Sometimes a single white pixel shows in the top-left corner

[Hernando Torque]

From time to time a single white pixel shows up in the top-left corner. The pixel stays above fullscreen windows, and xwininfo reports whatever is under the pixel (Unity panel, VLC player). Restarting Compiz gets rid of the pixel.

I tried hard, but unfortunately I haven't found a way to reproduce it.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: unity 5.4.0-0ubuntu2
ProcVersionSignature: Ubuntu 3.2.0-17.27-generic 3.2.6
Uname: Linux 3.2.0-17-generic x86_64
.tmp.unity.support.test.0:

ApportVersion: 1.93-0ubuntu2
Architecture: amd64
CompizPlugins: [core,composite,opengl,decor,mousepoll,vpswitch,regex,animation,snap,expo,move,compiztoolbox,place,grid,imgpng,gnomecompat,wall,ezoom,workarounds,resize,fade,unitymtgrabhandles,scale,session,unityshell]
CompositorRunning: compiz
Date: Fri Mar 2 11:45:04 2012
DistUpgraded: Fresh install
DistroCodename: precise
DistroVariant: ubuntu
DkmsStatus: virtualbox, 4.1.8, 3.2.0-17-generic, x86_64: installed
GraphicsCard:
 Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller [8086:0112] (rev 09) (prog-if 00 [VGA controller])
   Subsystem: ASUSTeK Computer Inc. Device [1043:844d]
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Beta amd64 (20110901)
MachineType: System manufacturer System Product Name
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.2.0-17-generic root=UUID=64497123-e956-42c2-82d8-b6319a96ee9f ro quiet splash bootchart=disable elevator=deadline vt.handoff=7
SourcePackage: unity
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 09/19/2011
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 0902
dmi.board.asset.tag: To be filled by O.E.M.
dmi.board.name: P8Z68-V
dmi.board.vendor: ASUSTeK Computer INC.
dmi.board.version: Rev 1.xx
dmi.chassis.asset.tag: Asset-1234567890
dmi.chassis.type: 3
dmi.chassis.vendor: Chassis Manufacture
dmi.chassis.version: Chassis Version
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr0902:bd09/19/2011:svnSystemmanufacturer:pnSystemProductName:pvrSystemVersion:rvnASUSTeKComputerINC.:rnP8Z68-V:rvrRev1.xx:cvnChassisManufacture:ct3:cvrChassisVersion:
dmi.product.name: System Product Name
dmi.product.version: System Version
dmi.sys.vendor: System manufacturer
version.compiz: compiz 1:0.9.7.0~bzr2995-0ubuntu5
version.ia32-libs: ia32-libs 20090808ubuntu33
version.libdrm2: libdrm2 2.4.30-1ubuntu1
version.libgl1-mesa-dri: libgl1-mesa-dri 8.0.1-0ubuntu2
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental 8.0.1-0ubuntu2
version.libgl1-mesa-glx: libgl1-mesa-glx 8.0.1-0ubuntu2
version.xserver-xorg-core: xserver-xorg-core 2:1.11.4-0ubuntu4
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.6.99.901+git20120126-0ubuntu2
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:6.14.99~git20111219.aacbd629-0ubuntu2
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.17.0-1ubuntu4
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:0.0.16+git20111201+b5534a1-1build2

[Miklos Juhasz (mjuhasz)]

I experience this problem on Oneiric as well, both with fglrx and with Intel drivers.
The white pixel disappears if I activate the workspace switcher (Super+S) but comes back as soon as I exit it (Super+S again). The white pixel disappears for a short moment if I navigate to a different workspace with Ctrl+Alt+Arrow.

[Hernando Torque (htorque)]

I can confirm your observation. The pixel is gone with the activated workspace switcher and during workspace switches using Ctrl+Alt+Arrow.

[Hernando Torque (htorque)]

No definite way to reproduce it, but watching a YouTube clip (not HTML5) and browsing a flash-heavy site like http://www.tmz.com with Chromium raises the possibility for the pixel to show (and it persists after closing the browser).

[Hernando Torque (htorque)]

Just ran Unity with the -v switch and found lots of window stacking warnings from Compiz:

    compiz (core) - Debug: stacks are out of sync

so maybe this isn't a Unity problem.

[Daniel van Vugt (vanvugt)]

I've had this bug for a long time. Since 11.04 I think. I swear it was logged already though.

It's likely this is a duplicate of bug 940603.

[Hernando Torque (htorque)]

Probably (I have seen the examples there too, but not at the high frequency of this one). I subscribed to it and will update this one accordingly.

Opening sites with flash content definitely helps getting the stack out of sync.

[Hernando Torque (htorque)]

Should the trigger for bug 940603 indeed be the focus mode of Compiz' "Animation" plugin, then this one is no dupe as I just got the pixel again. However, it appeared less frequent over the last few days.

[Hernando Torque (htorque)]

Disabling the animation plugin in Compiz makes this bug and bug 940603 stop. Marking as duplicate.