[PATCH v5 wayland] protocol: add wl_pointer.frame, axis_source, axis_stop, and axis_discrete

[Carlos Garnacho]

On Wed, Oct 28, 2015 at 6:34 AM, Peter Hutterer
<peter.hutterer at who-t.net> wrote:
> The frame event groups separate pointer events together. The primary use-case
> for this at the moment is diagonal scrolling - a vertical/horizontal scroll
> event can be grouped together to calculate the correct motion vector.
> Frame events group all wl_pointer events. An example sequence of motion events
> followed by a diagonal scroll followed by a button event is:
> wl_pointer.motion
> wl_pointer.frame
> wl_pointer.motion
> wl_pointer.frame
> wl_pointer.axis
> wl_pointer.axis
> wl_pointer.frame
> wl_pointer.button
> wl_pointer.frame
>
> In the future, other extensions may insert additional information about an
> event into the frame. For example, an extension may add information about the
> physical device that generated an event into the frame. For this reason,
> enter/leave events are grouped by a frame event too.
>
> The axis_source event determines how an axis event was generated. That enables
> clients to judge when to use kinetic scrolling. Only one axis_source event is
> allowed per frame and applies to all events in this frame.
>
> The axis_stop event notifies a client about the termination of a scroll
> sequence, likewise needed to calculate kinetic scrolling parameters.
> Multiple axis_stop events within the same frame indicate that scrolling has
> stopped in all these axis at the same time.
>
> The axis_discrete event provides the wheel click count. Previously the axis
> value was some hardcoded number (10), with the discrete steps this enables a
> client to differ between line-based scrolling on a mouse wheel and smooth
> scrolling with a touchpad.
>
> We can't extend the existing wl_pointer.axis events so we introduce a new
> concept: latching events. These events (currently only axis_discrete)
> are prefixed before a wl_pointer.axis event. A client must build the full
> state of the event until the respective top-level event arrives.
> i.e. a single event frame for a diagonal scroll with discrete information may
> be:
>
> wl_pointer.axis_source
> wl_pointer.axis_discrete
> wl_pointer.axis
> wl_pointer.axis_discrete
> wl_pointer.axis
> wl_pointer.frame
>
> Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>

FWIW, with mutter/gtk+ implementations at hand:

Reviewed-by: Carlos Garnacho <carlosg at gnome.org>