LOD_EdgeCollapser.cpp

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/*
 * $Id: LOD_EdgeCollapser.cpp 35147 2011-02-25 10:47:28Z jesterking $
 * ***** BEGIN GPL LICENSE BLOCK *****
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program 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 program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * The Original Code is Copyright (C) 2001-2002 by NaN Holding BV.
 * All rights reserved.
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 * The Original Code is: all of this file.
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 * Contributor(s): none yet.
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 * ***** END GPL LICENSE BLOCK *****
 */

#include "LOD_EdgeCollapser.h"

#include "LOD_ManMesh2.h"
#include "CTR_TaggedSetOps.h"
#include <algorithm>
#include <functional>


using namespace std;


        LOD_EdgeCollapser * 
LOD_EdgeCollapser::
New(
){
        return new LOD_EdgeCollapser();
}


        bool
LOD_EdgeCollapser::
TJunctionTest(
        LOD_ManMesh2 &mesh,
        vector<LOD_EdgeInd> &e_v0v1,
        LOD_EdgeInd collapse_edge
){

        // we need to copy the egdes in e_v0v1 from the mesh
        // into a new buffer -> we are going to modify them

        int original_size = e_v0v1.size();
        if (original_size == 0) return true;

        vector<LOD_Edge> &edge_set = mesh.EdgeSet();

        LOD_VertexInd c_v0 = edge_set[collapse_edge].m_verts[0];
        LOD_VertexInd c_v1 = edge_set[collapse_edge].m_verts[1];

        vector<LOD_Edge> temp_edges;
        temp_edges.reserve(e_v0v1.size());

        vector<LOD_EdgeInd>::iterator edge_it = e_v0v1.begin();
        vector<LOD_EdgeInd>::const_iterator edge_end = e_v0v1.end();

        for (;edge_it != edge_end; ++edge_it) {
                temp_edges.push_back(edge_set[*edge_it]);
        }

        // in the copied edges replace all instances of c_v0 with c_v1

        vector<LOD_Edge>::iterator e_it = temp_edges.begin();
        vector<LOD_Edge>::const_iterator e_it_end = temp_edges.end();
                
        for (; e_it != e_it_end; ++e_it) {

                if (e_it->m_verts[0] == c_v0) {
                        e_it->m_verts[0] = c_v1;
                }
                if (e_it->m_verts[1] == c_v0) {
                        e_it->m_verts[1] = c_v1;
                }

                // normalize the edge
                if (int(e_it->m_verts[0]) > int(e_it->m_verts[1])) {
                        LOD_EdgeInd temp = e_it->m_verts[0];
                        e_it->m_verts[0] = e_it->m_verts[1];
                        e_it->m_verts[1] = temp;
                }
        }

        // sort the edges using the edge less functional 

        sort(temp_edges.begin(),temp_edges.end(),LOD_EdgeCollapser::less());
        // count the unique edges.

        e_it = temp_edges.begin();
        e_it_end = temp_edges.end();
        
        int coincedent_edges = 0;

        vector<LOD_Edge>::const_iterator last_edge = e_it;
        ++e_it;
                
        for (; e_it != e_it_end; ++e_it) {
        
                if ((e_it->m_verts[0] == last_edge->m_verts[0]) &&
                        (e_it->m_verts[1] == last_edge->m_verts[1])
                ) {
                        ++coincedent_edges;
                }
                last_edge = e_it;
        }

        // now if the collapse edge is a boundary edges 
        // then we are alloved at most one coincedent edge

        // otherwise at most 2 coincedent edges

        if (edge_set[collapse_edge].BoundaryEdge()) {
                return (coincedent_edges > 1);
        } else {
                return (coincedent_edges > 2);
        }


}


        
        bool
LOD_EdgeCollapser::
CollapseEdge(
        LOD_EdgeInd ei,
        LOD_ManMesh2 &mesh,
        vector<LOD_EdgeInd> & degenerate_edges,
        vector<LOD_FaceInd> & degenerate_faces,
        vector<LOD_VertexInd> & degenerate_vertices,
        vector<LOD_EdgeInd> & new_edges,
        vector<LOD_FaceInd> & update_faces,
        vector<LOD_VertexInd> & update_vertices
){

        vector<LOD_Vertex>      &verts = mesh.VertexSet();
        vector<LOD_Edge>        &edges = mesh.EdgeSet();
        vector<LOD_TriFace> &faces = mesh.FaceSet();

        // shouldn't do this (use mesh interface instead!)
        LOD_VertexInd v0_ind = edges[ei].m_verts[0];
        LOD_VertexInd v1_ind = edges[ei].m_verts[1];
#if 0
        LOD_Vertex &v0 = verts[v0_ind];
        LOD_Vertex &v1 = verts[v1_ind];
#endif
        vector<vector<LOD_EdgeInd> > e_v01(2);
        e_v01[0].reserve(32);
        e_v01[1].reserve(32);
        
        mesh.VertexEdges(v0_ind,e_v01[0]);
        mesh.VertexEdges(v1_ind,e_v01[1]);


        // compute the union of e_v0 and e_v1 -> this is the degenerate edges of the collapse
        // we remove old edges and replace edges inside the collapse zone with new ones 

        CTR_TaggedSetOps<LOD_EdgeInd,LOD_Edge>::Union(e_v01,edges,degenerate_edges);

        vector< vector<LOD_FaceInd> > p_v01(2);
        p_v01[0].reserve(32);
        p_v01[1].reserve(32);

        mesh.VertexFaces(v0_ind,p_v01[0]);
        mesh.VertexFaces(v1_ind,p_v01[1]);

        // compute the union of p_v0 anf p_v1
        vector<LOD_FaceInd> p_v0v1;
        p_v0v1.reserve(32);

        CTR_TaggedSetOps<LOD_FaceInd,LOD_TriFace>::Union(p_v01,faces,p_v0v1);

        // compute the union of all the edges in p_v0v1 this is the collapse zone

        vector<vector<LOD_EdgeInd> > e_input_vectors(p_v0v1.size());

        vector<LOD_FaceInd>::iterator p_v0v1_end = p_v0v1.end();
        vector<LOD_FaceInd>::iterator p_v0v1_start = p_v0v1.begin();

        vector<vector<LOD_FaceInd> >::iterator vector_insert_it = e_input_vectors.begin();
        
        for (;p_v0v1_start != p_v0v1_end; ++p_v0v1_start , ++vector_insert_it) {
                mesh.FaceEdges(*p_v0v1_start,*vector_insert_it);
        }

        vector<LOD_EdgeInd> collapse_zone;
        collapse_zone.reserve(32);

        CTR_TaggedSetOps<LOD_EdgeInd,LOD_Edge>::Union(e_input_vectors,edges,collapse_zone);

        // compute the ring edges = collpase_zone - e_v0v1

        vector<LOD_EdgeInd> edge_ring;
        edge_ring.reserve(32);

        CTR_TaggedSetOps<LOD_EdgeInd,LOD_Edge>::Difference(collapse_zone,degenerate_edges,edges,edge_ring);

        // T Junction test
        // At this point we check to see if any of the polygons
        // in p_v0v1 are coninceddent - this leads
        // to errors later on if we try and insert a polygon
        // into the mesh to an edge which already has 2 polygons.

        // not that t junctions occur naturally from edge collapses
        // and are not just the result of coincedent polygons
        // for example consider collapsing an edge that forms part
        // of a triangular bottle neck.

        // Really we need to make sure that we don't create t-junctions.

        // I think that a sufficient test is to check the number of
        // coincedent edge pairs after a collapse. If it is more than 2
        // then collapsing the edge may result in an undeleted edge 
        // sharing more than 2 polygons. This test probably is too 
        // restictive though.
        
        // To perform this test we need to make a copy of the edges
        // in e_v0v1. We then apply the contraction to these edge
        // copies. Sort them using a function that places coincedent 
        // edges next to each other. And then count the number
        // of coincedent pairs. 

        // Of course we have to do this test before we change any of the
        // mesh -> so we can back out safely.

        if (TJunctionTest(mesh,degenerate_edges,ei)) return false; 

        // Compute the set of possibly degenerate vertices
        // this is the union of all the vertices of polygons
        // of v0 and v1

        vector<LOD_FaceInd>::iterator face_it = p_v0v1.begin();
        vector<LOD_FaceInd>::const_iterator face_end = p_v0v1.end();


        vector<vector<LOD_VertexInd> > p_v0v1_vertices(p_v0v1.size());
        
        for (int i = 0; face_it != face_end; ++face_it, ++i) {
                mesh.FaceVertices(*face_it,p_v0v1_vertices[i]);
        }
        
        vector<LOD_VertexInd> vertex_ring;
        vertex_ring.reserve(32);

        CTR_TaggedSetOps<LOD_VertexInd,LOD_Vertex>::Union(p_v0v1_vertices,verts,vertex_ring);

        // remove all the internal edges e_v0v1 from the mesh.
        // for each edge remove the egde from it's vertices edge lists.

        vector<LOD_EdgeInd>::iterator edge_it = degenerate_edges.begin();
        vector<LOD_EdgeInd>::const_iterator edge_end = degenerate_edges.end();

        for (; !(edge_it == edge_end); ++edge_it) {
                        
                LOD_EdgeInd ed = (*edge_it);
                LOD_Edge & edge = edges[ed];//*edge_it];
        
                verts[edge.m_verts[0]].RemoveEdge(ed);
                verts[edge.m_verts[1]].RemoveEdge(ed);
        }

        // we postpone deletion of the internal edges untill the end
        // this is because deleting edges invalidates all of the 
        // EdgeInd vectors above.

                
        // now untie all the polygons in p_v0v1 from the edge ring

        // select all polygons in p_v0v1

        face_it = p_v0v1.begin();
        face_end = p_v0v1.end();

        for (;face_it != face_end; ++face_it) {
                faces[*face_it].SetSelectTag(true);
        }

        edge_it = edge_ring.begin();
        edge_end = edge_ring.end();

        for (;edge_it != edge_end; ++edge_it) {
                LOD_Edge & edge = edges[*edge_it];

                // presumably all edges in edge_ring point to at least
                // one polygon from p_v0v1
                
                if (!edge.m_faces[0].IsEmpty() && faces[edge.m_faces[0]].SelectTag()) {
                        edge.m_faces[0].Invalidate();
                }

                if (!edge.m_faces[1].IsEmpty() && faces[edge.m_faces[1]].SelectTag()) {
                        edge.m_faces[1].Invalidate();
                }
        }
        
        // deselect the faces

        face_it = p_v0v1.begin();
        face_end = p_v0v1.end();

        for (;face_it != face_end; ++face_it) {
                faces[*face_it].SetSelectTag(false);
        }

        // perform the edge collapse

        // iterate through the polygons of p_v0 and replace the vertex
        // index v0 with v1

        face_it = p_v01[0].begin();
        face_end = p_v01[0].end();
        
        for (;face_it != face_end; ++face_it) {
                faces[*face_it].SwapVertex(v0_ind,v1_ind);
        }

        face_it = p_v0v1.begin();
        face_end = p_v0v1.end();
        
        for (;face_it != face_end; ++face_it) {
                if (faces[*face_it].Degenerate()) {
                        degenerate_faces.push_back(*face_it);
                } else {
                        update_faces.push_back(*face_it);
                }
        }
        
        // Add all the non-degenerate faces back into the 
        // mesh. Get a record of the new edges created in
        // this process.

        face_it = update_faces.begin();
        face_end = update_faces.end();

        for (;face_it != face_end; ++face_it) {
                mesh.ConnectTriangle(*face_it,new_edges);
        }

        // degenerate ring primitives

        // we now need to examine each of the edges on the ring
        // and work out if they are degenerate - if so we attempt
        // to delete them -> add them to the other edges to delete
        // in e_v0v1

        edge_it = edge_ring.begin();
        edge_end = edge_ring.end();

        for (;edge_it != edge_end; ++edge_it) {
                if (edges[*edge_it].Degenerate()) {
                        degenerate_edges.push_back(*edge_it);
                }
        }

        // do the same for the ring vertices.
                
        vector<LOD_VertexInd>::iterator vertex_it = vertex_ring.begin();
        vector<LOD_VertexInd>::const_iterator vertex_end = vertex_ring.end();

        for (;vertex_it != vertex_end; ++vertex_it) {
                if (verts[*vertex_it].Degenerate()) {
                        degenerate_vertices.push_back(*vertex_it);
                } else {
                        update_vertices.push_back(*vertex_it);
                }
        }

        // we now know all the degenerate primitives
        // and the new primitives we have inserted into the mesh

        // We now delete the mesh primitives, mesh.DeleteXXXXXX() methods
        // assume that the index vectors are sorted into descending order.
        // we do that now.

        sort(degenerate_edges.begin(),degenerate_edges.end(),LOD_EdgeInd::greater());
        sort(degenerate_faces.begin(),degenerate_faces.end(),LOD_FaceInd::greater());
        sort(degenerate_vertices.begin(),degenerate_vertices.end(),LOD_VertexInd::greater());

        
        return true;
        
}

LOD_EdgeCollapser::
LOD_EdgeCollapser(
){
        // nothing to do
}