fix crucial bug in get method, hide add and remove methods from user

modules/viz/include/opencv2/viz.hpp

@@ -101,8 +101,6 @@ namespace cv
             static void release();
             
             Viz3d get(const String &window_name);
-            void add(Viz3d window);
-            void remove(const String &window_name);
             
             //! window names automatically have Viz - prefix even though not provided by the users
             static void generateWindowName(const String &window_name, String &output);
@@ -111,9 +109,14 @@ namespace cv
             VizAccessor(); // Singleton
             ~VizAccessor();
             
+            void add(Viz3d window);
+            void remove(const String &window_name);
+            
             static VizAccessor * instance_;
             static bool is_instantiated_;
             static VizMap viz_map_;
+            
+            friend class Viz3d;
         };
     } /* namespace viz */
 } /* namespace cv */

modules/viz/src/viz.cpp

@@ -126,7 +126,7 @@ cv::viz::Viz3d cv::viz::VizAccessor::get(const String & window_name)
     VizMap::iterator vm_itr = viz_map_.find(name);
     bool exists = vm_itr != viz_map_.end();
     if (exists) return vm_itr->second;
-    else return viz_map_.insert(VizPair(window_name, Viz3d(window_name))).first->second;
+    else return Viz3d(window_name);
 }
 
 void cv::viz::VizAccessor::add(Viz3d window)
@@ -135,7 +135,7 @@ void cv::viz::VizAccessor::add(Viz3d window)
     VizMap::iterator vm_itr = viz_map_.find(window_name);
     bool exists = vm_itr != viz_map_.end();
     if (exists) return ;
-    viz_map_.insert(std::pair<String,Viz3d>(window_name, window));
+    viz_map_.insert(VizPair(window_name, window));
 }
 
 void cv::viz::VizAccessor::remove(const String &window_name)