1148006 - Panning start tolerance impacts offset between finger and scrolled content

Status: RESOLVED WONTFIX

(Core :: Panning and Zooming, defect)

Description

[Markus Stange [:mstange]]

I don't know what the behavior is called, but when I pan slowly on my Flame, there is a minimum distance my finger needs to travel before the screen actually starts panning. When that threshold is crossed, the scroll position is not adjusted by that threshold - instead, there is now an offset between the position of the touch start and the position the finger is now anchored on.
This feels really bad.

Comment 1

[Botond Ballo [:botond] [away until Oct 19]]

So you're saying that, after we cross the threshold, the page should jump by the amount of the threshold, so that the content that was under your finger at touchstart remains under your finger?

Comment 2

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

This is intentional, in both Fennec [1] and the C++ APZ [2]. It feels worse if the page "jumps" so that the spot you put your finger down on realigns with your finger. At least in the common case where the user is moving their finger fast.

[1] http://mxr.mozilla.org/mozilla-central/source/mobile/android/base/gfx/JavaPanZoomController.java?rev=4d66d5d58232#632
[2] http://mxr.mozilla.org/mozilla-central/source/gfx/layers/apz/src/AsyncPanZoomController.cpp#1941

Comment 3

[Markus Stange [:mstange]]

Yes, I'm saying it should jump, and if it feels bad then I think that's a sign that the threshold is too high.

Comment 4

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

Bug 1116569 is on file for reducing the threshold, so that might help. Note that the flip side of reducing the threshold means that your finger will have less wiggle room when tapping things as we'll more easily go into a pan. I'm fine with adjusting it a bit though.

Comment 5

[Botond Ballo [:botond] [away until Oct 19]]

Markus, could you try the behaviour now that bug 1116569 had landed, and say whether you think a change should still be made?

Comment 6

[Markus Stange [:mstange]]

The panning behavior on the Foxfooding device seems fine to me.