Here's some notes from my investigations:
* It is only reproducible on a full multitouch trackpad, which currently are
only Apple trackpads
* There seems to be some smooth scrolling and then a snap reversion
* On a touchscreen, two touch drags produce inconsistent smooth scrolling but
no snap reversions
This leads me to believe there is some code in the Qt scroll view class
that subscribes to two touch drag gestures from Qt. Qt has its own
gesture recognizer that is not hooked up to uTouch, though that's beside
the point. The trackpad issue can be explained by the scroll view
performing smooth scrolling for a bit and then snapping back when an X
scroll event (button presses 4, 5, 6, or 7) is received. Touchscreens
don't emit X scroll events, so there's no snap reversion in that case.
I don't trust the Qt smooth scrolling based on what I see when using a
touchscreen. It's not a 1:1 scroll and it often doesn't work. Our best
course of action for now is to patch out the gesture subscription from
the Qt scroll view class.
** Changed in: qt4-x11 (Ubuntu)
Status: Confirmed => Triaged
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https://bugs.launchpad.net/bugs/805972
Title:
Touchpad scrolling bounces
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