834010 - Consolidate gesture detection and event handling code for nsEventStateManager and BrowserElementScrolling

Status: RESOLVED WORKSFORME

(Core :: Widget, defect)

Description

[Chris Peterson [:cpeterson]]

Android, B2G, and Metro have separate implementations of gesture detection, event handling, and APZC. We should try to consolidate this code and teach nsEventStateManager about gestures, if necessary.

mbrubeck says: "[For Metro] We plan to re-use B2G's AsyncPanZoomController if possible, which should let us share code for panning and zooming gestures.  We haven't looked into this in detail yet; I think it will depend on getting OMTC working on Metro."

cjones says: "There are really two things here, APZC and gesture detection. Bug 745136 is probably the closest to a tracking bug. ... We need to unify event handling done by BrowserElementScrolling/browser.js/TabChild/nsEventStateManager/widget/fennec frontend."

Comment 1

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

I think the ideal end result of this work should be that, either a gesture is handled by an APZC, or it's handled by EventStateManager.

I'm not too familiar with ESM, but I think we need to teach it to
 - handle touch events "natively", to the same degree as mouse events
 - infer "tap" and "drag" gestures from raw series of touch events
 - understand externally-delivered "tap" and "doubletap" gestures (sent from APZC).  This code may exist already.
 - infer "fling" gestures from raw touch-event series and implement the induced animations

I suspect this would not be easy, but it would completely obsolete BrowserElementPanning.js, the TabChild mouse-event inference, and whatever hacks fennec/metro use for synchronously-scrolled subframes.  It would also fix whatever bugs there most likely are in BrowserElementPanning pseudo-class creation.

Ideally, ESM and APZC should share the same C++ gesture-detection code.

This "refactoring" is also the only way we have to implement the pointer-events spec generically across gecko products.  So I consider this a major technical issue.

Comment 2

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

Oh, probably obvious, but ESM also needs to be able to synthesize mouse events from touch events when appropriate.

Comment 3

[Olli Pettay [:smaug][[e-mail]]]

ESM sounds too late place to handle gestures. ESM is called when presshell has already done
all the hit testing etc.

Comment 4

[Kartikaya Gupta (email:[e-mail])]

Gesture detection pretty much completely happens in APZ these days. I'm going to close this bug.