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 .

#include <opencv2/viz.hpp>
#include <iostream>

using namespace cv;
using namespace std;

static 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
    << "./launching_viz"                                                            << 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::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.

    /// 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.

    /// 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.

    /// Access window via its name
viz::Viz3d sameWindow = viz::getWindowByName("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.

    /// 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.

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