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ArchitectureDesign.md

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Software design

Architecture design

  • cross-platform: All selected components must be cross-platform. In this early development stage, only baseline platform is documented: 64 bit Ubuntu 18.04 with a c++17 compiler and python3

  • modular and extensible: cover all aspects of CAE

    • parallel preprocessing infrastructure which can be used in scenarios other than CAE
    • CAD preprocessing, shape check, fixing, imprinting, etc
    • parallel meshing
    • solver setup.

  • scalable: from single node multiple-threading to MPI on super-computer

  • pipeline style workflow: VTK style tensorflow style graph topology may be supported in the future

  • python3 language binding: based on pybind11 javascript binding is also under consideration

  • Industry standard compliant:

    • standard CAD exchange format: STEP P214 (AP242 is not supported by OpenCASCADE yet)
    • JTOpen: there is no open source library available
    • FreeCAD/BREP

  • UTF8 encoding is assumed and stored in std::string Note: 1. this may work for MasOS and Linux of utf8 locale; 2. filesystem::path::string() not filesystem::path::u8string()

Modular design

Folder structure corresponds to modular design, inspired by FreeCAD project. see CodeStructure.md for description for each header file.

  • third-party/Base: type system and BaseClass for c++ (extracted from FreeCAD project)
  • PropertyContainer: heterogenous container based on std::any, may be replaced with FreeCAD's in the future
  • PPP: framework infrastructure for parallel preprocessing, depends only on STL and some header-only third-party libraries.
  • Geom: geometry processing relies on OCCT, including 2D surface meshing (facetizing)
  • Mesh: 3D volume meshing (planned yet coded)
  • third-party: json, catch2, loguru, SGeom, etc
  • test: unit test
  • python: python wrapping and python script exectuables
  • scripts: utility script
  • data: testing data

Note: any namespace and module name of FreeCAD module should be avoided. E.g. PPP module's function can be mapped to App but PPP is used insrtead; Base module should be compatible with FreeCAD. This arrangement can help into the future to integrate with FreeCAD at source code level.

Data driven pipeline design

This software has the data-driven design, users can just write a json configuration file to build up the pipeline and specify parameters to each processor. There is no need to program in C++, if existing processors are sufficient. Each action has a default pipeline, a series of geometry processors, see example in the generated config.json.

json file is the input configuration format. Pipeline can be built from the json configuration, i.e. a list of class names. Each processor can be weaked by processor specific parameters and global parameters such tolerance.

Parameter<T> mappable to json repr. Furthermore, enum types can be converted into json string, such as, ShapeType , which has string name identical to FreeCAD ShapeType enum.

User interface design

  • Console: basic command line with json as input configuration file
  • Python: bindings for Python3 by pybind11
  • Gui: Qt based, embedded into each module
  • Web: web interface for remote operator

Note: UI design is yet completed, some untested code are not merged into the repository yet

======================================================================

Component design

OCCT as the first CAD kernel

OCCT is the only available industry-strenth LGPL open source CAD kernel.

OCCT official does not have a python binding, therefore, C++ is chosen as the programming language.

cmake OpenCascade detection

  • FreeCAD provided
  • OpenCASCADE official cmake config, provided by package "occt-misc" from Ubuntu PPA /usr/lib/cmake/opencascade/OpenCASCADEConfig.cmake each module has /usr/lib/cmake/opencascade/OpenCASCADEApplicationFrameworkTargets.cmake

Note: geometry exported form one CAD kernel then imported to another CAD kernel may cause some problems.

parallel-preprocessor, should work without X-windows, but some modules (data-exchange, XCAF) of OpenCASCADE has dep on X-windows

Most classes are header only

hpp for header only, h and cpp for other pairs (currently my header only is still called *.h, it will be split into h and cpp after API stabalised) .

Third-party libraries license

Only MIT and BSD open source libraries can be included into this LGPLv2 repository

  • magic_enum.hpp: MIT License
  • half.hpp: BSD
  • mm_io.h and mm_io.cpp: NIST as a US government institution, so these 2 files should be in public domain
  • pybind_json.hpp: BSD 3-Clause

software components that will be downloaded during compiling, e.g. git submodules

software it links:

  • OpenCASCDE: LGPLv2.1
  • intel TBB: MIT
  • boost libraries: boost license, like MIT/BSD
  • QT: LGPLv2.1