Touch input is offset with two screens (even appearing on the wrong screen) in Xorg sessions

[Will Cooke]

Using touch input with one screen seems fine.
However, when connecting a second screen the touch event happens at the wrong coordinates.

Steps to reproduce
1. Starting with a single screen touch and hold on the background and drag. The rubber band selector shows up with the moving corner at your finger.
2. Connect a second screen
3. Do the same touch and drag as in step 1 and notice that the moving corner is offset to the right and slightly below where the touch is happening.
---
ProblemType: Bug
ApportVersion: 2.20.10-0ubuntu23
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
DisplayManager: gdm3
DistroRelease: Ubuntu 19.04
GsettingsChanges: b'org.gnome.desktop.interface' b'gtk-im-module' b"'ibus'"
InstallationDate: Installed on 2019-03-28 (0 days ago)
InstallationMedia: Ubuntu 19.04 "Disco Dingo" - Alpha amd64 (20190326.2)
Package: gnome-shell 3.32.0-1ubuntu1
PackageArchitecture: amd64
ProcVersionSignature: Ubuntu 5.0.0-7.8-generic 5.0.0
Tags: disco
Uname: Linux 5.0.0-7-generic x86_64
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo
_MarkForUpload: True

[Daniel van Vugt (vanvugt)]

Will,

Can you detail what scaling factors you are using, as well as running:

  xrandr > xrandr.txt

and attach the file 'xrandr.txt'?

[Daniel van Vugt (vanvugt)]

Please also run:

  apport-collect 1821933

so it's clear in the bug what package versions are affected.

[Will Cooke (willcooke)]

No scaling set. So 100%

[Will Cooke (willcooke)]

apport information

[Will Cooke (willcooke)]

apport information

[Will Cooke (willcooke)]

apport information

[Daniel van Vugt (vanvugt)]

Will,

1. Is the external monitor also a touch screen or just the laptop?

2. Would you say the offset is the same as that of the desktop workarea? (thickness of the top panel plus thickness of the Ubuntu dock)

[Will Cooke (willcooke)]

Just the laptop is touch screen. Monitor is normal monitor.

I recorded a quick video to try and show what's going on:

https://www.youtube.com/watch?v=bbr1ywNpIgc

[Daniel van Vugt (vanvugt)]

More questions:

  * From the video it looks like the rubber band moves faster than your finger. Does it only happen when desktop scaling is >100%?

  * Does touch respond in the right place for the shell or apps?

[Will Cooke (willcooke)]

No additional scaling is set, everything is 100%.
It does feel like there is some acceleration going on though.

The offset seems consistent to shell, apps and the backdrop. e.g. I position a window on the right hand screen and I can grab the top of it by dragging on the left screen.

[Daniel van Vugt (vanvugt)]

It sounds like touches are being scaled to stage coordinates instead of view coordinates. So a touch halfway across the touch screen gets mapped to a desktop location halfway across all monitors. Just a guess.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Daniel van Vugt (vanvugt)]

The problem appears to be that clutter_input_device_evdev_translate_coordinates has no idea that the stage might include multiple monitors:

https://gitlab.gnome.org/GNOME/mutter/blob/master/clutter/clutter/evdev/clutter-input-device-evdev.c#L1509

Sadly I can't see any information that would help to correct it either. It would be a bit of a redesign.

[Daniel van Vugt (vanvugt)]

That would be a consequence of the "touch screen" input device not having any relation in software to the "screen" output device. They are very separate things :(

[Daniel van Vugt (vanvugt)]

Experimental fix:

https://gitlab.gnome.org/GNOME/mutter/commit/4a06424b9c1de7242cec0613bc1fd53c832d9144.patch

[Daniel van Vugt (vanvugt)]

Untested fix as a PPA:

https://launchpad.net/~vanvugt/+archive/ubuntu/lp1821933

[Daniel van Vugt (vanvugt)]

Sorry, ignore the above, they are wrong. It is a bit more non-trivial than that.

[Will Cooke (willcooke)]

More testing:

Testing on Fedora with GNOME 3.32 under their default wayland session, touch events seem to be positioned correctly.

Testing on Disco under the Wayland session touch on the dock and parts of shell that are on the left of the screen seems to work, but touch-dragging on the background doesnt seem to work at all.

[Will Cooke (willcooke)]

This bug is being marked notfixing. That doesn't mean it wont get fixed, but that we won't block release on it.

[Will Cooke (willcooke)]

Added to Trello: https://trello.com/c/zteRvbzR/300-bug1821933-touch-input-is-offset-with-two-screens-even-appearing-on-the-wrong-screen

[Daniel van Vugt (vanvugt)]

Will,

Please test the previous mutter release debs, just in case it's an xrandr scaling regression. The previous release is here:

  https://launchpad.net/ubuntu/+source/mutter/3.32.0-1/+build/16489975

[Daniel van Vugt (vanvugt)]

If ^^^ reverting the version of mutter installed ^^^ doesn't fix the bug then please try the PPA (https://launchpad.net/~vanvugt/+archive/ubuntu/lp1821933). Because your feedback on that will guide the design of a proper fix then.

[Will Cooke (willcooke)]

In reply to comment #21:

$ apt-cache policy mutter
mutter:
  Installed: 3.32.0-1
  Candidate: 3.32.0-1ubuntu1
  Version table:
     3.32.0-1ubuntu1 500
        500 http://gb.archive.ubuntu.com/ubuntu disco/main amd64 Packages
 *** 3.32.0-1 100
        100 /var/lib/dpkg/status

The result is the same. Same offset etc.

[Will Cooke (willcooke)]

In reply to comment #22:

$ apt-cache policy mutter
mutter:
  Installed: 3.32.0-1ubuntu1vv1
  Candidate: 3.32.0-1ubuntu1vv1
  Version table:
 *** 3.32.0-1ubuntu1vv1 500
        500 http://ppa.launchpad.net/vanvugt/lp1821933/ubuntu disco/main amd64 Packages
        100 /var/lib/dpkg/status
     3.32.0-1ubuntu1 500
        500 http://gb.archive.ubuntu.com/ubuntu disco/main amd64 Packages

Made no difference I'm afraid.

[Will Cooke (willcooke)]

Removed the upstream but I logged and replaced it with one which was already logged, and fixed.

[Daniel van Vugt (vanvugt)]

Oh, wow, fixed in mutter 3.32.1 already?!

https://gitlab.gnome.org/GNOME/mutter/merge_requests/503

[Daniel van Vugt (vanvugt)]

Fix committed via Debian:

mutter (3.32.0+git20190410-1) experimental; urgency=medium

[Launchpad Janitor (janitor)]

This bug was fixed in the package mutter - 3.32.0+git20190410-1ubuntu1

---------------
mutter (3.32.0+git20190410-1ubuntu1) disco; urgency=medium

  * Merge with debian git snapshot (LP: #1820542), remaining changes:
    + debian/control:
      - Update VCS flags to point to launchpad
      - Update maintainer to ubuntu
    + debian/gbp.conf: update branch to point to ubuntu/master
    + debian/patches/x11-Add-support-for-fractional-scaling-using-Randr.patch:
      - X11: Add support for fractional scaling using Randr
  * d/p/x11-Add-support-for-fractional-scaling-using-Randr.patch:
    - Refreshed.

 -- Marco Trevisan (Treviño) <email address hidden> Wed, 10 Apr 2019 20:12:29 -0500