Return the cursor data for a given event.
This method is intended to be overridden by artist subclasses. As an end-user of Matplotlib you will most likely not call this method yourself.
Cursor data can be used by Artists to provide additional context information for a given event. The default implementation just returns None.
Subclasses can override the method and return arbitrary data. However, when doing so, they must ensure that
format_cursor_datacan convert the data to a string representation.
The only current use case is displaying the z-value of an
AxesImagein the status bar of a plot window, while moving the mouse.