Having trouble creating a class based implementation of OpenCV's mouseCallback function

Question

As the title suggest, I\'m having some trouble implementing OpenCV\'s mouseCallback function in a class based C++ structure. Allow me to explain. I have defined a class called B

Answer 1

I was using this method too, however I realized that the static helper class was quite rigid and type and method bound.

Just for further reference I've defined a templated free function that looks like:

template<typename TClass, void (TClass::*MouseClickType)(int, int, int, int)>
void FreeOnMouseCallback(int event, int x, int y, int flags, void* ptr)
{
    auto* mcPtr = static_cast<TClass*>(ptr);
    if(mcPtr != NULL)
    {
      (mcPtr->*MouseClickType)(event, x, y, flags);
    }
}

And I can now call arbitrary functions (matching the signature, but not the name) inside classes with

 cv::setMouseCallback( WindowName, FreeOnMouseCallback<Calibrator, &Calibrator::OnMouseCallback>, this );

It might be extended if the void* ptr is also required, but I've omitted it here.

Answer 2

Since a member function takes a this pointer, you will need a static wrapper function. Typically, you use the param parameter to be the address of the object that the member function belongs to, so you end up with something like this:

...
static void mouseCallback(int event, int x, int y, int flags, void *param);

void doMouseCallback(int event, int x, int y, int flags);

And then inside the mouseCallback:

void BriskMatching::mouseCallback(int event, int x, int y, int flags, void *param)
{
    BriskMatching *self = static_cast<BriskMatching*>(param);
    self->doMouseCallback(event, x, y, flags);
}