Feature: OpenFOAM reader [1/n] - First structure by sandro-elsweijer · Pull Request #2256 · DLR-AMR/t8code

sandro-elsweijer · 2026-04-01T13:54:52Z

Describe your changes here:
Implements a first structure of the OpenFOAM reader.
The first draft of the OpenFOAM reader struct reads the files inside an OpenFOAM case and fills internal data structures.
The conversion of this data into a cmesh follows in the next PRs. Otherwise this PR would be too big to review.
The reader is not inside cmesh/IO/OpenFOAM, since the reader will not only provide a cmesh, but also a forest with data. So there is no clear distinction between the reader cmesh and forest and the OpenFOAM functionality is its own category.

This PR also implements an OpenFOAM example and it has two purposes:

The OpenFOAM reader is a header file and this example makes cmake compile the header.
During development, the example can be used to test and debug the code.

There is no test yet, since the OpenFOAM reader is not finished yet. I plan to implement two tests:

A test where a very simple mesh is read and manually checked.
A component test where we use an OpenFOAM writer to write a mesh and afterwards we read it using the OpenFOAM reader. The output and input mesh should be equal.
Both tests can only be written, when the reader is finished.

All these boxes must be checked by the AUTHOR before requesting review:

The PR is small enough to be reviewed easily. If not, consider splitting up the changes in multiple PRs.
The title starts with one of the following prefixes: Documentation:, Bugfix:, Feature:, Improvement: or Other:.
If the PR is related to an issue, make sure to link it.
The author made sure that, as a reviewer, he/she would check all boxes below.

All these boxes must be checked by the REVIEWERS before merging the pull request:

As a reviewer please read through all the code lines and make sure that the code is fully understood, bug free, well-documented and well-structured.

General

The reviewer executed the new code features at least once and checked the results manually.
The code follows the t8code coding guidelines.
New source/header files are properly added to the CMake files.
The code is well documented. In particular, all function declarations, structs/classes and their members have a proper doxygen documentation. Make sure to add a file documentation for each file!
All new algorithms and data structures are sufficiently optimal in terms of memory and runtime (If this should be merged, but there is still potential for optimization, create a new issue).

Tests

The code is covered in an existing or new test case using Google Test.
The code coverage of the project (reported in the CI) should not decrease. If coverage is decreased, make sure that this is reasonable and acceptable.
Valgrind doesn't find any bugs in the new code. This script can be used to check for errors; see also this wiki article.

If the Pull request introduces code that is not covered by the github action (for example coupling with a new library):

Should this use case be added to the github action?
If not, does the specific use case compile and all tests pass (check manually).

Scripts and Wiki

If a new directory with source files is added, it must be covered by the scripts/internal/find_all_source_files.sh to check the indentation of these files.
If this PR introduces a new feature, it must be covered in an example or tutorial and a Wiki article.

License

The author added a BSD statement to doc/ (or already has one).

codecov · 2026-04-01T14:41:22Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.50%. Comparing base (e34672a) to head (958cd64).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2256   +/-   ##
=======================================
  Coverage   78.50%   78.50%           
=======================================
  Files         115      115           
  Lines       19198    19198           
=======================================
  Hits        15071    15071           
  Misses       4127     4127

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spenke91

Thanks a lot for this feature @sandro-elsweijer ! I really like the code structure and style 👍 I do have some remarks, though, most of them being minor issues...

I went through the code, but did not run the example myself yet, since I did not have an OpenFOAM case readily available and would argue that we should add an example case anyway 😇

spenke91 · 2026-05-04T09:04:06Z

+  using t8_path = std::filesystem::path;
+
+  /**
+   * Reader for OpenFOAM cases.


Suggested change

* Reader for OpenFOAM cases.

* Constructor of OpenFOAM reader.

spenke91 · 2026-05-04T09:11:32Z

+    error = !read_points (case_points_dir);
+    error &= !read_faces (case_faces_dir);
+    error &= !read_owner (case_owner_dir);
+    error &= !read_neighbor (case_neighbor_dir);


As far as I know, &= is for bitwise AND, not logical AND. While it does in fact work for bools, I think we should reseve it for bitwise operations for code readability. I thus suggest:

Suggested change

error = !read_points (case_points_dir);

error &= !read_faces (case_faces_dir);

error &= !read_owner (case_owner_dir);

error &= !read_neighbor (case_neighbor_dir);

error = !read_points (case_points_dir);

error = error && !read_faces (case_faces_dir);

error = error && !read_owner (case_owner_dir);

error = error && !read_neighbor (case_neighbor_dir);

or with and instead of &&, which, personally, I like even more ;-)

spenke91 · 2026-05-04T09:18:22Z

@@ -0,0 +1,490 @@
+/*


What is your motivation behind having the full implementation in the header file instead of a source file? None of the standard cases (template, inline, ...) seems to apply, or did I miss something? 🤔

spenke91 · 2026-05-04T09:21:56Z

+    std::string line;
+    bool format_checked = false;
+
+    /* Loop through file till end of file or thill we break manually at the right position. */


Suggested change

/* Loop through file till end of file or thill we break manually at the right position. */

/* Loop through file till end of file or till we break manually at the right position. */

spenke91 · 2026-05-04T10:38:41Z

+        size_t numeric_value;
+        if (line_stream >> numeric_value) {
+          /* Numeric value found, move stream to start of line again */
+          input_stream.seekg (-static_cast<std::streamoff> (line.size ()) - 1, std::ios_base::cur);


Why do we have to move input_stream back to the start of the line? Isn't it still at the start of the line anyway? Because the only command in the while loop modifying it is in the condition, i.e., std::getline (input_stream, line)). Or did I miss something?

spenke91 · 2026-05-05T13:30:27Z

+    }
+
+    /* The number of cells in the mesh is the highest owner_id + 1 (since it starts at 0). */
+    const size_t num_cells = *std::max_element (owner_list.begin (), owner_list.end ()) + 1;


I guess this part is not expected to be very performance-critical. Otherwise it might make sense to keep track of the maximum already in the for loop above filling the vector. This way we would not have to iterate through the whole vector again. But it would just be a memory access / caching thing, not so much a complexity issue, so I guess it is not important at all :D

spenke91 · 2026-05-05T13:33:30Z

+  }
+
+  /**
+   * Reads in an OpenFOAM owner file, assigns the faces to their cells and


Suggested change

* Reads in an OpenFOAM owner file, assigns the faces to their cells and

* Reads in an OpenFOAM neighbor file, assigns the faces to their cells and

Right?

spenke91 · 2026-05-05T13:33:45Z

+  /**
+   * Reads in an OpenFOAM owner file, assigns the faces to their cells and
+   * also fills the other half of the neighborhoods.
+   * \param [in] neighbor_dir  The path to the points file.


As above, maybe neighbor_file?

spenke91 · 2026-05-05T13:35:14Z

+  build_cmesh ()
+  {
+    t8_global_errorf ("ERROR: Not implemented yet. \n");
+    return 0;


Suggested change

return 0;

return false;

spenke91 · 2026-05-05T13:45:19Z

@@ -0,0 +1,120 @@
+/*


Could you add an example case file? I think it would really improve this example if the user could test it for an example file easily without having to find one him-/herself 😬

sandro-elsweijer added 2 commits April 1, 2026 15:34

add basic structure of OpenFOAM reader

f95434d

add an OpenFOAM reader example

d885fcb

sandro-elsweijer changed the title ~~Feature: First structure of the OpenFOAM reader~~ Feature: OpenFOAM reader [1/n] - First structure Apr 1, 2026

fix documentation

a0c86a7

makr comm as unused

a612eca

sandro-elsweijer marked this pull request as draft April 2, 2026 09:06

sandro-elsweijer and others added 2 commits April 2, 2026 11:07

removed unused comm

95badc8

Merge branch 'main' into feature-openfoam_reader_0

440c46f

sandro-elsweijer marked this pull request as ready for review April 2, 2026 10:44

remove unused comm

958cd64

spenke91 self-assigned this Apr 27, 2026

spenke91 self-requested a review April 27, 2026 13:24

spenke91 requested changes May 5, 2026

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spenke91 assigned sandro-elsweijer and unassigned spenke91 May 5, 2026

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Feature: OpenFOAM reader [1/n] - First structure#2256

Feature: OpenFOAM reader [1/n] - First structure#2256
sandro-elsweijer wants to merge 7 commits intomainfrom
feature-openfoam_reader_0

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	* Reader for OpenFOAM cases.
	* Constructor of OpenFOAM reader.

	/* Loop through file till end of file or thill we break manually at the right position. */
	/* Loop through file till end of file or till we break manually at the right position. */

	* Reads in an OpenFOAM owner file, assigns the faces to their cells and
	* Reads in an OpenFOAM neighbor file, assigns the faces to their cells and

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sandro-elsweijer commented Apr 1, 2026 •

edited by t8ddy

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