multi-touch-dev team mailing list archive

[Henrik Rydberg <rydberg@xxxxxxxxxxx>]

On 10/08/2010 05:10 PM, Chase Douglas wrote:

> On Fri, 2010-10-08 at 13:37 +0200, Henrik Rydberg wrote:
>> On 10/05/2010 10:22 PM, Chase Douglas wrote:
>> [...]
>>
>>> The reason this is useful is to lower the latency when there's
>>> system-wide and application specific gesture recognition to be
>>> performed. It requires a trust of the client applications to not handle
>>> the events as though they owned them, but X trusts client applications
>>> with lots of similar things today without issue.
>>
>>
>> It seems to me that the idea of tentative events is not so much about latency as
>> it is about implementing user feedback which helps resolve ambiguities.
> 
> It's the latency to the user feedback that's important. In my mind,
> these two concepts are one in the same.
> 
>> There are at least three stages in gesture recognition in this respect. In the
>> first stage, the engine builds up a reaction based on user input, from nothing
>> to something. I see no reason to send this buildup anywhere at all. In the
>> second stage, something is happening, and the user may need feedback from the
>> system to tell that something has been registered. This is equivalent to our
>> notion of gesture primitives, and could well be represented by tentative events,
>> although I see no compelling reason to change views. The third stage is to
>> perform a user-approved gesture, which is on a higher level than what we have
>> implemented so far, and could be a good target for geis.
> 
> The sticky point comes when we need to handle the possibility for both
> gestures and low-latency multitouch input. For example, think of the
> three finger hold to unlock many finger MT and gestures occurring over a
> paint application. With the proposed XI 2.1 passive grabbing paradigm,
> gimp will receive tentative events and may start painting, knowing that
> it will need to undo those paints if the events should be discarded.
> This should occur as immediately as possible after touches hit the
> screen.


I agree that tentative events allows the possibility to start painting and later
rollback. I do not see how grabbing affects this particular solution.

Cheers,
Henrik