With the help and suggestions of Bluesabre on #xubuntu-devel we've tracked it down to a recent change in xfwm4 where it switched from using glx to xpresent:
https://git.xfce.org/xfce/xfwm4/commit/?id=23900123ad8418149897a094d1096d6ecb984d3c which seems to be a bug in the driver as mentioned orginally: https://bugzilla.xfce.org/show_bug.cgi?id=16716 => https://gitlab.freedesktop.org/xorg/driver/xf86-video-amdgpu/-/issues/10 It is also SPECIFIC to the resolution selected on the external HDMI display. In our case the Lenovo E495 has eDP 1920x1080 and external HDMI are 168x1050 and are affected. I tried with another external HDMI that is natively 1920x1200 and couldn't reproduce UNTIL I set it to use 1680x1050 instead of its preferred resolution, at which point the blocked staircase returned. As I said above it feels like an off-by-one bug on the assumption rendering the display is split into regions (columns) and it is rendering 1920 pixels to a 1680 wide output with the pixels 1680-1919 wrapping to the next 'row'. ** Bug watch added: Xfce Bugzilla #16716 https://bugzilla.xfce.org/show_bug.cgi?id=16716 ** Bug watch added: gitlab.freedesktop.org/xorg/driver/xf86-video-amdgpu/-/issues #10 https://gitlab.freedesktop.org/xorg/driver/xf86-video-amdgpu/-/issues/10 -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to libxcb in Ubuntu. https://bugs.launchpad.net/bugs/1873895 Title: Regression: block staircase display with side-by-side monitors Status in libxcb package in Ubuntu: New Status in xfwm4 package in Ubuntu: New Status in xserver-xorg-video-amdgpu package in Ubuntu: New Bug description: 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 https://gitlab.freedesktop.org/xorg/driver/xf86-video- amdgpu/-/issues/10 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 problem. 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 GraphicsCard: 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 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/libxcb/+bug/1873895/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp
