opencv/doc/tutorials/viz/launching_viz/launching_viz.markdown

Launching Viz

Goal

In this tutorial you will learn how to

• Open a visualization window.
• Access a window by its name.
• Start event loop.
• Start event loop for a given amount of time.

Code

You can download the code from here . @code{.cpp} #include <opencv2/viz.hpp> #include

using namespace cv; using namespace std;

/*

• @function main */ int main() { /// 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::getWindowByName("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; } @endcode Explanation

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Here is the general structure of the program:

• Create a window. @code{.cpp} /// Create a window viz::Viz3d myWindow("Viz Demo"); @endcode

• Start event loop. This event loop will run until user terminates it by pressing e, E, q, Q. @code{.cpp} /// Start event loop myWindow.spin(); @endcode

• Access same window via its name. Since windows are implicitly shared, sameWindow is exactly the same with myWindow. If the name does not exist, a new window is created. @code{.cpp} /// Access window via its name viz::Viz3d sameWindow = viz::get("Viz Demo"); @endcode

• Start a controlled event loop. Once it starts, wasStopped is set to false. Inside the while loop, in each iteration, spinOnce is called to prevent event loop from completely stopping. Inside the while loop, user can execute other statements including those which interact with the window. @code{.cpp} /// 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); } @endcode Results

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Here is the result of the program.