added helper functions for SLIM

Former-commit-id: 7548c6bad7e385fdf48fd3e099252b3c08f7cf06

.gitignore

@@ -95,3 +95,4 @@ python/build3
 python/build4
 python/scripts/generated
 python/builddebug
+tutorial/.idea

include/igl/euler_characteristic.cpp

@@ -0,0 +1,32 @@
+// This file is part of libigl, a simple c++ geometry processing library.
+//
+// Copyright (C) 2016 Michael Rabinovich <michaelrabinovich27@gmail.com@gmail.com>
+//
+// This Source Code Form is subject to the terms of the Mozilla Public License
+// v. 2.0. If a copy of the MPL was not distributed with this file, You can
+// obtain one at http://mozilla.org/MPL/2.0/.
+#include "euler_characteristic.h"
+
+#include <igl/edge_topology.h>
+
+template <typename Scalar, typename Index>
+IGL_INLINE int igl::euler_characteristic(
+  const Eigen::PlainObjectBase<Scalar> & V,
+  const Eigen::PlainObjectBase<Index> & F)
+{
+
+  int euler_v = V.rows();
+  Eigen::MatrixXi EV, FE, EF;
+  igl::edge_topology(V, F, EV, FE, EF);
+  int euler_e = EV.rows();
+  int euler_f = F.rows();
+
+  int euler_char = euler_v - euler_e + euler_f;
+  return euler_char;
+
+}
+
+#ifdef IGL_STATIC_LIBRARY
+// Explicit template specialization
+// generated by autoexplicit.sh
+#endif

include/igl/euler_characteristic.h

@@ -0,0 +1,37 @@
+// This file is part of libigl, a simple c++ geometry processing library.
+//
+// Copyright (C) 2016 Michael Rabinovich <michaelrabinovich27@gmail.com@gmail.com>
+//
+// This Source Code Form is subject to the terms of the Mozilla Public License
+// v. 2.0. If a copy of the MPL was not distributed with this file, You can
+// obtain one at http://mozilla.org/MPL/2.0/.
+#ifndef IGL_EULER_CHARACTERISTIC_H
+#define IGL_EULER_CHARACTERISTIC_H
+#include "igl_inline.h"
+
+#include <Eigen/Dense>
+#include <Eigen/Sparse>
+#include <vector>
+namespace igl
+{
+  // Computes the Euler characteristic of a given mesh (V,F)
+  // Templates:
+  //   Scalar  should be a floating point number type
+  //   Index   should be an integer type
+  // Inputs:
+  //   V       #V by dim list of mesh vertex positions
+  //   F       #F by dim list of mesh faces (must be triangles)
+  // Outputs:
+  //   An int containing the Euler characteristic
+  template <typename Scalar, typename Index>
+  IGL_INLINE int euler_characteristic(
+    const Eigen::PlainObjectBase<Scalar> & V,
+    const Eigen::PlainObjectBase<Index> & F);
+
+}
+
+#ifndef IGL_STATIC_LIBRARY
+#  include "euler_characteristic.cpp"
+#endif
+
+#endif

include/igl/flipped_triangles_ids.cpp

@@ -0,0 +1,45 @@
+// This file is part of libigl, a simple c++ geometry processing library.
+//
+// Copyright (C) 2016 Michael Rabinovich <michaelrabinovich27@gmail.com@gmail.com>
+//
+// This Source Code Form is subject to the terms of the Mozilla Public License
+// v. 2.0. If a copy of the MPL was not distributed with this file, You can
+// obtain one at http://mozilla.org/MPL/2.0/.
+#include "flipped_triangles_ids.h"
+
+#include <igl/edge_topology.h>
+
+template <typename Scalar, typename Index>
+IGL_INLINE Eigen::VectorXi flipped_triangles_ids(
+  const Eigen::PlainObjectBase<Scalar> & V,
+  const Eigen::PlainObjectBase<Index> & F
+)
+{
+  assert(V.cols() == 2);
+  std::vector<int> flip_idx;
+  for (int i = 0; i < F.rows(); i++) {
+
+    Eigen::Vector2d v1_n = V.row(F(i,0)); Eigen::Vector2d v2_n = V.row(F(i,1)); Eigen::Vector2d v3_n = V.row(F(i,2));
+
+    Eigen::MatrixXd T2_Homo(3,3);
+    T2_Homo.col(0) << v1_n(0),v1_n(1),1;
+    T2_Homo.col(1) << v2_n(0),v2_n(1),1;
+    T2_Homo.col(2) << v3_n(0),v3_n(1),1;
+    double det = T2_Homo.determinant();
+    assert (det == det);
+    if (det < 0) {
+      flip_idx.push_back(i);
+    }
+  }
+
+  Eigen::VectorXi ret(flip_idx.size());
+  for (unsigned i=0; i<flip_idx.size();++i)
+    ret[i] = flip_idx[i];
+
+  return ret;
+}
+
+#ifdef IGL_STATIC_LIBRARY
+// Explicit template specialization
+// generated by autoexplicit.sh
+#endif

include/igl/flipped_triangles_ids.h

@@ -0,0 +1,38 @@
+// This file is part of libigl, a simple c++ geometry processing library.
+//
+// Copyright (C) 2016 Michael Rabinovich <michaelrabinovich27@gmail.com@gmail.com>
+//
+// This Source Code Form is subject to the terms of the Mozilla Public License
+// v. 2.0. If a copy of the MPL was not distributed with this file, You can
+// obtain one at http://mozilla.org/MPL/2.0/.
+#ifndef IGL_FLIPPED_TRIANGLES_IDS_H
+#define IGL_FLIPPED_TRIANGLES_IDS_H
+#include "igl_inline.h"
+
+#include <Eigen/Dense>
+#include <Eigen/Sparse>
+#include <vector>
+namespace igl
+{
+  // Finds the ids of the flipped triangles of the mesh V,F in the UV mapping uv
+  // Templates:
+  //   Scalar  should be a floating point number type
+  //   Index   should be an integer type
+  // Inputs:
+  //   V       #V by 2 list of mesh vertex positions
+  //   F       #F by dim list of mesh faces (must be triangles)
+  // Outputs:
+  //   A vector containing the ids of the flipped triangles
+  template <typename Scalar, typename Index>
+  IGL_INLINE Eigen::VectorXi flipped_triangles_ids(
+    const Eigen::PlainObjectBase<Scalar> & V,
+    const Eigen::PlainObjectBase<Index> & F
+  );
+
+}
+
+#ifndef IGL_STATIC_LIBRARY
+#  include "flipped_triangles_ids.cpp"
+#endif
+
+#endif