Using shared_ptr/cv::Ptr as userdata in callbacks

edit

I am tracking mouse clicks inside an OpenCV display window by using:

void on_buttonClick(int event, int x, int y, int flags, void* userdata) 
{
    // Callback function received
}

void main() {
    cv::setMouseCallback(win_name, on_buttonClick, (void*) fun_ptr);
}

The last parameter fun_ptr is returned as part of user_data in the callback. And this is fine as long as I want to use function pointers for userdata.

But now I need to instead pass something equivalent of std::shared_ptr<CustomClass> as part of user_data. The reason I want to pass a shared_ptr is so that the object automatically get destroyed whenever the context of display window is refreshed.

I tried using two mechanisms:
- std::shared_ptr
- cv::Ptr (Similar in functionality to std::shared_ptr)

Example code below:

class CustomClass {
    int x;
    int y;
}

int main() {
    cv::Ptr<CustomClass> x(new CustomClass());
    cv::setMouseCallback(win_name, on_buttonClick, (void*) x);
}

But the shared_ptr would lose it's purpose as soon as I cast it to (void*). Is there a way to resolve this in OpenCV (afaik, using the typical new, delete would not be good since the time to delete cannot be ascertained).