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

Launching Viz {#tutorial_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 ](samples/cpp/tutorial_code/viz/launching_viz.cpp).
@code{.cpp}
#include <opencv2/viz.hpp>
#include <iostream>

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
-----------

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
-------

Here is the result of the program.

![image](images/window_demo.png)