Add the Paraview parallel output format (.pvtu with one piece per rank)

.github/workflows/regression.yml

@@ -235,7 +235,7 @@ jobs:
         uses: docker://ghcr.io/su2code/su2/test-su2:261011-1107
         with:
           # -t <Tutorials-branch> -c <Testcases-branch>
-          args: -b ${{github.ref}} -t develop -c develop -s ${{matrix.testscript}}
+          args: -b ${{github.ref}} -t develop -c paraviewParallelOutput -s ${{matrix.testscript}}
       - name: Cleanup
         uses: docker://ghcr.io/su2code/su2/test-su2:261011-1107
         with:
@@ -284,7 +284,7 @@ jobs:
         uses: docker://ghcr.io/su2code/su2/test-su2:261011-1107
         with:
           # -t <Tutorials-branch> -c <Testcases-branch>
-          args: -b ${{github.ref}} -t develop -c develop -s ${{matrix.testscript}} -a "--tapetests"
+          args: -b ${{github.ref}} -t develop -c paraviewParallelOutput -s ${{matrix.testscript}} -a "--tapetests"
       - name: Cleanup
         uses: docker://ghcr.io/su2code/su2/test-su2:261011-1107
         with:
@@ -334,7 +334,7 @@ jobs:
           PMIX_MCA_gds: hash
         with:
           # -t <Tutorials-branch> -c <Testcases-branch>
-          args: -b ${{github.ref}} -t develop -c develop -s ${{matrix.testscript}} -a "--tsan"
+          args: -b ${{github.ref}} -t develop -c paraviewParallelOutput -s ${{matrix.testscript}} -a "--tsan"
       - name: Cleanup
         uses: docker://ghcr.io/su2code/su2/test-su2-tsan:261011-1107
         with:
@@ -379,7 +379,7 @@ jobs:
         uses: docker://ghcr.io/su2code/su2/test-su2-asan:261011-1107
         with:
           # -t <Tutorials-branch> -c <Testcases-branch>
-          args: -b ${{github.ref}} -t develop -c develop -s ${{matrix.testscript}} -a "--asan"
+          args: -b ${{github.ref}} -t develop -c paraviewParallelOutput -s ${{matrix.testscript}} -a "--asan"
       - name: Cleanup
         uses: docker://ghcr.io/su2code/su2/test-su2-asan:261011-1107
         with:

Common/include/option_structure.hpp

@@ -2408,6 +2408,8 @@ enum class OUTPUT_TYPE {
   PARAVIEW_XML,            /*!< \brief Paraview XML with binary data format */
   SURFACE_PARAVIEW_XML,    /*!< \brief Surface Paraview XML with binary data format */
   PARAVIEW_MULTIBLOCK,     /*!< \brief Paraview XML Multiblock */
+  PARAVIEW_PARALLEL,       /*!< \brief Paraview parallel XML (.pvtu), one piece per rank. */
+  SURFACE_PARAVIEW_PARALLEL, /*!< \brief Surface Paraview parallel XML (.pvtu), one piece per rank. */
   CGNS,                    /*!< \brief CGNS format. */
   SURFACE_CGNS,            /*!< \brief CGNS format. */
   STL_ASCII,               /*!< \brief STL ASCII format for surface solution output. */
@@ -2427,6 +2429,8 @@ static const MapType<std::string, OUTPUT_TYPE> Output_Map = {
   MakePair("PARAVIEW", OUTPUT_TYPE::PARAVIEW_XML)
   MakePair("SURFACE_PARAVIEW", OUTPUT_TYPE::SURFACE_PARAVIEW_XML)
   MakePair("PARAVIEW_MULTIBLOCK", OUTPUT_TYPE::PARAVIEW_MULTIBLOCK)
+  MakePair("PARAVIEW_PARALLEL", OUTPUT_TYPE::PARAVIEW_PARALLEL)
+  MakePair("SURFACE_PARAVIEW_PARALLEL", OUTPUT_TYPE::SURFACE_PARAVIEW_PARALLEL)
   MakePair("MESH", OUTPUT_TYPE::MESH)
   MakePair("MESH_BINARY", OUTPUT_TYPE::MESH_BINARY)
   MakePair("RESTART_ASCII", OUTPUT_TYPE::RESTART_ASCII)
@@ -2449,6 +2453,8 @@ inline bool isParaview(OUTPUT_TYPE format) {
     case OUTPUT_TYPE::PARAVIEW_XML:
     case OUTPUT_TYPE::SURFACE_PARAVIEW_XML:
     case OUTPUT_TYPE::PARAVIEW_MULTIBLOCK:
+    case OUTPUT_TYPE::PARAVIEW_PARALLEL:
+    case OUTPUT_TYPE::SURFACE_PARAVIEW_PARALLEL:
       return true;
     default:
       return false;

SU2_CFD/include/output/filewriter/CParaviewPVTUFileWriter.hpp

@@ -0,0 +1,105 @@
+/*!
+ * \file CParaviewPVTUFileWriter.hpp
+ * \brief Headers of the Paraview parallel XML file writer (.pvtu and one .vtu piece per rank).
+ * \author A. Rausa
+ * \version 8.5.0 "Harrier"
+ *
+ * SU2 Project Website: https://su2code.github.io
+ *
+ * The SU2 Project is maintained by the SU2 Foundation
+ * (http://su2foundation.org)
+ *
+ * Copyright 2012-2026, SU2 Contributors (cf. AUTHORS.md)
+ *
+ * SU2 is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * SU2 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with SU2. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <cstdint>
+
+#include "CFileWriter.hpp"
+
+/*!
+ * \class CParaviewPVTUFileWriter
+ * \brief Writes the data as a Paraview parallel unstructured grid: a .pvtu file that lists one .vtu
+ *        piece per rank. Each rank writes its own piece, so no rank gathers data of other ranks and
+ *        ParaView can read, filter and render the pieces in parallel (unlike a single .vtu file,
+ *        which one process has to load as a whole).
+ */
+class CParaviewPVTUFileWriter final : public CFileWriter {
+ private:
+  /*!
+   * \brief Boolean storing whether we are on a big or little endian machine.
+   */
+  bool bigEndian;
+
+  /*!
+   * \brief True to write the coordinates and fields in double precision instead of single.
+   */
+  bool doublePrecision;
+
+  /*!
+   * \brief Points of the piece of this rank: those used by its elements, wherever they belong.
+   */
+  vector<passivedouble> pieceData;    /*!< \brief Fields of the points of the piece, field by field. */
+  vector<unsigned long> usedPoints;   /*!< \brief Global indices of the points of the piece, sorted. */
+
+  /*!
+   * \brief Collect the points used by the elements of this rank and get their data from the ranks that own
+   *        them, so that the piece of this rank is self-contained.
+   * \returns The number of points of the piece.
+   */
+  unsigned long CollectExternalPoints();
+
+  /*!
+   * \brief Write the piece of this rank.
+   * \param[in] val_filename - Name of the piece file.
+   * \param[in] nPointsPiece - Number of points of the piece.
+   * \param[in] connInt64 - Write the connectivity and offsets as Int64 instead of Int32.
+   */
+  void WritePiece(const string& val_filename, unsigned long nPointsPiece, bool connInt64);
+
+  /*!
+   * \brief Write the .pvtu file that lists the pieces, only the master node writes it.
+   * \param[in] val_filename - Name of the .pvtu file.
+   * \param[in] pieceNames - Names of the pieces, relative to the .pvtu file.
+   * \param[in] connInt64 - The connectivity and offsets of the pieces are Int64 instead of Int32.
+   */
+  void WriteIndexFile(const string& val_filename, const vector<string>& pieceNames, bool connInt64);
+
+ public:
+  /*!
+   * \brief File extension
+   */
+  const static string fileExt;
+
+  /*!
+   * \brief Construct a file writer using field names and the data sorter.
+   * \param[in] valDataSorter - The parallel sorted data to write.
+   * \param[in] valDoublePrecision - Write the coordinates and fields in double precision.
+   */
+  CParaviewPVTUFileWriter(CParallelDataSorter* valDataSorter, bool valDoublePrecision = false);
+
+  /*!
+   * \brief Destructor
+   */
+  ~CParaviewPVTUFileWriter() override;
+
+  /*!
+   * \brief Write sorted data to the .pvtu file and its pieces.
+   * \param[in] val_filename - The name of the file.
+   */
+  void WriteData(string val_filename) override;
+};

SU2_CFD/src/meson.build

@@ -51,6 +51,7 @@ su2_cfd_src += files(['output/COutputFactory.cpp',
                       'output/filewriter/CSU2BinaryFileWriter.cpp',
                       'output/filewriter/CParaviewXMLFileWriter.cpp',
                       'output/filewriter/CParaviewVTMFileWriter.cpp',
+                      'output/filewriter/CParaviewPVTUFileWriter.cpp',
                       'output/filewriter/CSU2MeshFileWriter.cpp',
                       'output/filewriter/CSU2MeshBinaryFileWriter.cpp',
                       'output/filewriter/CCGNSFileWriter.cpp',

SU2_CFD/src/output/COutput.cpp

@@ -42,6 +42,7 @@
 #include "../../include/output/filewriter/CSTLFileWriter.hpp"
 #include "../../include/output/filewriter/CParaviewBinaryFileWriter.hpp"
 #include "../../include/output/filewriter/CParaviewXMLFileWriter.hpp"
+#include "../../include/output/filewriter/CParaviewPVTUFileWriter.hpp"
 #include "../../include/output/filewriter/CParaviewVTMFileWriter.hpp"
 #include "../../include/output/filewriter/CTecplotFileWriter.hpp"
 #include "../../include/output/filewriter/CTecplotBinaryFileWriter.hpp"
@@ -560,6 +561,46 @@ void COutput::WriteToFile(CConfig *config, CGeometry *geometry, OUTPUT_TYPE form
 
       break;
 
+    case OUTPUT_TYPE::PARAVIEW_PARALLEL:
+
+      extension = CParaviewPVTUFileWriter::fileExt;
+
+      if (fileName.empty())
+        fileName = config->GetFilename(volumeFilename, "", curTimeIter);
+
+      if (!config->GetWrt_Volume_Overwrite())
+        filename_iter = config->GetFilename_Iter(fileName, curInnerIter, curOuterIter);
+
+      /*--- Load the connectivity without sorting it: each rank then writes the elements of its own
+       partition, which are next to each other, so its piece needs few points of other ranks. ---*/
+
+      volumeDataSorter->SortConnectivity(config, geometry, false);
+
+      LogOutputFiles("Paraview parallel");
+      fileWriter = new CParaviewPVTUFileWriter(volumeDataSorter, config->GetVolume_Output_Double_Precision());
+
+      break;
+
+    case OUTPUT_TYPE::SURFACE_PARAVIEW_PARALLEL:
+
+      extension = CParaviewPVTUFileWriter::fileExt;
+
+      if (fileName.empty())
+        fileName = config->GetFilename(surfaceFilename, "", curTimeIter);
+
+      if (!config->GetWrt_Surface_Overwrite())
+        filename_iter = config->GetFilename_Iter(fileName, curInnerIter, curOuterIter);
+
+      /*--- Load and sort the output data and connectivity. ---*/
+
+      surfaceDataSorter->SortConnectivity(config, geometry);
+      surfaceDataSorter->SortOutputData();
+
+      LogOutputFiles("Paraview parallel surface");
+      fileWriter = new CParaviewPVTUFileWriter(surfaceDataSorter, config->GetVolume_Output_Double_Precision());
+
+      break;
+
     case OUTPUT_TYPE::PARAVIEW_LEGACY_BINARY:
 
       extension = CParaviewBinaryFileWriter::fileExt;