ovis: allow explicitly releasing window

Author: paroj

modules/ovis/include/opencv2/ovis.hpp

@@ -87,6 +87,13 @@ class CV_EXPORTS_W WindowScene {
 public:
     virtual ~WindowScene();
 
+    /**
+     * closes window and releases the scene
+     *
+     * The method is automatically called by the destructor
+     */
+    CV_WRAP virtual void release() = 0;
+
     /**
      * set window background to custom image
      * @param image

modules/ovis/src/ovis.cpp

@@ -392,8 +392,13 @@ class WindowSceneImpl : public WindowScene
         rWin->addViewport(cam);
     }
 
-    ~WindowSceneImpl()
+    ~WindowSceneImpl() { release(); }
+
+    void release() CV_OVERRIDE
     {
+        if(!sceneMgr)
+            return;
+
         if (flags & SCENE_SEPARATE)
         {
             TextureManager& texMgr =  TextureManager::getSingleton();
@@ -433,6 +438,8 @@ class WindowSceneImpl : public WindowScene
         {
             _app->destroyWindow(title);
         }
+
+        sceneMgr = NULL;
     }
 
     void setBackground(InputArray image) CV_OVERRIDE