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Re: [polymer-dev] PSA: PointerEvents and PointerGestures are being replaced by polymer-gestures, breaking changes for pointer* events

From: Daniel Freedman <dfreedm@google.com>
Date: Mon, 14 Apr 2014 16:41:50 -0700
Message-ID: <CAAUAVAjqYdvxnGsE_DkOvRgW_CwmkAhAK5A=s7QXieUYNcUDyA@mail.gmail.com>
To: Rick Byers <rbyers@google.com>
Cc: polymer-dev <polymer-dev@googlegroups.com>, "public-pointer-events@w3.org" <public-pointer-events@w3.org>
It is my hope that when PointerEvents has a few more native
implementations, then polymer-gestures can transition to being a consumer
of PointerEvents only, and we can reinstate the polyfill for other browers.
To that end, I plan to maintain the PointerEvents polyfill to follow the
spec as it evolves (thankfully there have been few breaking changes since
the WG started).

Unfortunately, the polyfill's performance penalty on mobile is an
information problem, and not one I see workarounds for in the near to
medium term.
Target finding seems to be expensive no matter which way I try to slice it,
and mobile already operates at a tremendous speed disadvantage.

I do not intend this change to be negative signal on the part of
PointerEvents, but an (unfortunate) acceptance of the practical realities
of mobile devices and polyfill performance.


On Mon, Apr 14, 2014 at 4:23 PM, Rick Byers <rbyers@google.com> wrote:

> +public-pointer-events
>
> What does this mean for other consumers of the PointerEvents polyfill?
> Will it be effectively orphaned?
> On Apr 14, 2014 7:15 PM, "Daniel Freedman" <dfreedm@google.com> wrote:
>
>> Hi Polymer users,
>>
>> We recently had a big perf investigation of mobile use cases and found
>> that our gesture layer was not performant enough to get 60 FPS[1].
>> For this reason, I have created the polymer-gestures library which
>> gesture events in a mobile-performant way.
>>
>> In the next release, polymer-gestures will replace (the now deprecated)
>> PointerGestures, and PointerEvents will be removed from the default build.
>>
>> These are the supported events of polymer-gestures:
>>
>>    - down
>>    - up
>>       - Same target as down, provides the element under the pointer with
>>       the relatedTarget property
>>    - trackstart
>>    - track
>>       - Same target as down
>>    - trackend
>>       - Same target as down, provides the element under the pointer with
>>       the relatedTarget property
>>    - tap
>>       - Targets the nearest common ancestor of down and up.relatedTarget
>>       - Can be prevented by calling any gesture event's preventTap
>>       function
>>    - flick *
>>    - hold *
>>    - holdpulse *
>>    - release *
>>    - pinchstart *
>>    - pinch *
>>    - pinchend *
>>
>> * = "Not yet implemented"
>>
>> If you listen for pointerdown, pointermove, pointerup, pointerover,
>> pointerout, pointerenter or pointerleave, you will need to change your code.
>> If you require an event for every movement of the pointer, you can use
>> the "track" event.
>>
>> This change was not made lightly, but only after careful consideration of
>> device constraints and lack of cross-browser PointerEvent implementations.
>> The Polymer team still believes that PointerEvents are the best technical
>> solution for handling user input, but mobile use cases are too important to
>> be gated on native implementations.
>>
>> I apologize for the churn.
>>
>>
>> [1]: The big culprit was the gymnastics the PointerEvents polyfill had to
>> make to be spec compliant and target the correct elements with ShadowDOM.
>> In particular, the encapsulation mechanics of ShadowDOM made target
>> finding for pointermove very expensive, requiring recursive
>> elementFromPoint calls.
>> Another large chunk of time was wasted on having gesture recognizers
>> listen for dispatched, normalized pointerevents.
>> Polymer-gestures will use the lower-level events directly without
>> spinning up the DOM event system N times each pointer movement.
>>
>> Follow Polymer on Google+: plus.google.com/107187849809354688692
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>
Received on Monday, 14 April 2014 23:42:38 UTC

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