Learning OpenCV, 2nd Edition

g_capture >> frame;

if( frame.empty() ) break;

cv::imshow( "Example", frame);

}

if( cv::waitKey(10)==27 ) break;

}

return 0;

}

You can see that this will turn on and off just like a light switch. In our example, whenever the trackbar

“switch” is set to 0, the callback executes the function switch_off_function(), and whenever it is

switched on, the switch_on_function() is called.

Working with the Qt Backend

As we described earlier, the trend in the development of the HighGUI portion of OpenCV is to rely

increasingly on a separate library for GUI functionality. This makes sense, as it is not OpenCV’s purpose to

reinvent that particular wheel, and there are plenty of great GUI toolkits out there that are well maintained

and which evolve and adapt to the changing times under their own development teams.

From the perspective of the OpenCV library, there is a great advantage to using such an outside toolkit.

Functionality is gained, and at the same time, development time is reduced (which would otherwise be

taken away from the core goal of the library).

However, an important clarification is that using HighGUI with the Qt backend is not the same as using Qt

directly (we will explore this possibility briefly at the end of this chapter). The HighGUI interface is still

the HighGUI interface; it simply uses Qt behind the ...