On Fri, Oct 15, 2010 at 05:23:43PM +0200, Henrik Rydberg wrote: > On 10/14/2010 09:39 PM, Chase Douglas wrote: > > > On Wed, 2010-10-13 at 20:43 +0200, Henrik Rydberg wrote: > >> On 10/13/2010 06:03 PM, Chase Douglas wrote: > >>>> Good point. Would you mind going through, step-by-step, the case where > >>>> we start > >>>> with two fingers inside a "window", scroll a bit, then add another > >>>> finger in a > >>>> different window, and perform a three-finger pinch? > >>> > >>> There's a few context questions we need to ask first (I'm trying to get > >>> at what your asking, maybe I'm going off in the wrong direction though): > >>> > >>> 1. Is a three finger pinch a system-wide gesture? I'll assume yes. Are > >>> two finger gestures system-wide gestures? I'll assume no. > >>> > >>> 2. Should a two-to-three finger movement that is not immediate, by which > >>> I mean this isn't a three finger movement from the start where the first > >>> couple of device touch frames caught only two fingers, trigger a three > >>> finger gesture? I don't believe we've explicitly answered this anywhere > >>> yet, but I think not. A three finger gesture must be initiated with > >>> three fingers within a short period of time on the order of 10s of > >>> milliseconds (I'm leaving aside the case of gesture continuation). > >> > >> > >> I tend to agree, although that is all about policy. I was intending this > >> example > >> to trigger a global gesture, since it makes the example more difficult. > >> > >>> Given these assumptions, I think the expected result is that the > >>> scrollable region continues to scroll according to the two fingers over > >>> it, and the single finger in the other window does whatever it should in > >>> that window. > >> > >> > >> Right, that is the easy path. So what about the one which triggers a > >> global gesture? > > > > I'm not sure we've defined a mechanism that would work in that case. > > What you would need is the ability to peek at all touch events > > individually and pick and choose which ones you want to keep and which > > you want to replay. The reason this gets dicey is what does the client > > do? Imagine the following: > > > > 1. Touch begins > > 2. WM replays touch events one at a time > > 3. Application gets touch begin, touch motion events > > 4. WM consumes some events > > 5. WM replays more events > > 6. WM consumes events > > 7. Touch ends > > > > Issues: > > > > * Does application get touch begin events when touch physically begins > > if WM starts consuming all events? Or does it only receive a begin event > > once the first replayed event is sent? > > * Is application notified when WM starts consuming events again? > > * What happens when events are replayed in step 5? It may seem that the > > touch moved from one are of the screen to another instantaneously when > > in reality the touches in between were consumed by the WM. > > * If the WM consumes the touch end, does the application then receive > > the touch end? > > > > I think this use case is opposite to good UI design, and I think the > > plumbing to make it possible opens up a big can of worms. X doesn't > > support any replay mechanism like this for even legacy pointer events. > > We seem to all agree that the original example bore the correct outcome, > > so I'm hesitant to continue down this path until we find a scenario that > > would require it. > > > > There's also nothing that prevents us from adding support for this in > > the future if we find we need it. > > > Thanks for showing the implications, Chase. I think it illustrates well that > MT > and Gestures cannot be separated. > > If we think of MT events as separate single-finger drags, MT becomes a subset > of > gestures.
I disagree with this point. Unless you expand the gesture dictionary ad infintum, you will always find some combination of single-finger drags that do not combine into a gesture. > In grail, a N-finger gesture overrides all other gestures that can be > performed with M < N fingers. At which point do you decide that N fingers are an N-finger gesture and not just a random bunch of touch events? This is quite important for my understanding, because right now I feel we're not always talking about the same thing. > This includes one-finger drags. Going back to your > example, the natural interpretation is that when the three-finger gesture > starts, the two single-finger drags end. [citation needed] I'm actually being serious here. "natural" is quite tricky to define and I'd love to see the research that confirms this statement. > Perhaps if XI2.1 had the ability to > chop a touch up into pieces during replay, the problem could be solved. > > This thread, as well as talking some more with Peter, makes me think we are > pretty close. The things I see we need to do is: > > 1. Add the ability to limit finger grouping to areas in grail. > > The separation into finger groups is already there, but it is only based on > the > incoming data. Adding the ability to split the fingers into groups based on > domains could be achieved by an api callback. > > The visible simplifications during natty would be more expressive power to the > application. In particular, the ability to have a dedicated scroll area. It > would also enable the possibility to perform all event propagation from within > the same process, although we would not push this scenario at all. > > 2. Add the ability to split touches in XI2.1 > > The passive grab mechanism needs to be able to gracefully handle consumption > of > touches, such that touch-up and touch-down events are inserted appropriately > if > the consumer of a touch changes. urgh. wouldn't you then get random touch down/up events on the screen, depending on which application is currently listened to, and completely disconnected from the user's interaction? Cheers, Peter > 3. Skip the tentative events in XI2.1 > > From Peter's explanation, it seems the original reason for this was to not run > out of buffer space. Since the semantics is still unclear (just follow this > thread for an example), it is probably best pushed to future expansions. > > So, Gentlemen, what do you think of this? > > Cheers, > Henrik > _______________________________________________ Mailing list: https://launchpad.net/~multi-touch-dev Post to : multi-touch-dev@lists.launchpad.net Unsubscribe : https://launchpad.net/~multi-touch-dev More help : https://help.launchpad.net/ListHelp
