add observer pattern to all decimaters

closes #2366

git-svn-id: http://www.openmesh.org/svnrepo/OpenMesh/trunk@1197 fdac6126-5c0c-442c-9429-916003d36597

src/OpenMesh/Tools/Decimater/MixedDecimaterT.cc

@@ -92,6 +92,11 @@ size_t MixedDecimaterT<Mesh>::decimate(const size_t _n_collapses, const float _m
   size_t r_collapses = 0;
   if (_mc_factor > 0.0)
     r_collapses = McDecimaterT<Mesh>::decimate(n_collapses_mc);
+
+  // returns, if the previous steps were aborted by the observer
+  if (this->observer() && this->observer()->abort())
+      return r_collapses;
+
   if (_mc_factor < 1.0)
     r_collapses += DecimaterT<Mesh>::decimate(n_collapses_inc);
 
@@ -147,6 +152,10 @@ size_t MixedDecimaterT<Mesh>::decimate_to_faces(const size_t  _n_vertices,const
   //Update the mesh::n_vertices function, otherwise the next Decimater function will delete too much
   this->mesh().garbage_collection();
 
+  // returns, if the previous steps were aborted by the observer
+  if (this->observer() && this->observer()->abort())
+      return r_collapses;
+
   //reduce the rest of the mesh
   if (_mc_factor < 1.0) {
     r_collapses += DecimaterT<Mesh>::decimate_to_faces(_n_vertices,_n_faces);