# libigl - A simple C++ geometry processing library

https://github.com/libigl/libigl/

libigl is a simple C++ geometry processing library. We have a wide functionality including construction of sparse discrete differential geometry operators and finite-elements matrices such as the cotangent Laplacian and diagonalized mass matrix, simple facet and edge-based topology data structures, mesh-viewing utilities for OpenGL and GLSL, and many core functions for matrix manipulation which make Eigen feel a lot more like MATLAB.

It is first and foremost a header library. Each header file contains a single function. Most are tailored to operate on a generic triangle mesh stored in an n-by–3 matrix of vertex positions V and an m-by–3 matrix of triangle indices F. The library may also be compiled into a statically linked library, for faster compile times with your projects.

We use the Eigen library heavily in our code. Our group prototypes a lot in MATLAB, and we have a useful conversion table from MATLAB to libigl/Eigen.

## Tutorial

As of version 1.0, libigl includes an introductory tutorial that covers its basic functionalities.

## Installation

Libigl is a header library. You do not need to build anything to install. Simply add `igl/` to your include path and include relevant headers. Here is a small “Hello, World” program:

    #include <igl/cotmatrix.h>
    #include <Eigen/Dense>
    #include <Eigen/Sparse>
    #include <iostream>
    int main()
    {
      Eigen::MatrixXd V(4,2);
      V<<0,0,
         1,0,
         1,1,
         0,1;
      Eigen::MatrixXi F(2,3);
      F<<0,1,2,
         0,2,3;
      Eigen::SparseMatrix<double> L;
      igl::cotmatrix(V,F,L);
      std::cout<<"Hello, mesh: "<<std::endl<<L*V<<std::endl;
      return 0;
    }

If you save this in `hello.cpp`, then you could compile this with (assuming Eigen is installed in /opt/local/include/eigen3):

    gcc -I/opt/local/include/eigen3 -I./igl/ hello.cpp -o hello

Running `./hello` would then produce

    Hello, mesh:
     0.5  0.5
    -0.5  0.5
    -0.5 -0.5
     0.5 -0.5

## Dependencies

Dependencies are on a per-include basis and the majority of the functions in libigl depends only on the Eigen library.

For more information see our tutorial.

### GCC and the optional CGAL dependency

The `include/igl/cgal/*.h` headers depend on CGAL. It has come to our attention that CGAL does not work properly with GCC 4.8. To the best of our knowledge, GCC 4.7 and clang will work correctly.

### OpenMP and Windows

Some of our functions will take advantage of OpenMP if available. However, it has come to our attention that Visual Studio + Eigen does not work properly with OpenMP. Since OpenMP only improves performance without affecting functionality we recommend avoiding OpenMP on Windows or proceeding with caution.

## Download

You can keep up to date by cloning a read-only copy of our GitHub repository.

## Known Issues

We really heavily on Eigen. Nearly all inputs and outputs are Eigen matrices of some kind. However, we currently only support Eigen’s default column-major ordering. That means, we do not expect our code to work for matrices using the `Eigen::RowMajor` flag. If you can, change definitions like: `cpp Eigen::Matrix<double, Eigen::Dynamic, 3, Eigen::RowMajor> A;` to `cpp Eigen::Matrix<double, Eigen::Dynamic, 3, Eigen::ColMajor> A; // or simply Eigen::Matrix<double, Eigen::Dynamic, 3> A;` We hope to fix this, or at least identify which functions are safe (many of them probably work just fine). This requires setting up unit testing, which is a major todo for our development.

## How to contribute

If you are interested in joining development, please fork the repository and submit a pull request with your changes.

## License

libigl is primarily MPL2 licensed (FAQ). Some files contain third-party code under other licenses. We’re currently in the processes of identifying these and marking appropriately.

## Attribution

If you use libigl in your academic projects, please cite the papers we implement as appropriate. To cite the library in general, you could use this BibTeX entry:

    @misc{libigl,
      title = {{libigl}: A simple {C++} geometry processing library},
      author = {Alec Jacobson and Daniele Panozzo and others},
      note = {http://libigl.github.io/libigl/},
      year = {2015},
    }

## Contact

Libigl is a group endeavor led by Alec Jacobson and Daniele Panozzo. Please contact us if you have questions or comments. We are happy to get feedback!

If you’re using libigl in your projects, quickly drop us a note. Tell us who you are and what you’re using it for. This helps us apply for funding and justify spending time maintaining this.

If you find bugs or have problems please use our github issue tracking page.

## Copyright

2015 Alec Jacobson, Daniele Panozzo, Olga Diamanti, Christian Schüller, Kenshi Takayama, Leo Sacht, Wenzel Jacob, Nico Pietroni, Amir Vaxman