Bug 90990 - AlpsPS/2 ALPS DualPoint TouchPad scrolling is jumpy
Summary: AlpsPS/2 ALPS DualPoint TouchPad scrolling is jumpy
Alias: None
Product: Wayland
Classification: Unclassified
Component: libinput (show other bugs)
Version: unspecified
Hardware: Other All
: medium normal
Assignee: Wayland bug list
QA Contact:
Depends on:
Reported: 2015-06-16 09:10 UTC by Ignacio Casal Quinteiro
Modified: 2015-06-23 22:42 UTC (History)
3 users (show)

See Also:
i915 platform:
i915 features:

jumpy log (142.74 KB, text/plain)
2015-06-16 09:12 UTC, Ignacio Casal Quinteiro

Description Ignacio Casal Quinteiro 2015-06-16 09:10:36 UTC
<nacho> whot, btw I have another bug but not sure whether it could be in libinput or in gtk itself
<nacho> whot, scrolling seems a bit jumpy
<nacho> whot, and if in i.e gedit I go to the end of the document, I keep scrolling even though it is the end of the document, and I scroll up right after that, I get a big jump up

For other bug reports related to my touchpad see #90980 and #90590

evemu log file is following
Comment 1 Ignacio Casal Quinteiro 2015-06-16 09:12:09 UTC
Created attachment 116530 [details]
jumpy log

And here the log
Comment 2 Peter Hutterer 2015-06-18 23:06:37 UTC
ok, afaict what's happening here is that you set the finger down, then move it and edge scrolling doesn't trigger until you pass the built-in motion threshold (5mm). When you pass it, the first scroll event includes the full motion so far but it's accelerated too which causes that massive jump.

I guess that leaves three options:
* reduce the initial threshold, but would likely cause the same jump even at 3mm and I don't want to go below that
* don't release the full distance but just the last delta when we hit the threshold. this would add a dead zone to scrolling
* replay the motion history in full once the threshold is hit. this would only add a slight delay to scrolling
Comment 3 Peter Hutterer 2015-06-19 00:17:16 UTC
Test packages for the three outlined above:
1) 3mm threshold: http://koji.fedoraproject.org/koji/taskinfo?taskID=10152166
2) last-delta: http://koji.fedoraproject.org/koji/taskinfo?taskID=10152173
3) replay: http://koji.fedoraproject.org/koji/taskinfo?taskID=10152180

Note that 3 is the technically best solution but is mostly pointless in X since we don't use the event timestamps - the server adds their own. So I don't expect that to be much of an improvement. This may actually work better in a pure wayland context but even there I doubt it since the events still come in simultaneously and thus render at the same time.

For 2: that's not the complete solution yet since it'll have the same deadzone for scroll timeouts (and we def. don't want that). I just felt lazy :)
Comment 4 Ignacio Casal Quinteiro 2015-06-21 16:15:57 UTC
So 3 I am not going to try it since I am with X. I just tried 2 and it seems much better, at least I do not see the jumpy problem with it. Do you want me to try 1 as well?
Comment 5 Peter Hutterer 2015-06-21 23:52:24 UTC
2 includes 1, they're all on top of each other. It' be interesting if 1 alone is enough so please do give it a try.
Comment 6 Peter Hutterer 2015-06-22 02:18:19 UTC
(In reply to Peter Hutterer from comment #3)
> For 2: that's not the complete solution yet since it'll have the same
> deadzone for scroll timeouts (and we def. don't want that). I just felt lazy
> :)

note to self: we already have that deadzone anyway for timeout-based scrolling, so leaving the current behaviour shouldn't be much of an issue then.
Comment 7 Ignacio Casal Quinteiro 2015-06-22 21:37:38 UTC
So I just tried 1 and it seems to be less jumpy than before, though I still feel it a bit jumpy even though now it is hard to notice. From 1 to 2 I'd say 2 is a bit better but dunno it is hard to say without being able to test both side by side :)
Comment 9 Peter Hutterer 2015-06-23 22:42:16 UTC
commit abc8c0d6c29ce60275ff8a35fc7bdbbf6407969b
Author: Peter Hutterer <peter.hutterer@who-t.net>
Date:   Fri Jun 19 10:11:13 2015 +1000

    touchpad: reduce edge scroll motion threshold to 3mm

commit f783dae0a70e660f8fc0175b4a702bd3f9953d7d
Author: Peter Hutterer <peter.hutterer@who-t.net>
Date:   Fri Jun 19 09:21:58 2015 +1000

    touchpad: only send most recent edge delta when triggering threshold

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