[RFC PATCH] Pointer axis source events (for kinetic scrolling)

[Peter Hutterer]

This is a draft/RFC for adding axis sources to the wayland protocol and
weston. It's an early version to spark discussion.

libinput exports pointer axis sources with each event to tell the caller how
an event was generated. The interesting one is FINGER which signals
finger-based scrolling (2-finger or edge), libinput also guarantees that
there is a terminating 0 scroll event for that source when the finger is
lifted. The client can use that information to implement kinetic scrolling.

We talked about adding this at XDC 2014 and the limitation in extending
events requires sending additional events. This is what this patchset does,
it prefixes a wl_pointer.axis_source event to each wl_pointer.axis event,
with the data about the event. They need to be merged together in the
client. The rest is fairly straightforward and just forwarding events from
libinput.

Any comments appreciated.

Cheers,
  Peter