[Bug 1873895] [NEW] Regression: block staircase display with side-by-side monitors of different pixel widths

Launchpad Bug Tracker 1873895 at bugs.launchpad.net
Tue Apr 6 10:35:05 UTC 2021

You have been subscribed to a public bug by Sean Davis (bluesabre):


 * This issue affects AMD graphics on Xfwm4 4.14.1.

 * Windows are displayed staggered with a multi-window layout

[Test Plan]

 * Use AMD graphics drivers

 * Connect a second display at a different resolution

 * Open multiple windows

 * While the issue is present, the windows and desktop will appeared

 * Once fixed, they display normally.

[Where problems could occur]

 * Regression potential should be relatively low, as the release between
4.14.1 and 4.14.5 are bug releases.

 * With window managers, some changes could lead to different behavior
and other broken displays. Non-AMD graphics users should also test for

[Other Info]
 * Please see the Xfwm4 release notes for changes between 4.14.1 and 4.14.5: https://gitlab.xfce.org/xfce/xfwm4/-/blob/xfce-4.14/NEWS#L7-44

[Original Report]

Update based on further research.

This only happens when the secondary external display is operating at a
different pixel width to the internal. In this case eDP is 1920x1080
whereas the external HDMI-A-0 is natively 1680x1050.

It is caused by xfwm4's recent switch from using glx to xpresent for AMD

The underlying bug is in the AMD driver.

I was able to reproduce on an external 1920x1200 display only when it
was set to a non-native 1680x1050 resolution.

Two identical Lenovo E495 laptops with 20.04 installed. The problem occurred initially on the laptop that is having package upgrades applied regularly.

With dual monitors and the external monitor placed left or right the
display has a blocked staircase effect shown in the attached photograph,
and seems related to


More detailed investigation suggests it only happens when the X
coordinate of the two monitors is different. The symptom looks like an
off-by-one error because it appears as if the display is divided into,
say, 10 rows and 15 columns but the first row has 16 'columns' worth of
blocks on it and so wraps to the beginning of the 2nd row, and so on.

On the laptop without package upgrades being applied this didn't happen.
So I upgraded it (314 packages) and restarted and it too sees the same

I suspected libxcomposite1 and downgraded it to 1:0.4.5-0ubuntu1 but
that didn't solve it.

I now suspect libxcb but so far haven't been able to prove it.
ProblemType: Bug
ApportVersion: 2.20.11-0ubuntu27
Architecture: amd64
BootLog: Error: [Errno 13] Permission denied: '/var/log/boot.log'
CasperMD5CheckResult: skip
CompositorRunning: None
CurrentDesktop: XFCE
DistUpgraded: Fresh install
DistroCodename: focal
DistroRelease: Ubuntu 20.04
DistroVariant: ubuntu
 Advanced Micro Devices, Inc. [AMD/ATI] Picasso [1002:15d8] (rev c1) (prog-if 00 [VGA controller])
   Subsystem: Lenovo ThinkPad E595 [17aa:5124]
InstallationDate: Installed on 2020-04-08 (11 days ago)
InstallationMedia: Xubuntu 20.04 LTS "Focal Fossa" - Beta amd64 (20200408)
MachineType: LENOVO 20NECTO1WW
Package: xserver-xorg-video-amdgpu 19.1.0-1
PackageArchitecture: amd64
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-5.4.0-21-generic root=/dev/mapper/ELLOE000-rootfs ro acpi_osi=! "acpi_osi=Windows 2016" quiet splash vt.handoff=7
ProcVersionSignature: Ubuntu 5.4.0-21.25-generic 5.4.27
Tags:  focal ubuntu ubuntu
Uname: Linux 5.4.0-21-generic x86_64
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom dip libvirt lp lpadmin lxd plugdev sambashare sudo users
_MarkForUpload: True
dmi.bios.date: 12/23/2019
dmi.bios.vendor: LENOVO
dmi.bios.version: R11ET32W (1.12 )
dmi.board.asset.tag: Not Available
dmi.board.name: 20NECTO1WW
dmi.board.vendor: LENOVO
dmi.board.version: Not Defined
dmi.chassis.asset.tag: No Asset Information
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: None
dmi.modalias: dmi:bvnLENOVO:bvrR11ET32W(1.12):bd12/23/2019:svnLENOVO:pn20NECTO1WW:pvrThinkPadE495:rvnLENOVO:rn20NECTO1WW:rvrNotDefined:cvnLENOVO:ct10:cvrNone:
dmi.product.family: ThinkPad E495
dmi.product.name: 20NECTO1WW
dmi.product.sku: LENOVO_MT_20NE_BU_Think_FM_ThinkPad E495
dmi.product.version: ThinkPad E495
dmi.sys.vendor: LENOVO
version.compiz: compiz N/A
version.libdrm2: libdrm2 2.4.101-2
version.libgl1-mesa-dri: libgl1-mesa-dri 20.0.4-2ubuntu1
version.libgl1-mesa-glx: libgl1-mesa-glx N/A
version.xserver-xorg-core: xserver-xorg-core 2:1.20.8-2ubuntu2
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev N/A
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:19.1.0-1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20200226-1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.16-1

** Affects: linux
     Importance: Unknown
         Status: Unknown

** Affects: libxcb (Ubuntu)
     Importance: High
         Status: Confirmed

** Affects: xfwm4 (Ubuntu)
     Importance: High
         Status: Confirmed

** Affects: xserver-xorg-video-amdgpu (Ubuntu)
     Importance: High
         Status: Confirmed

** Affects: libxcb (Ubuntu Focal)
     Importance: Undecided
         Status: New

** Affects: xfwm4 (Ubuntu Focal)
     Importance: Undecided
         Status: Confirmed

** Affects: xserver-xorg-video-amdgpu (Ubuntu Focal)
     Importance: Undecided
         Status: New

** Affects: libxcb (Ubuntu Groovy)
     Importance: Undecided
         Status: New

** Affects: xfwm4 (Ubuntu Groovy)
     Importance: Undecided
         Status: Fix Released

** Affects: xserver-xorg-video-amdgpu (Ubuntu Groovy)
     Importance: Undecided
         Status: New

** Tags: apport-collected focal third-party-packages ubuntu
Regression: block staircase display with side-by-side monitors of different pixel widths
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