namespace worklet

vtkm/worklet/particleadvection/GridEvaluators.h

@@ -26,7 +26,6 @@
 #include <vtkm/worklet/particleadvection/CellInterpolationHelper.h>
 #include <vtkm/worklet/particleadvection/Field.h>
 #include <vtkm/worklet/particleadvection/GridEvaluatorStatus.h>
-#include <vtkm/worklet/particleadvection/IntegratorBase.h>
 
 namespace vtkm
 {
@@ -127,7 +126,7 @@ public:
       vtkm::VecVariable<vtkm::Vec3f, 8> fieldValues;
       InterpolationHelper->GetCellInfo(cellId, cellShape, nVerts, ptIndices);
 
-      this->Field->GetValue(ptIndices, nVerts, parametric, cellShape, out);
+      this->Field.GetValue(ptIndices, nVerts, parametric, cellShape, out);
       status.SetOk();
     }
 
@@ -146,7 +145,7 @@ private:
   using GhostCellPortal = typename vtkm::cont::ArrayHandle<vtkm::UInt8>::ReadPortalType;
 
   vtkm::Bounds Bounds;
-  const vtkm::worklet::particleadvection::ExecutionField* Field;
+  typename FieldType::ExecutionType Field;
   GhostCellPortal GhostCells;
   bool HaveGhostCells;
   const vtkm::exec::CellInterpolationHelper* InterpolationHelper;

vtkm/worklet/particleadvection/IntegratorBase.h

@@ -1,252 +0,0 @@
-//=============================================================================
-//
-//  Copyright (c) Kitware, Inc.
-//  All rights reserved.
-//  See LICENSE.txt for details.
-//
-//  This software is distributed WITHOUT ANY WARRANTY; without even
-//  the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
-//  PURPOSE.  See the above copyright notice for more information.
-//
-//=============================================================================
-
-#ifndef vtk_m_worklet_particleadvection_IntegratorBase_h
-#define vtk_m_worklet_particleadvection_IntegratorBase_h
-
-#include <limits>
-
-#include <vtkm/Bitset.h>
-#include <vtkm/TypeTraits.h>
-#include <vtkm/Types.h>
-#include <vtkm/VectorAnalysis.h>
-
-#include <vtkm/cont/DataSet.h>
-#include <vtkm/cont/VirtualObjectHandle.h>
-
-#include <vtkm/worklet/particleadvection/GridEvaluators.h>
-#include <vtkm/worklet/particleadvection/IntegratorStatus.h>
-#include <vtkm/worklet/particleadvection/Particles.h>
-
-namespace vtkm
-{
-namespace worklet
-{
-namespace particleadvection
-{
-
-class IntegratorBase : public vtkm::cont::ExecutionObjectBase
-{
-protected:
-  VTKM_CONT
-  IntegratorBase() = default;
-
-  VTKM_CONT
-  IntegratorBase(vtkm::FloatDefault stepLength)
-    : StepLength(stepLength)
-  {
-  }
-
-public:
-  class ExecObject : public vtkm::VirtualObjectBase
-  {
-  protected:
-    VTKM_EXEC_CONT
-    ExecObject(const vtkm::FloatDefault stepLength, vtkm::FloatDefault tolerance)
-      : StepLength(stepLength)
-      , Tolerance(tolerance)
-    {
-    }
-
-  public:
-    VTKM_EXEC
-    virtual IntegratorStatus Step(vtkm::Particle* inpos,
-                                  vtkm::FloatDefault& time,
-                                  vtkm::Vec3f& outpos) const = 0;
-
-    VTKM_EXEC
-    virtual IntegratorStatus SmallStep(vtkm::Particle* inpos,
-                                       vtkm::FloatDefault& time,
-                                       vtkm::Vec3f& outpos) const = 0;
-
-  protected:
-    vtkm::FloatDefault StepLength = 1.0f;
-    vtkm::FloatDefault Tolerance = 0.001f;
-  };
-
-  template <typename Device>
-  VTKM_CONT const ExecObject* PrepareForExecution(Device, vtkm::cont::Token& token) const
-  {
-    this->PrepareForExecutionImpl(
-      Device(),
-      const_cast<vtkm::cont::VirtualObjectHandle<ExecObject>&>(this->ExecObjectHandle),
-      token);
-    return this->ExecObjectHandle.PrepareForExecution(Device(), token);
-  }
-
-private:
-  vtkm::cont::VirtualObjectHandle<ExecObject> ExecObjectHandle;
-
-protected:
-  vtkm::FloatDefault StepLength;
-  vtkm::FloatDefault Tolerance =
-    std::numeric_limits<vtkm::FloatDefault>::epsilon() * static_cast<vtkm::FloatDefault>(100.0f);
-
-  VTKM_CONT virtual void PrepareForExecutionImpl(
-    vtkm::cont::DeviceAdapterId device,
-    vtkm::cont::VirtualObjectHandle<ExecObject>& execObjectHandle,
-    vtkm::cont::Token& token) const = 0;
-
-  template <typename FieldEvaluateType, typename DerivedType>
-  class ExecObjectBaseImpl : public ExecObject
-  {
-  protected:
-    VTKM_EXEC_CONT
-    ExecObjectBaseImpl(const FieldEvaluateType& evaluator,
-                       vtkm::FloatDefault stepLength,
-                       vtkm::FloatDefault tolerance)
-      : ExecObject(stepLength, tolerance)
-      , Evaluator(evaluator)
-    {
-    }
-
-  public:
-    VTKM_EXEC
-    IntegratorStatus Step(vtkm::Particle* particle,
-                          vtkm::FloatDefault& time,
-                          vtkm::Vec3f& outpos) const override
-    {
-      vtkm::Vec3f velocity(0, 0, 0);
-      auto status = this->CheckStep(particle, this->StepLength, velocity);
-      if (status.CheckOk())
-      {
-        outpos = particle->Pos + this->StepLength * velocity;
-        time += this->StepLength;
-      }
-      else
-        outpos = particle->Pos;
-
-      return status;
-    }
-
-    VTKM_EXEC
-    IntegratorStatus SmallStep(vtkm::Particle* particle,
-                               vtkm::FloatDefault& time,
-                               vtkm::Vec3f& outpos) const override
-    {
-      //Stepping by this->StepLength goes beyond the bounds of the dataset.
-      //We need to take an Euler step that goes outside of the dataset.
-      //Use a binary search to find the largest step INSIDE the dataset.
-      //Binary search uses a shrinking bracket of inside / outside, so when
-      //we terminate, the outside value is the stepsize that will nudge
-      //the particle outside the dataset.
-
-      //The binary search will be between {0, this->StepLength}
-      vtkm::FloatDefault stepRange[2] = { 0, this->StepLength };
-
-      vtkm::Vec3f currPos(particle->Pos);
-      vtkm::Vec3f currVelocity(0, 0, 0);
-      vtkm::VecVariable<vtkm::Vec3f, 2> currValue, tmp;
-      auto evalStatus = this->Evaluator.Evaluate(currPos, particle->Time, currValue);
-      if (evalStatus.CheckFail())
-        return IntegratorStatus(evalStatus);
-
-      const vtkm::FloatDefault eps = vtkm::Epsilon<vtkm::FloatDefault>() * 10;
-      vtkm::FloatDefault div = 1;
-      while ((stepRange[1] - stepRange[0]) > eps)
-      {
-        //Try a step midway between stepRange[0] and stepRange[1]
-        div *= 2;
-        vtkm::FloatDefault currStep = stepRange[0] + (this->StepLength / div);
-
-        //See if we can step by currStep
-        IntegratorStatus status = this->CheckStep(particle, currStep, currVelocity);
-
-        if (status.CheckOk()) //Integration step succedded.
-        {
-          //See if this point is in/out.
-          auto newPos = particle->Pos + currStep * currVelocity;
-          evalStatus = this->Evaluator.Evaluate(newPos, particle->Time + currStep, tmp);
-          if (evalStatus.CheckOk())
-          {
-            //Point still in. Update currPos and set range to {currStep, stepRange[1]}
-            currPos = newPos;
-            stepRange[0] = currStep;
-          }
-          else
-          {
-            //The step succedded, but the next point is outside.
-            //Step too long. Set range to: {stepRange[0], currStep} and continue.
-            stepRange[1] = currStep;
-          }
-        }
-        else
-        {
-          //Step too long. Set range to: {stepRange[0], stepCurr} and continue.
-          stepRange[1] = currStep;
-        }
-      }
-
-      evalStatus = this->Evaluator.Evaluate(currPos, particle->Time + stepRange[0], currValue);
-      //The eval at Time + stepRange[0] better be *inside*
-      VTKM_ASSERT(evalStatus.CheckOk() && !evalStatus.CheckSpatialBounds());
-      if (evalStatus.CheckFail() || evalStatus.CheckSpatialBounds())
-        return IntegratorStatus(evalStatus);
-
-      //Update the position and time.
-      outpos = currPos + stepRange[1] * particle->Velocity(currValue, stepRange[1]);
-      time += stepRange[1];
-
-      //Get the evaluation status for the point that is *just* outside of the data.
-      evalStatus = this->Evaluator.Evaluate(outpos, time, currValue);
-
-      //The eval should fail, and the point should be outside either spatially or temporally.
-      VTKM_ASSERT(evalStatus.CheckFail() &&
-                  (evalStatus.CheckSpatialBounds() || evalStatus.CheckTemporalBounds()));
-
-      IntegratorStatus status(evalStatus);
-      status.SetOk(); //status is ok.
-
-      return status;
-    }
-
-    VTKM_EXEC
-    IntegratorStatus CheckStep(vtkm::Particle* particle,
-                               vtkm::FloatDefault stepLength,
-                               vtkm::Vec3f& velocity) const
-    {
-      return static_cast<const DerivedType*>(this)->CheckStep(particle, stepLength, velocity);
-    }
-
-  protected:
-    FieldEvaluateType Evaluator;
-  };
-};
-
-namespace detail
-{
-
-template <template <typename> class IntegratorType>
-struct IntegratorPrepareForExecutionFunctor
-{
-  template <typename Device, typename EvaluatorType>
-  VTKM_CONT bool operator()(
-    Device,
-    vtkm::cont::VirtualObjectHandle<IntegratorBase::ExecObject>& execObjectHandle,
-    const EvaluatorType& evaluator,
-    vtkm::FloatDefault stepLength,
-    vtkm::FloatDefault tolerance,
-    vtkm::cont::Token& token) const
-  {
-    IntegratorType<Device>* integrator = new IntegratorType<Device>(
-      evaluator.PrepareForExecution(Device(), token), stepLength, tolerance);
-    execObjectHandle.Reset(integrator);
-    return true;
-  }
-};
-
-} //namespace detail
-} //namespace particleadvection
-} //namespace worklet
-} //namespace vtkm
-
-#endif // vtk_m_worklet_particleadvection_IntegratorBase_h

vtkm/worklet/particleadvection/ParticleAdvectionWorklets.h

@@ -22,8 +22,8 @@
 
 #include <vtkm/Particle.h>
 #include <vtkm/worklet/WorkletMapField.h>
-#include <vtkm/worklet/particleadvection/IntegratorBase.h>
 #include <vtkm/worklet/particleadvection/Particles.h>
+#include <vtkm/worklet/particleadvection/Stepper.h>
 
 #ifdef VTKM_CUDA
 #include <vtkm/cont/cuda/internal/ScopedCudaStackSize.h>
@@ -48,7 +48,7 @@ public:
 
   template <typename IntegratorType, typename IntegralCurveType>
   VTKM_EXEC void operator()(const vtkm::Id& idx,
-                            const IntegratorType* integrator,
+                            const IntegratorType& integrator,
                             IntegralCurveType& integralCurve,
                             const vtkm::Id& maxSteps) const
   {
@@ -66,7 +66,7 @@ public:
     do
     {
       vtkm::Vec3f outpos;
-      auto status = integrator->Step(&particle, time, outpos);
+      auto status = integrator.Step(particle, time, outpos);
       if (status.CheckOk())
       {
         integralCurve.StepUpdate(idx, time, outpos);
@@ -78,7 +78,7 @@ public:
       //Try and take a step just past the boundary.
       else if (status.CheckSpatialBounds())
       {
-        status = integrator->SmallStep(&particle, time, outpos);
+        status = integrator.SmallStep(particle, time, outpos);
         if (status.CheckOk())
         {
           integralCurve.StepUpdate(idx, time, outpos);

vtkm/worklet/particleadvection/RK4Integrator.h

@@ -13,8 +13,6 @@
 #ifndef vtk_m_worklet_particleadvection_RK4Integrator_h
 #define vtk_m_worklet_particleadvection_RK4Integrator_h
 
-#include <vtkm/worklet/particleadvection/IntegratorBase.h>
-
 namespace vtkm
 {
 namespace worklet
@@ -22,116 +20,98 @@ namespace worklet
 namespace particleadvection
 {
 
-template <typename FieldEvaluateType>
-class RK4Integrator : public IntegratorBase
+template <typename ExecEvaluatorType>
+class ExecRK4Integrator
 {
+public:
+  VTKM_EXEC_CONT
+  ExecRK4Integrator(const ExecEvaluatorType& evaluator)
+    : Evaluator(evaluator)
+  {
+  }
+
+  template <typename Particle>
+  VTKM_EXEC IntegratorStatus CheckStep(Particle& particle,
+                                       vtkm::FloatDefault stepLength,
+                                       vtkm::Vec3f& velocity) const
+  {
+    auto time = particle.Time;
+    auto inpos = particle.Pos;
+    vtkm::FloatDefault boundary = this->Evaluator.GetTemporalBoundary(static_cast<vtkm::Id>(1));
+    if ((time + stepLength + vtkm::Epsilon<vtkm::FloatDefault>() - boundary) > 0.0)
+      stepLength = boundary - time;
+
+    //k1 = F(p,t)
+    //k2 = F(p+hk1/2, t+h/2
+    //k3 = F(p+hk2/2, t+h/2
+    //k4 = F(p+hk3, t+h)
+    //Yn+1 = Yn + 1/6 h (k1+2k2+2k3+k4)
+
+    vtkm::FloatDefault var1 = (stepLength / static_cast<vtkm::FloatDefault>(2));
+    vtkm::FloatDefault var2 = time + var1;
+    vtkm::FloatDefault var3 = time + stepLength;
+
+    vtkm::Vec3f v1 = vtkm::TypeTraits<vtkm::Vec3f>::ZeroInitialization();
+    vtkm::Vec3f v2 = v1, v3 = v1, v4 = v1;
+    vtkm::VecVariable<vtkm::Vec3f, 2> k1, k2, k3, k4;
+
+    GridEvaluatorStatus evalStatus;
+
+    evalStatus = this->Evaluator.Evaluate(inpos, time, k1);
+    if (evalStatus.CheckFail())
+      return IntegratorStatus(evalStatus);
+    v1 = particle.Velocity(k1, stepLength);
+
+    evalStatus = this->Evaluator.Evaluate(inpos + var1 * v1, var2, k2);
+    if (evalStatus.CheckFail())
+      return IntegratorStatus(evalStatus);
+    v2 = particle.Velocity(k2, stepLength);
+
+    evalStatus = this->Evaluator.Evaluate(inpos + var1 * v2, var2, k3);
+    if (evalStatus.CheckFail())
+      return IntegratorStatus(evalStatus);
+    v3 = particle.Velocity(k3, stepLength);
+
+    evalStatus = this->Evaluator.Evaluate(inpos + stepLength * v3, var3, k4);
+    if (evalStatus.CheckFail())
+      return IntegratorStatus(evalStatus);
+    v4 = particle.Velocity(k4, stepLength);
+
+    velocity = (v1 + 2 * v2 + 2 * v3 + v4) / static_cast<vtkm::FloatDefault>(6);
+
+    return IntegratorStatus(evalStatus);
+  }
+
+private:
+  ExecEvaluatorType Evaluator;
+};
+
+template <typename EvaluatorType>
+class RK4Integrator
+{
+private:
+  EvaluatorType Evaluator;
+
 public:
   VTKM_CONT
   RK4Integrator() = default;
 
   VTKM_CONT
-  RK4Integrator(const FieldEvaluateType& evaluator, vtkm::FloatDefault stepLength)
-    : IntegratorBase(stepLength)
-    , Evaluator(evaluator)
+  RK4Integrator(const EvaluatorType& evaluator)
+    : Evaluator(evaluator)
   {
   }
 
-  template <typename Device>
-  class ExecObject
-    : public IntegratorBase::ExecObjectBaseImpl<
-        vtkm::cont::internal::ExecutionObjectType<FieldEvaluateType, Device>,
-        typename RK4Integrator::template ExecObject<Device>>
+  VTKM_CONT auto PrepareForExecution(vtkm::cont::DeviceAdapterId device,
+                                     vtkm::cont::Token& token) const
+    -> ExecRK4Integrator<decltype(this->Evaluator.PrepareForExecution(device, token))>
   {
-    VTKM_IS_DEVICE_ADAPTER_TAG(Device);
-
-    using FieldEvaluateExecType =
-      vtkm::cont::internal::ExecutionObjectType<FieldEvaluateType, Device>;
-    using Superclass =
-      IntegratorBase::ExecObjectBaseImpl<FieldEvaluateExecType,
-                                         typename RK4Integrator::template ExecObject<Device>>;
-
-  public:
-    VTKM_EXEC_CONT
-    ExecObject(const FieldEvaluateExecType& evaluator,
-               vtkm::FloatDefault stepLength,
-               vtkm::FloatDefault tolerance)
-      : Superclass(evaluator, stepLength, tolerance)
-    {
-    }
-
-    VTKM_EXEC
-    IntegratorStatus CheckStep(vtkm::Particle* particle,
-                               vtkm::FloatDefault stepLength,
-                               vtkm::Vec3f& velocity) const
-    {
-      auto time = particle->Time;
-      auto inpos = particle->Pos;
-      vtkm::FloatDefault boundary = this->Evaluator.GetTemporalBoundary(static_cast<vtkm::Id>(1));
-      if ((time + stepLength + vtkm::Epsilon<vtkm::FloatDefault>() - boundary) > 0.0)
-        stepLength = boundary - time;
-
-      //k1 = F(p,t)
-      //k2 = F(p+hk1/2, t+h/2
-      //k3 = F(p+hk2/2, t+h/2
-      //k4 = F(p+hk3, t+h)
-      //Yn+1 = Yn + 1/6 h (k1+2k2+2k3+k4)
-
-      vtkm::FloatDefault var1 = (stepLength / static_cast<vtkm::FloatDefault>(2));
-      vtkm::FloatDefault var2 = time + var1;
-      vtkm::FloatDefault var3 = time + stepLength;
-
-      vtkm::Vec3f v1 = vtkm::TypeTraits<vtkm::Vec3f>::ZeroInitialization();
-      vtkm::Vec3f v2 = v1, v3 = v1, v4 = v1;
-      vtkm::VecVariable<vtkm::Vec3f, 2> k1, k2, k3, k4;
-
-      GridEvaluatorStatus evalStatus;
-
-      evalStatus = this->Evaluator.Evaluate(inpos, time, k1);
-      if (evalStatus.CheckFail())
-        return IntegratorStatus(evalStatus);
-      v1 = particle->Velocity(k1, stepLength);
-
-      evalStatus = this->Evaluator.Evaluate(inpos + var1 * v1, var2, k2);
-      if (evalStatus.CheckFail())
-        return IntegratorStatus(evalStatus);
-      v2 = particle->Velocity(k2, stepLength);
-
-      evalStatus = this->Evaluator.Evaluate(inpos + var1 * v2, var2, k3);
-      if (evalStatus.CheckFail())
-        return IntegratorStatus(evalStatus);
-      v3 = particle->Velocity(k3, stepLength);
-
-      evalStatus = this->Evaluator.Evaluate(inpos + stepLength * v3, var3, k4);
-      if (evalStatus.CheckFail())
-        return IntegratorStatus(evalStatus);
-      v4 = particle->Velocity(k4, stepLength);
-
-      velocity = (v1 + 2 * v2 + 2 * v3 + v4) / static_cast<vtkm::FloatDefault>(6);
-
-      return IntegratorStatus(evalStatus);
-    }
-  };
-
-private:
-  FieldEvaluateType Evaluator;
-
-protected:
-  VTKM_CONT virtual void PrepareForExecutionImpl(
-    vtkm::cont::DeviceAdapterId device,
-    vtkm::cont::VirtualObjectHandle<IntegratorBase::ExecObject>& execObjectHandle,
-    vtkm::cont::Token& token) const override
-  {
-    vtkm::cont::TryExecuteOnDevice(device,
-                                   detail::IntegratorPrepareForExecutionFunctor<ExecObject>(),
-                                   execObjectHandle,
-                                   this->Evaluator,
-                                   this->StepLength,
-                                   this->Tolerance,
-                                   token);
+    auto evaluator = this->Evaluator.PrepareForExecution(device, token);
+    using ExecEvaluatorType = decltype(evaluator);
+    return ExecRK4Integrator<ExecEvaluatorType>(evaluator);
   }
 };
 
-
 } //namespace particleadvection
 } //namespace worklet
 } //namespace vtkm

vtkm/worklet/particleadvection/Stepper.h

@@ -0,0 +1,206 @@
+//=============================================================================
+//
+//  Copyright (c) Kitware, Inc.
+//  All rights reserved.
+//  See LICENSE.txt for details.
+//
+//  This software is distributed WITHOUT ANY WARRANTY; without even
+//  the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+//  PURPOSE.  See the above copyright notice for more information.
+//
+//=============================================================================
+
+#ifndef vtk_m_worklet_particleadvection_Stepper_h
+#define vtk_m_worklet_particleadvection_Stepper_h
+
+#include <limits>
+
+#include <vtkm/Bitset.h>
+#include <vtkm/TypeTraits.h>
+#include <vtkm/Types.h>
+#include <vtkm/VectorAnalysis.h>
+
+#include <vtkm/cont/DataSet.h>
+#include <vtkm/cont/VirtualObjectHandle.h>
+
+#include <vtkm/worklet/particleadvection/GridEvaluators.h>
+#include <vtkm/worklet/particleadvection/IntegratorStatus.h>
+#include <vtkm/worklet/particleadvection/Particles.h>
+
+namespace vtkm
+{
+namespace worklet
+{
+namespace particleadvection
+{
+
+template <typename ExecIntegratorType, typename ExecEvaluatorType>
+class StepperImpl
+{
+private:
+  ExecIntegratorType Integrator;
+  ExecEvaluatorType Evaluator;
+  vtkm::FloatDefault DeltaT;
+  vtkm::FloatDefault Tolerance;
+
+public:
+  VTKM_EXEC_CONT
+  StepperImpl(const ExecIntegratorType& integrator,
+              const ExecEvaluatorType& evaluator,
+              const vtkm::FloatDefault deltaT,
+              const vtkm::FloatDefault tolerance)
+    : Integrator(integrator)
+    , Evaluator(evaluator)
+    , DeltaT(deltaT)
+    , Tolerance(tolerance)
+  {
+  }
+
+  template <typename Particle>
+  VTKM_EXEC IntegratorStatus Step(Particle& particle,
+                                  vtkm::FloatDefault& time,
+                                  vtkm::Vec3f& outpos) const
+  {
+    vtkm::Vec3f velocity(0, 0, 0);
+    auto status = this->Integrator.CheckStep(particle, this->DeltaT, velocity);
+    if (status.CheckOk())
+    {
+      outpos = particle.Pos + this->DeltaT * velocity;
+      time += this->DeltaT;
+    }
+    else
+      outpos = particle.Pos;
+
+    return status;
+  }
+
+  template <typename Particle>
+  VTKM_EXEC IntegratorStatus SmallStep(Particle particle,
+                                       vtkm::FloatDefault& time,
+                                       vtkm::Vec3f& outpos) const
+  {
+    //Stepping by this->DeltaT goes beyond the bounds of the dataset.
+    //We need to take an Euler step that goes outside of the dataset.
+    //Use a binary search to find the largest step INSIDE the dataset.
+    //Binary search uses a shrinking bracket of inside / outside, so when
+    //we terminate, the outside value is the stepsize that will nudge
+    //the particle outside the dataset.
+
+    //The binary search will be between {0, this->DeltaT}
+    vtkm::FloatDefault stepRange[2] = { 0, this->DeltaT };
+
+    vtkm::Vec3f currPos(particle.Pos);
+    vtkm::Vec3f currVelocity(0, 0, 0);
+    vtkm::VecVariable<vtkm::Vec3f, 2> currValue, tmp;
+    auto evalStatus = this->Evaluator.Evaluate(currPos, particle.Time, currValue);
+    if (evalStatus.CheckFail())
+      return IntegratorStatus(evalStatus);
+
+    const vtkm::FloatDefault eps = vtkm::Epsilon<vtkm::FloatDefault>() * 10;
+    vtkm::FloatDefault div = 1;
+    while ((stepRange[1] - stepRange[0]) > eps)
+    {
+      //Try a step midway between stepRange[0] and stepRange[1]
+      div *= 2;
+      vtkm::FloatDefault currStep = stepRange[0] + (this->DeltaT / div);
+
+      //See if we can step by currStep
+      IntegratorStatus status = this->Integrator.CheckStep(particle, currStep, currVelocity);
+
+      if (status.CheckOk()) //Integration step succedded.
+      {
+        //See if this point is in/out.
+        auto newPos = particle.Pos + currStep * currVelocity;
+        evalStatus = this->Evaluator.Evaluate(newPos, particle.Time + currStep, tmp);
+        if (evalStatus.CheckOk())
+        {
+          //Point still in. Update currPos and set range to {currStep, stepRange[1]}
+          currPos = newPos;
+          stepRange[0] = currStep;
+        }
+        else
+        {
+          //The step succedded, but the next point is outside.
+          //Step too long. Set range to: {stepRange[0], currStep} and continue.
+          stepRange[1] = currStep;
+        }
+      }
+      else
+      {
+        //Step too long. Set range to: {stepRange[0], stepCurr} and continue.
+        stepRange[1] = currStep;
+      }
+    }
+
+    evalStatus = this->Evaluator.Evaluate(currPos, particle.Time + stepRange[0], currValue);
+    // The eval at Time + stepRange[0] better be *inside*
+    VTKM_ASSERT(evalStatus.CheckOk() && !evalStatus.CheckSpatialBounds());
+    if (evalStatus.CheckFail() || evalStatus.CheckSpatialBounds())
+      return IntegratorStatus(evalStatus);
+
+    // Update the position and time.
+    outpos = currPos + stepRange[1] * particle.Velocity(currValue, stepRange[1]);
+    time += stepRange[1];
+
+    // Get the evaluation status for the point that is *just* outside of the data.
+    evalStatus = this->Evaluator.Evaluate(outpos, time, currValue);
+
+    // The eval should fail, and the point should be outside either spatially or temporally.
+    VTKM_ASSERT(evalStatus.CheckFail() &&
+                (evalStatus.CheckSpatialBounds() || evalStatus.CheckTemporalBounds()));
+
+    IntegratorStatus status(evalStatus);
+    status.SetOk(); //status is ok.
+
+    return status;
+  }
+};
+
+
+template <typename IntegratorType, typename EvaluatorType>
+class Stepper : public vtkm::cont::ExecutionObjectBase
+{
+private:
+  IntegratorType Integrator;
+  EvaluatorType Evaluator;
+  vtkm::FloatDefault DeltaT;
+  vtkm::FloatDefault Tolerance =
+    std::numeric_limits<vtkm::FloatDefault>::epsilon() * static_cast<vtkm::FloatDefault>(100.0f);
+
+public:
+  VTKM_CONT
+  Stepper() = default;
+
+  VTKM_CONT
+  Stepper(const EvaluatorType& evaluator, const vtkm::FloatDefault deltaT)
+    : Integrator(IntegratorType(evaluator))
+    , Evaluator(evaluator)
+    , DeltaT(deltaT)
+  {
+  }
+
+  VTKM_CONT
+  void SetTolerance(vtkm::FloatDefault tolerance) { this->Tolerance = tolerance; }
+
+public:
+  /// Return the StepperImpl object
+  /// Prepares the execution object of Stepper
+  VTKM_CONT auto PrepareForExecution(vtkm::cont::DeviceAdapterId device,
+                                     vtkm::cont::Token& token) const
+    -> StepperImpl<decltype(this->Integrator.PrepareForExecution(device, token)),
+                   decltype(this->Evaluator.PrepareForExecution(device, token))>
+  {
+    auto integrator = this->Integrator.PrepareForExecution(device, token);
+    auto evaluator = this->Evaluator.PrepareForExecution(device, token);
+    using ExecIntegratorType = decltype(integrator);
+    using ExecEvaluatorType = decltype(evaluator);
+    return StepperImpl<ExecIntegratorType, ExecEvaluatorType>(
+      integrator, evaluator, this->DeltaT, this->Tolerance);
+  }
+};
+
+} //namespace particleadvection
+} //namespace worklet
+} //namespace vtkm
+
+#endif // vtk_m_worklet_particleadvection_Stepper_h

vtkm/worklet/testing/UnitTestParticleAdvection.cxx

@@ -19,9 +19,9 @@
 #include <vtkm/worklet/particleadvection/EulerIntegrator.h>
 #include <vtkm/worklet/particleadvection/Field.h>
 #include <vtkm/worklet/particleadvection/GridEvaluators.h>
-#include <vtkm/worklet/particleadvection/IntegratorBase.h>
 #include <vtkm/worklet/particleadvection/Particles.h>
 #include <vtkm/worklet/particleadvection/RK4Integrator.h>
+#include <vtkm/worklet/particleadvection/Stepper.h>
 #include <vtkm/worklet/testing/GenerateTestDataSets.h>
 
 #include <random>
@@ -189,16 +189,16 @@ public:
 
   using ExecutionSignature = void(_1, _2, _3, _4);
 
-  template <typename IntegratorType>
-  VTKM_EXEC void operator()(vtkm::Particle& pointIn,
-                            const IntegratorType* integrator,
+  template <typename Particle, typename IntegratorType>
+  VTKM_EXEC void operator()(Particle& pointIn,
+                            const IntegratorType integrator,
                             vtkm::worklet::particleadvection::IntegratorStatus& status,
                             vtkm::Vec3f& pointOut) const
   {
     vtkm::FloatDefault time = 0;
-    status = integrator->Step(&pointIn, time, pointOut);
+    status = integrator.Step(pointIn, time, pointOut);
     if (status.CheckSpatialBounds())
-      status = integrator->SmallStep(&pointIn, time, pointOut);
+      status = integrator.SmallStep(pointIn, time, pointOut);
   }
 };
 
@@ -272,6 +272,7 @@ void TestEvaluators()
   using FieldType = vtkm::worklet::particleadvection::VelocityField<FieldHandle>;
   using GridEvalType = vtkm::worklet::particleadvection::GridEvaluator<FieldType>;
   using RK4Type = vtkm::worklet::particleadvection::RK4Integrator<GridEvalType>;
+  using Stepper = vtkm::worklet::particleadvection::Stepper<RK4Type, GridEvalType>;
 
   std::vector<vtkm::Vec3f> vecs;
   vtkm::FloatDefault vals[3] = { -1., 0., 1. };
@@ -351,7 +352,7 @@ void TestEvaluators()
           GridEvalType gridEval(ds.GetCoordinateSystem(), ds.GetCellSet(), velocities);
           ValidateEvaluator(gridEval, pointIns, vec, "grid evaluator");
 
-          RK4Type rk4(gridEval, stepSize);
+          Stepper rk4(gridEval, stepSize);
           ValidateIntegrator(rk4, pointIns, stepResult, "constant vector RK4");
           ValidateIntegratorForBoundary(bound, rk4, boundaryPoints, "constant vector RK4");
         }
@@ -366,6 +367,7 @@ void TestGhostCellEvaluators()
   using FieldType = vtkm::worklet::particleadvection::VelocityField<FieldHandle>;
   using GridEvalType = vtkm::worklet::particleadvection::GridEvaluator<FieldType>;
   using RK4Type = vtkm::worklet::particleadvection::RK4Integrator<GridEvalType>;
+  using Stepper = vtkm::worklet::particleadvection::Stepper<RK4Type, GridEvalType>;
 
   constexpr vtkm::Id nX = 6;
   constexpr vtkm::Id nY = 6;
@@ -391,7 +393,7 @@ void TestGhostCellEvaluators()
     GridEvalType gridEval(ds, velocities);
 
     vtkm::FloatDefault stepSize = static_cast<vtkm::FloatDefault>(0.1);
-    RK4Type rk4(gridEval, stepSize);
+    Stepper rk4(gridEval, stepSize);
 
     vtkm::worklet::ParticleAdvection pa;
     std::vector<vtkm::Particle> seeds;
@@ -494,14 +496,16 @@ void TestIntegrators()
     {
       auto seeds = vtkm::cont::make_ArrayHandle(points, vtkm::CopyFlag::On);
       using IntegratorType = vtkm::worklet::particleadvection::RK4Integrator<GridEvalType>;
-      IntegratorType rk4(eval, stepSize);
+      using Stepper = vtkm::worklet::particleadvection::Stepper<IntegratorType, GridEvalType>;
+      Stepper rk4(eval, stepSize);
       res = pa.Run(rk4, seeds, maxSteps);
       ValidateParticleAdvectionResult(res, nSeeds, maxSteps);
     }
     {
       auto seeds = vtkm::cont::make_ArrayHandle(points, vtkm::CopyFlag::On);
       using IntegratorType = vtkm::worklet::particleadvection::EulerIntegrator<GridEvalType>;
-      IntegratorType euler(eval, stepSize);
+      using Stepper = vtkm::worklet::particleadvection::Stepper<IntegratorType, GridEvalType>;
+      Stepper euler(eval, stepSize);
       res = pa.Run(euler, seeds, maxSteps);
       ValidateParticleAdvectionResult(res, nSeeds, maxSteps);
     }
@@ -514,6 +518,7 @@ void TestParticleWorkletsWithDataSetTypes()
   using FieldType = vtkm::worklet::particleadvection::VelocityField<FieldHandle>;
   using GridEvalType = vtkm::worklet::particleadvection::GridEvaluator<FieldType>;
   using RK4Type = vtkm::worklet::particleadvection::RK4Integrator<GridEvalType>;
+  using Stepper = vtkm::worklet::particleadvection::Stepper<RK4Type, GridEvalType>;
   vtkm::FloatDefault stepSize = 0.01f;
 
   const vtkm::Id3 dims(5, 5, 5);
@@ -555,7 +560,7 @@ void TestParticleWorkletsWithDataSetTypes()
     for (auto& ds : dataSets)
     {
       GridEvalType eval(ds.GetCoordinateSystem(), ds.GetCellSet(), velocities);
-      RK4Type rk4(eval, stepSize);
+      Stepper rk4(eval, stepSize);
 
       //Do 4 tests on each dataset.
       //Particle advection worklet with and without steps taken.
@@ -616,13 +621,15 @@ void TestParticleStatus()
     using FieldType = vtkm::worklet::particleadvection::VelocityField<FieldHandle>;
     using GridEvalType = vtkm::worklet::particleadvection::GridEvaluator<FieldType>;
     using RK4Type = vtkm::worklet::particleadvection::RK4Integrator<GridEvalType>;
+    using Stepper = vtkm::worklet::particleadvection::Stepper<RK4Type, GridEvalType>;
+
     vtkm::Id maxSteps = 1000;
     vtkm::FloatDefault stepSize = 0.01f;
 
     FieldType velocities(fieldArray);
 
     GridEvalType eval(ds, velocities);
-    RK4Type rk4(eval, stepSize);
+    Stepper rk4(eval, stepSize);
 
     vtkm::worklet::ParticleAdvection pa;
     std::vector<vtkm::Particle> pts;
@@ -645,6 +652,7 @@ void TestWorkletsBasic()
   using FieldType = vtkm::worklet::particleadvection::VelocityField<FieldHandle>;
   using GridEvalType = vtkm::worklet::particleadvection::GridEvaluator<FieldType>;
   using RK4Type = vtkm::worklet::particleadvection::RK4Integrator<GridEvalType>;
+  using Stepper = vtkm::worklet::particleadvection::Stepper<RK4Type, GridEvalType>;
   vtkm::FloatDefault stepSize = 0.01f;
 
   const vtkm::Id3 dims(5, 5, 5);
@@ -665,7 +673,7 @@ void TestWorkletsBasic()
   for (auto& ds : dataSets)
   {
     GridEvalType eval(ds, velocities);
-    RK4Type rk4(eval, stepSize);
+    Stepper rk4(eval, stepSize);
 
     vtkm::Id maxSteps = 83;
     std::vector<std::string> workletTypes = { "particleAdvection", "streamline" };
@@ -825,6 +833,7 @@ void TestParticleAdvectionFile(const std::string& fname,
   using FieldType = vtkm::worklet::particleadvection::VelocityField<FieldHandle>;
   using GridEvalType = vtkm::worklet::particleadvection::GridEvaluator<FieldType>;
   using RK4Type = vtkm::worklet::particleadvection::RK4Integrator<GridEvalType>;
+  using Stepper = vtkm::worklet::particleadvection::Stepper<RK4Type, GridEvalType>;
 
   VTKM_TEST_ASSERT(ds.HasField("vec"), "Data set missing a field named 'vec'");
   vtkm::cont::Field& field = ds.GetField("vec");
@@ -842,7 +851,7 @@ void TestParticleAdvectionFile(const std::string& fname,
 
   FieldType velocities(fieldArray);
   GridEvalType eval(ds.GetCoordinateSystem(), ds.GetCellSet(), velocities);
-  RK4Type rk4(eval, stepSize);
+  Stepper rk4(eval, stepSize);
 
   for (int i = 0; i < 2; i++)
   {

vtkm/worklet/testing/UnitTestTemporalAdvection.cxx

@@ -19,8 +19,8 @@
 #include <vtkm/cont/testing/Testing.h>
 #include <vtkm/worklet/ParticleAdvection.h>
 #include <vtkm/worklet/particleadvection/Field.h>
-#include <vtkm/worklet/particleadvection/IntegratorBase.h>
 #include <vtkm/worklet/particleadvection/Particles.h>
+#include <vtkm/worklet/particleadvection/Stepper.h>
 #include <vtkm/worklet/particleadvection/TemporalGridEvaluators.h>
 
 template <typename ScalarType>