how to use cv::setMouseCallback

Question

I'm trying to use cv::setMouseCallback in my c++ project. I just don't get it. let that I habe a class Stuff how can tell this class you got a frame and run the cv::setMouseCallback on this frame here is an example of what I'm trying to do :

 class Stuff{
 public: 
Stuff();
void setFrame(cv::Mat); 
void mouse (int,int, int, int,void*);
  private :
cv::Mat frame;
int key;
 };

 Stuff::Stuff(){}

 void Stuff::setFrame(cv::Mat framex){
frame = framex;
 }


  int main (){
Stuff  obj;

cv::Mat frame = cv::imread ("examople.jpg");
char* name;
cv::imshow(name,frame);
cv::setMouseCallback(name,obj.mouse,&frame) // I' stop here because that's exactlly what just don't work 
    }

this the error message that get:

   Stuff::mouse : function call missing argument list; use '&Stuff::mouse ' to create a pointer to member 

the real program is too big to put its code here that why I'm trying to simplify the question

Answer 1

you must declare a mouse handler as static inside your class. For instance, I have a dragger with a member mouser, that I want to be called. I declare an helper static void mouser, that cast the void* received and calls the member:

class dragger {

void mouser(int event, int x, int y) {
  current_img = original_img.clone();
  Point P(x, y);
  ...
}
static void mouser(int event, int x, int y, int, void* this_) {
  static_cast<dragger*>(this_)->mouser(event, x, y);
}

and instance in dragger constructor in this way

dragger(string w, Mat m) :
    window_id(w), status(0), original_img(m), /*black(0, 0, 0),*/ K(5, 5)
{
   ...
   setMouseCallback(w, mouser, this);
}

...
}