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If you take a look at the most recent documentation you can see that you can supply a user defined pointer to an object, defined as a void pointer.

If it handles a single value, you can pass that around using its pointer. If you want to pass multiple data, then you will need to construct a struct and pass all the data with a pointer to the struct. An example is below:

int ref = 1;
createTrackbar("Name","Window",0, 1, myFunc, &ref);

void myFunc(int value, void *userdata)
{
    // Retrieve the data
    // Needs explicit type declaration
    int val = *((int*)&userdata);
}

If you take a look at the most recent documentation you can see that you can supply a user defined pointer to an object, defined as a void pointer.

If it handles a single value, you can pass that around using its pointer. If you want to pass multiple data, then you will need to construct a struct and pass all the data with a pointer to the struct. An example is below:

int ref = 1;
createTrackbar("Name","Window",0, 1, myFunc, &ref);

void myFunc(int value, void *userdata)
{
    // Retrieve the data
    // Needs explicit type declaration
    int val = *((int*)&userdata);
}

cv:createTrackbar("Label", "Window" &variable, MAX_VAL, &MyClass::func, this);

void MyClass:func(int newValue, void * object) {
    MyClass* myClass = (MyClass*) object;
    // ...do stuff.
}

If you take a look at the most recent documentation you can see that you can supply a user defined pointer to an object, defined as a void pointer.

If it handles a single value, you can pass that around using its pointer. If you want to pass multiple data, then you will need to construct a struct and pass all the data with a pointer to the struct. An example is below:

int ref = 1;
createTrackbar("Name","Window",0, 1, myFunc, &ref);

void myFunc(int value, void *userdata)
{
    // Retrieve the data
    // Needs explicit type declaration
    int val = *((int*)&userdata);
}

And more general you can do it as below

cv:createTrackbar("Label", "Window" &variable, MAX_VAL, &MyClass::func, this);

void MyClass:func(int newValue, void * object) {
    MyClass* myClass = (MyClass*) object;
    // ...do stuff.
}

struct myData{
   int variable1 = 0;
   int variable2 = 0;
}

void myFunc(int value, void *userdata)
{
     // Retrieve the data
     // Needs explicit type declaration
     myData pushed_data = *((myData*)&userdata);
}

myData test;
test.variable1 = 5;
test.variable2 = 17;

createTrackbar("Name","Window",0, 1, myFunc, &test);

If you take a look at the most recent documentation you can see that you can supply a user defined pointer to an object, defined as a void pointer.

If it handles a single value, you can pass that around using its pointer. If you want to pass multiple data, then you will need to construct a struct and pass all the data with a pointer to the struct. An example is below:

int ref = 1;
createTrackbar("Name","Window",0, 1, myFunc, &ref);

void myFunc(int value, void *userdata)
{
    // Retrieve the data
    // Needs explicit type declaration
    int val = *((int*)&userdata);
}

And more general you can do it as below

cv:createTrackbar("Label", "Window" &variable, MAX_VAL, &MyClass::func, this);

static void MyClass:func(int newValue, void * object) {
    MyClass* myClass = (MyClass*) object;
    // ...do stuff.
}

To add multiple variables you will need to create a struct and provide a pointer to that

struct myData{
   int variable1 = 0;
   int variable2 = 0;
}

void myFunc(int value, void *userdata)
{
     // Retrieve the data
     // Needs explicit type declaration
     myData pushed_data = *((myData*)&userdata);
}

myData test;
test.variable1 = 5;
test.variable2 = 17;

createTrackbar("Name","Window",0, 1, myFunc, &test);