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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