Table of Contents

1. Dependencies
2. Build
3. Install with CMake
4. Install with Spack
5. Using CSG-EB in your project

This library is for parsing Constructive Solid Geometry (CSG) for use in AMReX Embedded Boundaries (EB).

CSG is a file format used by the open source CAD modelling tool OpenSCAD. CSG is a subset of the SCAD language, equivalent in the kinds of geometries that can be expressed, but with fewer primitives (OpenSCAD can export .scad files to .csg). SCAD code is easier to read and write by humans; CSG files are easier to parse and process by software.

Dependencies

If installing with Spack, dependencies will be installed automatically.

Install the following dependencies before building csg-eb

• C++17 compiler (GCC >=7.x, Clang >=5.x)
• CMake >=3.14
• PEGTL for parsing
• Catch2 for testing framework
• CGAL for geometry computation

Build

> cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
> cmake --build build

Run tests

> cd build
> ctest

Install with CMake

To install csg-eb to a location $CSGEB_HOME:

cmake -S . -B build -DCMAKE_INSTALL_PREFIX=$CSGEB_HOME
cmake --build build --target install

Install with Spack

Another way to install csg-eb is with Spack .

To install with spack:

spack repo add .spack/repo  # add repo with csg-eb recipe
spack spec csg-eb           # preview install
spack install csg-eb        # install csg-eb (with CGAL support)
spack install csg-eb ~cgal  # install csg-eb (without CGAL support)
spack load csg-eb           # Adds libcsg-eb.a to LD_LIBRARY_PATH and csg.hpp to CPATH

Using CSG-EB in your project

• Include the header file csg.hpp
• Call csg::get_csgif with the path to a CSG file to create an Implicit Function object.

#include <csg.hpp>

// for EB2::makeShop
#include <AMReX_EB2_GeometryShop.H>

...


auto csg_file = "~/my_geometry.csg";
auto is_internal_flow = true;

auto csg_if = csg::get_csgif(csg_file, is_internal_flow);

auto gshop = EB2::makeShop(*csg_if);

Note on the return value

If is_internal_flow==true, the CSG geometry defines a hollow space for the domain:

• csg_if(x, y, z) < 0 ⇒ (x, y, z) is INSIDE
• csg_if(x, y, z) > 0 ⇒ (x, y, z) is OUTSIDE

If is_internal_flow==false, the CSG geometry defines a solid boundary to the domain:

• csg_if(x, y, z) < 0 ⇒ (x, y, z) is OUTSIDE
• csg_if(x, y, z) > 0 ⇒ (x, y, z) is INSIDE

Add to the CMake build

• Add this repo as a CMake subdirectory in your CMakeLists.txt:

add_subdirectory(/path/to/repo/csg-eb)

• Add the csg target to the CMake target that uses code like in the the above example:

target_link_libraries(<target> PRIVATE csg)