Surface Field Driven Strongly Hex-Dominant Meshing

This repository contains the meshing software developed as part of the publication

LoopyCuts: Practical Feature-Preserving Block Decomposition for Strongly Hex-Dominant Meshing
Marco Livesu, Nico Pietroni, Enrico Puppo, Alla Sheffer, Paolo Cignoni
ACM Transactions on Graphics (SIGGRAPH 2020)
PDF

Code and external dependencies

To install LoopyCuts on your machine clone this repo in recursive mode with

git clone --recursive https://github.com/mlivesu/LoopyCuts.git

The software has a number of external dependencies, some of which must be downloaded and installed in your system separately

• Qt: download and install it
• Tetgen: install it on your machine and verify that references in volumetric_cutter/volumetric_cutter.pro are correct
• CinoLib: already included in the project as a submodule, no action required
• VcgLib: already included in the project as a submodule, no action required
• AntTweakBar1.16: already included in the project

Step 1: Generation of cutting loops

This part reads an input mesh, the sharp features and the field. The software depends on Qt for the GUI, vcgLibrary for geometry processing, and AntTweakBar1.16. To compile it, open a terminal in loop_distributor and type

qmake .
make -j4

The program can be used either with a GUI, or by command line (useful to batch run entire datasets of models).

./loop_distributor <mesh> [batch]

The mesh can be either an obj or a ply. It requires to have in the same folder a .rosy and a .sharp file (with the same name of the mesh file)

Rosy file format

fn                   // number of faces of the mesh
4                    // directions of the field (always 4 for a cross-field)
x0 y0 z0             // xyz directions of one vector of the cross field of the first face
...
xn yn zn             // xyz directions of one vector of the cross field of the n-th face

Sharp file format

sn                   // number of sharp features
t0 f0 e0             // for each sharp edge: first integer is 0 if the edge is concave 1 if convex then the face and the index of the sharp edge
...
tn fn en             // nth sharp edge

Output files

_splitted mesh file : the mesh traced and splitted _loop file : the mesh traced and splitted

Loop file format

ln                  // number of loops
for each loop:
REGULAR|CONCAVE|CONVEX      //the kind of loop
Closed|Open                 //if the loop has been succesfully closed or not
Cross OK|FAIL               //if the loop has the right number of cross for topology of the cut
en                          //number of edges of the loop
indexF indexE 0|1           //the index of the face, the edge and if is on a sharp feature or not

Step 2: Cutting and Hex-dominant meshing

This part reads the refined mesh and loops generated at the previous step, and outputs a hex-dominant mesh. The software depends on Qt for the GUI, CinoLib for geometry processing, and Tetgen for tetrahedralization. To compile it, open a terminal in volumetric_cutter and type

qmake .
make -j4

The program can be used either with a GUI, or by command line (useful to batch run entire datasets of models).

./volumetric_cutter <mesh> <loops> [ -batch-mode <output_folder> ]

We recommend using the command line version, because it is much faster. The scripts folder contains a useful bash script for processing large collections of shapes with a single call.

Output Format

Although almost entirely composed of hexahedra, our output meshes may contain arbitrary polyhedra which cannot be ecnoded in popular volumetric mesh formats such as .mesh and .vtk. All our outputs are therefore encoded using the .hedra format, which is structured as follows

nv nf np             // number of vertices, faces and polyhedra, respectively
x0 y0 z0             // xyz coordinates of the 1st point 
x1 y1 z1             // xyz coordinates of the 2nd point
...                  // 
f0 v1 v2 ... vf1     // f1: number of vertices of the 1st face, followed by the (CCW ordered) list of vertices
f1 v1 v2 ... vf2     // f2: number of vertices of the 2nd face, followed by the (CCW ordered) list of vertices
...                  //
p1  f1 -f2 ...  fp1  // p1: number of faces of the 1st polyhedron, followed by the list of faces
p2 -f1  f2 ... -fp2  // p2: number of faces of the 2nd polyhedron, followed by the list of faces
...                  // (references with negative numbers (e.g. -f) denote that face |f| is seen CW by the polyhedron)

These meshes can be visualized using CinoLib (see e.g. example #06). Note that in case the output is a full hexahedral mesh a .mesh file will be also produced. Such a file can be visually inspected directly on browser connecting to HexaLab.

Acknowldegment

If you use LoopyCuts, please consider citing the associated scientific paper using the following BibTeX entry:

@article{LoopyCuts2020,
  title   = {LoopyCuts: Practical Feature-Preserving Block Decomposition for Strongly Hex-Dominant Meshing},
  author  = {Livesu, Marco and Pietroni, Nico and Puppo, Enrico and Sheffer, Alla and Cignoni, Paolo},
  journal = {ACM Transactions on Graphics},
  year    = {2020},
  volume  = {39},
  number  = {4},
  doi     = {(10.1145/3386569.3392472)}}