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Re: Send touchcancel when scrolling starts?

From: Alexandre Elias <aelias@chromium.org>
Date: Wed, 26 Jun 2013 17:28:06 -0700
Message-ID: <CADeTeo43u5Je7uio=ZsPLWBCOtG8noFfZb0WTZDSMW8dpkHqHQ@mail.gmail.com>
To: Rick Byers <rbyers@google.com>
Cc: Wes Johnston <wjohnston@mozilla.com>, Tim Abraldes <tabraldes@mozilla.com>, "olli@pettay.fi" <olli@pettay.fi>, Paul Kinlan <paulkinlan@google.com>, "public-webevents@w3.org" <public-webevents@w3.org>, Jim Mathies <jmathies@mozilla.com>, Matt Brubeck <mbrubeck@mozilla.com>, Yufeng Shen <miletus@google.com>
On Fri, Jun 21, 2013 at 6:53 AM, Rick Byers <rbyers@google.com> wrote:

> I haven't yet been able to find a real-world example of a site
> legitimately handling touch events while scrolling.  Your side-swipe
> example seems the most likely, but it'll be broken when zoomed or when
> horizontal panning is otherwise permitted (I think touch-action: pan-y is a
> better solution for this).  *Alexandre / Paul*, have you guys come across
> any sites that actually want this functionality from Android browser /
> Firefox / iOS?

I haven't come across a compelling real-life example, no.  Certainly there
are use cases such as horizontal carousels on a vertically scrolling page,
but in that case it's not clear that allowing both movements at once is
better than locking to one axis (in my opinion locking is somewhat
preferable and matches the typical behavior of native touch apps).

> So perhaps the main disadvantage of sending the touchcancel is the
> compatibility implications.  Some developers don't realize they need to
> listen for it (although this can cause bugs elsewhere too), or that they
> need to cancel touchmove events they've handled.
> The main advantage of sending touchcancel is probably that it makes this
> choice explicit and lowers the risk that touchmove handlers will be
> accidentally causing reflow or other changes while scrolling.  Also being
> consistent with the pointer-events model is a benefit, but I think we could
> still implement touch-action for touch events without this property.  *Alexandre,
> *any other reason you guys prefer touchcancel to what Firefox is doing?

No, the only benefit I'm aware of is the explicit nature of the
notification (which in principle may be useful, but in practice I'd be
surprised if any sites are doing anything with it today).

> Thanks,
>   Rick
>> - Wes
Received on Thursday, 27 June 2013 00:28:34 UTC

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