# libigl - A simple C++ geometry processing library

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

> Get started with:

>     git clone --recursive https://github.com/libigl/libigl.git

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 a header-only library. You do not need to compile anything to use, just include igl headers (e.g. `#include <igl/cotmatrix.h>`) and run. Each header file contains a single function (e.g. `igl/cotmatrix.h` contains `igl::cotmatrix()`). 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`.

Optionally the library may also be pre-compiled into a statically linked library, for faster compile times with your projects. This only effects compile time (run-time performance and behavior is identical). If in doubt, use the header-only default mode: (i.e. just include the headers you want to use).

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

We regularly test compiling our library on Mac OS X with clang, Linux with gcc and Windows with Visual Studio 2015 Community Edition.

## Tutorial

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

## libigl Example Project

We provide a blank project example showing how to use libigl and cmake. Feel free and encouraged to copy or fork this project as a way of starting a new personal project using libigl.

## Coding Guidelines and Tips

libigl follows strict coding guidelines, please take a look here before submitting your pull requests. We also have a set of general coding tips on how to code a geometry processing research project.

## Installation

Libigl is a header-only library. You do not need to build anything to install. Simply add `libigl/include` 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 `/usr/local/include/eigen3`):

    g++ -std=c++11 -I/usr/local/include/eigen3 -I./libigl/include/ 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.

### Optional Dependencies

Libigl compartmentalizes its optional dependences via its directory organization in the `include/` folder. All header files located directly in the `include/igl/` folder have only stl and Eigen as dependencies. For example, all of the headers that depend on CGAL are located in `include/igl/cgal`. For a full list of optional dependencies check `optional/CMakeLists.txt`.

### 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 + OpenMP does not work properly. Since we use OpenMP only to improve performance, 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 rely heavily on Eigen. Nearly all inputs and outputs are Eigen matrices of some kind. However, we currently only officially 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:

    Eigen::Matrix<double, Eigen::Dynamic, 3, Eigen::RowMajor> A;

to

    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.

## Git Submodules

Libigl uses git submodules for its optional dependencies, in particular, those needed by the OpenGL viewer to run the examples in the tutorial. Git submodules allow use to treat clones of other libraries as sub-directories within ours while separating our commits. Read the documentation for a detailed explanation, but essentially our libigl repo stores a hash for each of its subrepos containing which version to update to. When a change is introduced in a dependencies repo we can incorporate that change by pulling in our sub-repo and updating (i.e. committing) that change to the hash.

When pulling new changes to libigl it’s also a good idea to update changes to subrepos:

    git pull
    git submodule update --recursive

## Unit Testing

Libigl maintains separate repository for unit testing.

## How to Contribute

If you are interested in joining development, please fork the repository and submit a pull request with your changes. libigl follows strict coding guidelines, please take a look at our style guidelines before submitting your pull requests.

## 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 = {2016},
    }

## Projects/Universities using libigl

Libigl is used by many research groups around the world. In 2015, it won the Eurographics/ACM Symposium on Geometry Processing software award. Here are a few labs/companies/institutions using libigl:

- Activision
- Adobe Research
- Electronic Arts, Inc
- Epic Games
- Google Research
- Mesh, consultants, Canada
- Pixar Research
- Spine by Esoteric Software is an animation tool dedicated to 2D characters.
- Columbia University, Columbia Computer Graphics Group, USA
- Cornell University, USA
- Czech Technical University in Prague, Czech
- EPF Lausanne, Computer Graphics and Geometry Laboratory, Switzerland
- ETH Zurich, Interactive Geometry Lab and Advanced Technologies Lab, Swizterland
- George Mason University, CraGL, USA
- Hong Kong University of Science and Technology, Hong Kong
- Inria, Université Grenoble Alpes, France
- Jiangnan university, China
- National Institute of Informatics, Japan
- New York University, Media Research Lab, USA
- NYUPoly, Game Innovation Lab, USA
- TU Berlin, Germany
- TU Delft, Netherlands
- TU Wien, Austria
- Telecom ParisTech, Paris, France
- Utrecht University, The Netherlands
- Universidade Federal de Santa Catarina, Brazil
- University College London, England
- University of California Berkeley, USA
- University of Cambridge, England
- University of Pennsylvania, USA
- University of Texas at Austin, USA
- University of Toronto, Canada
- University of Victoria, Canada
- University of Wisconsin-Eau Claire, USA
- Università della Svizzera Italiana, Switzerland
- Université Toulouse III Paul Sabatier, France
- Zhejiang University, China

## Contact

Libigl is a group endeavor led by Alec Jacobson and Daniele Panozzo. Please contact us if you have questions or comments. For troubleshooting, please post an issue on github.

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

2017 Alec Jacobson, Daniele Panozzo, Christian Schüller, Olga Diamanti, Qingnan Zhou, Sebastian Koch, Amir Vaxman, Nico Pietroni, Stefan Brugger, Kenshi Takayama, Wenzel Jakob, Nikolas De Giorgis, Luigi Rocca, Leonardo Sacht, Kevin Walliman, Olga Sorkine-Hornung, and others.

Please see individual files for appropriate copyright notices.