Re: Queries on pointer events with respect to multi-pointer(touch) events

Hey Vivek,
Sorry for the delay in responding.  See inline.


On Fri, Oct 11, 2013 at 1:38 AM, Vivek Galatage <vivekg@webkit.org> wrote:

> Hi,
>
> I have few questions in pointer events with respect to multi-touch
> scenario.
>
> I am not sure if these are already discussed or valid questions at all in
> the current context, so please excuse me if being so.
>
> *Q1.*
> In case of multi-touch, would there exist any relation between the primary
> and non-primary pointer events.
> e.g. While building multi-touch gesture WebApp, it would be really great
> to have the associated pointer events sent to the
> callback as an array of pointer events. Is it how the specification
> defines it?
>

 No, there are several challenges to doing this properly (a preview build
of IE10 originally had such an API, but it was removed after the problems
became apparent).  However, it's relatively easy to build yourself in JS.
 We've got this on the list for things to look at adding in the future
(last line on http://www.w3.org/wiki/PointerEvents/UseCasesAndRequirements).
 See
http://lists.w3.org/Archives/Public/public-pointer-events/2013JanMar/0202.html
for
more details.

*Q2.*
> With multi-point touch, assume we started with the index finger as first
> point of contact while rest of the fingers
> being pointed subsequently. What would happen in the below mentioned
> sequence of events:
>         a. All non-primary pointers are in pointerdown state
>         b. The primary pointer is taken away thereby in pointerup state
>         c. All non-primary pointer are in pointermove state
> Questions:
>         A. Would there be any fallback primary pointer once the primary is
> taken away?
>

No - there are no primary pointers active at that time.  From the spec:
"A pointer representing touch input is considered the primary touch input
if its pointerdown event was dispatched when no other active pointers
representing touch input existed."


>         B. If there is no such fallback mechanism, would these non-primary
> pointer events be ignored?
>

Apps (or browser code) operating only on primary pointers would choose to
ignore them, yes.  But they will of course still be dispatched to the app.
 Basically an app that cares only about simple single-touch scenarios can
just ignore all pointer events for non-primary pointers.  But an app that
wants rich multi-touch support will want to make it's own decisions about
what to do in such scenarios.


> Thank you for taking a look.
>
> BR,
> Vivek
>