Gallery (and other apps that use shared/js/gesture_detector.js) don't detect swipes and zoom/pinch gestures until the touch movement has exceeded a threshold. Then, when the movement does exceed that threshold, then send an initial swipe or zoom event that includes all of that threshold movement, which results in the user seeing a sudden lurch. It would be much better start the pan or zoom only when the threshold is exceeded, so the gesture begins smoothly. But also, it seems that the thresholds are too large, also, and should be reduced. I've spoken with Josh about this and he thinks it would be good to fix. We both thought there was already a bug filed on it, but neither of us could find it. So I'm filing this bug for it. Josh is this a UX-P1 bug? would you set the appropriate flags so that its priority is high enough for me to work on? I know I want to fix this for gallery. I can modify gesture detector on an opt in basis, so that other apps that use the library can get the fix if they want it, or I could just modify the library unconditionally so that all apps get it with no change required. I'll have to research what other app use gesture detector and see whether the bug is a problem for them.

Assigning to myself, cc'ing Josh.

Vivien showed me an implementation of this in Berlin, Sunday night, so work may already be done?

What he showed me was an appreciable improvement, BTW, and we should land if at all possible.

(In reply to Josh Carpenter [:jcarpenter] from comment #2) > Vivien showed me an implementation of this in Berlin, Sunday night, so work > may already be done? What I showed you was a hack that affects all the other scroll (not part of $GAIA/shared/js/gesture_detector.js) but of $GECKO/dom/browser-element/BrowserElementScrolling.js). My code was mostly about small movements in order to add some inertia to it. So this is likely not related to this bug :)

I've got a fix for this bug, but it has ended up in the same patch as the fix for the more serious bug 827969, so I've attached it there instead of here. See https://github.com/mozilla-b2g/gaia/pull/7400

Fix landed with the fix for bug 827969: https://github.com/mozilla-b2g/gaia/commit/28f2eb778f5d12e1d13fcd965160519d6593bf2e