+ for(iter=duck_map.begin();iter!=duck_map.end();++iter) if (iter->second->get_type()&Duck::TYPE_POSITION) ret.push_back(iter->second);
+ for(iter=duck_map.begin();iter!=duck_map.end();++iter) if (iter->second->get_type()&Duck::TYPE_VERTEX ) ret.push_back(iter->second);
+ for(iter=duck_map.begin();iter!=duck_map.end();++iter) if (iter->second->get_type()&Duck::TYPE_TANGENT ) ret.push_back(iter->second);