unzip corners (of an obj-style mesh with attributes)

Former-commit-id: a7c1298d09c9e8090a15f77d0ad1adb01df68199

include/igl/unzip_corners.cpp

@@ -0,0 +1,41 @@
+#include "unzip_corners.h"
+
+#include "unique.h"
+#include "slice.h"
+
+template < typename DerivedA, typename DerivedU, typename DerivedG, typename DerivedJ >
+IGL_INLINE void igl::unzip_corners(
+  const std::vector<std::reference_wrapper<DerivedA> > & A,
+  Eigen::PlainObjectBase<DerivedU> & U,
+  Eigen::PlainObjectBase<DerivedG> & G,
+  Eigen::PlainObjectBase<DerivedJ> & J)
+{
+  if(A.size() == 0)
+  {
+    U.resize(0,0);
+    G.resize(0,3);
+    J.resize(0,0);
+    return;
+  }
+  const size_t num_a = A.size();
+  const typename DerivedA::Index m = A[0].get().rows();
+  DerivedU C(m*3,num_a);
+  for(int a = 0;a<num_a;a++)
+  {
+    assert(A[a].get().rows() == m && "All attributes should be same size");
+    assert(A[a].get().cols() == 3 && "Must be triangles");
+    C.block(0*m,a,m,1) = A[a].get().col(0);
+    C.block(1*m,a,m,1) = A[a].get().col(1);
+    C.block(2*m,a,m,1) = A[a].get().col(2);
+  }
+  DerivedJ I;
+  igl::unique_rows(C,U,I,J);
+  G.resize(m,3);
+  for(int f = 0;f<m;f++)
+  {
+    for(int c = 0;c<3;c++)
+    {
+      G(f,c) = J(f+c*m);
+    }
+  }
+}

include/igl/unzip_corners.h

@@ -0,0 +1,54 @@
+// This file is part of libigl, a simple c++ geometry processing library.
+// 
+// Copyright (C) 2016 Alec Jacobson <alecjacobson@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_UNZIP_CORNERS_H
+#define IGL_UNZIP_CORNERS_H
+#include "igl_inline.h"
+#include <Eigen/Core>
+#include <vector>
+#include <functional>
+
+namespace igl
+{
+  // UNZIP_CORNERS Given a triangle mesh where corners of each triangle index
+  // different matrices of attributes (e.g. read from an OBJ file), unzip the
+  // corners into unique efficiently: attributes become properly vertex valued
+  // (usually creating greater than #V but less than #F*3 vertices).
+  //
+  // To pass a list of attributes this function takes an std::vector of
+  // std::reference_wrapper of an Eigen::... type. This allows you to use list
+  // initializers **without** incurring a copy, but means you'll need to
+  // provide the derived type of A as an explicit template parameter:
+  //
+  //     unzip_corners<Eigen::MatrixXi>({F,FTC,FN},U,G,J);
+  //
+  // Inputs:
+  //   A  #A list of #F by 3 attribute indices, typically {F,FTC,FN}
+  // Outputs:
+  //   U  #U by #A list of indices into each attribute for each unique mesh
+  //     vertex: U(v,a) is the attribute index of vertex v in attribute a.
+  //   G  #F by 3 list of triangle indices into U
+  // Example:
+  //   [V,F,TC,FTC] = readOBJ('~/Downloads/kiwis/kiwi.obj');
+  //   [U,G] = unzip_corners(cat(3,F,FTC));
+  //   % display mesh
+  //   tsurf(G,V(U(:,1),:));
+  //   % display texture coordinates
+  //   tsurf(G,TC(U(:,2),:));
+  //
+  template < typename DerivedA, typename DerivedU, typename DerivedG, typename DerivedJ>
+  IGL_INLINE void unzip_corners(
+    const std::vector<std::reference_wrapper<DerivedA> > & A,
+    Eigen::PlainObjectBase<DerivedU> & U,
+    Eigen::PlainObjectBase<DerivedG> & G,
+    Eigen::PlainObjectBase<DerivedJ> & J);
+}
+
+#ifndef IGL_STATIC_LIBRARY
+#  include "unzip_corners.cpp"
+#endif
+#endif