834996 - mouse_event_shim doesn't forward stopPropagation() (?)

Status: RESOLVED DUPLICATE of bug 831656

(Firefox OS Graveyard :: Gaia, defect)

Description

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

Behavior seen in profile of Homescreen app

 - user puts finger down
 - touchstart handled by mouse_event_shim.js
   - emits mousedown to homescreen
   - homescreen eats event and calls evt.stopPropagation()
 - ... but then BrowserElementScrolling processes onTouchStart()

In this case, I expect the stopPropagation() on the synthetic mouse event to stop propagation of the original touchstart, and BrowserElementScrolling to not show up in the profile.

This puts 20-30ms of unused code on the critical path of responsiveness to touch events.

Not sure if this was done on purpose or is NYI.

Comment 1

[David Flanagan [:djf]]

I don't think we have a way to tell if an event has had propagationStopped called on it. So I don't know how we could forward this.

Calling preventDefault() on an event sets event.defaultPrevented.  But calling stopPropagation() does not (at least per the standard) set event.propagationStopped.

Comment 2

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

Hm.  Can we inject a wrapper stopPropagation() into the synthetic event?

Comment 3

[David Flanagan [:djf]]

The problem went away with this commit which removes the shim:

https://github.com/mozilla-b2g/gaia/commit/7a505331d9fbdd277e5d1c59a9f230200d494c93#apps/homescreen/index.html

And here it is for the 1.0.0 branch:

https://github.com/mozilla-b2g/gaia/commit/8d7803635ced3f4507ed82d0a72a3cc12f5d1585#apps/homescreen/index.html

I'm not sure what the best way to resolve this is, so I'm going to mark it as a dupe of the bug that removed the shim.

Comment 4

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

The mouse_event_shim work went away, but we're still not blocking BrowserElementScrolling.