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mfem/mesh/vtk.hpp
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// Copyright (c) 2010-2025, Lawrence Livermore National Security, LLC. Produced
// at the Lawrence Livermore National Laboratory. All Rights reserved. See files
// LICENSE and NOTICE for details. LLNL-CODE-806117.
//
// This file is part of the MFEM library. For more information and source code
// availability visit https://mfem.org.
//
// MFEM is free software; you can redistribute it and/or modify it under the
// terms of the BSD-3 license. We welcome feedback and contributions, see file
// CONTRIBUTING.md for details.
#ifndef MFEM_VTK
#define MFEM_VTK
#include <cstdint>
#include <string>
#include "../fem/geom.hpp"
#include "../general/binaryio.hpp"
namespace mfem
{
// Helpers for reading and writing VTK format
/// @brief Helper class for converting between MFEM and VTK geometry types.
///
/// Note: The VTK element types defined are at: https://git.io/JvZLm
struct VTKGeometry
{
/// @name VTK geometry types
///@{
static const int POINT = 1;
/// @name Low-order (linear, straight-sided) VTK geometric types
///@{
static const int SEGMENT = 3;
static const int TRIANGLE = 5;
static const int SQUARE = 9;
static const int TETRAHEDRON = 10;
static const int CUBE = 12;
static const int PRISM = 13;
static const int PYRAMID = 14;
///@}
/// @name Legacy quadratic VTK geometric types
///@{
static const int QUADRATIC_SEGMENT = 21;
static const int QUADRATIC_TRIANGLE = 22;
static const int BIQUADRATIC_SQUARE = 28;
static const int QUADRATIC_TETRAHEDRON = 24;
static const int TRIQUADRATIC_CUBE = 29;
static const int QUADRATIC_PRISM = 26;
static const int BIQUADRATIC_QUADRATIC_PRISM = 32;
static const int QUADRATIC_PYRAMID = 27;
///@}
/// @name Arbitrary-order VTK geometric types
///@{
static const int LAGRANGE_SEGMENT = 68;
static const int LAGRANGE_TRIANGLE = 69;
static const int LAGRANGE_SQUARE = 70;
static const int LAGRANGE_TETRAHEDRON = 71;
static const int LAGRANGE_CUBE = 72;
static const int LAGRANGE_PRISM = 73;
static const int LAGRANGE_PYRAMID = 74;
///@}
///@}
/// Permutation from MFEM's prism ordering to VTK's prism ordering.
static const int PrismMap[6];
/// @brief Permutation from MFEM's vertex ordering to VTK's vertex ordering.
/// @note If the MFEM and VTK orderings are the same, the vertex permutation
/// will be NULL.
static const int *VertexPermutation[Geometry::NUM_GEOMETRIES];
/// Map from MFEM's Geometry::Type to linear VTK geometries.
static const int Map[Geometry::NUM_GEOMETRIES];
/// Map from MFEM's Geometry::Type to legacy quadratic VTK geometries/
static const int QuadraticMap[Geometry::NUM_GEOMETRIES];
/// Map from MFEM's Geometry::Type to arbitrary-order Lagrange VTK geometries
static const int HighOrderMap[Geometry::NUM_GEOMETRIES];
/// Given a VTK geometry type, return the corresponding MFEM Geometry::Type.
static Geometry::Type GetMFEMGeometry(int vtk_geom);
/// @brief Does the given VTK geometry type describe an arbitrary-order
/// Lagrange element?
static bool IsLagrange(int vtk_geom);
/// @brief Does the given VTK geometry type describe a legacy quadratic
/// element?
static bool IsQuadratic(int vtk_geom);
/// @brief For the given VTK geometry type and number of points, return the
/// order of the element.
static int GetOrder(int vtk_geom, int npoints);
};
/// Data array format for VTK and VTU files.
enum class VTKFormat
{
/// Data arrays will be written in ASCII format.
ASCII,
/// Data arrays will be written in binary format. Floating point numbers will
/// be output with 64 bits of precision.
BINARY,
/// Data arrays will be written in binary format. Floating point numbers will
/// be output with 32 bits of precision.
BINARY32
};
/// @brief Create the VTK element connectivity array for a given element
/// geometry and refinement level.
///
/// The output array @a con will be such that, for the @a ith VTK node index,
/// con[i] will contain the index of the corresponding node in MFEM ordering.
void CreateVTKElementConnectivity(Array<int> &con, Geometry::Type geom,
int ref);
/// @brief Outputs encoded binary data in the base 64 format needed by VTK.
///
/// The binary data will be base 64 encoded, and compressed if @a
/// compression_level is not zero. The proper header will be prepended to the
/// data.
void WriteVTKEncodedCompressed(std::ostream &os, const void *bytes,
uint32_t nbytes, int compression_level);
/// @brief Return the VTK node index of the barycentric point @a b in a
/// triangle with refinement level @a ref.
///
/// The barycentric index @a b has three components, satisfying b[0] + b[1] +
/// b[2] == ref.
int BarycentricToVTKTriangle(int *b, int ref);
/// Determine the byte order and return either "BigEndian" or "LittleEndian"
const char *VTKByteOrder();
/// @brief Write either ASCII data to the stream or binary data to the buffer
/// depending on the given format.
///
/// If @a format is VTK::ASCII, write the canonical ASCII representation of @a
/// val to the output stream. Subnormal floating point numbers are rounded to
/// zero. Otherwise, append its raw binary data to the byte buffer @a buf.
///
/// Note that there are specializations for @a uint8_t (to write as a numeric
/// value rather than a character), and for @a float and @a double values to use
/// the precision specified by @a format.
template <typename T>
void WriteBinaryOrASCII(std::ostream &os, std::vector<char> &buf, const T &val,
const char *suffix, VTKFormat format)
{
if (format == VTKFormat::ASCII) { os << val << suffix; }
else { bin_io::AppendBytes(buf, val); }
}
/// @brief Specialization of @ref WriteBinaryOrASCII for @a uint8_t to ensure
/// ASCII output is numeric (rather than interpreting @a val as a character.)
template <>
void WriteBinaryOrASCII<uint8_t>(std::ostream &os, std::vector<char> &buf,
const uint8_t &val, const char *suffix,
VTKFormat format);
/// @brief Specialization of @ref WriteBinaryOrASCII for @a double.
///
/// If @a format is equal to VTKFormat::BINARY32, @a val is converted to a @a
/// float and written as 32 bits. Subnormals are rounded to zero in ASCII
/// output.
template <>
void WriteBinaryOrASCII<double>(std::ostream &os, std::vector<char> &buf,
const double &val, const char *suffix,
VTKFormat format);
/// @brief Specialization of @ref WriteBinaryOrASCII<T> for @a float.
///
/// If @a format is equal to VTKFormat::BINARY, @a val is converted to a @a
/// double and written as 64 bits. Subnormals are rounded to zero in ASCII
/// output.
template <>
void WriteBinaryOrASCII<float>(std::ostream &os, std::vector<char> &buf,
const float &val, const char *suffix,
VTKFormat format);
/// @brief Encode in base 64 (and potentially compress) the given data, write it
/// to the output stream (with a header) and clear the buffer.
///
/// @sa WriteVTKEncodedCompressed.
void WriteBase64WithSizeAndClear(std::ostream &os, std::vector<char> &buf,
int compression_level);
/// @brief Returns a string defining the component labels for vector-valued data
/// arrays for use in XML VTU files.
std::string VTKComponentLabels(int vdim);
} // namespace mfem
#endif