Added many Vertex-Edge adjacency helper functions. Needed for simpler 1-manifold edge mesh processing

Degree, Edge-Collapse, Manifold testing, Detach/Append

vcg/simplex/edge/topology.h

@@ -32,7 +32,7 @@ namespace vcg {
 namespace edge {
 /** \addtogroup edge */
 /*@{*/template <class EdgeType>
-inline bool IsEdgeManifold( EdgeType const & e, const int j )
+inline bool IsEdgeManifoldFF( EdgeType const & e, const int j )
 {
   assert(e.cFFp(j) != 0); // never try to use this on uncomputed topology
 
@@ -80,7 +80,144 @@ void VEStarVE(const typename EdgeType::VertexType* vp, std::vector<EdgeType *> &
       }
 }
 
+/// Completely detach an edge from the VE adjacency. Useful before deleting it 
+template <class EdgeType>
+void VEDetach(EdgeType & e)
+{
+  VEDetach(e,0);
+  VEDetach(e,1);
+}
+
+/// It detaches the given edge e from the VE adjacency on the vertex z
+/// It is used for careful hand stictching of topologies.
+template <class EdgeType>
+void VEDetach(EdgeType & e, int z)
+{
+  typename EdgeType::VertexType *vz = e.V(z); // the vertex from which the edge must be detached.
+  
+  if(vz->VEp()==&e )  //if it is the first edge in the VE chain it detaches it from the begin
+    {
+        int fz = vz->VEi();
+        vz->VEp() = e.VEp(fz);
+        vz->VEi() = e.VEi(fz);
+    }
+    else  // scan the list of edges to find the current edge e to be detached
+    {
+    VEIterator<EdgeType> x(vz->VEp(),vz->VEi());
+    VEIterator<EdgeType> y;
+
+        for(;;)
+        {
+            y = x;
+            ++x;
+            assert(x.e!=0);
+            if(x.e==&e) // found!
+            {
+                y.e->VEp(y.z) = e.VEp(z);
+                y.e->VEi(y.z) = e.VEi(z);
+                break;
+            }
+        }
+    }
+}
+
+/// Append an edge in the VE list of vertex e->V(z)
+template <class EdgeType>
+void VEAppend(EdgeType* & e, int z)
+{
+    typename EdgeType::VertexType *v = e->V(z);
+    if (v->VEp()!=0)
+    {
+        EdgeType *e0=v->VEp();
+        int       z0=v->VEi();
+        //append
+        e->VEp(z)=e0;
+        e->VEi(z)=z0;
+    }
+    v->VEp()=e;
+    v->VEi()=z;
+}
+
+
+/*! Perform a simple edge collapse using VE adjacency
+ * 
+ * It collapses the two edges incidnent on the indicated vertex so that the passed edge survives, 
+ * the indicated vertex is deleted, and the edge ajacent to e0 along z is deleted too.
+ * It assumes that the edge mesh is 1-Manifold.
+ * If the indicated vertex <vd> is boundary or non manifold the function do nothing.
+ * 
+ *    v0     vd       v1
+ * ---O-------O-------O---
+ *   z0   e0  z   e1  z1 
+ * 
+ *    v0              v1
+ * ---O---------------O---
+ *           e0
+ * 
+ * 
+ */
+template <class MeshType>
+void VEEdgeCollapse(MeshType &poly, typename MeshType::EdgeType *e0, const int z)
+{
+  typedef typename MeshType::EdgeType EdgeType;
+  typedef typename MeshType::VertexType VertexType;
+  
+  VertexType *vd = e0->V(z);
+  
+  std::vector<EdgeType *> starVecEp;
+  edge::VEStarVE(vd,starVecEp);   
+  if(starVecEp.size()!=2) return;
+  
+  EdgeType *e1=0; // this edge will be deleted
+  if( starVecEp[0] == e0 ) e1 = starVecEp[1];
+  if( starVecEp[1] == e0 ) e1 = starVecEp[0];
+  assert(e1 && (e1!=e0) );
+
+  int z0 = (z+1)%2;
+  int z1 = -1;
+  if(e1->V(0) == vd) z1=1;
+  if(e1->V(1) == vd) z1=0;
+  assert(z1!=-1);
+  
+  VertexType *v1 = e1->V(z1); 
+      
+  edge::VEDetach(*e1);
+  edge::VEDetach(*e0,z);
+  e0->V(z) = v1;
+  edge::VEAppend(e0, z);
+  tri::Allocator<MeshType>::DeleteEdge(poly,*e1);
+  tri::Allocator<MeshType>::DeleteVertex(poly,*vd);
+}
+
+template <class MeshType>
+void VEEdgeCollapse(MeshType &poly, typename MeshType::VertexType *v)
+{
+  VEEdgeCollapse(poly,v->VEp(),v->VEi());
+}
+
+
+
+/*! Returns the number of incident edges over a vertex vp; Using the VE adjacency.  
+ * 
+ * It just follows the chain of incident edges of the VE adjacency.
+*/
+
+template <class EdgeType>
+int VEDegree(const typename EdgeType::VertexType* vp)
+{
+  int cnt=0;
+  edge::VEIterator<EdgeType> vei(vp);
+  while(!vei.End()) 
+  {
+    ++cnt;
+    ++vei;
+  }    
+  return cnt;
+}
+
+
 } // end namespace edge
 } // end namespace vcg
 
+
 #endif