libigl_Martin/tutorial/602_Matlab/main.cpp

#include <igl/jet.h>
#include <igl/readOFF.h>
#include <igl/cotmatrix.h>
#include <igl/matlab/matlabinterface.h>
#include <igl/viewer/Viewer.h>
#include <iostream>

// Base mesh
Eigen::MatrixXd V;
Eigen::MatrixXi F;

// Matlab instance
Engine* engine;

// Eigenvectors of the laplacian
Eigen::MatrixXd EV;

void plotEV(igl::viewer::Viewer& viewer, int id)
{
  Eigen::VectorXd v = EV.col(id);
  v = v.array() - v.minCoeff();
  v = v.array() / v.maxCoeff();

  // Map to colors using jet colorramp
  Eigen::MatrixXd C(V.rows(),3);
  for (unsigned i=0; i<V.rows(); ++i)
  {
    double r,g,b;
    igl::jet(v(i),r,g,b);
    C.row(i) << r,g,b;
  }

  viewer.data.set_colors(C);
}

// This function is called every time a keyboard button is pressed
bool key_down(igl::viewer::Viewer& viewer, unsigned char key, int modifier)
{
  if (key >= '1' && key <= '9')
    plotEV(viewer,(key - '1') + 1);

  return false;
}

int main(int argc, char *argv[])
{
  // Load a mesh in OFF format
  igl::readOFF("../shared/3holes.off", V, F);

  // Launch MATLAB
  igl::matlab::mlinit(&engine);

  // Compute the discrete Laplacian operator
  Eigen::SparseMatrix<double> L;
  igl::cotmatrix(V,F,L);

  // Send Laplacian matrix to matlab
  igl::matlab::mlsetmatrix(&engine,"L",L);

  // Plot the laplacian matrix using matlab spy
  igl::matlab::mleval(&engine,"spy(L)");

  // Extract the first 10 eigenvectors
  igl::matlab::mleval(&engine,"[EV,~] = eigs(-L,10,'sm')");

  // Plot the size of EV (only for demostration purposes)
  std::cerr << igl::matlab::mleval(&engine,"size(EV)") << std::endl;

  // Retrieve the result
  igl::matlab::mlgetmatrix(&engine,"EV",EV);

  // Plot the mesh
  igl::viewer::Viewer viewer;
  viewer.callback_key_down = &key_down;
  viewer.data.set_mesh(V, F);

  // Plot the first non-trivial eigenvector
  plotEV(viewer,1);

  // Launch the viewer
  viewer.launch();
}