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

  Program:   Visualization Toolkit
  Module:    vtkNormalEncoder.cxx
  Language:  C++
  Date:      $Date$
  Version:   $Revision$


Copyright (c) 1993-1998 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.

The authors hereby grant permission to use, copy, and distribute this
software and its documentation for any purpose, provided that existing
copyright notices are retained in all copies and that this notice is included
verbatim in any distributions. Additionally, the authors grant permission to
modify this software and its documentation for any purpose, provided that
such modifications are not distributed without the explicit consent of the
authors and that existing copyright notices are retained in all copies. Some
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
DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT
OF THE USE OF THIS SOFTWARE, ITS DOCUMENTATION, OR ANY DERIVATIVES THEREOF,
EVEN IF THE AUTHORS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

THE AUTHORS AND DISTRIBUTORS SPECIFICALLY DISCLAIM ANY WARRANTIES, INCLUDING,
BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
PARTICULAR PURPOSE, AND NON-INFRINGEMENT.  THIS SOFTWARE IS PROVIDED ON AN
"AS IS" BASIS, AND THE AUTHORS AND DISTRIBUTORS HAVE NO OBLIGATION TO PROVIDE
MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.


=========================================================================*/
#include <math.h>

#include "vtkNormalEncoder.h"
#include "vtkUnsignedCharScalars.h"
#include "vtkUnsignedShortScalars.h"
#include "vtkShortScalars.h"
#include "vtkIntScalars.h"
#include "vtkFloatScalars.h"

// Description:
// This is the templated function that actually computes the EncodedNormal
// and the GradientMagnitude
template <class T>
static void ComputeGradients( vtkNormalEncoder *encoder, T *data_ptr,
			      int thread_id, int thread_count )
{
  int            xstep, ystep, zstep;
  int            x, y, z;
  int            norm_size;
  int            offset;
  int            z_start, z_limit;
  T              *dptr;
  unsigned char  *gptr;
  unsigned short *nptr;
  float          nx, ny, nz, t;
  float          gvalue;

  // Compute steps through the volume in x, y, and z
  xstep = 1;
  ystep = encoder->ScalarInputSize[0];
  zstep = encoder->ScalarInputSize[0] * encoder->ScalarInputSize[1];

  // Compute the size of the normal grid - the large grid size is
  // NORM_SQR_SIZE * NORM_SQR_SIZE and the small grid of vertices
  // between each 4 of the large grid is ( NORM_SQR_SIZE - 1 ) * 
  // ( NORM_SQR_SIZE - 1 ).  The first norm_size normal indices have
  // normals with z components that are >= 0, and the normals with
  // indices from norm_size to 2*norm_size - 1 have z components
  // that are <= 0.  (There are NORM_SQR_SIZE * 4 - 4 duplicate
  // normals that have z components = 0 and are in both sets of
  // normals)
  norm_size = NORM_SQR_SIZE * NORM_SQR_SIZE + 
	( NORM_SQR_SIZE - 1 ) * ( NORM_SQR_SIZE - 1 );

  // Compute an offset based on the thread_id. The volume will
  // be broken into large slabs (thread_count slabs). For this thread
  // we need to access the correct slab. Also compute the z plane that
  // this slab starts on, and the z limit of this slab (one past the
  // end of the slab)
  z_start = (int)(( (float)thread_id / (float)thread_count ) *
		  encoder->ScalarInputSize[2] );
  offset = z_start * encoder->ScalarInputSize[0] * encoder->ScalarInputSize[1];
  z_limit = (int)(( (float)(thread_id + 1) / (float)thread_count ) *
		  encoder->ScalarInputSize[2] );

  // Make sure out z_limit didn't get too big - it shouldn't so print an
  // error message if this happens and return
  if ( z_limit > encoder->ScalarInputSize[2] )
    {
    return;
    }


  // Set some pointers
  dptr = data_ptr + offset;
  nptr = encoder->EncodedNormal + offset;
  gptr = encoder->GradientMagnitude + offset;

  // Loop through all the data and compute the encoded normal and
  // gradient magnitude for each scalar location
  for ( z = z_start; z < z_limit; z++ )
    for ( y = 0; y < encoder->ScalarInputSize[1]; y++ )
      for ( x = 0; x < encoder->ScalarInputSize[0]; x++ )
	{
	// Use a central difference method if possible,
	// otherwise use a forward or backward difference if
	// we are on the edge

	// Compute the X component
	if ( x > 0 && x < encoder->ScalarInputSize[0] - 1 )
	  nx = (float)*(dptr-xstep) - (float)*(dptr+xstep); 
	else if ( x == 0 )
	  nx = -((float)*(dptr+xstep));
	else
	  nx =  ((float)*(dptr-xstep));
	
	// Compute the Y component
	if ( y > 0 && y < encoder->ScalarInputSize[1] - 1 )
	  ny = (float)*(dptr-ystep) - (float)*(dptr+ystep); 
	else if ( y == 0 )
	  ny = -((float)*(dptr+ystep));
	else
	  ny =  ((float)*(dptr-ystep));
	
	// Compute the Z component
	if ( z > 0 && z < encoder->ScalarInputSize[2] - 1 )
	  nz = (float)*(dptr-zstep) - (float)*(dptr+zstep); 
	else if ( z == 0 )
	  nz = -((float)*(dptr+zstep));
	else
	  nz =  ((float)*(dptr-zstep));

	// Take care of the aspect ratio of the data
	// Scaling in the vtkVolume is isotropic, so this is the
	// only place we have to worry about non-isotropic scaling.
	nx *= encoder->ScalarInputAspect[1] * encoder->ScalarInputAspect[2];
	ny *= encoder->ScalarInputAspect[0] * encoder->ScalarInputAspect[2];
	nz *= encoder->ScalarInputAspect[0] * encoder->ScalarInputAspect[1];
	
	// Compute the gradient magnitude
	t = sqrt( (double)( nx*nx + ny*ny + nz*nz ) ) / 2.0;
	
	// Encode this into an 8 bit value - this method is changing
	// in the near future
	gvalue = 
	  255.0 * ( t - encoder->GradientMagnitudeRange[0] ) / 
	  ( encoder->GradientMagnitudeRange[1] - 
	    encoder->GradientMagnitudeRange[0] );
	  
	if ( gvalue < 0.0 )
	  *gptr = 0;
	else if ( gvalue > 255.0 )
	  *gptr = 255;
	else 
	  *gptr = (unsigned char) gvalue;
	
	// Normalize the gradient direction
	if ( t )
	  {
	  nx /= t;
	  ny /= t;
	  nz /= t;
	  }

	// Convert the gradient direction into an encoded index value
	// This is done by computing the (x,y) grid position of this 
	// normal in the 2*NORM_SQR_SIZE - 1 grid, then passing this
	// through the IndexTable to look up the 16 bit index value
	if (  fabs((double)nz) + fabs((double)nx) + fabs((double)ny) )
	  {
	  t = 1.0 / ( fabs((double)nz) + fabs((double)nx) + 
		      fabs((double)ny) );
	  
	  nx *= t;
	  ny *= t;
	  }
	
	*nptr = encoder->IndexTable
	  [(int)((float)(nx+1 + 1.0 / (float)(2*(NORM_SQR_SIZE-1))) * 
		 (float)(NORM_SQR_SIZE-1))]
	  [(int)((float)(ny+1 + 1.0 / (float)(2*(NORM_SQR_SIZE-1))) * 
		 (float)(NORM_SQR_SIZE-1))];
	
	// If the z component is less than 0.0, add norm_size to the
	// index 
	if ( nz < 0.0 ) *nptr += norm_size;

	nptr++;
	gptr++;
	dptr++;

	}
}

// Description:
// Construct a vtkNormalEncoder with initial values of NULL for
// the ScalarInput, EncodedNormal, and GradientMagnitude. Also,
// indicate that the IndexTable has not yet been initialized. The
// GradientMagnitudeRange and the GradientMangitudeTable are 
// initialized to default values - these will change in the future
// when magnitude of gradient opacities are included
vtkNormalEncoder::vtkNormalEncoder()
{
  int i;

  this->ScalarInput                = NULL;
  this->EncodedNormal              = NULL;
  this->GradientMagnitude          = NULL;
  this->GradientMagnitudeRange[0]  = 0.0;
  this->GradientMagnitudeRange[1]  = 256.0;
  this->IndexTableInitialized      = 0;
  this->NumberOfThreads            = this->Threader.GetNumberOfThreads();

  for ( i = 0; i < 256; i++ )
    this->GradientMagnitudeTable[i] = this->GradientMagnitudeRange[0] + 
	(float)i/ 256.0 * ( this->GradientMagnitudeRange[1] - 
	  this->GradientMagnitudeRange[0] );
}

// Description:
// Destruct a vtkNormalEncoder - free up any memory used
vtkNormalEncoder::~vtkNormalEncoder()
{
  if ( this->EncodedNormal )
    delete this->EncodedNormal;

  if ( this->GradientMagnitude )
    delete this->GradientMagnitude;
}

// Description:
// Set the gradient magnitude range - this will disappear soon
void vtkNormalEncoder::SetGradientMagnitudeRange( float v1, float v2 )
{
  int i;
 
  this->GradientMagnitudeRange[0] = v1;
  this->GradientMagnitudeRange[1] = v2;
  this->Modified();
  
  for ( i = 0; i < 256; i++ )
    this->GradientMagnitudeTable[i] = this->GradientMagnitudeRange[0] + 
	(float)i/ 256.0 * ( this->GradientMagnitudeRange[1] - 
	  this->GradientMagnitudeRange[0] );
}

// Description:
// Initialize the index table.  This is a 2*NORM_SQR_SIZE - 1 by
// 2*NORM_SQR_SIZE - 1 entry table that maps (x,y) grid position to
// encoded normal index.  The grid position is obtained by starting
// with an octahedron (comprised of 8 triangles forming a double
// pyramid). Each triangle is then replaced by 4 triangles by joining
// edge midpoints.  This is done recursively until NORM_SQR_SIZE
// vertices exist on each original edge. If you "squish" this octahedron,
// it will look like a diamond.  Then rotate it 45 degrees, it will
// look like a square.  Then look at the pattern of vertices - there
// is a NORM_SQR_SIZE by NORM_SQR_SIZE grid, with a (NORM_SQR_SIZE-1) by
// NORM_SQR_SIZE - 1 grid inside of it.  The vertices all fall on
// (x,y) locatiions in a grid that is 2*NORM_SQR_SIZE - 1 by
// 2*NORM_SQR_SIZE - 1, although not every (x,y) location has a vertex.
void vtkNormalEncoder::InitializeIndexTable( void )
{
  int     i, j, index, max_index;
  float   x, y, z, tmp_x, tmp_y;
  float   norm;

  // Initialize the index
  index = 0;

  // max_index indicates the largest index we will get - the number
  // of vertices in the two-grid square.  This represents half the
  // normals, and max_index is used to offset from one half into the
  // other.  One half of the normals have z components >= 0, and the
  // second half (all with indices above max_index) have z components
  // that are <= 0.
  max_index =  NORM_SQR_SIZE * NORM_SQR_SIZE + 
               (NORM_SQR_SIZE - 1) * (NORM_SQR_SIZE - 1);

  // The outer loop is for 2*NORM_SQR_SIZE - 1 rows
  for ( i = 0; i <= (NORM_SQR_SIZE-1)*2; i++ )
    {
    // Compute the y component for this row
    tmp_y = (float)(2*i)/(float)(NORM_SQR_SIZE*2 - 1) - 1.0;

    // On the odd rows, we are doing the small grid which has
    // NORM_SQR_SIZE - 1 elements in it
    if ( i%2 )
      {
      for ( j = 0; j < NORM_SQR_SIZE - 1; j++ )
	{
	// compute the x component for this column
        tmp_x = (float)(2*j)/(float)(NORM_SQR_SIZE-1) - 
	  1.0 + (1.0/(float)(NORM_SQR_SIZE-1));

	// rotate by 45 degrees
        x = 0.5 * tmp_x - 0.5 * tmp_y;
        y = 0.5 * tmp_x + 0.5 * tmp_y;

	// compute the z based on the x and y values
        if ( x >= 0 && y >= 0 )
          z = 1.0 - x - y;
        else if ( x >= 0 && y < 0 )
          z = 1.0 - x + y;
        else if ( x < 0 && y < 0 )
          z = 1.0 + x + y;
        else 
          z = 1.0 + x - y;

	// Normalize this direction and set the DecodedNormal table for
	// this index to this normal.  Also set the corresponding 
	// entry for this normal with a negative z component
        norm = sqrt( (double)( x*x + y*y + z*z ) );
        this->DecodedNormal[3*index + 0] = x / norm;
        this->DecodedNormal[3*index + 1] = y / norm;
        this->DecodedNormal[3*index + 2] = z / norm;
        this->DecodedNormal[3*(index+max_index) + 0] =   x / norm;
        this->DecodedNormal[3*(index+max_index) + 1] =   y / norm;
        this->DecodedNormal[3*(index+max_index) + 2] = -(z / norm);

	// For this x,y grid location, set the index
	// The grid location ranges between 0 and 2*NORM_SQR_SIZE - 1
	// in both x and y
        this->IndexTable
	  [(int)((float)(x + 1 + 1.0 / 
			 (float)(2*(NORM_SQR_SIZE-1)))*
			 (float)(NORM_SQR_SIZE-1))] 
	  [(int)((float)(y + 1 + 1.0 / 
			 (float)(2*(NORM_SQR_SIZE-1)))*
			 (float)(NORM_SQR_SIZE-1))] 
	    = index;

	// Increment the index
        index++;
	}
      }
    // On the even rows we are doing the big grid which has
    // NORM_SQR_SIZE elements in it
    else
      {
      for ( j = 0; j < NORM_SQR_SIZE; j++ )
	{
	// compute the x component for this column
        tmp_x = (float)(2*j)/(float)(NORM_SQR_SIZE-1) - 1.0;

	// rotate by 45 degrees
        x = 0.5 * tmp_x - 0.5 * tmp_y;
        y = 0.5 * tmp_x + 0.5 * tmp_y;

	// compute the z based on the x and y values
        if ( x >= 0 && y >= 0 )
          z = 1.0 - x - y;
        else if ( x >= 0 && y < 0 )
          z = 1.0 - x + y;
        else if ( x < 0 && y < 0 )
          z = 1.0 + x + y;
        else 
          z = 1.0 + x - y;

	// Normalize this direction and set the DecodedNormal table for
	// this index to this normal.  Also set the corresponding 
	// entry for this normal with a negative z component
        norm = sqrt( (double)( x*x + y*y + z*z ) );
        this->DecodedNormal[3*index + 0] = x / norm;
        this->DecodedNormal[3*index + 1] = y / norm;
        this->DecodedNormal[3*index + 2] = z / norm;
        this->DecodedNormal[3*(index+max_index) + 0] =   x / norm;
        this->DecodedNormal[3*(index+max_index) + 1] =   y / norm;
        this->DecodedNormal[3*(index+max_index) + 2] = -(z / norm);

	// For this x,y grid location, set the index
	// The grid location ranges between 0 and 2*NORM_SQR_SIZE - 1
	// in both x and y
        this->IndexTable
	  [(int)((float)(x + 1 + 1.0 / 
			 (float)(2*(NORM_SQR_SIZE-1)))*
			 (float)(NORM_SQR_SIZE-1))] 
	  [(int)((float)(y + 1 + 1.0 / 
			 (float)(2*(NORM_SQR_SIZE-1)))*
			 (float)(NORM_SQR_SIZE-1))] 
	    = index;

	// Increment the index
        index++;
	}
      }
    }

  this->IndexTableInitialized = 1;
}

// Description:
// This method is used to compute the encoded normal and the
// magnitude of the gradient for each voxel location in the 
// ScalarInput.
void vtkNormalEncoder::UpdateNormals( )
{
  int                scalar_input_size[3];
  float              scalar_input_aspect[3];

  // If we haven't initialized the index table yet, we should do that now
  if ( !this->IndexTableInitialized )
    this->InitializeIndexTable();

  // Get the dimensions of the data and its aspect ration
  this->ScalarInput->GetDimensions( scalar_input_size );
  this->ScalarInput->GetSpacing( scalar_input_aspect );

  // If we previously have allocated space for the encoded normals,
  // and this space is no longer the right size, delete it
  if ( this->EncodedNormal &&
	( this->EncodedNormalSize[0] != scalar_input_size[0] ||
	  this->EncodedNormalSize[1] != scalar_input_size[1] ||
          this->EncodedNormalSize[2] != scalar_input_size[2] ) )
    {
    delete this->EncodedNormal;
    this->EncodedNormal = NULL;
    }

  // Allocate space for the encoded normals if necessary
  if ( !this->EncodedNormal )
    {
    this->EncodedNormal = new unsigned short[ scalar_input_size[0] *
					      scalar_input_size[1] *
 					      scalar_input_size[2] ];
    this->EncodedNormalSize[0] = scalar_input_size[0];
    this->EncodedNormalSize[1] = scalar_input_size[1];
    this->EncodedNormalSize[2] = scalar_input_size[2];
    }

  // If we previously have allocated space for the gradient magnitudes,
  // and this space is no longer the right size, delete it
  if ( this->GradientMagnitude &&
	( this->GradientMagnitudeSize[0] != scalar_input_size[0] ||
	  this->GradientMagnitudeSize[1] != scalar_input_size[1] ||
          this->GradientMagnitudeSize[2] != scalar_input_size[2] ) )
    {
    delete this->GradientMagnitude;
    this->GradientMagnitude = NULL;
    }

  // Allocate space for the encoded normals if necessary
  if ( !this->GradientMagnitude )
    {
    this->GradientMagnitude = new unsigned char[ scalar_input_size[0] *
					         scalar_input_size[1] *
 					         scalar_input_size[2] ];
    this->GradientMagnitudeSize[0] = scalar_input_size[0];
    this->GradientMagnitudeSize[1] = scalar_input_size[1];
    this->GradientMagnitudeSize[2] = scalar_input_size[2];
    }

  // Copy info that multi threaded function will need into temp variables
  memcpy( this->ScalarInputSize, scalar_input_size, 3 * sizeof(int) );
  memcpy( this->ScalarInputAspect, scalar_input_aspect, 3 * sizeof(float) );

  this->Threader.SetNumberOfThreads( this->NumberOfThreads );

  this->Threader.SetSingleMethod( SwitchOnDataType,
				  (vtkObject *)this );

  this->Threader.SingleMethodExecute();

}

VTK_THREAD_RETURN_TYPE SwitchOnDataType( void *arg )
{
  vtkNormalEncoder   *encoder;
  int                thread_count;
  int                thread_id;
  unsigned char      *uc_data_ptr;
  unsigned short     *us_data_ptr;
  short              *s_data_ptr;
  int                *i_data_ptr;
  float              *f_data_ptr;
  char               *data_type;

  thread_id = ((ThreadInfoStruct *)(arg))->ThreadID;
  thread_count = ((ThreadInfoStruct *)(arg))->NumberOfThreads;
  encoder = (vtkNormalEncoder *)(((ThreadInfoStruct *)(arg))->UserData);

  // Find the data type of the ScalarInput and call the correct 
  // templated function to actually compute the normals and magnitudes
  data_type = 
    encoder->ScalarInput->GetPointData()->GetScalars()->GetDataType();

  if ( strcmp( data_type, "unsigned char" ) == 0 )
    {
    uc_data_ptr = ((vtkUnsignedCharScalars *)
      (encoder->ScalarInput->GetPointData()->GetScalars()))->GetPointer(0);
    ComputeGradients( encoder, uc_data_ptr, thread_id, thread_count );
    }
  else if ( strcmp( data_type, "unsigned short" ) == 0 )
    {
    us_data_ptr = ((vtkUnsignedShortScalars *)
      (encoder->ScalarInput->GetPointData()->GetScalars()))->GetPointer(0);
    ComputeGradients( encoder, us_data_ptr, thread_id, thread_count );
    }
  else if ( strcmp( data_type, "short" ) == 0 )
    {
    s_data_ptr = ((vtkShortScalars *)
      (encoder->ScalarInput->GetPointData()->GetScalars()))->GetPointer(0);
    ComputeGradients( encoder, s_data_ptr, thread_id, thread_count );
    }
  else if ( strcmp( data_type, "int" ) == 0 )
    {
    i_data_ptr = ((vtkIntScalars *)
      (encoder->ScalarInput->GetPointData()->GetScalars()))->GetPointer(0);
    ComputeGradients( encoder, i_data_ptr, thread_id, thread_count );
    }
  else if ( strcmp( data_type, "float" ) == 0 )
    {
    f_data_ptr = ((vtkFloatScalars *)
      (encoder->ScalarInput->GetPointData()->GetScalars()))->GetPointer(0);
    ComputeGradients( encoder, f_data_ptr, thread_id, thread_count );
    }

  return VTK_THREAD_RETURN_VALUE;
}

// Description:
// Build a shading table for a light with the given direction and
// color, for a material of the given type. material[0] = ambient,
// material[1] = diffuse, material[2] = specular, material[3] = 
// specular exponent.  If update_flag is 0, the table is overwritten
// with the new values.  If update_flag is 1, the new intensity values
// are added into the table.  This way multiple light sources can
// be handled.
//
// Note: specular is currently missing and will be added soon
//
void vtkNormalEncoder::BuildShadingTable( float light_direction[3],
					  float light_color[3],
					  float light_intensity,
					  float view_direction[3],
					  float material[4],
					  int   update_flag )
{
  float    lx, ly, lz; 
  float    n_dot_l;   
  int      i;
  float    *nptr;
  float    *sdr_ptr;
  float    *sdg_ptr;
  float    *sdb_ptr;
  float    *ssr_ptr;
  float    *ssg_ptr;
  float    *ssb_ptr;
  float    Ka, Es, Kd_intensity, Ks_intensity;
  float    half_x, half_y, half_z;
  float    mag, n_dot_h, specular_value;

  // Move to local variables
  lx = light_direction[0];
  ly = light_direction[1];
  lz = light_direction[2];

  half_x = lx - view_direction[0];
  half_y = ly - view_direction[1];
  half_z = lz - view_direction[2];

  mag = sqrt( (double)(half_x*half_x + half_y*half_y + half_z*half_z ) );
  
  if( mag != 0.0 )
    {
    half_x /= mag;
    half_y /= mag;
    half_z /= mag;
    }

  Ka = material[0];
  Es = material[3];
  Kd_intensity = material[1] * light_intensity;
  Ks_intensity = material[2] * light_intensity;

  nptr = this->DecodedNormal;

  sdr_ptr = this->ShadingTable[0];
  sdg_ptr = this->ShadingTable[1];
  sdb_ptr = this->ShadingTable[2];

  ssr_ptr = this->ShadingTable[3];
  ssg_ptr = this->ShadingTable[4];
  ssb_ptr = this->ShadingTable[5];

  // For each possible normal, compute the intensity of light at
  // a location with that normal, and the given lighting and
  // material properties
  for ( i = 0; i < 2*(NORM_SQR_SIZE*NORM_SQR_SIZE + 
		      (NORM_SQR_SIZE-1)*(NORM_SQR_SIZE-1)); i++ )
    {
    // The dot product between the normal and the light vector
    n_dot_l = (*(nptr+0) * lx + *(nptr+1) * ly + *(nptr+2) * lz);
    
    // If we are updating, then begin by adding in ambient
    if ( update_flag )
      {
      *(sdr_ptr) += Ka * light_color[0];
      *(sdg_ptr) += Ka * light_color[1];
      *(sdb_ptr) += Ka * light_color[2];
      }
    // Otherwise begin by setting the value to the ambient contribution
    else
      {
      *(sdr_ptr) = Ka * light_color[0];
      *(sdg_ptr) = Ka * light_color[1];
      *(sdb_ptr) = Ka * light_color[2];
      *(ssr_ptr) = 0.0;
      *(ssg_ptr) = 0.0;
      *(ssb_ptr) = 0.0;
      }

    // If there is some diffuse contribution, add it in
    if ( n_dot_l > 0 )
      {
      *(sdr_ptr) += (Kd_intensity * n_dot_l * light_color[0]);
      *(sdg_ptr) += (Kd_intensity * n_dot_l * light_color[1]);
      *(sdb_ptr) += (Kd_intensity * n_dot_l * light_color[2]);

      n_dot_h = (*(nptr+0) * half_x + *(nptr+1) * half_y + *(nptr+2) * half_z);
      if ( n_dot_h > 0.001 )
	{
	specular_value = Ks_intensity * pow( (double)n_dot_h, (double)Es );
	*(ssr_ptr) += specular_value * light_color[0];
	*(ssg_ptr) += specular_value * light_color[1];
	*(ssb_ptr) += specular_value * light_color[2];
	}      
      }
    // Increment all the pointers
    nptr += 3;
    sdr_ptr++;
    sdg_ptr++;
    sdb_ptr++;
    ssr_ptr++;
    ssg_ptr++;
    ssb_ptr++;
    }
}

// Description:
// I still need to fill this in...
int vtkNormalEncoder::GetEncodedNormalIndex( int x_index, int y_index,
					     int z_index )
{
  int ystep, zstep;

  // Compute steps through the volume in x, y, and z
  ystep = this->ScalarInputSize[0];
  zstep = this->ScalarInputSize[0] * this->ScalarInputSize[1];

  return *(this->EncodedNormal + z_index * zstep + y_index * ystep + x_index);
}


// Description:
// Print the vtkNormalEncoder
void vtkNormalEncoder::PrintSelf(ostream& os, vtkIndent indent)
{
  if ( this->ScalarInput )
    {
    os << indent << "ScalarInput: (" << this->ScalarInput << ")\n";
    }
  else
    {
    os << indent << "ScalarInput: (none)\n";
    }

  os << indent << "Build Time: " <<this->BuildTime.GetMTime() << "\n";
}
