How to handle mouse wheel event in OpenCV?

asked 2013-10-22 05:48:59 -0600

younesken
21 ●1 ●1 ●4

Hello,

All is in the title: how to manage an event of mouse wheel on OpenCV ?

Here is my task : I would like to write a program that displays an image in OpenCV window. I click anywhere in the image to define the " upper left" corner of a square that I want to draw, and with the mouse wheel , I draw while controlling the size of his side .

It's that simple , but difficult to find out how. For now , the wheel gave me a zoom, so .. Event exists somewhere but I did find the following event:

CV_EVENT_MOUSEMOVE - When the mouse pointer moves over the specified window CV_EVENT_LBUTTONDOWN - When the left button of the mouse is pressed on the specified window CV_EVENT_RBUTTONDOWN - When the right button of the mouse is pressed on the specified window CV_EVENT_MBUTTONDOWN - When the middle button of the mouse is pressed on the specified window CV_EVENT_LBUTTONUP - When the left button of the mouse is released on the specified window CV_EVENT_RBUTTONUP - When the right button of the mouse is released on the specified window CV_EVENT_MBUTTONUP - When the middle button of the mouse is released on the specified window

hoping to find an answer , Thank you for your help,

answered 2013-10-22 08:21:03 -0600

Pedro Batista

2213 ●5 ●18 ●42 https://lnkd.in/bw9XGH8

updated 2013-10-22 08:23:45 -0600

There is no standard event to handle mousewheel down or up on the onMouse method. You can, however, combine more than one event to create a drag mouse effect, which would complete your task.

Something like

void MouseCB::onMouse( int event, int x, int y, int flags, void* userData)
{
    if (event == CV_EVENT_LBUTTONDOWN)
       {
        int leftcornerX = x;
        int leftcornerY = y;

        while( event != CV_EVENT_LBUTTONUP)
             {
            //method to retrieve your originalframe with no rectangles drawn -> either the original frame is a
            //global variable, or you have to pass it using the void* userData input argument.

                Mat copy = originalframe;
            rectangle(copy, Point(leftcornerX, leftcornerY), Point(x, y), Scalar(255, 0, 0), 1, 8, 0);
            imshow("Frame", copy);
            waitKey(10);


           }
      }

}

This draws a rectangle between the point you first clicked with the left mouse button and the current mouse position, until you lift the mouse button.

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Comments

Thank You Median !

younesken ( 2013-10-24 10:52:37 -0600 )edit

Sorry, but how should the while loop ever terminate? I dont think this can work, as the loop exit condition will never be satisfied

AR0x7E7 ( 2014-05-01 09:17:31 -0600 )edit

The while loop only verifies if user presses mouse button 1, then the while cycle runs until user lifts mouse button

Pedro Batista ( 2014-05-04 18:04:17 -0600 )edit

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