libigl/tutorial/702_WindingNumber/main.cpp

#include <igl/barycenter.h>
#include <igl/boundary_facets.h>
#include <igl/parula.h>
#include <igl/readMESH.h>
#include <igl/marching_tets.h>
#include <igl/winding_number.h>
#include <igl/opengl/glfw/Viewer.h>
#include <Eigen/Sparse>
#include <iostream>


Eigen::MatrixXd V,BC;
Eigen::VectorXd W;
Eigen::MatrixXi T,F,G;
double slice_z = 0.5;
enum OverLayType
{
  OVERLAY_NONE = 0,
  OVERLAY_INPUT = 1,
  OVERLAY_OUTPUT = 2,
  NUM_OVERLAY = 3,
} overlay = OVERLAY_NONE;

void update_visualization(igl::opengl::glfw::Viewer & viewer)
{
  using namespace Eigen;
  using namespace std;
  Eigen::Vector4d plane(
    0,0,1,-((1-slice_z)*V.col(2).minCoeff()+slice_z*V.col(2).maxCoeff()));
  MatrixXd V_vis;
  MatrixXi F_vis;
  VectorXi J;
  {
    SparseMatrix<double> bary;
    // Value of plane's implicit function at all vertices
    const VectorXd IV = 
      (V.col(0)*plane(0) + 
        V.col(1)*plane(1) + 
        V.col(2)*plane(2)).array()
      + plane(3);
    igl::marching_tets(V,T,IV,V_vis,F_vis,J,bary);
  }
  VectorXd W_vis = W(J);
  MatrixXd C_vis;
  // color without normalizing
  igl::parula(W_vis,false,C_vis);


  const auto & append_mesh = [&C_vis,&F_vis,&V_vis](
    const Eigen::MatrixXd & V,
    const Eigen::MatrixXi & F,
    const RowVector3d & color)
  {
    F_vis.conservativeResize(F_vis.rows()+F.rows(),3);
    F_vis.bottomRows(F.rows()) = F.array()+V_vis.rows();
    V_vis.conservativeResize(V_vis.rows()+V.rows(),3);
    V_vis.bottomRows(V.rows()) = V;
    C_vis.conservativeResize(C_vis.rows()+F.rows(),3);
    C_vis.bottomRows(F.rows()).rowwise() = color;
  };
  switch(overlay)
  {
    case OVERLAY_INPUT:
      append_mesh(V,F,RowVector3d(1.,0.894,0.227));
      break;
    case OVERLAY_OUTPUT:
      append_mesh(V,G,RowVector3d(0.8,0.8,0.8));
      break;
    default:
      break;
  }
  viewer.data().clear();
  viewer.data().set_mesh(V_vis,F_vis);
  viewer.data().set_colors(C_vis);
  viewer.data().set_face_based(true);
}

bool key_down(igl::opengl::glfw::Viewer& viewer, unsigned char key, int mod)
{
  switch(key)
  {
    default:
      return false;
    case ' ':
      overlay = (OverLayType)((1+(int)overlay)%NUM_OVERLAY);
      break;
    case '.':
      slice_z = std::min(slice_z+0.01,0.99);
      break;
    case ',':
      slice_z = std::max(slice_z-0.01,0.01);
      break;
  }
  update_visualization(viewer);
  return true;
}

int main(int argc, char *argv[])
{
  using namespace Eigen;
  using namespace std;

  cout<<"Usage:"<<endl;
  cout<<"[space]  toggle showing input mesh, output mesh or slice "<<endl;
  cout<<"         through tet-mesh of convex hull."<<endl;
  cout<<"'.'/','  push back/pull forward slicing plane."<<endl;
  cout<<endl;

  // Load mesh: (V,T) tet-mesh of convex hull, F contains facets of input
  // surface mesh _after_ self-intersection resolution
  igl::readMESH(TUTORIAL_SHARED_PATH "/big-sigcat.mesh",V,T,F);

  // Compute barycenters of all tets
  igl::barycenter(V,T,BC);

  // Compute generalized winding number at all barycenters
  cout<<"Computing winding number over all "<<T.rows()<<" tets..."<<endl;
  igl::winding_number(V,F,BC,W);

  // Extract interior tets
  MatrixXi CT((W.array()>0.5).count(),4);
  {
    size_t k = 0;
    for(size_t t = 0;t<T.rows();t++)
    {
      if(W(t)>0.5)
      {
        CT.row(k) = T.row(t);
        k++;
      }
    }
  }
  // find bounary facets of interior tets
  igl::boundary_facets(CT,G);
  // boundary_facets seems to be reversed...
  G = G.rowwise().reverse().eval();

  // normalize
  W = (W.array() - W.minCoeff())/(W.maxCoeff()-W.minCoeff());

  // Plot the generated mesh
  igl::opengl::glfw::Viewer viewer;
  update_visualization(viewer);
  viewer.callback_key_down = &key_down;
  viewer.launch();
}