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

[Bill Spitzak]

On Mon, Nov 16, 2015 at 4:02 AM, Auke Booij <auke at tulcod.com> wrote:

>
> > 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
>

Since the "frame" event groups everything together, it does not seem like
there is a need to talk about "latching". _descrete events are "latching"
in that they are in the same frame. This could remove some complexity from
your description I think.

Objections I see is that it makes it impossible to have both discreet and
non-discreet axis events in the same frame, but I find it hard to imagine
an input device where this would be physically possible. Also that this
allows the order to be random rather than forcing the discrete events to be
immediately before the axis, but I don't see any way a useful client could
take advantage of this (a client is pretty much forced to accumulate the
information in a structure until the frame event happens, so enforced
ordering is of no help).
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