[RFC] Multitouch proposal v2 + implementation

[Daniel Stone]

Hi,

On Mon, Sep 20, 2010 at 04:54:37PM +0200, Benjamin Tissoires wrote:
> Le 20/09/2010 06:45, Daniel Stone a écrit :
> >During a touchpoint's short lifetime, all motion events will be sent to
> >one client and one client only.  Only TouchBegin rather than TouchMotion
> >events can be selected for or grabbed, and akin to ButtonPress, only one
> >client per window can select for TouchBegin events.  Once a delivery has
> >been made to a client without a synchronous grab, all TouchMotion events
> >and the TouchFini event will be sent to the same client.
> 
> It seems to me, that for feedback reasons, Peter suggested to send
> the events in case of a passive grab to all the stack of clients (2
> seemed to be the common case) and not to only one: the underlying
> clients can start gesture recognition, early feedbacks even if they
> know that this particular touch may not be their but will be
> retained by the Window Manager.
> 
> That's all I wanted to add. :-)

Hm, do you mean support for replaying events a la XISyncDevice for
normal grabs, or do you mean for sending touchstreams to all clients who
have selected on a particular window?

The former I can be talked around into (especially if someone says that
it's vital for their usecase), but as for the latter, it's intended to
follow ButtonPress semantics for the same reasons: you really don't want
two people attempting to act on the same touch stream.  I'd much, much
rather be conservative and drop an event rather than possibly have the
same touch stream do two things.

Would a motion history-like API do the trick here? That would let any
client get the entire history of a touch stream they have the touchid
for.  Or is the problem that gesture recognition is computationally
expensive, so you just need to get a head start for latency reasons?

Thanks a lot for the feedback!

Cheers,
Daniel
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