Bug 45611 - erratic scrolling in 1.12
Summary: erratic scrolling in 1.12
Alias: None
Product: xorg
Classification: Unclassified
Component: Server/Input/Core (show other bugs)
Version: unspecified
Hardware: Other All
: medium normal
Assignee: Peter Hutterer
QA Contact: Xorg Project Team
Depends on:
Blocks: xserver-1.12
  Show dependency treegraph
Reported: 2012-02-04 02:42 UTC by Timo Aaltonen
Modified: 2015-08-04 06:58 UTC (History)
4 users (show)

See Also:
i915 platform:
i915 features:

0001-dix-reset-last.scroll-when-resetting-the-valuator-45.patch (1.66 KB, patch)
2012-02-10 07:31 UTC, Peter Hutterer
no flags Details | Splinter Review

Description Timo Aaltonen 2012-02-04 02:42:46 UTC
forwarded from https://bugs.launchpad.net/ubuntu/+source/xorg-server/+bug/925785

TL;DR, plug another pointer device with horiz scroll support, then after touching the other device try to scroll with the second device and notice how "many" scroll button events are emitted.
Comment 1 Timo Aaltonen 2012-02-04 02:54:41 UTC
Actually, the scroll axis doesn't matter, it's the same for both horizontal and vertical (meant vertical originally). Just that for vertical scrolls the jumping happens to the other direction (since the axis seems reversed, I'll file another bug about that..).
Comment 2 Timo Aaltonen 2012-02-04 03:05:40 UTC
another observation:

- touch device 1
- scroll device 2, note that it jumps
- touch device 1
- scroll device 2 to the same direction as before, note that nothing happens on the first click, the next one is normal
- touch device 2
- scroll device 2 to the same direction as before, note that you get _opposite_ action on the first click, next one is normal

... :)
Comment 3 Peter Hutterer 2012-02-04 09:57:33 UTC
verified on master, thanks.

Appears to be a bad update of last.valuators[], resetting that value to 0 whenever the SD changes. As a result, the next value isn't on top of the previous one but rather starting from 0, causing a bad in value. The jumps come from that
Comment 4 Peter Hutterer 2012-02-10 07:31:33 UTC
Created attachment 56877 [details] [review]

How does this one work for you?
Comment 5 Timo Aaltonen 2012-02-10 07:47:52 UTC
Nice! Works great.

Tested-by: Timo Aaltonen <timo.aaltonen@canonical.com>
Comment 6 Peter Hutterer 2012-02-21 21:13:18 UTC
commit 6f28388187cffae9e5bc9bfc9425acff4f478b59
Author: Peter Hutterer <peter.hutterer@who-t.net>
Date:   Sat Feb 11 01:29:26 2012 +1000

    dix: reset last.scroll when resetting the valuator (#45611)
Comment 7 Richard W.M. Jones 2015-07-20 21:09:51 UTC
This bug -- or something remarkably similar to it -- has reappeared in 1.17.2 (latest X package in Fedora 22).
Comment 8 Peter Hutterer 2015-08-04 06:58:21 UTC
This ended up being a GTK3 bug, not an xorg bug, see https://bugzilla.redhat.com/show_bug.cgi?id=1245247. Closing again

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