Alt-Grave (`) switcher has flickering/pulsing shadow artifacts

[Nathaniel W. Turner]

1. Hold down Alt and keep it held down.
2. Press and release the key above Tab (Grave, or `). Keep alt held down.

While Alt is held down, the drop shadows for the window or windows of the current application will keep building up and then going back to normal and building up again. It's almost as though the windows are being redrawn may times per second into a buffer without clearing it first each time (but clearing it every second or so).

While this is happening, I notice that the drop shadow for the top bar does the same thing. This can also be observed if one uses Alt-Tab to select an app that has multiple windows that then expand out into a similar display.

I've observed this on systems with Intel, NVIDIA, and ATI display hardware, so I don't think it's hardware-specific.
All my Ubuntu systems have 2 or 3 monitors. I suspect multiple monitors are needed to reproduce this.

[Launchpad Janitor (janitor)]

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

[sumarlidason (sumarlidason)]

Affects me under workstation 9.0.4 (unity 7.2.5) & metal powered by nvidia gtx680

[Amr Ibrahim (amribrahim1987)]

A related (older and still open) bug https://bugs.launchpad.net/ubuntu/+source/unity/+bug/1328053

[Eleni Maria Stea (hikiko)]

Thank you, the video of #1328053 was really helpful!

[Amr Ibrahim (amribrahim1987)]

Eleni, should I mark this bug as a duplicate of the older one LP: #1328053?

[Jonathan Sahagun (jsahagun)]

Hello, a workaround that I have discovered is to disable framebuffer objects in the Compiz OpenGL plugin:

gsettings set org.compiz.opengl:/org/compiz/profiles/unity/plugins/opengl/ framebuffer-object false

Enter that in the terminal and it would take effect immediately; no logout required. Of course, we can expect that other desktop features that absolutely need OpenGL framebuffer objects might glitch or be affected in some way.

And again, this is just a workaround to make the unsightly behaviour go away, and by no means a fix. It does give a clue, though, that it's related to the use of framebuffer objects by whatever it is that renders shadows and glow effects.

[Jonathan Sahagun (jsahagun)]

Hello, one question: Is everyone affected by this bug using indicator-multiload?

I noticed just now that the frequency of the "pulsing" effect depends directly on the rate of update of the multiload indicator.

Removing the multiload indicator here on my computer also stopped the pulsing effect.

Also, just speculating here but I think it's possible that other animated indicator applets might cause the same behavior.

[Amr Ibrahim (amribrahim1987)]

I still have this in Xenial.

[sumarlidason (sumarlidason)]

@jsahagun it's been almost a year, but I think I was/am running indicator-multiload or similar.