misc.hh

// Copyright (C) 2008, 2009 EPITA Research and Development Laboratory
// (LRDE)
//
// This file is part of the Milena Library.  This library is free
// software; you can redistribute it and/or modify it under the terms
// of the GNU General Public License version 2 as published by the
// Free Software Foundation.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this library; see the file COPYING.  If not, write to
// the Free Software Foundation, 51 Franklin Street, Fifth Floor,
// Boston, MA 02111-1307, USA.
//
// As a special exception, you may use this file as part of a free
// software library without restriction.  Specifically, if other files
// instantiate templates or use macros or inline functions from this
// file, or you compile this file and link it with other files to
// produce an executable, this file does not by itself cause the
// resulting executable to be covered by the GNU General Public
// License.  This exception does not however invalidate any other
// reasons why the executable file might be covered by the GNU General
// Public License.

// FIXME: Split this file.
// FIXME: Address license-related issues?

#ifndef MILENA_APPS_STATUES_MISC_HH
# define MILENA_APPS_STATUES_MISC_HH

# include <algorithm>  // For std::swap.
# include <utility>    // For std::pair.

# include <mln/algebra/vec.hh>
# include <mln/algebra/mat.hh>

# include <mln/norm/l2.hh>

# include <mln/data/fill.hh>


// FIXME: We should turn `likely' and `unlikely' into functions.
#ifndef likely
#  if !defined(__GNUC__) || (__GNUC__ == 2 && __GNUC_MINOR__ < 96)
#    define likely(x) (x)
#    define unlikely(x) (x)
#  else
#    define likely(x)   (__builtin_expect((x), 1))
#    define unlikely(x) (__builtin_expect((x), 0))
#  endif
#endif

namespace mln
{

  namespace algebra
  {

    // From Trimesh.
    // FIXME: Doc (input, return value, etc.).
    // FIXME: Idea: Add reference to Numerical Recipes.

    template <unsigned N, typename T>
    inline
    bool
    ldlt_decomp(mat<N, N, T>& A, vec<N, T>& rdiag)
    {
      vec<N - 1, T> v;
      for (unsigned i = 0; i < N; ++i)
        {
          for (unsigned k = 0; k < i; ++k)
            v[k] = A(i, k) * rdiag[k];
          for (unsigned j = i; j < N; ++j)
            {
              T sum = A(i, j);
              for (unsigned k = 0; k < i; k++)
                sum -= v[k] * A(j, k);
              if (i == j)
                {
                  if (unlikely(sum <= T(0)))
                    return false;
                  rdiag[i] = T(1) / sum;
                }
              else
                A(j, i) = sum;
            }
        }
      return true;
    }

    // From Trimesh.
    // FIXME: Doc (input, return value, etc.).
    // FIXME: Idea: Add reference to Numerical Recipes.

    template <unsigned N, typename T>
    inline
    void
    ldlt_solve(const mat<N, N, T>& A, const vec<N, T>& rdiag,
               const vec<N, T>& B, vec<N, T>& x)
    {
      for (unsigned i = 0; i < N; ++i)
        {
          T sum = B[i];
          for (unsigned k = 0; k < i; ++k)
            sum -= A(i, k) * x[k];
          x[i] = sum * rdiag[i];
        }
      for (int i = N - 1; i >= 0; --i)
        {
          T sum = 0;
          for (unsigned k = i + 1; k < N; ++k)
            sum += A(k, i) * x[k];
          x[i] -= sum * rdiag[i];
        }
    }

  } // end of namespace mln::algebra

} // end of namespace mln


// FIXME: To be moved elsewhere (in mln/geom)?

// Inspired from Trimesh.

namespace mln
{

  namespace geom
  {

    // FIXME: More doc (see Trimesh's).

    /* FIXME: We should restrict attached data to vertices in return
       value.  */
    inline
    complex_image< 2, mln::space_2complex_geometry, algebra::vec<3, float> >
    mesh_normal(const p_complex<2, space_2complex_geometry>& mesh)
    {
      // Shortcuts.
      static const unsigned D = 2;
      typedef space_2complex_geometry G;
      typedef algebra::vec<3, float> vec3f;
      typedef complex_image< D, G, vec3f > normal_t;

      normal_t normal(mesh);
      data::fill(normal, literal::zero);

      mln::p_n_faces_fwd_piter<D, G> f(mesh, 2);
      // A neighborhood where neighbors are the set of 0-faces
      // transitively adjacent to the reference point.
      typedef mln::complex_m_face_neighborhood<D, G> adj_vertices_nbh_t;
      adj_vertices_nbh_t adj_vertices_nbh;
      mln_niter_(adj_vertices_nbh_t) adj_v(adj_vertices_nbh, f);
      /* FIXME: We should be able to pas this value (m) either at the
         construction of the neighborhood or at the construction of
         the iterator.  Alas, we can't inherit ctors (yet), so we
         can't rely on a simple mixin approach.  */
      adj_v.iter().set_m(0);

      // Iterate on 2-faces (triangles).
      for_all(f)
      {
        std::vector<mln_psite_(normal_t)> p;
        p.reserve(3);
        for_all(adj_v)
          p.push_back(adj_v);
        mln_assertion(p.size() == 3);

        /* FIXME: Is the explicit conversion to_site() really needed?
           If not, we could provide a local shortcut like

             vec(p[0])   // Instead of p[0].to_site().front().to_vec()

           to shorten these lines.  */
        // FIXME: Factor as well?
        vec3f a =
          p[0].to_site().front().to_vec() - p[1].to_site().front().to_vec();
        vec3f b =
          p[1].to_site().front().to_vec() - p[2].to_site().front().to_vec();
        vec3f c =
          p[2].to_site().front().to_vec() - p[0].to_site().front().to_vec();

        // FIXME: Factor as well?
        float l2a = norm::sqr_l2(a);
        float l2b = norm::sqr_l2(b);
        float l2c = norm::sqr_l2(c);
        vec3f face_normal = algebra::vprod(a, b);

        normal(p[0]) += face_normal * (1.0f / (l2a * l2c));
        normal(p[1]) += face_normal * (1.0f / (l2b * l2a));
        normal(p[2]) += face_normal * (1.0f / (l2c * l2b));
      }

      // Normalize normals.  We don't need to iterate on all faces, just
      // 0-faces.
      mln::p_n_faces_fwd_piter<D, G> v(mesh, 0);
      for_all(v)
        normal(v).normalize();

      return normal;
    }


    /* FIXME: We should restrict attached data to vertices in return
       value.  */
    inline
    std::pair<
      complex_image< 2, mln::space_2complex_geometry, algebra::vec<3, float> >,
      complex_image< 2, mln::space_2complex_geometry, float >
      >
    mesh_corner_point_area(const p_complex<2, space_2complex_geometry>& mesh)
    {
      // Shortcuts.
      static const unsigned D = 2;
      typedef space_2complex_geometry G;
      typedef algebra::vec<3, float> vec3f;

      // Hold data for 2-faces only.
      typedef complex_image< D, G, vec3f > corner_area_t;
      // Hold data for 0-faces only.
      typedef complex_image< D, G, float > point_area_t;
      // Packed output.
      typedef std::pair<corner_area_t, point_area_t> output_t;

      // Initialize output.
      output_t output(mesh, mesh);
      corner_area_t& corner_area = output.first;
      point_area_t& point_area = output.second;
      data::fill(corner_area, literal::zero);
      data::fill(point_area, literal::zero);

      mln::p_n_faces_fwd_piter<D, G> f(mesh, 2);
      // A neighborhood where neighbors are the set of 0-faces
      // transitively adjacent to the reference point.
      typedef mln::complex_m_face_neighborhood<D, G> adj_vertices_nbh_t;
      adj_vertices_nbh_t adj_vertices_nbh;
      mln_niter_(adj_vertices_nbh_t) adj_v(adj_vertices_nbh, f);
      /* FIXME: We should be able to pas this value (m) either at the
         construction of the neighborhood or at the construction of
         the iterator.  Alas, we can't inherit ctors (yet), so we
         can't rely on a simple mixin approach.  */
      adj_v.iter().set_m(0);

      for_all(f)
      {
        std::vector<mln_psite_(corner_area_t)> p;
        p.reserve(3);
        for_all(adj_v)
          p.push_back(adj_v);
        mln_assertion(p.size() == 3);

        // (Opposite) edge vectors.
        algebra::vec<3, vec3f> e;
        // FIXME: See above.
        e.set
          (p[2].to_site().front().to_vec() - p[1].to_site().front().to_vec(),
           p[0].to_site().front().to_vec() - p[2].to_site().front().to_vec(),
           p[1].to_site().front().to_vec() - p[0].to_site().front().to_vec());

        // Compute corner weights.
        float area = 0.5f * norm::l2(algebra::vprod(e[0], e[1]));
        vec3f sqr_norm;
        sqr_norm.set(norm::sqr_l2(e[0]),
                     norm::sqr_l2(e[1]),
                     norm::sqr_l2(e[2]));
        vec3f edge_weight;
        edge_weight.set
          (sqr_norm[0] * (sqr_norm[1] + sqr_norm[2] - sqr_norm[0]),
           sqr_norm[1] * (sqr_norm[2] + sqr_norm[0] - sqr_norm[1]),
           sqr_norm[2] * (sqr_norm[0] + sqr_norm[1] - sqr_norm[2]));

        if (edge_weight[0] <= 0.0f)
          {
            corner_area(f)[1] = -0.25f * sqr_norm[2] * area / (e[0] * e[2]);
            corner_area(f)[2] = -0.25f * sqr_norm[1] * area / (e[0] * e[1]);
            corner_area(f)[0] = area - corner_area(f)[1] - corner_area(f)[2];
          }
        else if (edge_weight[1] <= 0.0f)
          {
            corner_area(f)[2] = -0.25f * sqr_norm[0] * area / (e[1] * e[0]);
            corner_area(f)[0] = -0.25f * sqr_norm[2] * area / (e[1] * e[2]);
            corner_area(f)[1] = area - corner_area(f)[2] - corner_area(f)[0];
          }
        else if (edge_weight[2] <= 0.0f)
          {
            corner_area(f)[0] = -0.25f * sqr_norm[1] * area / (e[2] * e[1]);
            corner_area(f)[1] = -0.25f * sqr_norm[0] * area / (e[2] * e[0]);
            corner_area(f)[2] = area - corner_area(f)[0] - corner_area(f)[1];
          }
        else
          {
            float ewscale =
              0.5f * area / (edge_weight[0] + edge_weight[1] + edge_weight[2]);
            for (int i = 0; i < 3; ++i)
              corner_area(f)[i] =
                ewscale * (edge_weight[(i+1)%3] + edge_weight[(i+2)%3]);
          }

        for (int i = 0; i < 3; ++i)
          point_area(p[i]) += corner_area(f)[i];
      }

      return output;
    }


    namespace internal
    {

      static inline unsigned next(unsigned i) { return (i + 1) % 3; }
      static inline unsigned prev(unsigned i) { return (i - 1) % 3; }

      inline
      void
      rot_coord_sys(const algebra::vec<3, float> &old_u,
                    const algebra::vec<3, float> &old_v,
                    const algebra::vec<3, float> &new_norm,
                    algebra::vec<3, float> &new_u,
                    algebra::vec<3, float> &new_v)
      {
        new_u = old_u;
        new_v = old_v;
        algebra::vec<3, float> old_norm = vprod(old_u, old_v);
        float ndot = old_norm * new_norm;
        if (unlikely(ndot <= -1.0f))
          {
            new_u = -new_u;
            new_v = -new_v;
            return;
          }
        algebra::vec<3, float> perp_old = new_norm - ndot * old_norm;
        algebra::vec<3, float> dperp =
          1.0f / (1 + ndot) * (old_norm + new_norm);
        new_u -= dperp * (new_u * perp_old);
        new_v -= dperp * (new_v * perp_old);
      }


      // FIXME: Add const to formals whenever we can.

      // Reproject a curvature tensor from the basis spanned by old_u and old_v
      // (which are assumed to be unit-length and perpendicular) to the
      // new_u, new_v basis.
      inline
      void
      proj_curv(const algebra::vec<3, float>& old_u,
                const algebra::vec<3, float>& old_v,
                float old_ku, float old_kuv, float old_kv,
                const algebra::vec<3, float>& new_u,
                const algebra::vec<3, float>& new_v,
                float& new_ku, float& new_kuv, float& new_kv)
      {
        algebra::vec<3, float> r_new_u, r_new_v;
        rot_coord_sys(new_u, new_v, vprod(old_u, old_v), r_new_u, r_new_v);

        float u1 = r_new_u * old_u;
        float v1 = r_new_u * old_v;
        float u2 = r_new_v * old_u;
        float v2 = r_new_v * old_v;
        new_ku  = old_ku * u1*u1 + old_kuv * (2.0f  * u1*v1) + old_kv * v1*v1;
        new_kuv = old_ku * u1*u2 + old_kuv * (u1*v2 + u2*v1) + old_kv * v1*v2;
        new_kv  = old_ku * u2*u2 + old_kuv * (2.0f  * u2*v2) + old_kv * v2*v2;
      }

      inline
      void
      diagonalize_curv(const algebra::vec<3, float>& old_u,
                       const algebra::vec<3, float>& old_v,
                       float ku, float kuv, float kv,
                       const algebra::vec<3, float>& new_norm,
                       algebra::vec<3, float>& pdir1,
                       algebra::vec<3, float>& pdir2,
                       float& k1, float& k2)
      {
        algebra::vec<3, float> r_old_u, r_old_v;
        rot_coord_sys(old_u, old_v, new_norm, r_old_u, r_old_v);

        float c = 1, s = 0, tt = 0;
        if (likely(kuv != 0.0f))
          {
            // Jacobi rotation to diagonalize.
            float h = 0.5f * (kv - ku) / kuv;
            tt = (h < 0.0f) ?
              1.0f / (h - sqrt(1.0f + h*h)) :
              1.0f / (h + sqrt(1.0f + h*h));
            c = 1.0f / sqrt(1.0f + tt*tt);
            s = tt * c;
          }

        k1 = ku - tt * kuv;
        k2 = kv + tt * kuv;

        if (fabs(k1) >= fabs(k2))
          pdir1 = c*r_old_u - s*r_old_v;
        else
          {
            std::swap(k1, k2);
            pdir1 = s*r_old_u + c*r_old_v;
          }
        pdir2 = vprod(new_norm, pdir1);
      }

    } // end of namespace mln::geom::internal


    /* FIXME: We should restrict attached data to vertices in return
       value.  */
    /* FIXME: Have a typedef for this return type?  */
    inline
    std::pair<
      complex_image< 2, mln::space_2complex_geometry, float >,
      complex_image< 2, mln::space_2complex_geometry, float >
      >
    mesh_curvature(const p_complex<2, space_2complex_geometry>& mesh)
    {
      // Shortcuts.
      static const unsigned D = 2;
      typedef space_2complex_geometry G;
      typedef algebra::vec<3, float> vec3f;
      typedef algebra::mat<3, 3, float> mat3f;

      typedef complex_image< D, G, vec3f > corner_area_t;
      typedef complex_image< D, G, float > point_area_t;

      // Normals at vertices.
      typedef complex_image< 2, mln::space_2complex_geometry, vec3f > normal_t;
      normal_t normal = mesh_normal(mesh);

      // Areas ``belonging'' to a normal.
      typedef complex_image< D, G, vec3f > corner_area_t;
      typedef complex_image< D, G, float > point_area_t;
      typedef std::pair<corner_area_t, point_area_t> corner_point_area_t;
      corner_point_area_t corner_point_area = mesh_corner_point_area(mesh);
      // Shortcuts.
      corner_area_t& corner_area = corner_point_area.first;
      point_area_t& point_area = corner_point_area.second;

      // Curvatures at each vertex.
      typedef complex_image< 2, mln::space_2complex_geometry, float > curv_t;
      typedef std::pair<curv_t, curv_t> output_t;
      output_t output(mesh, mesh);
      curv_t& curv1 = output.first;
      curv_t& curv2 = output.second;
      // ??
      complex_image< 2, mln::space_2complex_geometry, float > curv12(mesh);
      // Principal directions at each vertex.
      complex_image< 2, mln::space_2complex_geometry, vec3f > pdir1(mesh);
      complex_image< 2, mln::space_2complex_geometry, vec3f > pdir2(mesh);

      /*-------------------------------------------------.
      | Set up an initial coordinate system per vertex.  |
      `-------------------------------------------------*/

      mln::p_n_faces_fwd_piter<D, G> f(mesh, 2);
      // A neighborhood where neighbors are the set of 0-faces
      // transitively adjacent to the reference point.
      typedef mln::complex_m_face_neighborhood<D, G> adj_vertices_nbh_t;
      adj_vertices_nbh_t adj_vertices_nbh;
      mln_niter_(adj_vertices_nbh_t) adj_v(adj_vertices_nbh, f);
      /* FIXME: We should be able to pas this value (m) either at the
         construction of the neighborhood or at the construction of
         the iterator.  Alas, we can't inherit ctors (yet), so we
         can't rely on a simple mixin approach.  */
      adj_v.iter().set_m(0);

      for_all(f)
      {
        std::vector<mln_psite_(curv_t)> p;
        p.reserve(3);
        for_all(adj_v)
          p.push_back(adj_v);
        mln_assertion(p.size() == 3);

        // FIXME: See above.
        pdir1(p[0]) =
          p[1].to_site().front().to_vec() - p[0].to_site().front().to_vec();
        pdir1(p[1]) =
          p[2].to_site().front().to_vec() - p[1].to_site().front().to_vec();
        pdir1(p[2]) =
          p[0].to_site().front().to_vec() - p[2].to_site().front().to_vec();
      }

      mln::p_n_faces_fwd_piter<D, G> v(mesh, 0);
      for_all(v)
      {
        pdir1(v) = algebra::vprod(pdir1(v), normal(v));
        pdir1(v).normalize();
        pdir2(v) = algebra::vprod(normal(v), pdir1(v));
      }

      /*-----------------------------.
      | Compute curvature per-face.  |
      `-----------------------------*/

      for_all(f)
      {
        std::vector<mln_psite_(curv_t)> p;
        p.reserve(3);
        for_all(adj_v)
          p.push_back(adj_v);
        mln_assertion(p.size() == 3);

        // (Opposite) edge vectors.
        algebra::vec<3, vec3f> e;
        // FIXME: See above.
        e.set
          (p[2].to_site().front().to_vec() - p[1].to_site().front().to_vec(),
           p[0].to_site().front().to_vec() - p[2].to_site().front().to_vec(),
           p[1].to_site().front().to_vec() - p[0].to_site().front().to_vec());

        // N-T-B coordinate system per face.
        vec3f t = e[0];
        t.normalize();
        vec3f n = algebra::vprod(e[0], e[1]);
        /* FIXME: Why don't we normalize N?  Is it a normal vector by
           construction?  Or maybe we don't need it to be normal?  */
        vec3f b = algebra::vprod(n, t);
        b.normalize();

        // Estimate curvature based on variation of normals along edges.
        vec3f m = literal::zero;
        mat3f w = literal::zero;
        for (int j = 0; j < 3; ++j)
          {
            float u = e[j] * t;
            float v = e[j] * b;
            w(0, 0) += u * u;
            w(0, 1) += u * v;
            /* FIXME: Those two lines were commented in Trimesh's
               original code.

                 //w(1, 1) += v*v + u*u;
                 //w(1, 2) += u*v;

            */
            w(2, 2) += v * v; 
            vec3f dn =
              normal(p[internal::prev(j)]) - normal(p[internal::next(j)]);
            float dnu = dn * t;
            float dnv = dn * b;
            m[0] += dnu*u;
            m[1] += dnu*v + dnv*u;
            m[2] += dnv*v;
          }
          w(1, 1) = w(0, 0) + w(2, 2);
          w(1, 2) = w(0, 1);

          // Least squares solution.
          vec3f diag;
#ifndef NDEBUG
          bool ldlt_decomp_sucess_p = algebra::ldlt_decomp(w, diag);
#endif // ! NDEBUG
          mln_assertion(ldlt_decomp_sucess_p);
          algebra::ldlt_solve(w, diag, m, m);

          // Push it back out to the vertices
          for (int j = 0; j < 3; ++j)
            {
              float c1, c12, c2;
              internal::proj_curv(t, b, m[0], m[1], m[2],
                                  pdir1(p[j]), pdir2(p[j]), c1, c12, c2);
              float wt = corner_area(f)[j] / point_area(p[j]);
              curv1(p[j])  += wt * c1;
              curv12(p[j]) += wt * c12;
              curv2(p[j])  += wt * c2;
            }
      }

      /*-------------------------------------------------------------.
      | Compute principal directions and curvatures at each vertex.  |
      `-------------------------------------------------------------*/

      for_all(v)
        internal::diagonalize_curv(pdir1(v), pdir2(v),
                                   curv1(v), curv12(v), curv2(v),
                                   normal(v), pdir1(v), pdir2(v),
                                   curv1(v), curv2(v));

      return output;
    }

  } // end of namespace mln::geom

} // end of namespace mln

#endif // ! MILENA_APPS_STATUES_MISC_HH