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

  Program:   Visualization Toolkit
  Module:    vtkVolumeRayCastFunction.h
  Language:  C++
  Date:      $Date$
  Version:   $Revision$


Copyright (c) 1993-2000 Ken Martin, Will Schroeder, Bill Lorensen 
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// .NAME vtkVolumeRayCastFunction - a superclass for ray casting functions

// .SECTION Description
// vtkVolumeRayCastFunction is a superclass for ray casting functions that 
// can be used within a vtkVolumeRayCastMapper. This includes for example,
// vtkVolumeRayCastCompositeFunction, vtkVolumeRayCastMIPFunction, and
// vtkVolumeRayCastIsosurfaceFunction.

// .SECTION See Also
// vtkVolumeRayCastCompositeFunction vtkVolumeRayCastMIPFunction
// vtkVolumeRayCastIsosurfaceFunction vtkVolumeRayCastMapper

#ifndef __vtkVolumeRayCastFunction_h
#define __vtkVolumeRayCastFunction_h

#include "vtkObject.h"
#include "vtkRayCastStructures.h"
#include "vtkVolumeRayCastStructures.h"

class vtkRenderer;
class vtkVolume;
class vtkVolumeRayCastMapper;

class VTK_EXPORT vtkVolumeRayCastFunction : public vtkObject
{
public:
  vtkTypeMacro(vtkVolumeRayCastFunction,vtkObject);

  // Description:
  // Do the basic initialization. This includes saving the parameters
  // passed in into local variables, as well as grabbing some useful
  // info from the volume property and normal encoder. This initialize
  // routine is called once per render. It also calls the 
  // SpecificFunctionInitialize of the subclass function.
//BTX
  void FunctionInitialize( vtkRenderer *ren,
			   vtkVolume   *vol,
			   VTKRayCastVolumeInfo *volumeInfo,
			   vtkVolumeRayCastMapper *mapper );

  virtual void CastRay( VTKRayCastRayInfo *rayInfo,
			VTKRayCastVolumeInfo *volumeInfo )=0;
//ETX

  // Description:
  // Get the value below which all scalar values are considered to
  // have 0 opacity.
  virtual float GetZeroOpacityThreshold( vtkVolume *vol )=0;

protected:
  vtkVolumeRayCastFunction() {};
  ~vtkVolumeRayCastFunction() {};
  vtkVolumeRayCastFunction(const vtkVolumeRayCastFunction &) {};
  void operator=(const vtkVolumeRayCastFunction &) {};

  // Description:
  // This method gives the subclass a chance to do any special
  // initialization that it may need to do
//BTX
  virtual void SpecificFunctionInitialize( vtkRenderer *ren,
					   vtkVolume   *vol,
					   VTKRayCastVolumeInfo *volumeInfo,
					   vtkVolumeRayCastMapper *mapper )=0;
//ETX
};

#endif
