OpenCV: How to get data in main() from MouseCallback function? - c++

Question

I am printing the pixel location on mouse left button click like this:
void CallBackFunc(int event, int x, int y, int flags, void* values)
{
if ( event == EVENT_LBUTTONDOWN )
{
cout << "Left button clicked at (" << x << ", " << y << ")" << endl;
}
}
int main(int argc, char** argv)
{
Mat img = imread("yava.bmp");
namedWindow(" Window", 1);
setMouseCallback(" Window", CallBackFunc, NULL);
position(x,y); //to be implemneted
imshow(" Window", img);
waitKey(0);
return 0;
}
Now I want to get this location, i.e x and y from CallBackFunc to back in main(), which will be processed by my position(x,y) function.
How do i do this?

Answer 1

First of all, read the documentation on setMouseCallback, etc.
This is what I would do (this is the typical example) without changing your code too much:
vector<Point> points; // Store the points as global variables
void CallBackFunc(int event, int x, int y, int flags, void* values)
{
if ( event == EVENT_LBUTTONDOWN )
{
points.push_back(Point(x,y));
}
}
int main(int argc, char** argv)
{
Mat img = imread("yava.bmp");
namedWindow(" Window", 1);
setMouseCallback(" Window", CallBackFunc, NULL); // Add the pointer to the callback
while (1)
{
//Draw your points
for (int i=0;i<points.size();i++) circle(img,points.at(i),3,CV_RGB(255,0,0),-1);
imshow(" Window", img);
waitKey(10);// -> This is when your callback is called everytime you click
}
return 0;
}
For a better solution, consider avoiding global variables and use a class for storing those "clicks".