/*
  This file is part of p4est.
  p4est is a C library to manage a collection (a forest) of multiple
  connected adaptive quadtrees or octrees in parallel.

  Copyright (C) 2010 The University of Texas System
  Additional copyright (C) 2011 individual authors
  Written by Carsten Burstedde, Lucas C. Wilcox, and Tobin Isaac

  p4est is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation; either version 2 of the License, or
  (at your option) any later version.

  p4est is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with p4est; if not, write to the Free Software Foundation, Inc.,
  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/

/*
 * There are several configure options that affect the VTK output.
 * --enable-vtk-binary (default) uses binary/base64 encoding.
 * --enable-vtk-compression (default) uses zlib compression.
 * --enable-vtk-doubles (default) uses 64-bit binary reals.
 * These may be disabled using the --disable-vtk-* forms.
 *
 * These options translate into the preprocessor #defines
 * P4EST_ENABLE_VTK_BINARY,
 * P4EST_ENABLE_VTK_COMPRESSION,
 * P4EST_ENABLE_VTK_DOUBLES.
 * The older version of the macros without _ENABLE_ is obsolete.
 *
 * We define further macros of the form P4EST_VTK_ in this file.
 * These are local to the code in this file and not exported.
 */

#ifdef P4_TO_P8
#include <p8est_vtk.h>
#include <p8est_nodes.h>
#define P4EST_VTK_CELL_TYPE     11      /* VTK_VOXEL */
#define P4EST_VTK_CELL_TYPE_HO  72      /* VTK_LAGRANGE_HEXAHEDRON */
#else
#include <p4est_vtk.h>
#include <p4est_nodes.h>
#define P4EST_VTK_CELL_TYPE      8      /* VTK_PIXEL */
#define P4EST_VTK_CELL_TYPE_HO  70      /* VTK_LAGRANGE_QUADRILATERAL */
#endif /* !P4_TO_P8 */

/* default parameters for the vtk context */
static const double p4est_vtk_scale = 0.95;
static const int    p4est_vtk_continuous = 0;

/* default parameters for p4est_vtk_write_file */
static const int    p4est_vtk_write_tree = 1;
static const int    p4est_vtk_write_level = 1;
static const int    p4est_vtk_write_rank = 1;
static const int    p4est_vtk_wrap_rank = 0;

/** Write a cell scalar field to the VTU file.
 *
 * Writing a VTK file is split into a few routines.
 * This allows there to be an arbitrary number of fields.
 * When in doubt, please use \ref p4est_vtk_write_cell_data instead.
 *
 * \param [in,out] cont    A VTK context created by \ref p4est_vtk_context_new.
 * \param [in] scalar_name The name of the scalar field.
 * \param [in] values      The cell values that will be written.
 *
 * \return          On success, the context that has been passed in.
 *                  On failure, returns NULL and deallocates the context.
 */
static
  p4est_vtk_context_t *p4est_vtk_write_cell_scalar (p4est_vtk_context_t *
                                                    cont,
                                                    const char *scalar_name,
                                                    sc_array_t * values);

/** Write a 3-vector cell field to the VTU file.
 *
 * Writing a VTK file is split into a few routines.
 * This allows there to be an arbitrary number of fields.
 * When in doubt, please use \ref p4est_vtk_write_cell_data instead.
 *
 * \param [in,out] cont    A VTK context created by \ref p4est_vtk_context_new.
 * \param [in] vector_name The name of the vector field.
 * \param [in] values      The cell values that will be written.
 *
 * \return          On success, the context that has been passed in.
 *                  On failure, returns NULL and deallocates the context.
 */
static
  p4est_vtk_context_t *p4est_vtk_write_cell_vector (p4est_vtk_context_t *
                                                    cont,
                                                    const char *vector_name,
                                                    sc_array_t * values);

/** Write a point scalar field to the VTU file.
 *
 * Writing a VTK file is split into a few routines.
 * This allows there to be an arbitrary number of fields.
 * When in doubt, please use \ref p4est_vtk_write_point_data instead.
 *
 * \param [in,out] cont    A VTK context created by \ref p4est_vtk_context_new.
 * \param [in] scalar_name The name of the scalar field.
 * \param [in] values      The point values that will be written.
 *
 * \return          On success, the context that has been passed in.
 *                  On failure, returns NULL and deallocates the context.
 */
static
  p4est_vtk_context_t *p4est_vtk_write_point_scalar (p4est_vtk_context_t *
                                                     cont,
                                                     const char *scalar_name,
                                                     sc_array_t * values);

/** Write a 3-vector point field to the VTU file.
 *
 * Writing a VTK file is split into a few routines.
 * This allows there to be an arbitrary number of fields.
 * When in doubt, please use \ref p4est_vtk_write_point_data instead.
 *
 * \param [in,out] cont    A VTK context created by \ref p4est_vtk_context_new.
 * \param [in] vector_name The name of the vector field.
 * \param [in] values      The point values that will be written.
 *
 * \return          On success, the context that has been passed in.
 *                  On failure, returns NULL and deallocates the context.
 */
static
  p4est_vtk_context_t *p4est_vtk_write_point_vector (p4est_vtk_context_t *
                                                     cont,
                                                     const char *vector_name,
                                                     sc_array_t * values);

#ifdef P4_TO_P8
#define p4est_vtk_context               p8est_vtk_context
#endif

#ifndef P4EST_ENABLE_VTK_DOUBLES
#define P4EST_VTK_FLOAT_NAME "Float32"
#define P4EST_VTK_FLOAT_TYPE float
#else
#define P4EST_VTK_FLOAT_NAME "Float64"
#define P4EST_VTK_FLOAT_TYPE double
#endif

#ifndef P4EST_ENABLE_VTK_BINARY
#define P4EST_VTK_ASCII 1
#define P4EST_VTK_FORMAT_STRING "ascii"
#else
#define P4EST_VTK_FORMAT_STRING "binary"

static int
p4est_vtk_write_binary (FILE * vtkfile, char *numeric_data,
                        size_t byte_length)
{
#ifndef P4EST_ENABLE_VTK_COMPRESSION
  return sc_vtk_write_binary (vtkfile, numeric_data, byte_length);
#else
  return sc_vtk_write_compressed (vtkfile, numeric_data, byte_length);
#endif /* P4EST_ENABLE_VTK_COMPRESSION */
}

#endif /* P4EST_ENABLE_VTK_BINARY */

/** Opaque context type for writing VTK output with multiple function calls.
 *
 * This structure holds all the information needed for the p4est vtk context.
 * It is used to relay necessary vtk information to the \b p4est_vtk_write_*
 * functions. This structure is initialized by \ref p4est_vtk_write_header and
 * destroyed by \b p4est_vtk_write_footer; it can also be destroyed manually
 * using the \b p4est_vtk_context_destroy function if necessary.
 *
 * The \a p4est member is a pointer to the local p4est.
 * The \a geom member is a pointer to the geometry used to create the p4est.
 * The \a num_points member holds the number of nodes present in the vtk output;
 * this is determined in \ref p4est_vtk_write_header using the \a scale parameter
 * and is used to assure the proper number of point variables are provided.
 * The \a filename member holds the vtk file basename: for error reporting.
 * The \a vtufilename, \a pvtufilename, and \a visitfilename members are the
 * vtk file names.
 * The \a vtufile, \a pvtufile, and \a visitfile members are the vtk file
 * pointers; opened by \ref p4est_vtk_write_header and closed by \b
 * p4est_vtk_write_footer.
 *
 */
struct p4est_vtk_context
{
  /* data passed initially */
  p4est_t            *p4est;       /**< The p4est structure must be alive. */
  char               *filename;    /**< Original filename provided is copied. */

  /* parameters that can optionally be set in a context */
  p4est_geometry_t   *geom;        /**< The geometry may be NULL. */
  double              scale;       /**< Parameter to shrink quadrants. */
  int                 continuous;  /**< Assume continuous point data? */

  /* internal context data */
  int                 writing;     /**< True after p4est_vtk_write_header. */
  p4est_locidx_t      num_corners; /**< Number of local element corners. */
  p4est_locidx_t      num_points;  /**< Number of VTK points written. */
  p4est_locidx_t     *node_to_corner;     /**< Map a node to an element corner. */
  p4est_nodes_t      *nodes;       /**< NULL? depending on scale/continuous. */
  const char         *endianstr;   /**< String to encode endianness in VTK. */
  char                vtufilename[BUFSIZ];   /**< Each process writes one. */
  char                pvtufilename[BUFSIZ];  /**< Only root writes this one. */
  char                visitfilename[BUFSIZ]; /**< Only root writes this one. */
  FILE               *vtufile;     /**< File pointer for the VTU file. */
  FILE               *pvtufile;    /**< Paraview meta file. */
  FILE               *visitfile;   /**< Visit meta file. */
};

p4est_vtk_context_t *
p4est_vtk_context_new (p4est_t * p4est, const char *filename)
{
  p4est_vtk_context_t *cont;
  volatile uint32_t   uint;

  P4EST_ASSERT (p4est != NULL);
  P4EST_ASSERT (filename != NULL);

  /* Allocate, initialize the vtk context.  Important to zero all fields. */
  cont = P4EST_ALLOC_ZERO (p4est_vtk_context_t, 1);

  cont->p4est = p4est;
  cont->filename = P4EST_STRDUP (filename);

  cont->scale = p4est_vtk_scale;
  cont->continuous = p4est_vtk_continuous;

  /* determine endianness of the machine */
  uint = 1;
  if (*(char *) &uint == 1) {
    P4EST_ASSERT (sc_is_littleendian ());
    cont->endianstr = "LittleEndian";
  }
  else {
    cont->endianstr = "BigEndian";
  }

  return cont;
}

void
p4est_vtk_context_set_geom (p4est_vtk_context_t * cont,
                            p4est_geometry_t * geom)
{
  P4EST_ASSERT (cont != NULL);
  P4EST_ASSERT (!cont->writing);

  cont->geom = geom;
}

void
p4est_vtk_context_set_scale (p4est_vtk_context_t * cont, double scale)
{
  P4EST_ASSERT (cont != NULL);
  P4EST_ASSERT (!cont->writing);
  P4EST_ASSERT (0. < scale && scale <= 1.);

  cont->scale = scale;
}

void
p4est_vtk_context_set_continuous (p4est_vtk_context_t * cont, int continuous)
{
  P4EST_ASSERT (cont != NULL);
  P4EST_ASSERT (!cont->writing);

  cont->continuous = continuous;
}

void
p4est_vtk_context_destroy (p4est_vtk_context_t * context)
{
  P4EST_ASSERT (context != NULL);
  P4EST_ASSERT (context->p4est != NULL);

  /* since this function is called inside write_header and write_footer,
   * we cannot assume a consistent state of all member variables */

  P4EST_ASSERT (context->filename != NULL);
  P4EST_FREE (context->filename);

  /* deallocate node storage */
  if (context->nodes != NULL) {
    p4est_nodes_destroy (context->nodes);
  }
  P4EST_FREE (context->node_to_corner);

  /* Close all file pointers. */
  if (context->vtufile != NULL) {
    if (fclose (context->vtufile)) {
      P4EST_LERRORF (P4EST_STRING "_vtk: Error closing <%s>.\n",
                     context->vtufilename);
    }
    context->vtufile = NULL;
  }

  /* Close paraview master file */
  if (context->pvtufile != NULL) {
    /* Only the root process opens/closes these files. */
    P4EST_ASSERT (context->p4est->mpirank == 0);
    if (fclose (context->pvtufile)) {
      P4EST_LERRORF (P4EST_STRING "_vtk: Error closing <%s>.\n",
                     context->pvtufilename);
    }
    context->pvtufile = NULL;
  }

  /* Close visit master file */
  if (context->visitfile != NULL) {
    /* Only the root process opens/closes these files. */
    P4EST_ASSERT (context->p4est->mpirank == 0);
    if (fclose (context->visitfile)) {
      P4EST_LERRORF (P4EST_STRING "_vtk: Error closing <%s>.\n",
                     context->visitfilename);
    }
    context->visitfile = NULL;
  }

  /* Free context structure. */
  P4EST_FREE (context);
}

void
p4est_vtk_write_file (p4est_t * p4est, p4est_geometry_t * geom,
                      const char *filename)
{
  int                 retval;
  p4est_vtk_context_t *cont;

  /* allocate context and set parameters */
  cont = p4est_vtk_context_new (p4est, filename);
  p4est_vtk_context_set_geom (cont, geom);

  /* We do not write point data, so it is safe to set continuous to true.
   * This will not save any space though since the default scale is < 1. */
  p4est_vtk_context_set_continuous (cont, 1);

  /* write header, that is, vertex positions and quadrant-to-vertex map */
  cont = p4est_vtk_write_header (cont);
  SC_CHECK_ABORT (cont != NULL, P4EST_STRING "_vtk: Error writing header");

  /* write the tree/level/rank data */
  cont =
    p4est_vtk_write_cell_dataf (cont, p4est_vtk_write_tree,
                                p4est_vtk_write_level, p4est_vtk_write_rank,
                                p4est_vtk_wrap_rank, 0, 0, cont);
  SC_CHECK_ABORT (cont != NULL, P4EST_STRING "_vtk: Error writing cell data");

  /* properly write rest of the files' contents */
  retval = p4est_vtk_write_footer (cont);
  SC_CHECK_ABORT (!retval, P4EST_STRING "_vtk: Error writing footer");
}

p4est_vtk_context_t *
p4est_vtk_write_header (p4est_vtk_context_t * cont)
{
  const double        intsize = 1.0 / P4EST_ROOT_LEN;
  int                 mpirank;
  int                 conti;
  double              scale;
  const char         *filename;
  const double       *v;
  const p4est_topidx_t *tree_to_vertex;
  p4est_topidx_t      first_local_tree, last_local_tree;
  p4est_locidx_t      Ncells, Ncorners;
  p4est_t            *p4est;
  p4est_connectivity_t *connectivity;
  p4est_geometry_t   *geom;
#ifdef P4EST_VTK_ASCII
  double              wx, wy, wz;
#else
  int                 retval;
  uint8_t            *uint8_data;
  p4est_locidx_t     *locidx_data;
#endif
  int                 xi, yi, j, k;
#ifdef P4_TO_P8
  int                 zi;
#endif
  double              h2, eta_x, eta_y, eta_z = 0.;
  double              xyz[3], XYZ[3];   /* 3 not P4EST_DIM */
  size_t              num_quads, zz;
  p4est_topidx_t      jt;
  p4est_topidx_t      vt[P4EST_CHILDREN];
  p4est_locidx_t      quad_count, Npoints;
  p4est_locidx_t      sk, il, ntcid, *ntc;
  P4EST_VTK_FLOAT_TYPE *float_data;
  sc_array_t         *quadrants, *indeps;
  sc_array_t         *trees;
  p4est_tree_t       *tree;
  p4est_quadrant_t   *quad;
  p4est_nodes_t      *nodes;
  p4est_indep_t      *in;

  /* check a whole bunch of assertions, here and below */
  P4EST_ASSERT (cont != NULL);
  P4EST_ASSERT (!cont->writing);

  /* avoid uninitialized warning */
  for (k = 0; k < P4EST_CHILDREN; ++k) {
    vt[k] = -(k + 1);
  }

  /* from now on this context is officially in use for writing */
  cont->writing = 1;

  /* grab context variables */
  p4est = cont->p4est;
  filename = cont->filename;
  geom = cont->geom;
  scale = cont->scale;
  conti = cont->continuous;
  P4EST_ASSERT (filename != NULL);

  /* grab details from the forest */
  P4EST_ASSERT (p4est != NULL);
  mpirank = p4est->mpirank;
  connectivity = p4est->connectivity;
  P4EST_ASSERT (connectivity != NULL);
  v = connectivity->vertices;
  tree_to_vertex = connectivity->tree_to_vertex;
  if (geom == NULL) {
    SC_CHECK_ABORT (connectivity->num_vertices > 0,
                    "Must provide connectivity with vertex information");
    P4EST_ASSERT (v != NULL && tree_to_vertex != NULL);
  }
  trees = p4est->trees;
  first_local_tree = p4est->first_local_tree;
  last_local_tree = p4est->last_local_tree;
  Ncells = p4est->local_num_quadrants;

  cont->num_corners = Ncorners = P4EST_CHILDREN * Ncells;
  if (scale < 1. || !conti) {
    /* when we scale the quadrants we need each corner separately */
    cont->nodes = nodes = NULL;
    cont->num_points = Npoints = Ncorners;
    cont->node_to_corner = ntc = NULL;
    indeps = NULL;
  }
  else {
    /* if scale == 1. and the point data is continuous,
     * we can reuse shared quadrant corners */
    cont->nodes = nodes = p4est_nodes_new (p4est, NULL);
    indeps = &nodes->indep_nodes;
    cont->num_points = Npoints = nodes->num_owned_indeps;
    P4EST_ASSERT ((size_t) Npoints == indeps->elem_count);

    /* Establish a reverse lookup table from a node to its first reference.
     * It is slow to run twice through memory like this.  However, we also know
     * that writing data to disk is slower still, so we do not optimize.
     */
    cont->node_to_corner = ntc = P4EST_ALLOC (p4est_locidx_t, Npoints);
    memset (ntc, -1, Npoints * sizeof (p4est_locidx_t));
    for (sk = 0, il = 0; il < Ncells; ++il) {
      for (k = 0; k < P4EST_CHILDREN; ++sk, ++k) {
        ntcid = nodes->local_nodes[sk];
        P4EST_ASSERT (0 <= ntcid && ntcid < Npoints);
        if (ntc[ntcid] < 0) {
          ntc[ntcid] = sk;
        }
      }
    }
#ifdef P4EST_ENABLE_DEBUG
    /* the particular version of nodes we call makes sure they are tight */
    for (ntcid = 0; ntcid < Npoints; ++ntcid) {
      P4EST_ASSERT (0 <= ntc[ntcid] && ntc[ntcid] < Ncorners);
    }
#endif
  }

  /* Have each proc write to its own file */
  snprintf (cont->vtufilename, BUFSIZ, "%s_%04d.vtu", filename, mpirank);
  /* Use "w" for writing the initial part of the file.
   * For further parts, use "r+" and fseek so write_compressed succeeds.
   */
  cont->vtufile = fopen (cont->vtufilename, "wb");
  if (cont->vtufile == NULL) {
    P4EST_LERRORF ("Could not open %s for output\n", cont->vtufilename);
    p4est_vtk_context_destroy (cont);
    return NULL;
  }

  fprintf (cont->vtufile, "<?xml version=\"1.0\"?>\n");
  fprintf (cont->vtufile,
           "<VTKFile type=\"UnstructuredGrid\" version=\"0.1\"");
#if defined P4EST_ENABLE_VTK_BINARY && defined P4EST_ENABLE_VTK_COMPRESSION
  fprintf (cont->vtufile, " compressor=\"vtkZLibDataCompressor\"");
#endif
  fprintf (cont->vtufile, " byte_order=\"%s\">\n", cont->endianstr);
  fprintf (cont->vtufile, "  <UnstructuredGrid>\n");
  fprintf (cont->vtufile,
           "    <Piece NumberOfPoints=\"%lld\" NumberOfCells=\"%lld\">\n",
           (long long) Npoints, (long long) Ncells);
  fprintf (cont->vtufile, "      <Points>\n");

  float_data = P4EST_ALLOC (P4EST_VTK_FLOAT_TYPE, 3 * Npoints);

  /* write point position data */
  fprintf (cont->vtufile, "        <DataArray type=\"%s\" Name=\"Position\""
           " NumberOfComponents=\"3\" format=\"%s\">\n",
           P4EST_VTK_FLOAT_NAME, P4EST_VTK_FORMAT_STRING);

  if (nodes == NULL) {
    /* loop over the trees */
    for (jt = first_local_tree, quad_count = 0; jt <= last_local_tree; ++jt) {
      tree = p4est_tree_array_index (trees, jt);
      quadrants = &tree->quadrants;
      num_quads = quadrants->elem_count;

      /* retrieve corners of the tree */
      if (geom == NULL) {
        for (k = 0; k < P4EST_CHILDREN; ++k) {
          vt[k] = tree_to_vertex[jt * P4EST_CHILDREN + k];
        }
      }
      else {
        /* provoke crash on logic bug */
        P4EST_ASSERT (vt[0] == -1);
        v = NULL;
      }

      /* loop over the elements in tree and calculate vertex coordinates */
      for (zz = 0; zz < num_quads; ++zz, ++quad_count) {
        quad = p4est_quadrant_array_index (quadrants, zz);
        h2 = .5 * intsize * P4EST_QUADRANT_LEN (quad->level);
        k = 0;
#ifdef P4_TO_P8
        for (zi = 0; zi < 2; ++zi) {
          eta_z = intsize * quad->z + h2 * (1. + (zi * 2 - 1) * scale);
#endif
          for (yi = 0; yi < 2; ++yi) {
            eta_y = intsize * quad->y + h2 * (1. + (yi * 2 - 1) * scale);
            for (xi = 0; xi < 2; ++xi) {
              P4EST_ASSERT (0 <= k && k < P4EST_CHILDREN);
              eta_x = intsize * quad->x + h2 * (1. + (xi * 2 - 1) * scale);
              if (geom != NULL) {
                xyz[0] = eta_x;
                xyz[1] = eta_y;
                xyz[2] = eta_z;
                geom->X (geom, jt, xyz, XYZ);
                for (j = 0; j < 3; ++j) {
                  float_data[3 * (P4EST_CHILDREN * quad_count + k) + j] =
                    (P4EST_VTK_FLOAT_TYPE) XYZ[j];
                }
              }
              else {
                for (j = 0; j < 3; ++j) {
                  /* *INDENT-OFF* */
                xyz[j] =
            ((1. - eta_z) * ((1. - eta_y) * ((1. - eta_x) * v[3 * vt[0] + j] +
                                                   eta_x  * v[3 * vt[1] + j]) +
                                   eta_y  * ((1. - eta_x) * v[3 * vt[2] + j] +
                                                   eta_x  * v[3 * vt[3] + j]))
#ifdef P4_TO_P8
             +     eta_z  * ((1. - eta_y) * ((1. - eta_x) * v[3 * vt[4] + j] +
                                                   eta_x  * v[3 * vt[5] + j]) +
                                   eta_y  * ((1. - eta_x) * v[3 * vt[6] + j] +
                                                   eta_x  * v[3 * vt[7] + j]))
#endif
            );
                  /* *INDENT-ON* */
                  float_data[3 * (P4EST_CHILDREN * quad_count + k) + j] =
                    (P4EST_VTK_FLOAT_TYPE) xyz[j];
                }
              }
              ++k;
            }
          }
#ifdef P4_TO_P8
        }
#endif
        P4EST_ASSERT (k == P4EST_CHILDREN);
      }
    }
    P4EST_ASSERT (P4EST_CHILDREN * quad_count == Npoints);
  }
  else {
    for (zz = 0; zz < indeps->elem_count; ++zz) {
      in = (p4est_indep_t *) sc_array_index (indeps, zz);

      /* retrieve corners of the tree */
      jt = in->p.which_tree;
      if (geom == NULL) {
        for (k = 0; k < P4EST_CHILDREN; ++k) {
          vt[k] = tree_to_vertex[jt * P4EST_CHILDREN + k];
        }
      }
      else {
        /* provoke crash on logic bug */
        P4EST_ASSERT (vt[0] == -1);
        v = NULL;
      }

      /* calculate vertex coordinates */
      eta_x = intsize * in->x;
      eta_y = intsize * in->y;
#ifdef P4_TO_P8
      eta_z = intsize * in->z;
#endif
      if (geom != NULL) {
        xyz[0] = eta_x;
        xyz[1] = eta_y;
        xyz[2] = eta_z;
        geom->X (geom, jt, xyz, XYZ);
        for (j = 0; j < 3; ++j) {
          float_data[3 * zz + j] = (P4EST_VTK_FLOAT_TYPE) XYZ[j];
        }
      }
      else {
        for (j = 0; j < 3; ++j) {
          /* *INDENT-OFF* */
          xyz[j] =
            ((1. - eta_z) * ((1. - eta_y) * ((1. - eta_x) * v[3 * vt[0] + j] +
                                                   eta_x  * v[3 * vt[1] + j]) +
                                   eta_y  * ((1. - eta_x) * v[3 * vt[2] + j] +
                                                   eta_x  * v[3 * vt[3] + j]))
  #ifdef P4_TO_P8
             +     eta_z  * ((1. - eta_y) * ((1. - eta_x) * v[3 * vt[4] + j] +
                                                   eta_x  * v[3 * vt[5] + j]) +
                                   eta_y  * ((1. - eta_x) * v[3 * vt[6] + j] +
                                                   eta_x  * v[3 * vt[7] + j]))
  #endif
            );
          /* *INDENT-ON* */

          float_data[3 * zz + j] = (P4EST_VTK_FLOAT_TYPE) xyz[j];
        }
      }
    }
  }

#ifdef P4EST_VTK_ASCII
  for (il = 0; il < Npoints; ++il) {
    wx = float_data[3 * il + 0];
    wy = float_data[3 * il + 1];
    wz = float_data[3 * il + 2];

    fprintf (cont->vtufile,
#ifdef P4EST_ENABLE_VTK_DOUBLES
             "     %24.16e %24.16e %24.16e\n",
#else
             "          %16.8e %16.8e %16.8e\n",
#endif
             wx, wy, wz);
  }
#else
  fprintf (cont->vtufile, "          ");
  /* TODO: Don't allocate the full size of the array, only allocate
   * the chunk that will be passed to zlib and do this a chunk
   * at a time.
   */
  retval = p4est_vtk_write_binary (cont->vtufile, (char *) float_data,
                                   sizeof (*float_data) * 3 * Npoints);
  fprintf (cont->vtufile, "\n");
  if (retval) {
    P4EST_LERROR (P4EST_STRING "_vtk: Error encoding points\n");
    p4est_vtk_context_destroy (cont);
    P4EST_FREE (float_data);
    return NULL;
  }
#endif
  P4EST_FREE (float_data);

  fprintf (cont->vtufile, "        </DataArray>\n");
  fprintf (cont->vtufile, "      </Points>\n");
  fprintf (cont->vtufile, "      <Cells>\n");

  /* write connectivity data */
  fprintf (cont->vtufile,
           "        <DataArray type=\"%s\" Name=\"connectivity\""
           " format=\"%s\">\n", P4EST_VTK_LOCIDX, P4EST_VTK_FORMAT_STRING);
#ifdef P4EST_VTK_ASCII
  for (sk = 0, il = 0; il < Ncells; ++il) {
    fprintf (cont->vtufile, "         ");
    for (k = 0; k < P4EST_CHILDREN; ++sk, ++k) {
      fprintf (cont->vtufile, " %lld", nodes == NULL ?
               (long long) sk : (long long) nodes->local_nodes[sk]);
    }
    fprintf (cont->vtufile, "\n");
  }
#else
  fprintf (cont->vtufile, "          ");
  if (nodes == NULL) {
    locidx_data = P4EST_ALLOC (p4est_locidx_t, Ncorners);
    for (il = 0; il < Ncorners; ++il) {
      locidx_data[il] = il;
    }
    retval =
      p4est_vtk_write_binary (cont->vtufile, (char *) locidx_data,
                              sizeof (p4est_locidx_t) * Ncorners);
    P4EST_FREE (locidx_data);
  }
  else {
    retval =
      p4est_vtk_write_binary (cont->vtufile, (char *) nodes->local_nodes,
                              sizeof (p4est_locidx_t) * Ncorners);
  }
  fprintf (cont->vtufile, "\n");
  if (retval) {
    P4EST_LERROR (P4EST_STRING "_vtk: Error encoding connectivity\n");
    p4est_vtk_context_destroy (cont);
    return NULL;
  }
#endif
  fprintf (cont->vtufile, "        </DataArray>\n");

  /* write offset data */
  fprintf (cont->vtufile, "        <DataArray type=\"%s\" Name=\"offsets\""
           " format=\"%s\">\n", P4EST_VTK_LOCIDX, P4EST_VTK_FORMAT_STRING);
#ifdef P4EST_VTK_ASCII
  fprintf (cont->vtufile, "         ");
  for (il = 1, sk = 1; il <= Ncells; ++il, ++sk) {
    fprintf (cont->vtufile, " %lld", (long long) (P4EST_CHILDREN * il));
    if (!(sk % 8) && il != Ncells)
      fprintf (cont->vtufile, "\n         ");
  }
  fprintf (cont->vtufile, "\n");
#else
  locidx_data = P4EST_ALLOC (p4est_locidx_t, Ncells);
  for (il = 1; il <= Ncells; ++il)
    locidx_data[il - 1] = P4EST_CHILDREN * il;  /* same type */

  fprintf (cont->vtufile, "          ");
  retval = p4est_vtk_write_binary (cont->vtufile, (char *) locidx_data,
                                   sizeof (p4est_locidx_t) * Ncells);
  fprintf (cont->vtufile, "\n");

  P4EST_FREE (locidx_data);

  if (retval) {
    P4EST_LERROR (P4EST_STRING "_vtk: Error encoding offsets\n");
    p4est_vtk_context_destroy (cont);
    return NULL;
  }
#endif
  fprintf (cont->vtufile, "        </DataArray>\n");

  /* write type data */
  fprintf (cont->vtufile, "        <DataArray type=\"UInt8\" Name=\"types\""
           " format=\"%s\">\n", P4EST_VTK_FORMAT_STRING);
#ifdef P4EST_VTK_ASCII
  fprintf (cont->vtufile, "         ");
  for (il = 0, sk = 1; il < Ncells; ++il, ++sk) {
    fprintf (cont->vtufile, " %d", P4EST_VTK_CELL_TYPE);
    if (!(sk % 20) && il != (Ncells - 1))
      fprintf (cont->vtufile, "\n         ");
  }
  fprintf (cont->vtufile, "\n");
#else
  uint8_data = P4EST_ALLOC (uint8_t, Ncells);
  for (il = 0; il < Ncells; ++il)
    uint8_data[il] = P4EST_VTK_CELL_TYPE;

  fprintf (cont->vtufile, "          ");
  retval = p4est_vtk_write_binary (cont->vtufile, (char *) uint8_data,
                                   sizeof (*uint8_data) * Ncells);
  fprintf (cont->vtufile, "\n");

  P4EST_FREE (uint8_data);

  if (retval) {
    P4EST_LERROR (P4EST_STRING "_vtk: Error encoding types\n");
    p4est_vtk_context_destroy (cont);
    return NULL;
  }
#endif
  fprintf (cont->vtufile, "        </DataArray>\n");
  fprintf (cont->vtufile, "      </Cells>\n");

  if (ferror (cont->vtufile)) {
    P4EST_LERROR (P4EST_STRING "_vtk: Error writing header\n");
    p4est_vtk_context_destroy (cont);
    return NULL;
  }

  /* Only have the root write to the parallel vtk file */
  if (mpirank == 0) {
    snprintf (cont->pvtufilename, BUFSIZ, "%s.pvtu", filename);

    cont->pvtufile = fopen (cont->pvtufilename, "wb");
    if (!cont->pvtufile) {
      P4EST_LERRORF ("Could not open %s for output\n", cont->pvtufilename);
      p4est_vtk_context_destroy (cont);
      return NULL;
    }

    fprintf (cont->pvtufile, "<?xml version=\"1.0\"?>\n");
    fprintf (cont->pvtufile,
             "<VTKFile type=\"PUnstructuredGrid\" version=\"0.1\"");
#if defined P4EST_ENABLE_VTK_BINARY && defined P4EST_ENABLE_VTK_COMPRESSION
    fprintf (cont->pvtufile, " compressor=\"vtkZLibDataCompressor\"");
#endif
    fprintf (cont->pvtufile, " byte_order=\"%s\">\n", cont->endianstr);

    fprintf (cont->pvtufile, "  <PUnstructuredGrid GhostLevel=\"0\">\n");
    fprintf (cont->pvtufile, "    <PPoints>\n");
    fprintf (cont->pvtufile, "      <PDataArray type=\"%s\" Name=\"Position\""
             " NumberOfComponents=\"3\" format=\"%s\"/>\n",
             P4EST_VTK_FLOAT_NAME, P4EST_VTK_FORMAT_STRING);
    fprintf (cont->pvtufile, "    </PPoints>\n");

    if (ferror (cont->pvtufile)) {
      P4EST_LERROR (P4EST_STRING "_vtk: Error writing parallel header\n");
      p4est_vtk_context_destroy (cont);
      return NULL;
    }

    /* Create a master file for visualization in Visit; this will be used
     * only in p4est_vtk_write_footer().
     */
    snprintf (cont->visitfilename, BUFSIZ, "%s.visit", filename);
    cont->visitfile = fopen (cont->visitfilename, "wb");
    if (!cont->visitfile) {
      P4EST_LERRORF ("Could not open %s for output\n", cont->visitfilename);
      p4est_vtk_context_destroy (cont);
      return NULL;
    }
  }

  /* the nodes object is no longer needed */
  if (nodes != NULL) {
    p4est_nodes_destroy (cont->nodes);
    cont->nodes = NULL;
  }

  return cont;
}

#ifdef P4_TO_P8
/* Based on
 * https://github.com/Kitware/VTK/blob/99770c75c2df471c456323d66a4a0bd154cf3a82
 * /Common/DataModel/vtkHigherOrderHexahedron.cxx#L611
 */
static int
point_index_from_ijk (int i, int j, int k, const int *order)
{
  int                 ibdy = (i == 0 || i == order[0]);
  int                 jbdy = (j == 0 || j == order[1]);
  int                 kbdy = (k == 0 || k == order[2]);
  /* How many boundaries do we lie on at once? */
  int                 nbdy = (ibdy ? 1 : 0) + (jbdy ? 1 : 0) + (kbdy ? 1 : 0);

  if (nbdy == 3) {              /* Vertex DOF */
    /* ijk is a corner node. Return the proper index (somewhere in [0,7]): */
    return (i ? (j ? 2 : 1) : (j ? 3 : 0)) + (k ? 4 : 0);
  }

  int                 offset = 8;
  if (nbdy == 2) {              /* Edge DOF */
    if (!ibdy) {                /* On i axis */
      return (i - 1) + (j ? order[0] + order[1] - 2 : 0) +
        (k ? 2 * (order[0] + order[1] - 2) : 0) + offset;
    }
    if (!jbdy) {                /* On j axis */
      return (j - 1) + (i ? order[0] - 1 : 2 * (order[0] - 1) + order[1] -
                        1) + (k ? 2 * (order[0] + order[1] - 2) : 0) + offset;
    }
    /* !kbdy, On k axis */
    offset += 4 * (order[0] - 1) + 4 * (order[1] - 1);
    return (k - 1) + (order[2] - 1) * (i ? (j ? 3 : 1) : (j ? 2 : 0)) +
      offset;
  }

  offset += 4 * (order[0] + order[1] + order[2] - 3);
  if (nbdy == 1) {              /* Face DOF */
    if (ibdy) {                 /* On i-normal face */
      return (j - 1) + ((order[1] - 1) * (k - 1)) +
        (i ? (order[1] - 1) * (order[2] - 1) : 0) + offset;
    }
    offset += 2 * (order[1] - 1) * (order[2] - 1);
    if (jbdy) {                 /* On j-normal face */
      return (i - 1) + ((order[0] - 1) * (k - 1)) +
        (j ? (order[2] - 1) * (order[0] - 1) : 0) + offset;
    }
    offset += 2 * (order[2] - 1) * (order[0] - 1);
    /* kbdy, On k-normal face */
    return (i - 1) + ((order[0] - 1) * (j - 1)) +
      (k ? (order[0] - 1) * (order[1] - 1) : 0) + offset;
  }

  /* nbdy == 0: Body DOF */
  offset += 2 *
    ((order[1] - 1) * (order[2] - 1) + (order[2] - 1) * (order[0] - 1) +
     (order[0] - 1) * (order[1] - 1));
  return offset + (i - 1) + (order[0] - 1) *
    ((j - 1) + (order[1] - 1) * ((k - 1)));
}
#else
/* Based on
 * https://github.com/Kitware/VTK/blob/99770c75c2df471c456323d66a4a0bd154cf3a82
 * /Common/DataModel/vtkHigherOrderQuadrilateral.cxx#L446
 */
static int
point_index_from_ijk (int i, int j, const int *order)
{
  int                 ibdy = (i == 0 || i == order[0]);
  int                 jbdy = (j == 0 || j == order[1]);
  /* How many boundaries do we lie on at once? */
  int                 nbdy = (ibdy ? 1 : 0) + (jbdy ? 1 : 0);

  if (nbdy == 2) {              /* Vertex DOF */
    /* ijk is a corner node. Return the proper index (somewhere in [0,7]): */
    return (i ? (j ? 2 : 1) : (j ? 3 : 0));
  }

  int                 offset = 4;
  if (nbdy == 1) {              /* Edge DOF */
    if (!ibdy) {                /* On i axis */
      return (i - 1) + (j ? order[0] - 1 + order[1] - 1 : 0) + offset;
    }
    if (!jbdy) {                /* On j axis */
      return (j - 1) + (i ? order[0] - 1 : 2 * (order[0] - 1) + order[1] -
                        1) + offset;
    }
  }

  offset += 2 * (order[0] - 1 + order[1] - 1);
  /* nbdy == 0: Face DOF */
  return offset + (i - 1) + (order[0] - 1) * ((j - 1));
}
#endif

p4est_vtk_context_t *
p4est_vtk_write_header_ho (p4est_vtk_context_t * cont, sc_array_t * positions,
                           int Nnodes1D)
{
  /* positions in order of: x,y,z,x,y,z */
  int                 mpirank;
  const char         *filename;
  p4est_locidx_t      Ncells;
  p4est_t            *p4est;
  p4est_locidx_t     *locidx_data;
#ifdef P4EST_VTK_ASCII
  double              wx, wy, wz = 0.;
#else
  P4EST_VTK_FLOAT_TYPE *float_data;
  int                 retval;
  uint8_t            *uint8_data;
#endif
  int                 i, j;
#if defined P4_TO_P8 || defined P4EST_VTK_ASCII
  int                 k;
#endif
  int                 order[P4EST_DIM];
  p4est_locidx_t      Npoints, Npointscell;
  p4est_locidx_t      sk, il;

  /* check a whole bunch of assertions, here and below */
  P4EST_ASSERT (cont != NULL);
  P4EST_ASSERT (!cont->writing);

  /* from now on this context is officially in use for writing */
  cont->writing = 1;

  /* grab context variables */
  p4est = cont->p4est;
  filename = cont->filename;
  P4EST_ASSERT (filename != NULL);

  /* grab details from the forest */
  P4EST_ASSERT (p4est != NULL);
  mpirank = p4est->mpirank;
  Ncells = p4est->local_num_quadrants;

  cont->num_corners = P4EST_CHILDREN * Ncells;
  cont->nodes = NULL;
#ifdef P4_TO_P8
  Npointscell = Nnodes1D * Nnodes1D * Nnodes1D;
#else
  Npointscell = Nnodes1D * Nnodes1D;
#endif
  cont->num_points = Npoints = Npointscell * Ncells;
  cont->node_to_corner = NULL;

  /* Have each proc write to its own file */
  snprintf (cont->vtufilename, BUFSIZ, "%s_%04d.vtu", filename, mpirank);
  /* Use "w" for writing the initial part of the file.
   * For further parts, use "r+" and fseek so write_compressed succeeds.
   */
  cont->vtufile = fopen (cont->vtufilename, "wb");
  if (cont->vtufile == NULL) {
    P4EST_LERRORF ("Could not open %s for output\n", cont->vtufilename);
    p4est_vtk_context_destroy (cont);
    return NULL;
  }

  fprintf (cont->vtufile, "<?xml version=\"1.0\"?>\n");
  fprintf (cont->vtufile,
           "<VTKFile type=\"UnstructuredGrid\" version=\"0.1\"");
#if defined P4EST_ENABLE_VTK_BINARY && defined P4EST_ENABLE_VTK_COMPRESSION
  fprintf (cont->vtufile, " compressor=\"vtkZLibDataCompressor\"");
#endif
  fprintf (cont->vtufile, " byte_order=\"%s\">\n", cont->endianstr);
  fprintf (cont->vtufile, "  <UnstructuredGrid>\n");
  fprintf (cont->vtufile,
           "    <Piece NumberOfPoints=\"%lld\" NumberOfCells=\"%lld\">\n",
           (long long) Npoints, (long long) Ncells);
  fprintf (cont->vtufile, "      <Points>\n");

  /* write point position data */
  fprintf (cont->vtufile, "        <DataArray type=\"%s\" Name=\"Position\""
           " NumberOfComponents=\"3\" format=\"%s\">\n",
           P4EST_VTK_FLOAT_NAME, P4EST_VTK_FORMAT_STRING);

#ifdef P4EST_VTK_ASCII
  for (il = 0; il < Npoints; ++il) {
    wx = *(double *) sc_array_index (positions, (il * P4EST_DIM));
    wy = *(double *) sc_array_index (positions, (il * P4EST_DIM) + 1);
#ifdef P4_TO_P8
    wz = *(double *) sc_array_index (positions, (il * P4EST_DIM) + 2);
#endif

    fprintf (cont->vtufile,
#ifdef P4EST_ENABLE_VTK_DOUBLES
             "     %24.16e %24.16e %24.16e\n",
#else
             "          %16.8e %16.8e %16.8e\n",
#endif
             wx, wy, wz);
  }
#else
  float_data = P4EST_ALLOC (P4EST_VTK_FLOAT_TYPE, 3 * Npoints);
  fprintf (cont->vtufile, "          ");
  /* TODO: Don't allocate the full size of the array, only allocate
   * the chunk that will be passed to zlib and do this a chunk
   * at a time.
   */
  for (il = 0; il < Npoints; ++il) {
    for (j = 0; j < P4EST_DIM; ++j) {
      float_data[il * 3 + j] = (P4EST_VTK_FLOAT_TYPE) *
        ((double *) sc_array_index (positions, (il * P4EST_DIM) + j));
    }
#ifndef P4_TO_P8
    float_data[il * 3 + 2] = 0.;
#endif
  }
  retval = p4est_vtk_write_binary (cont->vtufile, (char *) float_data,
                                   sizeof (*float_data) * 3 * Npoints);
  fprintf (cont->vtufile, "\n");
  if (retval) {
    P4EST_LERROR (P4EST_STRING "_vtk: Error encoding points\n");
    p4est_vtk_context_destroy (cont);
    P4EST_FREE (float_data);
    return NULL;
  }
  P4EST_FREE (float_data);
#endif

  fprintf (cont->vtufile, "        </DataArray>\n");
  fprintf (cont->vtufile, "      </Points>\n");
  fprintf (cont->vtufile, "      <Cells>\n");

  /* write connectivity data */
  fprintf (cont->vtufile,
           "        <DataArray type=\"%s\" Name=\"connectivity\""
           " format=\"%s\">\n", P4EST_VTK_LOCIDX, P4EST_VTK_FORMAT_STRING);
  locidx_data = P4EST_ALLOC (p4est_locidx_t, Npoints);
  order[0] = order[1] = Nnodes1D - 1;
#ifdef P4_TO_P8
  order[2] = order[0];
#endif
  for (sk = 0, il = 0; il < Ncells; ++il) {
#ifdef P4_TO_P8
    for (k = 0; k < Nnodes1D; ++k) {
#endif
      for (j = 0; j < Nnodes1D; ++j) {
        for (i = 0; i < Nnodes1D; ++sk, ++i) {
          locidx_data[il * Npointscell +
#ifdef P4_TO_P8
                      point_index_from_ijk (i, j, k, order)
#else
                      point_index_from_ijk (i, j, order)
#endif
            ] = sk;
        }
      }
#ifdef P4_TO_P8
    }
#endif
  }
#ifdef P4EST_VTK_ASCII
  for (sk = 0, il = 0; il < Ncells; ++il) {
    fprintf (cont->vtufile, "         ");
    for (k = 0; k < Npointscell; ++sk, ++k) {
      fprintf (cont->vtufile, " %lld", (long long) locidx_data[sk]);
    }
    fprintf (cont->vtufile, "\n");
  }
#else
  fprintf (cont->vtufile, "          ");
  retval =
    p4est_vtk_write_binary (cont->vtufile, (char *) locidx_data,
                            sizeof (p4est_locidx_t) * Npoints);
  fprintf (cont->vtufile, "\n");
  if (retval) {
    P4EST_LERROR (P4EST_STRING "_vtk: Error encoding connectivity\n");
    p4est_vtk_context_destroy (cont);
    return NULL;
  }
#endif
  P4EST_FREE (locidx_data);
  fprintf (cont->vtufile, "        </DataArray>\n");

  /* write offset data */
  fprintf (cont->vtufile, "        <DataArray type=\"%s\" Name=\"offsets\""
           " format=\"%s\">\n", P4EST_VTK_LOCIDX, P4EST_VTK_FORMAT_STRING);
#ifdef P4EST_VTK_ASCII
  fprintf (cont->vtufile, "         ");
  for (il = 1, sk = 1; il <= Ncells; ++il, ++sk) {
    fprintf (cont->vtufile, " %lld", (long long) (Npointscell * il));
    if (!(sk % 8) && il != Ncells)
      fprintf (cont->vtufile, "\n         ");
  }
  fprintf (cont->vtufile, "\n");
#else
  locidx_data = P4EST_ALLOC (p4est_locidx_t, Ncells);
  for (il = 1; il <= Ncells; ++il)
    locidx_data[il - 1] = Npointscell * il;     /* same type */

  fprintf (cont->vtufile, "          ");
  retval = p4est_vtk_write_binary (cont->vtufile, (char *) locidx_data,
                                   sizeof (p4est_locidx_t) * Ncells);
  fprintf (cont->vtufile, "\n");

  P4EST_FREE (locidx_data);

  if (retval) {
    P4EST_LERROR (P4EST_STRING "_vtk: Error encoding offsets\n");
    p4est_vtk_context_destroy (cont);
    return NULL;
  }
#endif
  fprintf (cont->vtufile, "        </DataArray>\n");

  /* write type data */
  fprintf (cont->vtufile, "        <DataArray type=\"UInt8\" Name=\"types\""
           " format=\"%s\">\n", P4EST_VTK_FORMAT_STRING);
#ifdef P4EST_VTK_ASCII
  fprintf (cont->vtufile, "         ");
  for (il = 0, sk = 1; il < Ncells; ++il, ++sk) {
    fprintf (cont->vtufile, " %d", P4EST_VTK_CELL_TYPE_HO);
    if (!(sk % 20) && il != (Ncells - 1))
      fprintf (cont->vtufile, "\n         ");
  }
  fprintf (cont->vtufile, "\n");
#else
  uint8_data = P4EST_ALLOC (uint8_t, Ncells);
  for (il = 0; il < Ncells; ++il)
    uint8_data[il] = P4EST_VTK_CELL_TYPE_HO;

  fprintf (cont->vtufile, "          ");
  retval = p4est_vtk_write_binary (cont->vtufile, (char *) uint8_data,
                                   sizeof (*uint8_data) * Ncells);
  fprintf (cont->vtufile, "\n");

  P4EST_FREE (uint8_data);

  if (retval) {
    P4EST_LERROR (P4EST_STRING "_vtk: Error encoding types\n");
    p4est_vtk_context_destroy (cont);
    return NULL;
  }
#endif
  fprintf (cont->vtufile, "        </DataArray>\n");
  fprintf (cont->vtufile, "      </Cells>\n");

  if (ferror (cont->vtufile)) {
    P4EST_LERROR (P4EST_STRING "_vtk: Error writing header\n");
    p4est_vtk_context_destroy (cont);
    return NULL;
  }

  /* Only have the root write to the parallel vtk file */
  if (mpirank == 0) {
    snprintf (cont->pvtufilename, BUFSIZ, "%s.pvtu", filename);

    cont->pvtufile = fopen (cont->pvtufilename, "wb");
    if (!cont->pvtufile) {
      P4EST_LERRORF ("Could not open %s for output\n", cont->pvtufilename);
      p4est_vtk_context_destroy (cont);
      return NULL;
    }

    fprintf (cont->pvtufile, "<?xml version=\"1.0\"?>\n");
    fprintf (cont->pvtufile,
             "<VTKFile type=\"PUnstructuredGrid\" version=\"0.1\"");
#if defined P4EST_ENABLE_VTK_BINARY && defined P4EST_ENABLE_VTK_COMPRESSION
    fprintf (cont->pvtufile, " compressor=\"vtkZLibDataCompressor\"");
#endif
    fprintf (cont->pvtufile, " byte_order=\"%s\">\n", cont->endianstr);

    fprintf (cont->pvtufile, "  <PUnstructuredGrid GhostLevel=\"0\">\n");
    fprintf (cont->pvtufile, "    <PPoints>\n");
    fprintf (cont->pvtufile, "      <PDataArray type=\"%s\" Name=\"Position\""
             " NumberOfComponents=\"3\" format=\"%s\"/>\n",
             P4EST_VTK_FLOAT_NAME, P4EST_VTK_FORMAT_STRING);
    fprintf (cont->pvtufile, "    </PPoints>\n");

    if (ferror (cont->pvtufile)) {
      P4EST_LERROR (P4EST_STRING "_vtk: Error writing parallel header\n");
      p4est_vtk_context_destroy (cont);
      return NULL;
    }

    /* Create a master file for visualization in Visit; this will be used
     * only in p4est_vtk_write_footer().
     */
    snprintf (cont->visitfilename, BUFSIZ, "%s.visit", filename);
    cont->visitfile = fopen (cont->visitfilename, "wb");
    if (!cont->visitfile) {
      P4EST_LERRORF ("Could not open %s for output\n", cont->visitfilename);
      p4est_vtk_context_destroy (cont);
      return NULL;
    }
  }

  return cont;
}

/** Write VTK point data.
 *
 * This function exports custom point data to the vtk file; it is functionally
 * the same as \b p4est_vtk_write_point_dataf with the only difference being
 * that instead of a variable argument list, an initialized \a va_list is
 * passed as the last argument. The \a va_list is initialized from the variable
 * argument list of the calling function.
 *
 * \note This function is actually called from \b p4est_vtk_write_point_dataf
 *
 * \param [in,out] cont    A vtk context created by \ref p4est_vtk_context_new.
 * \param [in] num_point_scalars Number of point scalar datasets to output.
 * \param [in] num_point_vectors Number of point vector datasets to output.
 * \param [in,out] ap      An initialized va_list used to access the
 *                         scalar/vector data.
 *
 * \return          On success, the context that has been passed in.
 *                  On failure, returns NULL and deallocates the context.
 */
static p4est_vtk_context_t *
p4est_vtk_write_point_datav (p4est_vtk_context_t * cont,
                             int num_point_scalars,
                             int num_point_vectors, va_list ap)
{
  const int           num_point_all = num_point_scalars + num_point_vectors;
  int                 mpirank;
  int                 retval;
  int                 i, all;
  int                 scalar_strlen, vector_strlen;
  char                point_scalars[BUFSIZ], point_vectors[BUFSIZ];
  const char         *name, **names;
  p4est_vtk_context_t *list_end;
  sc_array_t        **values;
  p4est_locidx_t      ecount;

  P4EST_ASSERT (cont != NULL && cont->writing);
  P4EST_ASSERT (cont->p4est != NULL);

  /* This function needs to do nothing if there is no data. */
  if (!(num_point_scalars || num_point_vectors)) {
    return cont;
  }
  mpirank = cont->p4est->mpirank;

  /* Allocate storage to manage the data fields. */
  values = P4EST_ALLOC (sc_array_t *, num_point_all);
  names = P4EST_ALLOC (const char *, num_point_all);

  ecount =
    cont->node_to_corner == NULL ? cont->num_points : cont->num_corners;

  /* Gather point data. */
  all = 0;
  scalar_strlen = 0;
  point_scalars[0] = '\0';
  for (i = 0; i < num_point_scalars; ++all, ++i) {
    name = names[all] = va_arg (ap, const char *);
    retval = snprintf (point_scalars + scalar_strlen, BUFSIZ - scalar_strlen,
                       "%s%s", i == 0 ? "" : ",", name);
    SC_CHECK_ABORT (retval > 0,
                    P4EST_STRING "_vtk: Error collecting point scalars");
    scalar_strlen += retval;
    values[all] = va_arg (ap, sc_array_t *);

    /* Validate input. */
    SC_CHECK_ABORT (values[all]->elem_size == sizeof (double),
                    P4EST_STRING
                    "_vtk: Error: incorrect point scalar data type;"
                    " scalar data must contain doubles.");
    SC_CHECK_ABORT (values[all]->elem_count == (size_t) ecount,
                    P4EST_STRING
                    "_vtk: Error: incorrect point scalar data count; see "
                    P4EST_STRING "_vtk.h for more details.");
  }

  /* keep variable all at current value */
  vector_strlen = 0;
  point_vectors[0] = '\0';
  for (i = 0; i < num_point_vectors; ++all, ++i) {
    name = names[all] = va_arg (ap, const char *);
    retval = snprintf (point_vectors + vector_strlen, BUFSIZ - vector_strlen,
                       "%s%s", i == 0 ? "" : ",", name);
    SC_CHECK_ABORT (retval > 0,
                    P4EST_STRING "_vtk: Error collecting point vectors");
    vector_strlen += retval;
    values[all] = va_arg (ap, sc_array_t *);

    /* Validate input. */
    SC_CHECK_ABORT (values[all]->elem_size == sizeof (double),
                    P4EST_STRING
                    "_vtk: Error: incorrect point vector data type;"
                    " vector data must contain doubles.");
    SC_CHECK_ABORT (values[all]->elem_count == 3 * (size_t) ecount,
                    P4EST_STRING
                    "_vtk: Error: incorrect point vector data count; see "
                    P4EST_STRING "_vtk.h for more details.");
  }

  /* Check for pointer variable marking the end of variable data input. */
  list_end = va_arg (ap, p4est_vtk_context_t *);
  SC_CHECK_ABORT (list_end == cont,
                  P4EST_STRING "_vtk Error: the end of variable data must be"
                  " specified by passing, as the last argument, the current "
                  P4EST_STRING "_vtk_context_t pointer.  See " P4EST_STRING
                  "_vtk.h for more information.");

  fprintf (cont->vtufile, "      <PointData");
  fprintf (cont->vtufile, " Scalars=\"%s\"", point_scalars);
  fprintf (cont->vtufile, " Vectors=\"%s\"", point_vectors);
  fprintf (cont->vtufile, ">\n");

  if (ferror (cont->vtufile)) {
    P4EST_LERRORF (P4EST_STRING "_vtk: Error writing %s\n",
                   cont->vtufilename);
    p4est_vtk_context_destroy (cont);

    P4EST_FREE (values);
    P4EST_FREE (names);

    return NULL;
  }

  /* now we are done counting and checking we write the fields */
  all = 0;
  for (i = 0; i < num_point_scalars; ++all, ++i) {
    cont = p4est_vtk_write_point_scalar (cont, names[all], values[all]);
    SC_CHECK_ABORT (cont != NULL,
                    P4EST_STRING "_vtk: Error writing point scalars");
  }

  for (i = 0; i < num_point_vectors; ++all, ++i) {
    cont = p4est_vtk_write_point_vector (cont, names[all], values[all]);
    SC_CHECK_ABORT (cont != NULL,
                    P4EST_STRING "_vtk: Error writing point vectors");
  }

  fprintf (cont->vtufile, "      </PointData>\n");

  P4EST_FREE (values);

  if (ferror (cont->vtufile)) {
    P4EST_LERRORF (P4EST_STRING "_vtk: Error writing %s\n",
                   cont->vtufilename);
    p4est_vtk_context_destroy (cont);

    P4EST_FREE (names);

    return NULL;
  }

  /* Only have the root write to the parallel vtk file */
  if (mpirank == 0) {
    fprintf (cont->pvtufile, "    <PPointData>\n");

    all = 0;
    for (i = 0; i < num_point_scalars; ++all, i++)
      fprintf (cont->pvtufile, "      "
               "<PDataArray type=\"%s\" Name=\"%s\" format=\"%s\"/>\n",
               P4EST_VTK_FLOAT_NAME, names[all], P4EST_VTK_FORMAT_STRING);

    for (i = 0; i < num_point_vectors; ++all, i++)
      fprintf (cont->pvtufile, "      "
               "<PDataArray type=\"%s\" Name=\"%s\" NumberOfComponents=\"3\" "
               "format=\"%s\"/>\n",
               P4EST_VTK_FLOAT_NAME, names[all], P4EST_VTK_FORMAT_STRING);

    fprintf (cont->pvtufile, "    </PPointData>\n");

    if (ferror (cont->pvtufile)) {
      P4EST_LERROR (P4EST_STRING "_vtk: Error writing parallel header\n");
      p4est_vtk_context_destroy (cont);

      P4EST_FREE (names);

      return NULL;
    }
  }

  P4EST_FREE (names);

  return cont;
}

p4est_vtk_context_t *
p4est_vtk_write_point_dataf (p4est_vtk_context_t * cont,
                             int num_point_scalars, int num_point_vectors,
                             ...)
{
  va_list             ap;

  P4EST_ASSERT (cont != NULL && cont->writing);
  P4EST_ASSERT (num_point_scalars >= 0 && num_point_vectors >= 0);

  va_start (ap, num_point_vectors);
  cont = p4est_vtk_write_point_datav (cont, num_point_scalars,
                                      num_point_vectors, ap);
  va_end (ap);

  return cont;
}

p4est_vtk_context_t *
p4est_vtk_write_cell_datav (p4est_vtk_context_t * cont,
                            int write_tree, int write_level,
                            int write_rank, int wrap_rank,
                            int num_cell_scalars,
                            int num_cell_vectors, va_list ap)
{
  int                 i;
  const char        **names;
  sc_array_t        **values;
  p4est_vtk_context_t *list_end = NULL, *retContext = NULL;

  P4EST_ASSERT (cont != NULL && cont->writing);
  P4EST_ASSERT (num_cell_scalars >= 0 && num_cell_vectors >= 0);
  P4EST_ASSERT (wrap_rank >= 0);

  names = P4EST_ALLOC (const char *, num_cell_scalars + num_cell_vectors);
  values = P4EST_ALLOC (sc_array_t *, num_cell_scalars + num_cell_vectors);

  for (i = 0; i < num_cell_scalars + num_cell_vectors; ++i) {
    names[i] = va_arg (ap, const char *);
    values[i] = va_arg (ap, sc_array_t *);
  }

  /* Check for pointer variable marking the end of variable data input. */
  list_end = va_arg (ap, p4est_vtk_context_t *);
  SC_CHECK_ABORT (list_end == cont,
                  P4EST_STRING "_vtk Error: the end of variable data must be"
                  " specified by passing, as the last argument, the current "
                  P4EST_STRING "_vtk_context_t pointer.  See " P4EST_STRING
                  "_vtk.h for more information.");

  retContext = p4est_vtk_write_cell_data (cont, write_tree, write_level,
                                          write_rank, wrap_rank,
                                          num_cell_scalars, num_cell_vectors,
                                          names, values);

  P4EST_FREE (values);
  P4EST_FREE (names);

  return retContext;
}

p4est_vtk_context_t *
p4est_vtk_write_cell_dataf (p4est_vtk_context_t * cont,
                            int write_tree, int write_level,
                            int write_rank, int wrap_rank,
                            int num_cell_scalars, int num_cell_vectors, ...)
{
  va_list             ap;

  P4EST_ASSERT (cont != NULL && cont->writing);
  P4EST_ASSERT (num_cell_scalars >= 0 && num_cell_vectors >= 0);
  P4EST_ASSERT (wrap_rank >= 0);

  va_start (ap, num_cell_vectors);
  cont = p4est_vtk_write_cell_datav (cont,
                                     write_tree, write_level,
                                     write_rank, wrap_rank,
                                     num_cell_scalars, num_cell_vectors, ap);
  va_end (ap);

  return cont;
}

p4est_vtk_context_t *
p4est_vtk_write_cell_data (p4est_vtk_context_t * cont,
                           int write_tree,
                           int write_level,
                           int write_rank,
                           int wrap_rank,
                           int num_cell_scalars,
                           int num_cell_vectors,
                           const char *fieldnames[], sc_array_t * values[])
{
  const int           mpirank = cont->p4est->mpirank;
  int                 retval;
  int                 i, all = 0;
  int                 scalar_strlen, vector_strlen;
  sc_array_t         *trees = cont->p4est->trees;
  p4est_tree_t       *tree;
  const p4est_topidx_t first_local_tree = cont->p4est->first_local_tree;
  const p4est_topidx_t last_local_tree = cont->p4est->last_local_tree;
  const p4est_locidx_t Ncells = cont->p4est->local_num_quadrants;
  char                cell_scalars[BUFSIZ], cell_vectors[BUFSIZ];
  const char         *name, **names;
  size_t              num_quads, zz;
  sc_array_t         *quadrants;
  p4est_quadrant_t   *quad;
#ifdef P4EST_VTK_ASCII
  p4est_locidx_t      sk;
#else
  uint8_t            *uint8_data;
  p4est_locidx_t     *locidx_data;
#endif
  p4est_topidx_t      jt;
  p4est_locidx_t      il;

  char                vtkCellDataString[BUFSIZ] = "";
  int                 printed = 0;

  P4EST_ASSERT (cont != NULL && cont->writing);
  P4EST_ASSERT (num_cell_scalars >= 0 && num_cell_vectors >= 0);
  P4EST_ASSERT (wrap_rank >= 0);

  /* This function needs to do nothing if there is no data. */
  if (!
      (write_tree || write_level || write_rank || wrap_rank
       || num_cell_scalars || num_cell_vectors))
    return cont;

  names = P4EST_ALLOC (const char *, num_cell_scalars + num_cell_vectors);

  /* Gather cell data. */
  scalar_strlen = 0;
  cell_scalars[0] = '\0';
  for (i = 0; i < num_cell_scalars; ++all, ++i) {
    name = names[all] = fieldnames[all];
    retval = snprintf (cell_scalars + scalar_strlen, BUFSIZ - scalar_strlen,
                       "%s%s", i == 0 ? "" : ",", name);
    SC_CHECK_ABORT (retval > 0,
                    P4EST_STRING "_vtk: Error collecting cell scalars");
    scalar_strlen += retval;

    /* Validate input. */
    SC_CHECK_ABORT (values[all]->elem_size == sizeof (double),
                    P4EST_STRING
                    "_vtk: Error: incorrect cell scalar data type;"
                    " scalar data must contain doubles.");
    SC_CHECK_ABORT (values[all]->elem_count ==
                    (size_t) cont->p4est->local_num_quadrants,
                    P4EST_STRING
                    "_vtk: Error: incorrect cell scalar data count;"
                    " scalar data must contain exactly"
                    " p4est->local_num_quadrants doubles.");
  }

  vector_strlen = 0;
  cell_vectors[0] = '\0';
  for (i = 0; i < num_cell_vectors; ++all, ++i) {
    name = names[all] = fieldnames[all];
    retval = snprintf (cell_vectors + vector_strlen, BUFSIZ - vector_strlen,
                       "%s%s", i == 0 ? "" : ",", name);
    SC_CHECK_ABORT (retval > 0,
                    P4EST_STRING "_vtk: Error collecting cell vectors");
    vector_strlen += retval;

    /* Validate input. */
    SC_CHECK_ABORT (values[all]->elem_size == sizeof (double),
                    P4EST_STRING
                    "_vtk: Error: incorrect cell vector data type;"
                    " vector data must contain doubles.");
    SC_CHECK_ABORT (values[all]->elem_count ==
                    3 * (size_t) cont->p4est->local_num_quadrants,
                    P4EST_STRING
                    "_vtk: Error: incorrect cell vector data count;"
                    " vector data must contain exactly"
                    " 3 * p4est->local_num_quadrants doubles.");
  }

  if (write_tree)
    printed +=
      snprintf (vtkCellDataString + printed, BUFSIZ - printed, "treeid");

  if (write_level)
    printed +=
      snprintf (vtkCellDataString + printed, BUFSIZ - printed,
                printed > 0 ? ",level" : "level");

  if (write_rank)
    printed +=
      snprintf (vtkCellDataString + printed, BUFSIZ - printed,
                printed > 0 ? ",mpirank" : "mpirank");

  if (num_cell_scalars)
    printed +=
      snprintf (vtkCellDataString + printed, BUFSIZ - printed,
                printed > 0 ? ",%s" : "%s", cell_scalars);

  if (num_cell_vectors)
    printed +=
      snprintf (vtkCellDataString + printed, BUFSIZ - printed,
                printed > 0 ? ",%s" : "%s", cell_vectors);

  fprintf (cont->vtufile, "      <CellData Scalars=\"%s\">\n",
           vtkCellDataString);

#ifndef P4EST_VTK_ASCII
  locidx_data = P4EST_ALLOC (p4est_locidx_t, Ncells);
#endif

  if (write_tree) {
    fprintf (cont->vtufile, "        <DataArray type=\"%s\" Name=\"treeid\""
             " format=\"%s\">\n", P4EST_VTK_LOCIDX, P4EST_VTK_FORMAT_STRING);
#ifdef P4EST_VTK_ASCII
    fprintf (cont->vtufile, "         ");
    for (il = 0, sk = 1, jt = first_local_tree; jt <= last_local_tree; ++jt) {
      tree = p4est_tree_array_index (trees, jt);
      num_quads = tree->quadrants.elem_count;
      for (zz = 0; zz < num_quads; ++zz, ++sk, ++il) {
        fprintf (cont->vtufile, " %lld", (long long) jt);
        if (!(sk % 20) && il != (Ncells - 1))
          fprintf (cont->vtufile, "\n         ");
      }
    }
    fprintf (cont->vtufile, "\n");
#else
    for (il = 0, jt = first_local_tree; jt <= last_local_tree; ++jt) {
      tree = p4est_tree_array_index (trees, jt);
      num_quads = tree->quadrants.elem_count;
      for (zz = 0; zz < num_quads; ++zz, ++il) {
        locidx_data[il] = (p4est_locidx_t) jt;
      }
    }
    fprintf (cont->vtufile, "          ");
    retval = p4est_vtk_write_binary (cont->vtufile, (char *) locidx_data,
                                     sizeof (*locidx_data) * Ncells);
    fprintf (cont->vtufile, "\n");
    if (retval) {
      P4EST_LERROR (P4EST_STRING "_vtk: Error encoding types\n");
      p4est_vtk_context_destroy (cont);

      P4EST_FREE (names);
      P4EST_FREE (locidx_data);

      return NULL;
    }
#endif
    fprintf (cont->vtufile, "        </DataArray>\n");
    P4EST_ASSERT (il == Ncells);
  }

  if (write_level) {
#ifndef P4EST_VTK_ASCII
    uint8_data = P4EST_ALLOC (uint8_t, Ncells);
#endif

    fprintf (cont->vtufile, "        <DataArray type=\"%s\" Name=\"level\""
             " format=\"%s\">\n", "UInt8", P4EST_VTK_FORMAT_STRING);
#ifdef P4EST_VTK_ASCII
    fprintf (cont->vtufile, "         ");
    for (il = 0, sk = 1, jt = first_local_tree; jt <= last_local_tree; ++jt) {
      tree = p4est_tree_array_index (trees, jt);
      quadrants = &tree->quadrants;
      num_quads = quadrants->elem_count;
      for (zz = 0; zz < num_quads; ++zz, ++sk, ++il) {
        quad = p4est_quadrant_array_index (quadrants, zz);
        fprintf (cont->vtufile, " %d", (int) quad->level);
        if (!(sk % 20) && il != (Ncells - 1))
          fprintf (cont->vtufile, "\n         ");
      }
    }
    fprintf (cont->vtufile, "\n");
#else
    for (il = 0, jt = first_local_tree; jt <= last_local_tree; ++jt) {
      tree = p4est_tree_array_index (trees, jt);
      quadrants = &tree->quadrants;
      num_quads = quadrants->elem_count;
      for (zz = 0; zz < num_quads; ++zz, ++il) {
        quad = p4est_quadrant_array_index (quadrants, zz);
        uint8_data[il] = (uint8_t) quad->level;
      }
    }

    fprintf (cont->vtufile, "          ");
    retval = p4est_vtk_write_binary (cont->vtufile, (char *) uint8_data,
                                     sizeof (*uint8_data) * Ncells);
    fprintf (cont->vtufile, "\n");

    P4EST_FREE (uint8_data);

    if (retval) {
      P4EST_LERROR (P4EST_STRING "_vtk: Error encoding types\n");
      p4est_vtk_context_destroy (cont);

      P4EST_FREE (names);
      P4EST_FREE (locidx_data);

      return NULL;
    }
#endif
    fprintf (cont->vtufile, "        </DataArray>\n");
  }

  if (write_rank) {
    const int           wrapped_rank =
      wrap_rank > 0 ? mpirank % wrap_rank : mpirank;

    fprintf (cont->vtufile, "        <DataArray type=\"%s\" Name=\"mpirank\""
             " format=\"%s\">\n", P4EST_VTK_LOCIDX, P4EST_VTK_FORMAT_STRING);
#ifdef P4EST_VTK_ASCII
    fprintf (cont->vtufile, "         ");
    for (il = 0, sk = 1; il < Ncells; ++il, ++sk) {
      fprintf (cont->vtufile, " %d", wrapped_rank);
      if (!(sk % 20) && il != (Ncells - 1))
        fprintf (cont->vtufile, "\n         ");
    }
    fprintf (cont->vtufile, "\n");
#else
    for (il = 0; il < Ncells; ++il)
      locidx_data[il] = (p4est_locidx_t) wrapped_rank;

    fprintf (cont->vtufile, "          ");
    retval = p4est_vtk_write_binary (cont->vtufile, (char *) locidx_data,
                                     sizeof (*locidx_data) * Ncells);
    fprintf (cont->vtufile, "\n");

    if (retval) {
      P4EST_LERROR (P4EST_STRING "_vtk: Error encoding types\n");
      p4est_vtk_context_destroy (cont);

      P4EST_FREE (names);
      P4EST_FREE (locidx_data);

      return NULL;
    }
#endif
    fprintf (cont->vtufile, "        </DataArray>\n");
  }

  if (ferror (cont->vtufile)) {
    P4EST_LERRORF (P4EST_STRING "_vtk: Error writing %s\n",
                   cont->vtufilename);
    p4est_vtk_context_destroy (cont);

    P4EST_FREE (names);
#ifndef P4EST_VTK_ASCII
    P4EST_FREE (locidx_data);
#endif

    return NULL;
  }

#ifndef P4EST_VTK_ASCII
  P4EST_FREE (locidx_data);
#endif

  all = 0;
  for (i = 0; i < num_cell_scalars; ++all, ++i) {
    cont = p4est_vtk_write_cell_scalar (cont, names[all], values[all]);
    SC_CHECK_ABORT (cont != NULL,
                    P4EST_STRING "_vtk: Error writing cell scalars");
  }

  for (i = 0; i < num_cell_vectors; ++all, ++i) {
    cont = p4est_vtk_write_cell_vector (cont, names[all], values[all]);
    SC_CHECK_ABORT (cont != NULL,
                    P4EST_STRING "_vtk: Error writing cell vectors");
  }

  fprintf (cont->vtufile, "      </CellData>\n");

  if (ferror (cont->vtufile)) {
    P4EST_LERRORF (P4EST_STRING "_vtk: Error writing %s\n",
                   cont->vtufilename);
    p4est_vtk_context_destroy (cont);

    P4EST_FREE (names);

    return NULL;
  }

  /* Only have the root write to the parallel vtk file */
  if (mpirank == 0) {
    fprintf (cont->pvtufile, "    <PCellData Scalars=\"%s\">\n",
             vtkCellDataString);

    if (write_tree)
      fprintf (cont->pvtufile, "      "
               "<PDataArray type=\"%s\" Name=\"treeid\" format=\"%s\"/>\n",
               P4EST_VTK_LOCIDX, P4EST_VTK_FORMAT_STRING);

    if (write_level)
      fprintf (cont->pvtufile, "      "
               "<PDataArray type=\"%s\" Name=\"level\" format=\"%s\"/>\n",
               "UInt8", P4EST_VTK_FORMAT_STRING);

    if (write_rank)
      fprintf (cont->pvtufile, "      "
               "<PDataArray type=\"%s\" Name=\"mpirank\" format=\"%s\"/>\n",
               P4EST_VTK_LOCIDX, P4EST_VTK_FORMAT_STRING);

    all = 0;
    for (i = 0; i < num_cell_scalars; ++all, i++)
      fprintf (cont->pvtufile, "      "
               "<PDataArray type=\"%s\" Name=\"%s\" format=\"%s\"/>\n",
               P4EST_VTK_FLOAT_NAME, names[all], P4EST_VTK_FORMAT_STRING);

    for (i = 0; i < num_cell_vectors; ++all, i++)
      fprintf (cont->pvtufile, "      "
               "<PDataArray type=\"%s\" NumberOfComponents=\"3\" Name=\"%s\" "
               "format=\"%s\"/>\n",
               P4EST_VTK_FLOAT_NAME, names[all], P4EST_VTK_FORMAT_STRING);

    fprintf (cont->pvtufile, "    </PCellData>\n");

    if (ferror (cont->pvtufile)) {
      P4EST_LERROR (P4EST_STRING "_vtk: Error writing parallel header\n");
      p4est_vtk_context_destroy (cont);

      P4EST_FREE (names);

      return NULL;
    }
  }

  P4EST_FREE (names);

  return cont;
}

/* Write either a scalar or a vector field.
 * If is_vector is true then a vector field with 3 values per point
 * is written. */
static p4est_vtk_context_t *
p4est_vtk_write_point (p4est_vtk_context_t * cont,
                       const char *field_name, sc_array_t * values,
                       int is_vector)
{
  p4est_locidx_t      il, ddl;
  int                 use_nodes;
#ifdef P4EST_ENABLE_DEBUG
  int                 ecount;
  int                 Nentries;
#endif
  int                 Npoints;
#ifndef P4EST_VTK_ASCII
  int                 retval;
  P4EST_VTK_FLOAT_TYPE *float_data;
#endif
  p4est_locidx_t     *ntc;

  P4EST_ASSERT (cont != NULL && cont->writing);
  Npoints = cont->num_points;
  ntc = cont->node_to_corner;
#ifdef P4EST_ENABLE_DEBUG
  ecount = ntc == NULL ? Npoints : cont->num_corners;
  Nentries = ecount * (is_vector ? 3 : 1);
#endif

  P4EST_ASSERT (values != NULL && values->elem_count == (size_t) Nentries);

  if (ntc == NULL) {
    /* may be writing a discontinuous field, possibly due to vertex scaling */
    /* or we are writing higher order cells, relying on user coordinates */
    use_nodes = 0;
  }
  else {
    /* we are definitely writing a continuous field, reusing corner values */
    P4EST_ASSERT (cont->scale == 1. && cont->continuous);
    use_nodes = 1;
  }

  /* write point data */
  fprintf (cont->vtufile, "        <DataArray type=\"%s\" %s Name=\"%s\""
           " format=\"%s\">\n",
           P4EST_VTK_FLOAT_NAME,
           is_vector ? "NumberOfComponents=\"3\"" : "", field_name,
           P4EST_VTK_FORMAT_STRING);

#ifdef P4EST_VTK_ASCII
  if (!is_vector) {
    for (il = 0; il < Npoints; ++il) {
      ddl = use_nodes ? ntc[il] : il;
      P4EST_ASSERT (0 <= ddl && ddl < ecount);

      fprintf (cont->vtufile,
#ifdef P4EST_ENABLE_VTK_DOUBLES
               "     %24.16e\n",
#else
               "          %16.8e\n",
#endif
               *(double *) sc_array_index (values, ddl));
    }
  }
  else {
    for (il = 0; il < Npoints; ++il) {
      ddl = use_nodes ? ntc[il] : il;
      P4EST_ASSERT (0 <= ddl && ddl < ecount);

      fprintf (cont->vtufile,
#ifdef P4EST_ENABLE_VTK_DOUBLES
               "     %24.16e %24.16e %24.16e\n",
#else
               "          %16.8e %16.8e %16.8e\n",
#endif
               *(double *) sc_array_index (values, 3 * ddl),
               *(double *) sc_array_index (values, 3 * ddl + 1),
               *(double *) sc_array_index (values, 3 * ddl + 2));
    }
  }
#else
  if (!is_vector) {
    float_data = P4EST_ALLOC (P4EST_VTK_FLOAT_TYPE, Npoints);
    for (il = 0; il < Npoints; ++il) {
      ddl = use_nodes ? ntc[il] : il;
      P4EST_ASSERT (0 <= ddl && ddl < ecount);
      float_data[il] =
        (P4EST_VTK_FLOAT_TYPE) * ((double *) sc_array_index (values, ddl));
    }
  }
  else {
    float_data = P4EST_ALLOC (P4EST_VTK_FLOAT_TYPE, Npoints * 3);
    for (il = 0; il < Npoints; ++il) {
      ddl = use_nodes ? ntc[il] : il;
      P4EST_ASSERT (0 <= ddl && ddl < ecount);
      float_data[3 * il] =
        (P4EST_VTK_FLOAT_TYPE) *
        ((double *) sc_array_index (values, 3 * ddl));
      float_data[3 * il + 1] =
        (P4EST_VTK_FLOAT_TYPE) *
        ((double *) sc_array_index (values, 3 * ddl + 1));
      float_data[3 * il + 2] =
        (P4EST_VTK_FLOAT_TYPE) *
        ((double *) sc_array_index (values, 3 * ddl + 2));
    }
  }

  fprintf (cont->vtufile, "          ");
  /* TODO: Don't allocate the full size of the array, only allocate
   * the chunk that will be passed to zlib and do this a chunk
   * at a time.
   */
  retval = p4est_vtk_write_binary (cont->vtufile, (char *) float_data,
                                   sizeof (*float_data) * Npoints
                                   * (is_vector ? 3 : 1));
  fprintf (cont->vtufile, "\n");

  P4EST_FREE (float_data);

  if (retval) {
    P4EST_LERROR (P4EST_STRING "_vtk: Error encoding points\n");
    p4est_vtk_context_destroy (cont);
    return NULL;
  }
#endif
  fprintf (cont->vtufile, "        </DataArray>\n");

  if (ferror (cont->vtufile)) {
    P4EST_LERROR (P4EST_STRING "_vtk: Error writing point scalar\n");
    p4est_vtk_context_destroy (cont);
    return NULL;
  }

  return cont;
}

p4est_vtk_context_t *
p4est_vtk_write_point_scalar (p4est_vtk_context_t * cont,
                              const char *scalar_name, sc_array_t * values)
{
  return p4est_vtk_write_point (cont, scalar_name, values, 0);
}

p4est_vtk_context_t *
p4est_vtk_write_point_vector (p4est_vtk_context_t * cont,
                              const char *vector_name, sc_array_t * values)
{
  return p4est_vtk_write_point (cont, vector_name, values, 1);
}

/* Write either a scalar or a vector field.
 * If is_vector is true then a vector field with 3 values per cell
 * is written. */
static p4est_vtk_context_t *
p4est_vtk_write_cell (p4est_vtk_context_t * cont,
                      const char *field_name, sc_array_t * values,
                      int is_vector)
{
  const p4est_locidx_t Ncells = cont->p4est->local_num_quadrants;
  p4est_locidx_t      il;
#ifndef P4EST_VTK_ASCII
  int                 retval;
  P4EST_VTK_FLOAT_TYPE *float_data;
#endif

  P4EST_ASSERT (cont != NULL && cont->writing);

  /* Write cell data. */
  fprintf (cont->vtufile, "        <DataArray type=\"%s\" %s Name=\"%s\""
           " format=\"%s\">\n",
           P4EST_VTK_FLOAT_NAME, is_vector ? "NumberOfComponents=\"3\"" : "",
           field_name, P4EST_VTK_FORMAT_STRING);
#ifdef P4EST_VTK_ASCII
  if (!is_vector) {
    for (il = 0; il < Ncells; ++il) {
      fprintf (cont->vtufile,
#ifdef P4EST_ENABLE_VTK_DOUBLES
               "     %24.16e\n",
#else
               "          %16.8e\n",
#endif
               *(double *) sc_array_index (values, il));
    }
  }
  else {
    /* Write vector data */
    for (il = 0; il < Ncells; ++il) {
      fprintf (cont->vtufile,
#ifdef P4EST_ENABLE_VTK_DOUBLES
               "     %24.16e  %24.16e  %24.16e\n",
#else
               "          %16.8e  %16.8e  %16.8e\n",
#endif
               *(double *) sc_array_index (values, 3 * il),
               *(double *) sc_array_index (values, 3 * il + 1),
               *(double *) sc_array_index (values, 3 * il + 2));
    }
  }
#else
  if (!is_vector) {
    float_data = P4EST_ALLOC (P4EST_VTK_FLOAT_TYPE, Ncells);
    for (il = 0; il < Ncells; ++il) {
      float_data[il] =
        (P4EST_VTK_FLOAT_TYPE) * ((double *) sc_array_index (values, il));
    }
  }
  else {
    /* vector data */
    float_data = P4EST_ALLOC (P4EST_VTK_FLOAT_TYPE, 3 * Ncells);
    for (il = 0; il < Ncells; ++il) {
      float_data[3 * il] =
        (P4EST_VTK_FLOAT_TYPE) * ((double *) sc_array_index (values, 3 * il));
      float_data[3 * il + 1] =
        (P4EST_VTK_FLOAT_TYPE) *
        ((double *) sc_array_index (values, 3 * il + 1));
      float_data[3 * il + 2] =
        (P4EST_VTK_FLOAT_TYPE) *
        ((double *) sc_array_index (values, 3 * il + 2));
    }
  }

  fprintf (cont->vtufile, "          ");
  /* TODO: Don't allocate the full size of the array, only allocate
   * the chunk that will be passed to zlib and do this a chunk
   * at a time.
   */
  retval = p4est_vtk_write_binary (cont->vtufile, (char *) float_data,
                                   sizeof (*float_data) * Ncells
                                   * (is_vector ? 3 : 1));
  fprintf (cont->vtufile, "\n");

  P4EST_FREE (float_data);

  if (retval) {
    P4EST_LERROR (P4EST_STRING "_vtk: Error encoding scalar cell data\n");
    p4est_vtk_context_destroy (cont);
    return NULL;
  }
#endif
  fprintf (cont->vtufile, "        </DataArray>\n");

  if (ferror (cont->vtufile)) {
    P4EST_LERROR (P4EST_STRING "_vtk: Error writing cell scalar file\n");
    p4est_vtk_context_destroy (cont);
    return NULL;
  }

  return cont;
}

p4est_vtk_context_t *
p4est_vtk_write_cell_scalar (p4est_vtk_context_t * cont,
                             const char *scalar_name, sc_array_t * values)
{
  return p4est_vtk_write_cell (cont, scalar_name, values, 0);
}

p4est_vtk_context_t *
p4est_vtk_write_cell_vector (p4est_vtk_context_t * cont,
                             const char *vector_name, sc_array_t * values)
{
  return p4est_vtk_write_cell (cont, vector_name, values, 1);
}

int
p4est_vtk_write_footer (p4est_vtk_context_t * cont)
{
  int                 p;
  int                 procRank = cont->p4est->mpirank;
  int                 numProcs = cont->p4est->mpisize;
  char               *filename_basename, filename_cpy[BUFSIZ];

  P4EST_ASSERT (cont != NULL && cont->writing);

  fprintf (cont->vtufile, "    </Piece>\n");
  fprintf (cont->vtufile, "  </UnstructuredGrid>\n");
  fprintf (cont->vtufile, "</VTKFile>\n");

  if (ferror (cont->vtufile)) {
    P4EST_LERROR (P4EST_STRING "_vtk: Error writing footer\n");
    p4est_vtk_context_destroy (cont);
    return -1;
  }

  /* Only have the root write to the parallel vtk file */
  if (procRank == 0) {
    fprintf (cont->visitfile, "!NBLOCKS %d\n", numProcs);

    /* Write data about the parallel pieces into both files */
    for (p = 0; p < numProcs; ++p) {
      /* We want to write the basename of each processes file, since
       * the basename function could modify its argument, we create a
       * temporary copy. */
      snprintf (filename_cpy, BUFSIZ, "%s", cont->filename);
#ifdef _MSC_VER
      _splitpath (filename_cpy, NULL, NULL, NULL, NULL);
      filename_basename = filename_cpy;
#else
      filename_basename = basename (filename_cpy);
#endif
      fprintf (cont->pvtufile,
               "    <Piece Source=\"%s_%04d.vtu\"/>\n", filename_basename, p);
      fprintf (cont->visitfile, "%s_%04d.vtu\n", filename_basename, p);
    }
    fprintf (cont->pvtufile, "  </PUnstructuredGrid>\n");
    fprintf (cont->pvtufile, "</VTKFile>\n");

    if (ferror (cont->pvtufile)) {
      P4EST_LERROR (P4EST_STRING "_vtk: Error writing parallel footer\n");
      p4est_vtk_context_destroy (cont);
      return -1;
    }

    if (ferror (cont->visitfile)) {
      P4EST_LERROR (P4EST_STRING "_vtk: Error writing parallel footer\n");
      p4est_vtk_context_destroy (cont);
      return -1;
    }
  }

  /* Destroy context structure. */
  p4est_vtk_context_destroy (cont);

  return 0;
}
