Question

I am trying to register a keyboard callback function to a 3D viewer using the Point Cloud Library API.

Todo this I do:

viewer->registerKeyboardCallback(&(RailExtraction::keyboard_callback), (void*)(&gt_data));

But I get the following error message:

note: no known conversion for argument 1 from 'void (RailExtraction< pcl::PointXYZI >::*) 
(const pcl::visualization::KeyboardEvent&, void*)' to 'void (*)(const pcl::visualization::KeyboardEvent&, void*)'

I am trying to understand the error message. I understand what void and void * mean but what does void(*)(...) or void(RailExtraction< pcl::PointXYZI >::*>(...) mean ??

Answer 1

I figured out the problem I am using the wrong version of registerKeyBoardCallBack. I am currently trying to use this signature:

registerKeyboardCallback (void (*callback) (const pcl::visualization::KeyboardEvent&, void*), void* cookie = NULL)

But I should be using this signature:
registerKeyboardCallback (void (T::*callback) (const pcl::visualization::KeyboardEvent&, void*), T& instance, void* cookie = NULL)

This is because my keyboard_callback function is part of a class and therefore I need to specify the instance of the class so that the compiler can figure out which instance the keyboard_callback function to use. Therefore my new call to registerKeyboardCallBack looks like this:

viewer->registerKeyboardCallback(&RailExtraction::keyboard_callback, *this, (void*)&gt_data);