/*=========================================================================

  Program:   Visualization Toolkit
  Module:    vtkCompositeInterpolatedVelocityField.h

  Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
  All rights reserved.
  See Copyright.txt or http://www.kitware.com/Copyright.htm 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.

=========================================================================*/
/**
 * @class   vtkCompositeInterpolatedVelocityField
 * @brief   An abstract class for
 *  obtaining the interpolated velocity values at a point
 *
 *
 *  vtkCompositeInterpolatedVelocityField acts as a continuous velocity field
 *  by performing cell interpolation on the underlying vtkDataSet. This is an
 *  abstract sub-class of vtkFunctionSet, NumberOfIndependentVariables = 4
 *  (x,y,z,t) and NumberOfFunctions = 3 (u,v,w). With a brute-force scheme,
 *  every time an evaluation is performed, the target cell containing point
 *  (x,y,z) needs to be found by calling FindCell(), via either vtkDataSet or
 *  vtkAbstractCelllocator's sub-classes (vtkCellLocator & vtkModifiedBSPTree).
 *  As it incurs a large cost, one (for vtkCellLocatorInterpolatedVelocityField
 *  via vtkAbstractCellLocator) or two (for vtkInterpolatedVelocityField via
 *  vtkDataSet that involves vtkPointLocator in addressing vtkPointSet) levels
 *  of cell caching may be exploited to increase the performance.
 *
 *  For vtkInterpolatedVelocityField, level #0 begins with intra-cell caching.
 *  Specifically if the previous cell is valid and the next point is still in
 *  it ( i.e., vtkCell::EvaluatePosition() returns 1, coupled with newly created
 *  parametric coordinates & weights ), the function values can be interpolated
 *  and only vtkCell::EvaluatePosition() is invoked. If this fails, then level #1
 *  follows by inter-cell search for the target cell that contains the next point.
 *  By an inter-cell search, the previous cell provides an important clue or serves
 *  as an immediate neighbor to aid in locating the target cell via vtkPointSet::
 *  FindCell(). If this still fails, a global cell location / search is invoked via
 *  vtkPointSet::FindCell(). Here regardless of either inter-cell or global search,
 *  vtkPointLocator is in fact employed (for datasets of type vtkPointSet only, note
 *  vtkImageData and vtkRectilinearGrid are able to provide rapid and robust cell
 *  location due to the simple mesh topology) as a crucial tool underlying the cell
 *  locator. However, the use of vtkPointLocator makes vtkInterpolatedVelocityField
 *  non-robust in cell location for vtkPointSet.
 *
 *  For vtkCellLocatorInterpolatedVelocityField, the only caching (level #0) works
 *  by intra-cell trial. In case of failure, a global search for the target cell is
 *  invoked via vtkAbstractCellLocator::FindCell() and the actual work is done by
 *  either vtkCellLocator or vtkModifiedBSPTree (for datasets of type vtkPointSet
 *  only, while vtkImageData and vtkRectilinearGrid themselves are able to provide
 *  fast robust cell location). Without the involvement of vtkPointLocator, robust
 *  cell location is achieved for vtkPointSet.
 *
 * @warning
 *  vtkCompositeInterpolatedVelocityField is not thread safe. A new instance
 *  should be created by each thread.
 *
 * @sa
 *  vtkInterpolatedVelocityField vtkCellLocatorInterpolatedVelocityField
 *  vtkGenericInterpolatedVelocityField vtkCachingInterpolatedVelocityField
 *  vtkTemporalInterpolatedVelocityField vtkFunctionSet vtkStreamTracer
*/

#ifndef vtkCompositeInterpolatedVelocityField_h
#define vtkCompositeInterpolatedVelocityField_h

#include "vtkFiltersFlowPathsModule.h" // For export macro
#include "vtkAbstractInterpolatedVelocityField.h"

#include <vector> // STL Header; Required for vector

class vtkDataSet;

class vtkDataArray;

class vtkPointData;
class vtkGenericCell;
class vtkCompositeInterpolatedVelocityFieldDataSetsType;

class VTKFILTERSFLOWPATHS_EXPORT vtkCompositeInterpolatedVelocityField : public vtkAbstractInterpolatedVelocityField
{
public:
  vtkTypeMacro( vtkCompositeInterpolatedVelocityField, vtkAbstractInterpolatedVelocityField);
  void PrintSelf( ostream & os, vtkIndent indent ) override;

  //@{
  /**
   * Get the most recently visited dataset and it id. The dataset is used
   * for a guess regarding where the next point will be, without searching
   * through all datasets. When setting the last dataset, care is needed as
   * no reference counting or checks are performed. This feature is intended
   * for custom interpolators only that cache datasets independently.
   */
  vtkGetMacro( LastDataSetIndex, int );
  //@}


  /**
   * Add a dataset for implicit velocity function evaluation. If more than
   * one dataset is added, the evaluation point is searched in all until a
   * match is found. THIS FUNCTION DOES NOT CHANGE THE REFERENCE COUNT OF
   * dataset FOR THREAD SAFETY REASONS.
   */
  virtual void AddDataSet( vtkDataSet * dataset ) = 0;


protected:
  vtkCompositeInterpolatedVelocityField();
  ~vtkCompositeInterpolatedVelocityField() override;

  int       LastDataSetIndex;
  vtkCompositeInterpolatedVelocityFieldDataSetsType * DataSets;

private:
  vtkCompositeInterpolatedVelocityField
    ( const vtkCompositeInterpolatedVelocityField & ) = delete;
  void operator = ( const vtkCompositeInterpolatedVelocityField & ) = delete;
};

typedef std::vector< vtkDataSet * > DataSetsTypeBase;
class   vtkCompositeInterpolatedVelocityFieldDataSetsType: public DataSetsTypeBase { };

#endif
