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

  Program:   Visualization Toolkit
  Module:    vtkHexagonalPrism.cxx

  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.

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

// Thanks to Philippe Guerville who developed this class.
// Thanks to Charles Pignerol (CEA-DAM, France) who ported this class under
// VTK 4.
// Thanks to Jean Favre (CSCS, Switzerland) who contributed to integrate this
// class in VTK.
// Please address all comments to Jean Favre (jfavre at cscs.ch).

#include "vtkHexagonalPrism.h"

#include "vtkHexahedron.h"
#include "vtkLine.h"
#include "vtkQuad.h"
#include "vtkMath.h"
#include "vtkObjectFactory.h"
#include "vtkPolygon.h"
#include "vtkCellArray.h"
#include "vtkPointLocator.h"
#include "vtkDoubleArray.h"
#include "vtkCellData.h"
#include "vtkPoints.h"
#include "vtkPointData.h"

vtkCxxRevisionMacro(vtkHexagonalPrism, "1.5");
vtkStandardNewMacro(vtkHexagonalPrism);

static const double VTK_DIVERGED = 1.e6;

//----------------------------------------------------------------------------
// Construct the prism with twelve points.
vtkHexagonalPrism::vtkHexagonalPrism()
{
  int i;
  
  this->Points->SetNumberOfPoints(12+2);
  this->PointIds->SetNumberOfIds(12+2);

  // allocate enough room for the extra 2 points we insert on the hexagons
  for (i = 0; i < 12+2; i++)
    {
    this->Points->SetPoint(i, 0.0, 0.0, 0.0);
    this->PointIds->SetId(i,0);
    }
  this->Points->SetNumberOfPoints(12);
  this->PointIds->SetNumberOfIds(12);

  this->Line = vtkLine::New();
  this->Quad = vtkQuad::New();
  this->Hexahedron = vtkHexahedron::New();
  this->Polygon = vtkPolygon::New();
  this->Polygon->PointIds->SetNumberOfIds(6);
  this->Polygon->Points->SetNumberOfPoints(6);

  this->PointData = vtkPointData::New();
  this->CellData = vtkCellData::New();
  this->Scalars = vtkDoubleArray::New();
  this->Scalars->SetNumberOfTuples(8);  //num of vertices
}

//----------------------------------------------------------------------------
vtkHexagonalPrism::~vtkHexagonalPrism()
{
  this->Line->Delete();
  this->Quad->Delete();
  this->Polygon->Delete();
  this->Hexahedron->Delete();

  this->PointData->Delete();
  this->CellData->Delete();
  this->Scalars->Delete();
}

//  Method to calculate parametric coordinates in an eight noded
//  linear hexahedron element from global coordinates.
//
static const int VTK_HEX_MAX_ITERATION=10;
static const double VTK_HEX_CONVERGED=1.e-03f;

//----------------------------------------------------------------------------
int vtkHexagonalPrism::EvaluatePosition(double x[3], double* closestPoint,
                                    int& subId, double pcoords[3], 
                                    double& dist2, double *weights)
{
  int iteration, converged;
  double  params[3];
  double  fcol[3], rcol[3], scol[3], tcol[3];
  int i, j;
  double  d, pt[3];
  double derivs[24];

  //  set initial position for Newton's method
  subId = 0;
  pcoords[0] = pcoords[1] = pcoords[2] = params[0] = params[1] = params[2]=0.5;

  //  enter iteration loop
  for (iteration=converged=0;
       !converged && (iteration < VTK_HEX_MAX_ITERATION);  iteration++) 
    {
    //  calculate element interpolation functions and derivatives
    this->InterpolationFunctions(pcoords, weights);
    this->InterpolationDerivs(pcoords, derivs);

    //  calculate newton functions
    for (i=0; i<3; i++) 
      {
      fcol[i] = rcol[i] = scol[i] = tcol[i] = 0.0;
      }
    for (i=0; i<8; i++)
      {
      this->Points->GetPoint(i, pt);
      for (j=0; j<3; j++)
        {
        fcol[j] += pt[j] * weights[i];
        rcol[j] += pt[j] * derivs[i];
        scol[j] += pt[j] * derivs[i+8];
        tcol[j] += pt[j] * derivs[i+16];
        }
      }

    for (i=0; i<3; i++)
      {
      fcol[i] -= x[i];
      }

    //  compute determinants and generate improvements
    d=vtkMath::Determinant3x3(rcol,scol,tcol);
    if ( fabs(d) < 1.e-20) 
      {
      return -1;
      }

    pcoords[0] = params[0] - vtkMath::Determinant3x3 (fcol,scol,tcol) / d;
    pcoords[1] = params[1] - vtkMath::Determinant3x3 (rcol,fcol,tcol) / d;
    pcoords[2] = params[2] - vtkMath::Determinant3x3 (rcol,scol,fcol) / d;

    //  check for convergence
    if ( ((fabs(pcoords[0]-params[0])) < VTK_HEX_CONVERGED) &&
         ((fabs(pcoords[1]-params[1])) < VTK_HEX_CONVERGED) &&
         ((fabs(pcoords[2]-params[2])) < VTK_HEX_CONVERGED) )
      {
      converged = 1;
      }

    // Test for bad divergence (S.Hirschberg 11.12.2001)
    else if ((fabs(pcoords[0]) > VTK_DIVERGED) || 
             (fabs(pcoords[1]) > VTK_DIVERGED) || 
             (fabs(pcoords[2]) > VTK_DIVERGED))
      {
      return -1;
      }

    //  if not converged, repeat
    else 
      {
      params[0] = pcoords[0];
      params[1] = pcoords[1];
      params[2] = pcoords[2];
      }
    }

  //  if not converged, set the parametric coordinates to arbitrary values
  //  outside of element
  if ( !converged )
    {
    return -1;
    }

  this->InterpolationFunctions(pcoords, weights);

  if ( pcoords[0] >= -0.001 && pcoords[0] <= 1.001 &&
  pcoords[1] >= -0.001 && pcoords[1] <= 1.001 &&
  pcoords[2] >= -0.001 && pcoords[2] <= 1.001 )
    {
    if (closestPoint)
      {
      closestPoint[0] = x[0]; closestPoint[1] = x[1]; closestPoint[2] = x[2];
      dist2 = 0.0; //inside hexahedron
      }
    return 1;
    }
  else
    {
    double pc[3], w[8];
    if (closestPoint)
      {
      for (i=0; i<3; i++) //only approximate, not really true for warped hexa
        {
        if (pcoords[i] < 0.0)
          {
          pc[i] = 0.0;
          }
        else if (pcoords[i] > 1.0)
          {
          pc[i] = 1.0;
          }
        else
          {
          pc[i] = pcoords[i];
          }
        }
      this->EvaluateLocation(subId, pc, closestPoint, (double *)w);
      dist2 = vtkMath::Distance2BetweenPoints(closestPoint,x);
      }
    return 0;
    }
}

//----------------------------------------------------------------------------
//
// Compute iso-parametrix interpolation functions
//
void vtkHexagonalPrism::InterpolationFunctions(double pcoords[3], double sf[8])
{
  double r, s, t;

  r = pcoords[0];
  s = pcoords[1];
  t = pcoords[2];

  sf[0]  = -2*(r - 0.75)*(s - 1.0)*(t - 1.0);
  sf[1]  =  2*(r - 0.25)*(s - 1.0)*(t - 1.0);
  sf[2]  = (r - 0.0 )*(s - 0.0)*(s - 1.0)*(t - 1.0);
  sf[3]  = -2*(r - 0.25)*(s - 0.0)*(t - 1.0);
  sf[4]  =  2*(r - 0.75)*(s - 0.0)*(t - 1.0);
  sf[5]  = (r - 1.0 )*(s - 0.0)*(s - 1.0)*(t - 1.0);

  sf[6]  =  2*(r - 0.75)*(s - 1.0)*(t - 0.0);
  sf[7]  = -2*(r - 0.25)*(s - 1.0)*(t - 0.0);
  sf[8]  = (r - 0.0 )*          (t - 0.0);
  sf[9]  = (r - 0.25)*(s - 0.0)*(t - 0.0);
  sf[10] = (r - 0.75)*(s - 0.0)*(t - 0.0);
  sf[11] = (r - 1.0 )*          (t - 0.0);
}

//----------------------------------------------------------------------------
void vtkHexagonalPrism::InterpolationDerivs(double pcoords[3], double derivs[24])
{
  double rm, sm, tm;

  rm = 1. - pcoords[0];
  sm = 1. - pcoords[1];
  tm = 1. - pcoords[2];

  // r-derivatives
  derivs[0] = -sm*tm;
  derivs[1] = sm*tm;
  derivs[2] = pcoords[1]*tm;
  derivs[3] = -pcoords[1]*tm;
  derivs[4] = -sm*pcoords[2];
  derivs[5] = sm*pcoords[2];
  derivs[6] = pcoords[1]*pcoords[2];
  derivs[7] = -pcoords[1]*pcoords[2];

  // s-derivatives
  derivs[8] = -rm*tm;
  derivs[9] = -pcoords[0]*tm;
  derivs[10] = pcoords[0]*tm;
  derivs[11] = rm*tm;
  derivs[12] = -rm*pcoords[2];
  derivs[13] = -pcoords[0]*pcoords[2];
  derivs[14] = pcoords[0]*pcoords[2];
  derivs[15] = rm*pcoords[2];

  // t-derivatives
  derivs[16] = -rm*sm;
  derivs[17] = -pcoords[0]*sm;
  derivs[18] = -pcoords[0]*pcoords[1];
  derivs[19] = -rm*pcoords[1];
  derivs[20] = rm*sm;
  derivs[21] = pcoords[0]*sm;
  derivs[22] = pcoords[0]*pcoords[1];
  derivs[23] = rm*pcoords[1];
}

static int InternalWedges[3][8] = {{0,1,2,12,6,7,8,13},
                                   {2,3,4,12,8,9,10,13},
                                   {4,5,0,12,10,11,6,13}};

//----------------------------------------------------------------------------
void vtkHexagonalPrism::EvaluateLocation(int& vtkNotUsed(subId), 
                                         double pcoords[3], double x[3], 
                                         double *weights)
{
  int i, j;
  double pt[3];

  this->InterpolationFunctions(pcoords, weights);

  x[0] = x[1] = x[2] = 0.0;
  for (i = 0; i < 12; i++)
    {
    this->Points->GetPoint (i, pt);
    for (j = 0; j < 3; j++)
      {
      x[j] += pt [j] * weights [i];
      }
    }
}

//----------------------------------------------------------------------------
// Returns the closest face to the point specified. Closeness is measured
// parametrically.
int vtkHexagonalPrism::CellBoundary(int vtkNotUsed(subId), double pcoords[3], 
                                    vtkIdList *pts)
{
  int i;

  // define 9 planes that separate regions
  static double normals[9][3] = { 
    {0.0,0.83205,-0.5547}, {-0.639602,-0.639602,-0.426401}, {0.83205,0.0,-0.5547},
    {0.0,0.83205,0.5547}, {-0.639602,-0.639602,0.426401}, {0.83205,0.0,0.5547},
    {-0.707107,0.707107,0.0}, {0.447214,0.894427,0.0}, {0.894427,0.447214,0.0} };
  static double point[3] = {0.333333,0.333333,0.5};
  double vals[9];

  // evaluate 9 plane equations
  for (i=0; i<9; i++)
    {
    vals[i] = normals[i][0]*(pcoords[0]-point[0]) + 
      normals[i][1]*(pcoords[1]-point[1]) + normals[i][2]*(pcoords[2]-point[2]);
    }

  // compare against nine planes in parametric space that divide element
  // into five pieces (each corresponding to a face).
  if ( vals[0] >= 0.0 && vals[1] >= 0.0 && vals[2] >= 0.0 )
    {
    pts->SetNumberOfIds(3); //triangle face
    pts->SetId(0,this->PointIds->GetId(0));
    pts->SetId(1,this->PointIds->GetId(1));
    pts->SetId(2,this->PointIds->GetId(2));
    }

  else if ( vals[3] >= 0.0 && vals[4] >= 0.0 && vals[5] >= 0.0 )
    {
    pts->SetNumberOfIds(3); //triangle face
    pts->SetId(0,this->PointIds->GetId(3));
    pts->SetId(1,this->PointIds->GetId(4));
    pts->SetId(2,this->PointIds->GetId(5));
    }

  else if ( vals[0] <= 0.0 && vals[3] <= 0.0 && 
            vals[6] <= 0.0 && vals[7] <= 0.0 )
    {
    pts->SetNumberOfIds(4); //quad face
    pts->SetId(0,this->PointIds->GetId(0));
    pts->SetId(1,this->PointIds->GetId(1));
    pts->SetId(2,this->PointIds->GetId(4));
    pts->SetId(3,this->PointIds->GetId(3));
    }

  else if ( vals[1] <= 0.0 && vals[4] <= 0.0 && 
            vals[7] >= 0.0 && vals[8] >= 0.0 )
    {
    pts->SetNumberOfIds(4); //quad face
    pts->SetId(0,this->PointIds->GetId(1));
    pts->SetId(1,this->PointIds->GetId(2));
    pts->SetId(2,this->PointIds->GetId(5));
    pts->SetId(3,this->PointIds->GetId(4));
    }

  else //vals[2] <= 0.0 && vals[5] <= 0.0 && vals[8] <= 0.0 && vals[6] >= 0.0
    {
    pts->SetNumberOfIds(4); //quad face
    pts->SetId(0,this->PointIds->GetId(2));
    pts->SetId(1,this->PointIds->GetId(0));
    pts->SetId(2,this->PointIds->GetId(3));
    pts->SetId(3,this->PointIds->GetId(5));
    }

  if ( pcoords[0] < 0.0 || pcoords[0] > 1.0 ||
       pcoords[1] < 0.0 || pcoords[1] > 1.0 || 
       pcoords[2] < 0.0 || pcoords[2] > 1.0 )
    {
    return 0;
    }
  else
    {
    return 1;
    }
}

static int edges[18][2] = {  {0,1}, {1, 2}, {2, 3}, 
                             {3,4}, {4, 5}, {5, 0}, 
                             {6,7}, {7, 8}, {8, 9},
                             {9,10}, {10,11}, {11, 6}, 
                             {0,6}, {1, 7}, {2, 8}, 
                             {3,9}, {4, 10}, {5, 11} };

static int faces[8][6] = { {0,5,4,3,2,1}, {6,7,8,9,10,11}, 
                           {0,1,7,6,-1,-1}, {1,2,8,7,-1,-1}, 
                           {2,3,9,8,-1,-1}, {3,4,10,9,-1,-1}, 
                           {4,5,11,10,-1,-1}, {5,0,6,11,-1,-1} };

//----------------------------------------------------------------------------
void vtkHexagonalPrism::Contour(double value, vtkDataArray *cellScalars, 
                                vtkPointLocator *locator, vtkCellArray *verts, 
                                vtkCellArray *lines, vtkCellArray *polys, 
                                vtkPointData *inPd, vtkPointData *outPd,
                                vtkCellData *inCd, vtkIdType cellId,
                                vtkCellData *outCd)
{
  int i;
  double s1, s2;

  // subdivide into 3 internal hexahedra with two points added in the middle
  // of the 2 hexagonal faces
  this->Subdivide(inPd, inCd, cellId);

  vtkDoubleArray *newCellScalars=vtkDoubleArray::New();
  newCellScalars->SetNumberOfValues(8);

  s1 = s2 = 0.0;
  for(i=0; i<6; ++i)
    {
    s1 +=  cellScalars->GetComponent(i,0);
    s2 +=  cellScalars->GetComponent(i+6,0);
  }
  s1 /= 6;
  s2 /= 6;
  newCellScalars->SetValue(3, s1);
  newCellScalars->SetValue(7, s2);

  vtkDataArray *localScalars = this->PointData->GetScalars();

 //contour each internal hexahedron separately
  for(i=0; i<3; ++i) // for each hexahedron
    {
    for(int j=0; j<8; j++)
      {
      this->Hexahedron->Points->SetPoint(j, 
          this->Points->GetPoint(InternalWedges[i][j]));
      this->Hexahedron->PointIds->SetId(j, InternalWedges[i][j]);
      if(j!=3 && j!=7)
        {
        newCellScalars->SetValue(j, 
          cellScalars->GetTuple1(InternalWedges[i][j]));
        }
      this->Scalars->SetValue(j, 
        localScalars->GetTuple1(InternalWedges[i][j]));
      }
    this->Hexahedron->Contour(value, newCellScalars, locator, verts, lines, 
                              polys, this->PointData, outPd, this->CellData, 
                              0, outCd);
    }
  newCellScalars->Delete();
}

//----------------------------------------------------------------------------
void vtkHexagonalPrism::Clip(double value, vtkDataArray *cellScalars, 
                         vtkPointLocator *locator, vtkCellArray *tetras,
                         vtkPointData *inPd, vtkPointData *outPd,
                         vtkCellData *inCd, vtkIdType cellId, 
                         vtkCellData *outCd, int insideOut)
{
  int i;
  double s1, s2;

  // subdivide into 3 internal hexahedra with two points added in the middle
  // of the 2 hexagonal faces
  this->Subdivide(inPd, inCd, cellId);

  vtkDoubleArray *newCellScalars=vtkDoubleArray::New();
  newCellScalars->SetNumberOfValues(8);

  s1 = s2 = 0.;
  for(i=0; i<6; ++i)
    {
    s1 +=  cellScalars->GetComponent(i,0);
    s2 +=  cellScalars->GetComponent(i+6,0);
  }
  s1 /= 6;
  s2 /= 6;
  newCellScalars->SetValue(3, s1);
  newCellScalars->SetValue(7, s2);

  vtkDataArray *localScalars = this->PointData->GetScalars();

 //contour each internal hexahedron separately
  for(i=0; i<3; ++i) // for each hexahedron
    {
    for(int j=0; j<8; j++)
      {
      this->Hexahedron->Points->SetPoint(j, 
          this->Points->GetPoint(InternalWedges[i][j]));
      this->Hexahedron->PointIds->SetId(j,InternalWedges[i][j]);
      if(j!=3 && j!=7)
        {
        newCellScalars->SetValue(j, 
            cellScalars->GetTuple1(InternalWedges[i][j]));
        }
      this->Scalars->SetValue(j, localScalars->GetTuple1(InternalWedges[i][j]));
      }
    this->Hexahedron->Clip(value, newCellScalars, locator, tetras, 
                           this->PointData, outPd, this->CellData, cellId, 
                           outCd, insideOut);
    }
  newCellScalars->Delete();
}
//----------------------------------------------------------------------------
void vtkHexagonalPrism::Subdivide(vtkPointData *inPd, vtkCellData *inCd, vtkIdType cellId)
{
  int i, j;
  double x[3], x1[3], x2[3], weights[6];

  this->PointData->CopyAllocate(inPd, 12+2);
  this->CellData->CopyAllocate(inCd,8);
  for(i=0; i<12; i++)
    {
    this->PointData->CopyData(inPd, this->PointIds->GetId(i),i);
    }
  this->CellData->CopyData(inCd,cellId,0);
 
  this->PointIds->SetNumberOfIds(12);

  x1[0] = x1[1] = x1[2] = 0.;
  x2[0] = x2[1] = x2[2] = 0.;
  
  for(i=0; i<6; ++i)
    {
    weights[i] = 1.0/6.0;
    this->Points->GetPoint(i, x);
    for(j=0; j<3; ++j)
      {
      x1[j] += x[j]*weights[i];
      }
    this->Points->GetPoint(i+6, x);
    for(j=0; j<3; ++j)
      {
      x2[j] += x[j]*weights[i];
      }
    }
  this->PointData->InterpolatePoint(inPd, 12, GetFace(0)->GetPointIds(), weights);
  this->PointData->InterpolatePoint(inPd, 13, GetFace(1)->GetPointIds(), weights);

  this->Points->SetPoint(12, x1); 
  this->Points->SetPoint(13, x2);

  this->PointIds->SetNumberOfIds(14);
}

//----------------------------------------------------------------------------
int *vtkHexagonalPrism::GetEdgeArray(int edgeId)
{
  return edges[edgeId];
}

//----------------------------------------------------------------------------
vtkCell *vtkHexagonalPrism::GetEdge(int edgeId)
{
  int *verts;
  
  verts = edges[edgeId];

  // load point id's
  this->Line->PointIds->SetId(0,this->PointIds->GetId(verts[0]));
  this->Line->PointIds->SetId(1,this->PointIds->GetId(verts[1]));

  // load coordinates
  this->Line->Points->SetPoint(0,this->Points->GetPoint(verts[0]));
  this->Line->Points->SetPoint(1,this->Points->GetPoint(verts[1]));

  return this->Line;
}
//----------------------------------------------------------------------------
int *vtkHexagonalPrism::GetFaceArray(int faceId)
{
  return faces[faceId];
}
//----------------------------------------------------------------------------
vtkCell *vtkHexagonalPrism::GetFace(int faceId)
{
  int *verts;

  verts = faces[faceId];

  if ( verts[4] != -1 ) // polys cell
    {
    // load point id's
    this->Polygon->PointIds->SetId(0,this->PointIds->GetId(verts[0]));
    this->Polygon->PointIds->SetId(1,this->PointIds->GetId(verts[1]));
    this->Polygon->PointIds->SetId(2,this->PointIds->GetId(verts[2]));
    this->Polygon->PointIds->SetId(3,this->PointIds->GetId(verts[3]));
    this->Polygon->PointIds->SetId(4,this->PointIds->GetId(verts[4]));
    this->Polygon->PointIds->SetId(5,this->PointIds->GetId(verts[5]));

    // load coordinates
    this->Polygon->Points->SetPoint(0,this->Points->GetPoint(verts[0]));
    this->Polygon->Points->SetPoint(1,this->Points->GetPoint(verts[1]));
    this->Polygon->Points->SetPoint(2,this->Points->GetPoint(verts[2]));
    this->Polygon->Points->SetPoint(3,this->Points->GetPoint(verts[3]));
    this->Polygon->Points->SetPoint(4,this->Points->GetPoint(verts[4]));
    this->Polygon->Points->SetPoint(5,this->Points->GetPoint(verts[5]));

    return this->Polygon;
    }
  else
    {
    // load point id's
    this->Quad->PointIds->SetId(0,this->PointIds->GetId(verts[0]));
    this->Quad->PointIds->SetId(1,this->PointIds->GetId(verts[1]));
    this->Quad->PointIds->SetId(2,this->PointIds->GetId(verts[2]));
    this->Quad->PointIds->SetId(3,this->PointIds->GetId(verts[3]));

    // load coordinates
    this->Quad->Points->SetPoint(0,this->Points->GetPoint(verts[0]));
    this->Quad->Points->SetPoint(1,this->Points->GetPoint(verts[1]));
    this->Quad->Points->SetPoint(2,this->Points->GetPoint(verts[2]));
    this->Quad->Points->SetPoint(3,this->Points->GetPoint(verts[3]));

    return this->Quad;
    }
}
//----------------------------------------------------------------------------
// 
// Intersect prism faces against line. Each prism face is a quadrilateral.
//
int vtkHexagonalPrism::IntersectWithLine(double p1[3], double p2[3], double tol,
                                    double &t, double x[3], double pcoords[3],
                                    int& subId)
{
  int intersection=0;
  double pt1[3], pt2[3], pt3[3], pt4[3];
  double tTemp;
  double pc[3], xTemp[3];
  int faceNum;

  t = VTK_DOUBLE_MAX;
  for (faceNum=0; faceNum<6; faceNum++)
    {
    this->Points->GetPoint(faces[faceNum][0], pt1);
    this->Points->GetPoint(faces[faceNum][1], pt2);
    this->Points->GetPoint(faces[faceNum][2], pt3);
    this->Points->GetPoint(faces[faceNum][3], pt4);

    this->Quad->Points->SetPoint(0,pt1);
    this->Quad->Points->SetPoint(1,pt2);
    this->Quad->Points->SetPoint(2,pt3);
    this->Quad->Points->SetPoint(3,pt4);

    if ( this->Quad->IntersectWithLine(p1, p2, tol, tTemp, xTemp, pc, subId) )
      {
      intersection = 1;
      if ( tTemp < t )
        {
        t = tTemp;
        x[0] = xTemp[0]; x[1] = xTemp[1]; x[2] = xTemp[2]; 
        switch (faceNum)
          {
          case 0:
            pcoords[0] = 0.0; pcoords[0] = pc[0]; pcoords[1] = 0.0;
            break;

          case 1:
            pcoords[0] = 1.0; pcoords[0] = pc[0]; pcoords[1] = 0.0;
            break;

          case 2:
            pcoords[0] = pc[0]; pcoords[1] = 0.0; pcoords[2] = pc[1];
            break;

          case 3:
            pcoords[0] = pc[0]; pcoords[1] = 1.0; pcoords[2] = pc[1];
            break;

          case 4:
            pcoords[0] = pc[0]; pcoords[1] = pc[1]; pcoords[2] = 0.0;
            break;

          case 5:
            pcoords[0] = pc[0]; pcoords[1] = pc[1]; pcoords[2] = 1.0;
            break;
          }
        }
      }
    }
  return intersection;
}
//----------------------------------------------------------------------------
int vtkHexagonalPrism::Triangulate(int vtkNotUsed(index), vtkIdList *ptIds, vtkPoints *pts)
{
  ptIds->Reset();
  pts->Reset();
    
  for ( int i=0; i < 4; i++ )
    {
    ptIds->InsertId(i,this->PointIds->GetId(i));
    pts->InsertPoint(i,this->Points->GetPoint(i));
    }

  return 1;
}
//----------------------------------------------------------------------------
//
// Compute derivatives in x-y-z directions. Use chain rule in combination
// with interpolation function derivatives.
//
void vtkHexagonalPrism::Derivatives(int vtkNotUsed(subId), double pcoords[3], 
                                double *values, int dim, double *derivs)
{
  double *jI[3], j0[3], j1[3], j2[3];
  double functionDerivs[18], sum[3], value;
  int i, j, k;

  // compute inverse Jacobian and interpolation function derivatives
  jI[0] = j0; jI[1] = j1; jI[2] = j2;
  this->JacobianInverse(pcoords, jI, functionDerivs);

  // now compute derivates of values provided
  for (k=0; k < dim; k++) //loop over values per vertex
    {
    sum[0] = sum[1] = sum[2] = 0.0;
    for ( i=0; i < 6; i++) //loop over interp. function derivatives
      {
      value = values[dim*i + k];
      sum[0] += functionDerivs[i] * value;
      sum[1] += functionDerivs[6 + i] * value;
      sum[2] += functionDerivs[12 + i] * value;
      }

    for (j=0; j < 3; j++) //loop over derivative directions
      {
      derivs[3*k + j] = sum[0]*jI[j][0] + sum[1]*jI[j][1] + sum[2]*jI[j][2];
      }
    }
}
//----------------------------------------------------------------------------
// Given parametric coordinates compute inverse Jacobian transformation
// matrix. Returns 9 elements of 3x3 inverse Jacobian plus interpolation
// function derivatives.
void vtkHexagonalPrism::JacobianInverse(double pcoords[3], double **inverse,
                                    double derivs[24])
{
  int i, j;
  double *m[3], m0[3], m1[3], m2[3];
  double x[3];

  // compute interpolation function derivatives
  this->InterpolationDerivs(pcoords, derivs);

  // create Jacobian matrix
  m[0] = m0; m[1] = m1; m[2] = m2;
  for (i=0; i < 3; i++) //initialize matrix
    {
    m0[i] = m1[i] = m2[i] = 0.0;
    }

  for ( j=0; j < 8; j++ )
    {
    this->Points->GetPoint(j, x);
    for ( i=0; i < 3; i++ )
      {
      m0[i] += x[i] * derivs[j];
      m1[i] += x[i] * derivs[8 + j];
      m2[i] += x[i] * derivs[16 + j];
      }
    }

  // now find the inverse
  if ( vtkMath::InvertMatrix(m,inverse,3) == 0 )
    {
    vtkErrorMacro(<<"Jacobian inverse not found");
    return;
    }
}

//----------------------------------------------------------------------------
void vtkHexagonalPrism::GetEdgePoints(int edgeId, int* &pts)
{
  pts = this->GetEdgeArray(edgeId);
}

//----------------------------------------------------------------------------
void vtkHexagonalPrism::GetFacePoints(int faceId, int* &pts)
{
  pts = this->GetFaceArray(faceId);
}

static double vtkHexagonalPrismCellPCoords[36] = {0.25,0.0,0.0, 0.75,0.0,0.0,
                                                  1.0 ,0.5,0.0, 0.75,1.0,0.0,
                                                  0.25,1.0,0.0, 0.0 ,0.5,0.0,
                                                  0.25,0.0,1.0, 0.75,0.0,1.0,
                                                  1.0 ,0.5,1.0, 0.75,1.0,1.0,
                                                  0.25,1.0,1.0, 0.0 ,0.5,1.0};

//----------------------------------------------------------------------------
double *vtkHexagonalPrism::GetParametricCoords()
{
  return vtkHexagonalPrismCellPCoords;
}
