Intermittent display resolution issues

Discussions about using Windows guests in VirtualBox.
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Ian P
Posts: 7
Joined: 10. Sep 2021, 19:31

Intermittent display resolution issues

Post by Ian P »

Hi. I have a Windows 10 VM running in a Windows 10 host, and have a display resolution issue that pops up intermittently which I've hit a few times now. I have 3 1920x1080 monitors, all enabled in the guest, and have hit variants of the following a few times, but this was the worst one yet. Last night all was fine, and when I finished for the evening I left the guest running with all 3 monitors in full screen mode at 1920x1080. This morning the guest was still running, but two things had changed:

1. The primary monitor was now showing a smaller (1280x800 I think) screen (not scaled), and the other two had reduced vertically to something like 1920x997. When I tried to adjust the resolutions back in the guest OSes, none of them offered anything bigger than those. After dropping out of full screen mode, the vbox view menu did give options to resize the virtual screen that included 1920x1080, but when I tried to select that, it got ignored and nothing changed.

2. The desktop background had changed to that of the host. This is very strange because it is a photo that I took myself and I never copied the image file onto the guest (it is now there as %appdata%\local\microsoft\windows\themes\roamedthemefiles\desktopbackground\desktopwallpaper-1920x1080.jpg) so the guest seems to have somehow sucked it across from the host. I assume that this is something to do with having previously used seamless mode (I don't normally use it, but have switched to it to combat this issue in the past - see below).

I spent a lot of time powering off and changing the VM display settings, all to no effect. Disabling 2 of the 3 monitors left the primary display still with the reduced resolution. I then tried switching the VM display modes back and forth, and finally got it back to normal with the guest again operating at 1920x1080. I think that this is what did it:

1. Enabled seamless mode. I now got the guest desktop display showing over the host desktop on the primary monitor, taking the full 1920x1080 display apart from the host's taskbar.
2. Set the host's taskbar to auto-hide. The guest desktop now expanded to the full 1920x1080 size.
3. Switched the guest to full screen mode and, hey-presto, it went full screen at 1920x1080.

I don't remember if I had already re-enabled the other two monitors, or if I enabled them after that, but at the end I again had the guest with all 3 monitors displaying 1920x1080 resolution.

Anyone know anything about the reason for this, and any ideas on how to avoid it happening again?

Ian
Ian P
Posts: 7
Joined: 10. Sep 2021, 19:31

Re: Intermittent display resolution issues

Post by Ian P »

It just happened again. This time I was working in the guest Windows-10 OS using full-screen mode with the 3 monitor all at 1920x1080 resolution, when the power went out. When it came back on and I started up the VM, all 3 displays were initially showing as small windows, but then as Windows started up two of them disappeared. Once it was booted I found that the primary monitor was now limited to 1280x960, and Windows had disconnected the other two. I told it to extend the display to which re-enabled them, but this time limited to 1280x1024 (note, a bit bigger than the primary).

So I did the trick of switching the VM to seamless mode, setting the host Windows system to auto-hide its taskbar (allowing the guest display to take the full screen) and then switching back to full screen mode, and then all was good again with all 3 displays at 1920x1080 in the guest. Note that if I don't auto-hide the host system's taskbar then the guest display on that monitor ends up limited to 1920x1040.

At least I now have a quick-and-easy way to recover when it happens.
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