Merged branch 'dev_native' into lm_sla_supports_auto

Added igl library files

src/igl/grad.h

@@ -0,0 +1,46 @@
+// This file is part of libigl, a simple c++ geometry processing library.
+//
+// Copyright (C) 2013 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_GRAD_MAT_H
+#define IGL_GRAD_MAT_H
+#include "igl_inline.h"
+
+#include <Eigen/Core>
+#include <Eigen/Sparse>
+
+namespace igl {
+  // GRAD
+  // G = grad(V,F)
+  //
+  // Compute the numerical gradient operator
+  //
+  // Inputs:
+  //   V          #vertices by 3 list of mesh vertex positions
+  //   F          #faces by 3 list of mesh face indices [or a #faces by 4 list of tetrahedral indices]
+  //   uniform    boolean (default false) - Use a uniform mesh instead of the vertices V
+  // Outputs:
+  //   G  #faces*dim by #V Gradient operator
+  //
+
+  // Gradient of a scalar function defined on piecewise linear elements (mesh)
+  // is constant on each triangle [tetrahedron] i,j,k:
+  // grad(Xijk) = (Xj-Xi) * (Vi - Vk)^R90 / 2A + (Xk-Xi) * (Vj - Vi)^R90 / 2A
+  // where Xi is the scalar value at vertex i, Vi is the 3D position of vertex
+  // i, and A is the area of triangle (i,j,k). ^R90 represent a rotation of
+  // 90 degrees
+  //
+template <typename DerivedV, typename DerivedF>
+IGL_INLINE void grad(const Eigen::PlainObjectBase<DerivedV>&V,
+                     const Eigen::PlainObjectBase<DerivedF>&F,
+                    Eigen::SparseMatrix<typename DerivedV::Scalar> &G,
+                    bool uniform = false);
+}
+#ifndef IGL_STATIC_LIBRARY
+#  include "grad.cpp"
+#endif
+
+#endif