VirtualBox 5.0 regression: full screen mode with composite manager works incorrectly

[coriolan]

Just upgraded to VirtualBox 5.0 (host: Ubuntu 14.04 amd64, guest: Windows). Relevant extension pack and guest additions installed.

PROBLEM: When switching to full screen mode, the VM screen resizes all right to fill the screen, but the screen is dimmed (brightess is reduced). Looks similar to the effect when you pause the VM, but not quite.

INVESTIGATION: I narrowed down the problem to compton, a compositor for X11. When compton is killed, the fullscreen mode works fine.

Previously, with VirtualBox 4.3.30 (and many versions before that), fullscreen mode used to work correctly with compton.

[Michael Thayer]

Thanks for the report. While this is definitely of interest to us I suspect that we will not find time to look at it in the near future due to other high priority things we need to work on. If you want to speed things up you might ask the compton developers<1> (they apparently have an IRC channel on FreeNode) if they have any idea about this - if someone can point us quickly to the cause of the problem the chances we will be able to fix it soon are much higher.

Unrelated, but it is always a good idea to attach a log file from a virtual machine run to any bug ticket you open.

<1> ​https://github.com/chjj/compton

[Dsen]

That's curious,
This probably can be related to the mini-toolbar. Under X11 mini-toolbar in full-screen/seamless modes have to be of the same type/geometry as machine-window itself (required for multi-screen support under various WMs), that forced us to do it of the full-screen/seamless size as well (in current implementation). His visible part restricted by the shape extension while shadow removed by the composition extension (translucency support is required). So probably you see the shadow of the mini-toolbar which means your composition doesn't work properly. Could you please disable the mini-toolbar at all to confirm that there is no described issue in that case?
Thanks in advance!