Scrolling is sometimes going in the other direction than wanted

[taiebot65]

Nexus 4 Mako vivid. r.89 but notice since a year ago.

This happens in every app, dash or things where you can scroll down or up.
Not sure if its related to the sensitivity of the screen.

[Daniel van Vugt (vanvugt)]

Confirmed on mako today. Although the bug is very hard to reproduce on demand.

[Daniel van Vugt (vanvugt)]

I think this might be related to the QML scroll logic in Unity8. It's probably not a Mir bug.

[Albert Astals Cid (aacid)]

There's no "QML scroll logic in Unity8"

[Albert Astals Cid (aacid)]

This probably has to do with what we already discussed ages ago in a separate bug, Mir or the hardware is sending wrong fake positions well in advance of where the finger actually is and then on release it corrects those doing a swipe back that makes Qt Quick think you actually want to swipe back.

[Daniel van Vugt (vanvugt)]

Comment #4: That is Android's touch prediction logic (and the relevant un-prediction) which is very small -- never more than half a frame predicted ahead. So the un-prediction at the end of a gesture is at most one touch event. If Unity8 is doing fling velocity calculation on a granularity of one event then it's probably Unity8 that needs fixing more. That would also explain why Unity8 randomly gets the fling velocity wrong (my finger is moving slowly but the scroll is flung quickly on release).

Comment #3: What about this?
/usr/share/unity8/Components/ScrollCalculator.qml
/usr/share/unity8/Panel/PanelVelocityCalculator.qml
etc.

[Albert Astals Cid (aacid)]

ScrollCalculator and PanelVelocityCalculator are using only on the indicators panel and since reporter says "This happens in every app, dash" i don't think they're related to this at all.

[Daniel van Vugt (vanvugt)]

Well Qt then. This bug combined with a similar bug where the scroll goes overly fast on finger release suggests we're estimating fling velocity on finger release based on too few recent touch events.

[Daniel van Vugt (vanvugt)]

Retested the latest devel-proposed image today (includes Mir 0.18.0) and this bug is still present.

[Michał Sawicz (saviq)]

Syncing task from Mir.