libigl/include/igl/collapse_edge.cpp

// This file is part of libigl, a simple c++ geometry processing library.
// 
// Copyright (C) 2015 Alec Jacobson <[email protected]>
// 
// 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 "collapse_edge.h"
#include "circulation.h"
#include "edge_collapse_is_valid.h"
#include "decimate_trivial_callbacks.h"
#include <vector>

IGL_INLINE bool igl::collapse_edge(
  const int e,
  const Eigen::RowVectorXd & p,
  Eigen::MatrixXd & V,
  Eigen::MatrixXi & F,
  Eigen::MatrixXi & E,
  Eigen::VectorXi & EMAP,
  Eigen::MatrixXi & EF,
  Eigen::MatrixXi & EI,
  int & e1,
  int & e2,
  int & f1,
  int & f2)
{
  std::vector<int> /*Nse,*/Nsf,Nsv;
  circulation(e, true,F,EMAP,EF,EI,/*Nse,*/Nsv,Nsf);
  std::vector<int> /*Nde,*/Ndf,Ndv;
  circulation(e, false,F,EMAP,EF,EI,/*Nde,*/Ndv,Ndf);
  return collapse_edge(
    e,p,Nsv,Nsf,Ndv,Ndf,V,F,E,EMAP,EF,EI,e1,e2,f1,f2);
}

IGL_INLINE bool igl::collapse_edge(
  const int e,
  const Eigen::RowVectorXd & p,
  /*const*/ std::vector<int> & Nsv,
  const std::vector<int> & Nsf,
  /*const*/ std::vector<int> & Ndv,
  const std::vector<int> & Ndf,
  Eigen::MatrixXd & V,
  Eigen::MatrixXi & F,
  Eigen::MatrixXi & E,
  Eigen::VectorXi & EMAP,
  Eigen::MatrixXi & EF,
  Eigen::MatrixXi & EI,
  int & a_e1,
  int & a_e2,
  int & a_f1,
  int & a_f2)
{
  // Assign this to 0 rather than, say, -1 so that deleted elements will get
  // draw as degenerate elements at vertex 0 (which should always exist and
  // never get collapsed to anything else since it is the smallest index)
  using namespace Eigen;
  using namespace std;
  const int eflip = E(e,0)>E(e,1);
  // source and destination
  const int s = eflip?E(e,1):E(e,0);
  const int d = eflip?E(e,0):E(e,1);

  if(!edge_collapse_is_valid(Nsv,Ndv))
  {
    return false;
  }

  // OVERLOAD: caller may have just computed this
  //
  // Important to grab neighbors of d before monkeying with edges
  const std::vector<int> & nV2Fd = (!eflip ? Nsf : Ndf);

  // The following implementation strongly relies on s<d
  assert(s<d && "s should be less than d");
  // move source and destination to placement
  V.row(s) = p;
  V.row(d) = p;

  // Helper function to replace edge and associate information with NULL
  const auto & kill_edge = [&E,&EI,&EF](const int e)
  {
    E(e,0) = IGL_COLLAPSE_EDGE_NULL;
    E(e,1) = IGL_COLLAPSE_EDGE_NULL;
    EF(e,0) = IGL_COLLAPSE_EDGE_NULL;
    EF(e,1) = IGL_COLLAPSE_EDGE_NULL;
    EI(e,0) = IGL_COLLAPSE_EDGE_NULL;
    EI(e,1) = IGL_COLLAPSE_EDGE_NULL;
  };

  // update edge info
  // for each flap
  const int m = F.rows();
  for(int side = 0;side<2;side++)
  {
    const int f = EF(e,side);
    const int v = EI(e,side);
    const int sign = (eflip==0?1:-1)*(1-2*side);
    // next edge emanating from d
    const int e1 = EMAP(f+m*((v+sign*1+3)%3));
    // prev edge pointing to s
    const int e2 = EMAP(f+m*((v+sign*2+3)%3));
    assert(E(e1,0) == d || E(e1,1) == d);
    assert(E(e2,0) == s || E(e2,1) == s);
    // face adjacent to f on e1, also incident on d
    const bool flip1 = EF(e1,1)==f;
    const int f1 = flip1 ? EF(e1,0) : EF(e1,1);
    assert(f1!=f);
    assert(F(f1,0)==d || F(f1,1)==d || F(f1,2) == d);
    // across from which vertex of f1 does e1 appear?
    const int v1 = flip1 ? EI(e1,0) : EI(e1,1);
    // Kill e1
    kill_edge(e1);
    // Kill f
    F(f,0) = IGL_COLLAPSE_EDGE_NULL;
    F(f,1) = IGL_COLLAPSE_EDGE_NULL;
    F(f,2) = IGL_COLLAPSE_EDGE_NULL;
    // map f1's edge on e1 to e2
    assert(EMAP(f1+m*v1) == e1);
    EMAP(f1+m*v1) = e2;
    // side opposite f2, the face adjacent to f on e2, also incident on s
    const int opp2 = (EF(e2,0)==f?0:1);
    assert(EF(e2,opp2) == f);
    EF(e2,opp2) = f1;
    EI(e2,opp2) = v1;
    // remap e2 from d to s
    E(e2,0) = E(e2,0)==d ? s : E(e2,0);
    E(e2,1) = E(e2,1)==d ? s : E(e2,1);
    if(side==0)
    {
      a_e1 = e1;
      a_f1 = f;
    }else
    {
      a_e2 = e1;
      a_f2 = f;
    }
  }

  // finally, reindex faces and edges incident on d. Do this last so asserts
  // make sense.
  //
  // Could actually skip first and last, since those are always the two
  // collpased faces. Nah, this is handled by (F(f,v) == d)
  //
  // Don't attempt to use Nde,Nse here because EMAP has changed
  {
    int p1 = -1;
    for(auto f : nV2Fd)
    {
      for(int v = 0;v<3;v++)
      {
        if(F(f,v) == d)
        {
          const int e1 = EMAP(f+m*((v+1)%3));
          const int flip1 = (EF(e1,0)==f)?1:0;
          assert( E(e1,flip1) == d || E(e1,flip1) == s);
          E(e1,flip1) = s;
          const int e2 = EMAP(f+m*((v+2)%3));
          // Skip if we just handled this edge (claim: this will be all except
          // for the first non-trivial face)
          if(e2 != p1)
          {
            const int flip2 = (EF(e2,0)==f)?0:1;
            assert( E(e2,flip2) == d || E(e2,flip2) == s);
            E(e2,flip2) = s;
          }

          F(f,v) = s;
          p1 = e1;
          break;
        }
      }
    }
  }
  // Finally, "remove" this edge and its information
  kill_edge(e);
  return true;
}

IGL_INLINE bool igl::collapse_edge(
  const int e,
  const Eigen::RowVectorXd & p,
  Eigen::MatrixXd & V,
  Eigen::MatrixXi & F,
  Eigen::MatrixXi & E,
  Eigen::VectorXi & EMAP,
  Eigen::MatrixXi & EF,
  Eigen::MatrixXi & EI)
{
  int e1,e2,f1,f2;
  return collapse_edge(e,p,V,F,E,EMAP,EF,EI,e1,e2,f1,f2);
}

IGL_INLINE bool igl::collapse_edge(
  const decimate_cost_and_placement_callback & cost_and_placement,
  Eigen::MatrixXd & V,
  Eigen::MatrixXi & F,
  Eigen::MatrixXi & E,
  Eigen::VectorXi & EMAP,
  Eigen::MatrixXi & EF,
  Eigen::MatrixXi & EI,
  igl::min_heap< std::tuple<double,int,int> > & Q,
  Eigen::VectorXi & EQ,
  Eigen::MatrixXd & C)
{
  int e,e1,e2,f1,f2;
  decimate_pre_collapse_callback always_try;
  decimate_post_collapse_callback never_care;
  decimate_trivial_callbacks(always_try,never_care);
  return 
    collapse_edge(
      cost_and_placement,always_try,never_care,
      V,F,E,EMAP,EF,EI,Q,EQ,C,e,e1,e2,f1,f2);
}

IGL_INLINE bool igl::collapse_edge(
  const decimate_cost_and_placement_callback & cost_and_placement,
  const decimate_pre_collapse_callback       & pre_collapse,
  const decimate_post_collapse_callback      & post_collapse,
  Eigen::MatrixXd & V,
  Eigen::MatrixXi & F,
  Eigen::MatrixXi & E,
  Eigen::VectorXi & EMAP,
  Eigen::MatrixXi & EF,
  Eigen::MatrixXi & EI,
  igl::min_heap< std::tuple<double,int,int> > & Q,
  Eigen::VectorXi & EQ,
  Eigen::MatrixXd & C)
{
  int e,e1,e2,f1,f2;
  return 
    collapse_edge(
      cost_and_placement,pre_collapse,post_collapse,
      V,F,E,EMAP,EF,EI,Q,EQ,C,e,e1,e2,f1,f2);
}


IGL_INLINE bool igl::collapse_edge(
  const decimate_cost_and_placement_callback & cost_and_placement,
  const decimate_pre_collapse_callback       & pre_collapse,
  const decimate_post_collapse_callback      & post_collapse,
  Eigen::MatrixXd & V,
  Eigen::MatrixXi & F,
  Eigen::MatrixXi & E,
  Eigen::VectorXi & EMAP,
  Eigen::MatrixXi & EF,
  Eigen::MatrixXi & EI,
  igl::min_heap< std::tuple<double,int,int> > & Q,
  Eigen::VectorXi & EQ,
  Eigen::MatrixXd & C,
  int & e,
  int & e1,
  int & e2,
  int & f1,
  int & f2)
{
  using namespace Eigen;
  using namespace igl;
  std::tuple<double,int,int> p;
  while(true)
  {
    // Check if Q is empty
    if(Q.empty())
    {
      // no edges to collapse
      e = -1;
      return false;
    }
    // pop from Q
    p = Q.top();
    if(std::get<0>(p) == std::numeric_limits<double>::infinity())
    {
      e = -1;
      // min cost edge is infinite cost
      return false;
    }
    Q.pop();
    e = std::get<1>(p);
    // Check if matches timestamp
    if(std::get<2>(p) == EQ(e))
    {
      break;
    }
    // must be stale or dead.
    assert(std::get<2>(p)  < EQ(e) || EQ(e) == -1);
    // try again.
  }

  // Why is this computed up here?
  // If we just need original face neighbors of edge, could we gather that more
  // directly than gathering face neighbors of each vertex?
  std::vector<int> /*Nse,*/Nsf,Nsv;
  circulation(e, true,F,EMAP,EF,EI,/*Nse,*/Nsv,Nsf);
  std::vector<int> /*Nde,*/Ndf,Ndv;
  circulation(e, false,F,EMAP,EF,EI,/*Nde,*/Ndv,Ndf);


  bool collapsed = true;
  if(pre_collapse(V,F,E,EMAP,EF,EI,Q,EQ,C,e))
  {
    collapsed = collapse_edge(
      e,C.row(e),
      Nsv,Nsf,Ndv,Ndf,
      V,F,E,EMAP,EF,EI,e1,e2,f1,f2);
  }else
  {
    // Aborted by pre collapse callback
    collapsed = false;
  }
  post_collapse(V,F,E,EMAP,EF,EI,Q,EQ,C,e,e1,e2,f1,f2,collapsed);
  if(collapsed)
  {
    // Erase the two, other collapsed edges by marking their timestamps as -1
    EQ(e1) = -1;
    EQ(e2) = -1;
    // TODO: visits edges multiple times, ~150% more updates than should
    //
    // update local neighbors
    // loop over original face neighbors
    //
    // Can't use previous computed Nse and Nde because those refer to EMAP
    // before it was changed...
    std::vector<int> Nf;
    Nf.reserve( Nsf.size() + Ndf.size() ); // preallocate memory
    Nf.insert( Nf.end(), Nsf.begin(), Nsf.end() );
    Nf.insert( Nf.end(), Ndf.begin(), Ndf.end() );
    // https://stackoverflow.com/a/1041939/148668
    std::sort( Nf.begin(), Nf.end() );
    Nf.erase( std::unique( Nf.begin(), Nf.end() ), Nf.end() );
    // Collect all edges that must be updated
    std::vector<int> Ne;
    Ne.reserve(3*Nf.size());
    for(auto & n : Nf)
    {
      if(F(n,0) != IGL_COLLAPSE_EDGE_NULL ||
          F(n,1) != IGL_COLLAPSE_EDGE_NULL ||
          F(n,2) != IGL_COLLAPSE_EDGE_NULL)
      {
        for(int v = 0;v<3;v++)
        {
          // get edge id
          const int ei = EMAP(v*F.rows()+n);
          Ne.push_back(ei);
        }
      }
    }
    // Only process edge once
    std::sort( Ne.begin(), Ne.end() );
    Ne.erase( std::unique( Ne.begin(), Ne.end() ), Ne.end() );
    for(auto & ei : Ne)
    {
       // compute cost and potential placement
       double cost;
       RowVectorXd place;
       cost_and_placement(ei,V,F,E,EMAP,EF,EI,cost,place);
       // Increment timestamp
       EQ(ei)++;
       // Replace in queue
       Q.emplace(cost,ei,EQ(ei));
       C.row(ei) = place;
    }
  }else
  {
    // reinsert with infinite weight (the provided cost function must **not**
    // have given this un-collapsable edge inf cost already)
    // Increment timestamp
    EQ(e)++;
    // Replace in queue
    Q.emplace(std::numeric_limits<double>::infinity(),e,EQ(e));
  }
  return collapsed;
}