text: /*=========================================================================
   *
   *  Copyright Insight Software Consortium
   *
   *  Licensed under the Apache License, Version 2.0 (the "License");
   *  you may not use this file except in compliance with the License.
   *  You may obtain a copy of the License at
   *
   *         http://www.apache.org/licenses/LICENSE-2.0.txt
   *
   *  Unless required by applicable law or agreed to in writing, software
   *  distributed under the License is distributed on an "AS IS" BASIS,
   *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   *  See the License for the specific language governing permissions and
   *  limitations under the License.
   *
   *=========================================================================*/
  #ifndef itkCurvatureFlowFunction_h
  #define itkCurvatureFlowFunction_h
  
  #include "itkFiniteDifferenceFunction.h"
  #include "itkMacro.h"
  
  namespace itk
  {
  /** \class CurvatureFlowFunction
   *
   * \brief
   * This class encapsulate the finite difference equation which drives a
   * curvature flow denoising algorithm.
   *
   * This class uses a zero flux Neumann boundary condition when computing
   * derivatives near the data boundary.
   *
   * This class operates as part of the finite difference solver hierarchy.
   *
   * \sa CurvatureFlowImageFilter
   * \sa ZeroFluxNeumannBoundaryCondition
   * \ingroup FiniteDifferenceFunctions
   * \ingroup ITKCurvatureFlow
   */
  template< typename TImage >
  class ITK_TEMPLATE_EXPORT CurvatureFlowFunction:
    public FiniteDifferenceFunction< TImage >
  {
  public:
    /**  Standard class typedefs. */
    typedef CurvatureFlowFunction              Self;
    typedef FiniteDifferenceFunction< TImage > Superclass;
    typedef SmartPointer< Self >               Pointer;
    typedef SmartPointer< const Self >         ConstPointer;
  
    /** Method for creation through the object factory. */
    itkNewMacro(Self);
  
    /** Run-time type information (and related methods) */
    itkTypeMacro(CurvatureFlowFunction,
                 FiniteDifferenceFunction);
  
    /** Inherit some parameters from the superclass type. */
    typedef typename Superclass::ImageType              ImageType;
    typedef typename Superclass::PixelType              PixelType;
    typedef typename Superclass::RadiusType             RadiusType;
    typedef PixelType                                   ScalarValueType;
    typedef typename Superclass::PixelRealType          PixelRealType;
    typedef typename Superclass::NeighborhoodType       NeighborhoodType;
    typedef typename Superclass::NeighborhoodScalesType NeighborhoodScalesType;
    typedef typename Superclass::FloatOffsetType        FloatOffsetType;
    typedef typename Superclass::TimeStepType           TimeStepType;
  
    /** Extract superclass dimension. */
    itkStaticConstMacro(ImageDimension, unsigned int, Superclass::ImageDimension);
  
    /** Computes the time step for an update given a global data structure.
     * The data used in the computation may take different forms depending on
     * the nature of the equations.  This global data cannot be kept in the
     * instance of the equation object itself since the equation object must
     * remain stateless for thread safety.  The global data is therefore managed
     * for each thread by the finite difference solver filters.
     *
     * Currently, this function returns the user specified constant time step.
     * \todo compute timestep based on CFL condition.
     */
    virtual TimeStepType ComputeGlobalTimeStep(void *GlobalData) const ITK_OVERRIDE;
  
    /** Returns a pointer to a global data structure that is passed to this
     * object from the solver at each calculation.  The idea is that the solver
     * holds the state of any global values needed to calculate the time step,
     * while the equation object performs the actual calculations.  The global
     * data should also be initialized in this method. */
    virtual void * GetGlobalDataPointer() const ITK_OVERRIDE
    {
      GlobalDataStruct *ans = new GlobalDataStruct();
  
      ans->m_MaxChange   = NumericTraits< ScalarValueType >::ZeroValue();
      return ans;
    }
  
    /** When the finite difference solver filter has finished using a global
     * data pointer, it passes it to this method, which frees the memory.
     * The solver cannot free the memory because it does not know the type
     * to which the pointer points. */
    virtual void ReleaseGlobalDataPointer(void *GlobalData) const ITK_OVERRIDE
    { delete (GlobalDataStruct *)GlobalData; }
  
    /** Set the time step parameter */
    void SetTimeStep(const TimeStepType & t)
    { m_TimeStep = t; }
  
    /** Get the time step parameter */
    const TimeStepType & GetTimeStep() const
    { return m_TimeStep; }
  
    /** This method computes the solution update for each pixel that does not
     * lie on a the data set boundary. */
    virtual PixelType ComputeUpdate(const NeighborhoodType & neighborhood,
                                    void *globalData,
                                    const FloatOffsetType & offset = FloatOffsetType(0.0)
                                    ) ITK_OVERRIDE;
  
  protected:
  
    /** @cond HIDE_STRUCTURE */
  
    /** A global data type for this class of equations.  Used to store
     * values that are needed in calculating the time step. */
    struct GlobalDataStruct {
      GlobalDataStruct()
      {
        m_MaxChange = NumericTraits< ScalarValueType >::ZeroValue();
      }
  
      ~GlobalDataStruct() {}
  
      ScalarValueType m_MaxChange;
    };
    /// @endcond
  
    CurvatureFlowFunction();
    ~CurvatureFlowFunction() {}
  
  private:
    ITK_DISALLOW_COPY_AND_ASSIGN(CurvatureFlowFunction);
  
    TimeStepType m_TimeStep;
  };
  } // end namespace itk
  
  #ifndef ITK_MANUAL_INSTANTIATION
  #include "itkCurvatureFlowFunction.hxx"
  #endif
  
  #endif
  