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

  Program:   Visualization Toolkit
  Module:    vtkImplicitFunction.hh
  Language:  C++
  Date:      $Date$
  Version:   $Revision$


Copyright (c) 1993-1995 Ken Martin, Will Schroeder, Bill Lorensen.

This software is copyrighted by Ken Martin, Will Schroeder and Bill Lorensen.
The following terms apply to all files associated with the software unless
explicitly disclaimed in individual files. This copyright specifically does
not apply to the related textbook "The Visualization Toolkit" ISBN
013199837-4 published by Prentice Hall which is covered by its own copyright.

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of the algorithms implemented by this software are patented, observe all
applicable patent law.

IN NO EVENT SHALL THE AUTHORS OR DISTRIBUTORS BE LIABLE TO ANY PARTY FOR
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=========================================================================*/
// .NAME vtkImplicitFunction - abstract interface for implicit functions
// .SECTION Description
// vtkImplicitFunction specifies an abstract interface for implicit 
// functions. Implicit functions are of the form F(x,y,z) = 0. Two primitive 
// operations are required: the ability to evaluate the function and the 
// function gradient at a given point.
//
// vtkImplicitFunction provides a mechanism to transform the implicit
// function(s) via a transformation matrix. This capability can be used to 
// translate, orient, or scale implicit functions. For example, a sphere 
// implicit function can be transformed into an oriented ellipse. This is 
// accomplished by using an instance of vtkTransform.
// .SECTION Caveats
// The transformation matrix transforms a point into the space of the implicit
// function (i.e., the model space). Typically we want to transpose the 
// implicit model into world coordinates. In this case the inverse of the 
// transform is required.
// .SECTION See Also
// vtkTransform

#ifndef __vtkImplicitFunction_h
#define __vtkImplicitFunction_h

#include "vtkObject.hh"
#include "vtkTransform.hh"

class vtkImplicitFunction : public vtkObject
{
public:
  vtkImplicitFunction();
  char *GetClassName() {return "vtkImplicitFunction";};
  void PrintSelf(ostream& os, vtkIndent indent);

  float FunctionValue(float x[3]);
  void FunctionGradient(float x[3], float g[3]);

  // Description:
  // Evaluate function at position x-y-z and return value. Must be implemented
  // by derived class.
  virtual float EvaluateFunction(float x[3]) = 0;

  // Description:
  // Evaluate function gradient at position x-y-z and pass back vector. Must
  // be implemented by derived class.
  virtual void EvaluateGradient(float x[3], float g[3]) = 0;

  // Description:
  // Set/Get transformation matrix to transform implicit function.
  vtkSetObjectMacro(Transform,vtkTransform);
  vtkGetObjectMacro(Transform,vtkTransform);

protected:
  vtkTransform *Transform;

};

#endif
