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

  Program:   Visualization Toolkit
  Module:    vtkImplicitSum.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.

=========================================================================*/
// .NAME vtkImplicitSum - implicit sum of other implicit functions
// .SECTION Description
//  vtkImplicitSum produces a linear combination of other implicit functions.
//  The contribution of each function is weighted by a scalar coefficient.
//  The NormalizeByWeight option normalizes the output so that the 
//  scalar weights add up to 1.  Note that this function gives accurate
//  sums and gradients only if the input functions are linear.

#ifndef __vtkImplicitSum_h
#define __vtkImplicitSum_h

#include "vtkImplicitFunction.h"

class vtkDoubleArray;
class vtkImplicitFunctionCollection;

class VTK_FILTERING_EXPORT vtkImplicitSum : public vtkImplicitFunction
{
public:
  static vtkImplicitSum *New();

  vtkTypeRevisionMacro(vtkImplicitSum,vtkImplicitFunction);
  void PrintSelf(ostream& os, vtkIndent indent);

  // Description:
  // Evaluate implicit function using current functions and weights.
  double EvaluateFunction(double x[3]);
  double EvaluateFunction(double x, double y, double z)
    {return this->vtkImplicitFunction::EvaluateFunction(x, y, z); } ;

  // Description:
  // Evaluate gradient of the weighted sum of functions.  Input functions
  // should be linear.
  void EvaluateGradient(double x[3], double g[3]);

  // Description:
  // Override modified time retrieval because of object dependencies.
  unsigned long GetMTime();

  // Description:
  // Add another implicit function to the list of functions, along with a 
  // weighting factor.
  void AddFunction(vtkImplicitFunction *in, double weight);

  // Description:
  // Add another implicit function to the list of functions, weighting it by
  // a factor of 1.
  void AddFunction(vtkImplicitFunction *in) { this->AddFunction(in, 1.0); }

  // Description:
  // Remove all functions from the list.
  void RemoveAllFunctions();

  // Description:
  // Set the weight (coefficient) of the given function to be weight.
  void SetFunctionWeight(vtkImplicitFunction *f, double weight);

  // Description: 
  // When calculating the function and gradient values of the
  // composite function, setting NormalizeByWeight on will divide the
  // final result by the total weight of the component functions.
  // This process does not otherwise normalize the gradient vector.
  // By default, NormalizeByWeight is off.
  vtkSetMacro(NormalizeByWeight, int);
  vtkGetMacro(NormalizeByWeight, int);
  vtkBooleanMacro(NormalizeByWeight, int);

protected:
  vtkImplicitSum();
  ~vtkImplicitSum();

  vtkImplicitFunctionCollection *FunctionList;
  vtkDoubleArray *Weights;
  double TotalWeight;

  void CalculateTotalWeight(void);
  int NormalizeByWeight;

private:
  vtkImplicitSum(const vtkImplicitSum&);  // Not implemented.
  void operator=(const vtkImplicitSum&);  // Not implemented.
};

#endif
