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.. _launching_viz:
Launching Viz
*************
Goal
====
In this tutorial you will learn how to
.. container:: enumeratevisibleitemswithsquare
* 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 :download:`here <../../../../samples/cpp/tutorial_code/viz/launching_viz.cpp>`.
.. code-block:: cpp
#include <opencv2/viz/vizcore.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;
}
Explanation
===========
Here is the general structure of the program:
* Create a window.
.. code-block:: cpp
/// Create a window
viz::Viz3d myWindow("Viz Demo");
* Start event loop. This event loop will run until user terminates it by pressing **e**, **E**, **q**, **Q**.
.. code-block:: cpp
/// Start event loop
myWindow.spin();
* 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-block:: cpp
/// Access window via its name
viz::Viz3d sameWindow = viz::get("Viz Demo");
* 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-block:: 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);
}
Results
=======
Here is the result of the program.
.. image:: images/window_demo.png
:alt: Launching Viz
:align: center
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