CinoLib

CinoLib is a C++ library for processing polygonal and polyhedral meshes. It supports surface meshes made of triangles, quads or general polygons as well as volumetric meshes made of tetrahedra, hexahedra or general polyhedra.

A distinctive feature of the library is that all supported meshes inherit from a unique base class that implements their common traits, permitting to deploy algorithms that operate on abstract meshes that may be any of the above. This allows to implement algorithms just once and run the same code on any possible mesh, thus avoiding code duplication and reducing the debugging effort.

Positioning

Github hosts a whole variety of great academic libraries for mesh processing. If you do mainly geometry processing on triangle meshes, then tools like libigl, GeometryCentral or VCG may be what you want. If you are interested in rendering, Yocto/GL is extremely fast and implements many relevant algorithms. OpenMesh, CGoGN2 and PMP have a slightly broader scope and can handle general polygonal surfaces. For volumes, tiny portions of libigl and GeometryCentral offer rudimentary support for specific solid elements such as tetrahedra or hexahedra, but most of the library is focused on surfaces. Conversely, OpenVolumeMesh and CGoGN3 are focused on volumes and can operate on general polyhedral elements, but they do not support surface meshes. To the best of my knowledge, only Geogram has a unified data structure that can host both surface and volume elements, but it only supports hexahedra, tetrahedra, prisms and pyramids as volume cells. Differently from all these alternatives, CinoLib has a unique data structure that is designed to host any type of surface and volumetric element. If this comes handy to you, I am not aware of any existing alternative. Data structures based on combinatorial maps have the potential to offer similar capabilities, but these are not fully implemented yet (#171). Note that CinoLib trades generality for efficiency, hence all this flexibilty comes at a cost. Many optimizations that are possible when one operates on a restricted set of mesh elements cannot be applied here, especially memory-wise, where generic elements with an unpredictable number of vertices edges and faces demand the use of dynamic allocators. For this reason, in some cases CinoLib may be sligthly less efficient than the aforementioned alternatives.

Getting started

CinoLib is header only. It does not need to be installed, all you have to do is to clone the repo with

git clone https://github.com/mlivesu/cinolib.git

and include in your C++ application the header files you need. For small projects this could already be done by instructing the compiler on where to find the library sources, e.g. with the -I option. For more convoluted projects it is suggested to rely on a building system such as CMake, that can also handle optional external dependencies and compilation flags or symbols.

Build a sample project (with CMake)

Here is an example of a toy program that reads a triangle mesh and displays it on a window

#include <cinolib/meshes/drawable_trimesh.h>
#include <cinolib/gl/glcanvas.h>

int main()
{
    using namespace cinolib;
    DrawableTrimesh<> m("bunny.obj");
    GLcanvas gui;
    gui.push(&m);
    return gui.launch();
}

and this is the CMakeLists.txt that can be used to compile it

cmake_minimum_required(VERSION 3.2)
project(cinolib_demo)
add_executable(${PROJECT_NAME} main.cpp)
set(CINOLIB_USES_OPENGL_GLFW_IMGUI ON)
find_package(cinolib REQUIRED)
target_link_libraries(${PROJECT_NAME} cinolib)

Compiling should be as easy as opening a terminal in the folder containing the two files above and type

mkdir build
cd build
cmake .. -DCMAKE_BUILD_TYPE=Release -Dcinolib_DIR=<absolute-path-to-cinolib>
make

Note that for the rendering part CinoLib uses GLFW, which will be automatically installed and linked by the script cinolib-config.cmake, contained in the main directory of the library. The same script can automatically download and install any other external dependency, meaning that if you want to access a functionality that depends on some external library XXX, all you have to do is setting to ON a cmake variable that looks like CINOLIB_USES_XXX. Valid options are:

• CINOLIB_USES_OPENGL_GLFW_IMGUI, used for rendering with OpenGL
• CINOLIB_USES_TRIANGLE, used for polygon triangulation
• CINOLIB_USES_TETGEN, used for tetrahedralization
• CINOLIB_USES_SHEWCHUK_PREDICATES, used for exact geometric tests on input points
• CINOLIB_USES_INDIRECT_PREDICATES, used for exact geometric tests on implicit points
• CINOLIB_USES_GRAPH_CUT, used for graph clustering
• CINOLIB_USES_BOOST, used for 2D polygon operations (e.g. thickening, clipping, 2D booleans...)
• CINOLIB_USES_VTK, used just to support VTK file formats
• CINOLIB_USES_SPECTRA, used for matrix eigendecomposition
• CINOLIB_USES_CGAL, used for rational numbers with a lazy kernel

GUI

CinoLib is designed for researchers in computer graphics and geometry processing that need to quickly realize software prototypes that demonstate a novel algorithm or technique. In this context a simple OpenGL window and a side bar containing a few buttons and sliders are often more than enough. The library uses ImGui for the GUI and GLFW for OpenGL rendering. Typical visual controls for the rendering of a mesh (e.g. shading, wireframe, texturing, planar slicing, ecc) are all encoded in two classes cinolib::SurfaceMeshControls and cinolib::VolumeMeshControls, that operate on surface and volume meshes respectively. To add a side bar that displays all such controls one can modify the sample progam above as follows:

#include <cinolib/meshes/drawable_trimesh.h>
#include <cinolib/gl/glcanvas.h>
#include <cinolib/gl/surface_mesh_controls.h>

int main()
{
    using namespace cinolib;
    DrawableTrimesh<> m("bunny.obj");
    GLcanvas gui;
    SurfaceMeshControls<DrawableTrimesh<>> mesh_controls(&m, &gui);
    gui.push(&m);
    gui.push(&mesh_controls);
    return gui.launch();
}

The canvas can host multiple mesh controls, ideally one of each mesh in the scene. Additional GUI elements that may be necessary to control the application (e.g. the parameters of your algorithm) can be added by implementing a dedicated callback:

#include <cinolib/meshes/drawable_trimesh.h>
#include <cinolib/gl/glcanvas.h>
#include <cinolib/gl/surface_mesh_controls.h>

int main()
{
    using namespace cinolib;
    DrawableTrimesh<> m("bunny.obj");
    GLcanvas gui;
    SurfaceMeshControls<DrawableTrimesh<>> mesh_controls(&m, &gui);
    gui.push(&m);
    gui.push(&mesh_controls);
    float val = 1.0, min = 0.0, max = 10.0;
    gui.callback_app_controls = [&]()
    {
        if(ImGui::Button("MyButton"))
        {
            // button clicked: do something
        }
        if(ImGui::SliderFloat("MySlider", &val, min, max))
        {
            // slider moved: do something
        }       
    };
    return gui.launch();
}

The full list of callbacks exposed by GLcanvas to interact with user events (e.g. for scene navigation, mouse picking, ecc) are:

• callback_key_pressed(int key, int modifiers)
• callback_mouse_left_click(int modifiers)
• callback_mouse_left_click2(int modifiers) => double click
• callback_mouse_right_click(int modifiers)
• callback_mouse_right_click2(int modifiers) => double click
• callback_mouse_moved(double x_pos, double y_pos)
• callback_mouse_scroll(double x_offset, double y_offset)
• callback_app_controls(void)

Other examples

A tutorial with detailed info on how to use the library is under developement. In the meanwhile, you can explore the examples folder, which contains a constantly growing number of sample projects that showcase the core features of the library, and will be the backbone of the forthcoming tutorial.

Contributors

Marco Livesu is the creator and lead developer of the library. CinoLib has also received contributions from: Daniela Cabiddu (CNR IMATI), Claudio Mancinelli and Enrico Puppo (University of Genoa), Chrystiano Araújo (UBC), Thomas Alderighi (CNR ISTI), Fabrizio Corda (University of Cagliari), Gianmarco Cherchi (University of Cagliari) and Tommaso Sorgente (CNR IMATI).

Citing us

If you use CinoLib in your academic projects, please consider citing the library using the following BibTeX entry:

@article{cinolib,
  title   = {cinolib: a generic programming header only C++ library for processing polygonal and polyhedral meshes},
  author  = {Livesu, Marco},
  journal = {Transactions on Computational Science XXXIV},
  series  = {Lecture Notes in Computer Science},
  editor  = {Springer},
  note    = {https://github.com/mlivesu/cinolib/},
  year    = {2019},
  doi     = {10.1007/978-3-662-59958-7_4}}

Acknowledgment

The software collected in CinoLib spans across a large period of time, starting from the beginning of my PhD to today. Since 2015, this work has been partly supported by various research projects, such as

• ProMED
• CHANGE
• CAxMan