multi-touch-dev team mailing list archive

[Henrik Rydberg <rydberg@xxxxxxxxxxx>]

On 10/15/2010 09:56 PM, Chase Douglas wrote:
[...]
>> From what I gather, tentative events are passed during the time when an event is

>> neither replayed nor consumed. For gestures, this is exactly the time when
>> nothing at all should happen. If the gesture is accepted, the action will be
>> controlled by the entity detecting the gesture, and it is up to that entity to
>> make sure some kind of feedback is given. Nota bene, the *gesture* may very well
>> be tentative at this stage. If the gesture is cancelled, the real events will be
>> replayed and things will continue as normal. Thus, I see no reason at all to
>> introduce tentative events.
> 
> One example where a non-grabbing client would want to provide feedback
> is to allow for object highlighting while the grabbing client is waiting
> for a gesture recognition timeout. Even if there's delay in the
> non-grabbing client for performing an action, highlighting can reduce
> perceived delay to the user.


The question is really what it is that needs highlighting - the object or the
gesture? The first 20 ms before a second finger and a gesture attempt is even
known, how can a UI make any sensible use of this data? The notion of tentative
events providing quick response is misleading, since there is actually nothing
to respond to.

> During our discussion, Henrik wasn't 100% convinced of this approach,
> but couldn't find a good way around it at the time. Tentative grab
> events are still not set in stone, but I think will be part of an
> initial attempt at XI 2.1.


The decision what to react to has to be made before the reaction is made. There
is plenty of room for visual feedback in the 20-200 ms range, when it is known
which application is to receive events for what may eventually become a gesture.

If an window manager would like to display touches on the screen regardless of
what they mean, why not have the window manager grab the touches first, then
pass them on to the recognizer and friends?

I think we all agree that feedback is very important, and it has to be fast. I
just do not think tentative events solves the problem.

Cheers,
Henrik