In OpenCV I want to return the point position like Point(x,y) to the main() function that I click on the image in the mouse callback function . Is there anyway other than setting a global variable?
I don't want to write all the codes inside the on_mouse() function.
Thanks
to expand Safirs idea there, apart from a class or such, you could just pass in the point itself:
void on_mouse( int e, int x, int y, int d, void *ptr )
{
Point*p = (Point*)ptr;
p->x = x;
p->y = y;
}
Point p;
namedWindow("win");
setMouseCallback("win",on_mouse, (void*)(&p) );
// changed value of p will be accessible here
You can avoid using global variables by passing a pointer to your data as a parameter to setMouseCallback(). Agree with @berek, just wanted to show a full example below to avoid confusion about global variables.
using namespace cv;
void on_mouse( int e, int x, int y, int d, void *ptr )
{
Point*p = (Point*)ptr;
p->x = x;
p->y = y;
}
in main() {
Point p;
namedWindow("window");
Mat image = imread("someimage.jpg");
imshow(image);
//pass a pointer to `p` as parameter
setMouseCallback("window",on_mouse, &p );
// p will update with new mouse-click image coordinates
// whenever user clicks on the image window
}
No, this isn't possible, since the on_mouse() is a callback function. Here is the opencv documentation of it.
So, "global" variables are the only way to solve this problem. Alternatively, if you're looking for a nicer solution, you can create a wrapper class in which you have the namedWindow and the MouseCallback and a private member variable, which is manipulated when mouse callback function is called.
cv::Point in this case) as the parameter to on_mouse(). No need for the wrapper class. See the answer by @berak.Point still must be "global", in the scope of main function. For simple testing programmes, I'd go with @berak solution. However, if your application gets slightly bigger, I think it's better to create a wrapper class.