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

  Program:   Visualization Toolkit
  Module:    $RCSfile: vtkRecursiveSphereDirectionEncoder.h,v $

  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 vtkRecursiveSphereDirectionEncoder - A direction encoder based on the recursive subdivision of an octahedron
// .SECTION Description
// vtkRecursiveSphereDirectionEncoder is a direction encoder which uses the 
// vertices of a recursive subdivision of an octahedron (with the vertices
// pushed out onto the surface of an enclosing sphere) to encode directions
// into a two byte value. 
//
// .SECTION see also
// vtkDirectionEncoder

#ifndef __vtkRecursiveSphereDirectionEncoder_h
#define __vtkRecursiveSphereDirectionEncoder_h

#include "vtkDirectionEncoder.h"

class VTK_VOLUMERENDERING_EXPORT vtkRecursiveSphereDirectionEncoder : public vtkDirectionEncoder
{
public:
  vtkTypeRevisionMacro(vtkRecursiveSphereDirectionEncoder,vtkDirectionEncoder);
  void PrintSelf( ostream& os, vtkIndent indent );

// Description:
// Construct the object. Initialize the index table which will be
// used to map the normal into a patch on the recursively subdivided
// sphere.
  static vtkRecursiveSphereDirectionEncoder *New();


  // Description:
  // Given a normal vector n, return the encoded direction  
  int GetEncodedDirection( float n[3] );
  
  // Description:
  /// Given an encoded value, return a pointer to the normal vector
  float *GetDecodedGradient( int value );

  // Description:
  // Return the number of encoded directions
  int GetNumberOfEncodedDirections( void );

  // Description:
  // Get the decoded gradient table. There are 
  // this->GetNumberOfEncodedDirections() entries in the table, each
  // containing a normal (direction) vector. This is a flat structure - 
  // 3 times the number of directions floats in an array.
  float *GetDecodedGradientTable( void );

  // Description:
  // Set / Get the recursion depth for the subdivision. This
  // indicates how many time one triangle on the initial 8-sided
  // sphere model is replaced by four triangles formed by connecting
  // triangle edge midpoints. A recursion level of 0 yields 8 triangles
  // with 6 unique vertices. The normals are the vectors from the
  // sphere center through the vertices. The number of directions
  // will be 11 since the four normals with 0 z values will be
  // duplicated in the table - once with +0 values and the other
  // time with -0 values, and an addition index will be used to
  // represent the (0,0,0) normal. If we instead choose a recursion 
  // level of 6 (the maximum that can fit within 2 bytes) the number
  // of directions is 16643, with 16386 unique directions and a 
  // zero normal.
  vtkSetClampMacro( RecursionDepth, int, 0, 6 );
  vtkGetMacro( RecursionDepth, int );                                        

protected:
  vtkRecursiveSphereDirectionEncoder();
  ~vtkRecursiveSphereDirectionEncoder();

  // How far to recursively divide the sphere
  int                     RecursionDepth;
  
  // The index table which maps (x,y) position in the rotated grid
  // to an encoded normal 
  //int                   IndexTable[2*NORM_SQR_SIZE - 1][2*NORM_SQR_SIZE -1];
  int                     *IndexTable;

  // This is a table that maps encoded normal (2 byte value) to a 
  // normal (dx, dy, dz)
  //float                 DecodedNormal[3*(1 + 2*(NORM_SQR_SIZE*NORM_SQR_SIZE+
  //                             (NORM_SQR_SIZE-1)*(NORM_SQR_SIZE-1)))];
  float                   *DecodedNormal;

  // Method to initialize the index table and variable that
  // stored the recursion depth the last time the table was
  // built
  void                  InitializeIndexTable( void );
  int                   IndexTableRecursionDepth;

  int                   OuterSize;
  int                   InnerSize;
  int                   GridSize;
private:
  vtkRecursiveSphereDirectionEncoder(const vtkRecursiveSphereDirectionEncoder&);  // Not implemented.
  void operator=(const vtkRecursiveSphereDirectionEncoder&);  // Not implemented.
}; 


#endif

