launching viz tutorial

samples/cpp/tutorial_code/viz/launching_viz.cpp

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+#include <opencv2/viz.hpp>
+#include <iostream>
+
+using namespace cv;
+using namespace std;
+
+void help()
+{
+    cout
+    << "--------------------------------------------------------------------------" << endl
+    << "This program shows how to launch a 3D visualization window. You can stop event loop to continue executing. "
+    << "You can access the same window via its name. You can run event loop for a given period of time. " << endl
+    << "Usage:"                                                                     << endl
+    << "./window_demo"                                                              << endl
+    << endl;
+}
+
+int main()
+{
+    help();
+    /// Create a window
+    viz::Viz3d myWindow("Viz Demo");
+    
+    /// Start event loop
+    myWindow.spin();
+    
+    /// Event loop is over when pressed q, Q, e, E
+    cout << "First event loop is over" << endl;
+    
+    /// Access window via its name
+    viz::Viz3d sameWindow = viz::get("Viz Demo");
+    
+    /// Start event loop
+    sameWindow.spin();
+    
+    /// Event loop is over when pressed q, Q, e, E
+    cout << "Second event loop is over" << endl;
+    
+    /// Event loop is over when pressed q, Q, e, E
+    /// Start event loop once for 1 millisecond
+    sameWindow.spinOnce(1, true);
+    while(!sameWindow.wasStopped())
+    {
+	/// Interact with window
+	
+	/// Event loop for 1 millisecond
+	sameWindow.spinOnce(1, true);
+    }
+    
+    /// Once more event loop is stopped
+    cout << "Last event loop is over" << endl;
+    return 0;
+}