Need a per-subscription callback context parameter

[Jussi Pakkanen]

Suppose you have an application with an unspecified number of windows, which need e.g. drag gestures. Currently you can only have one function (existing at compile time) that as a callback. Thus the application can not tell which window should receive which gesture unless they maintain their own window id -> window object mapping table. This is cumbersome and extra work for developers.

An alternative is that the user can specify a per-subscription context (void pointer) that they can then extract from the event object, just like the callback parameters in Gtk+ and Qt.