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 BriskMatching in which I have created a member function named mouseCallback with the correct parameters that OpenCV requires (please see the code snippet below). ``` **Briskmatching.h** class BriskMatching { public: BriskMatching(); ~BriskMatching(); public: void mouseCallback(int event, int x, int y, int flags, void *param); }; ``` This is all fine, however my problem arises when I try to set this function as the designated mouse callback function through OpenCV's `cv::setMouseCallback` function. In my main function, I create an instance of the BriskMatching class called briskMatcher then when it comes time to set the mouse callback I attempt to do it like so... ``` cv::setMouseCallback("Matches", BriskMatching::mouseCallback, &matchesImg); ``` Unfortunately, this throws an error. ``` Error 3 error C3867: 'BriskM…

Accepted Answer

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);
}
```

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

Solution

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