[Resolved] Windows 10, 3d accelleration, and scaling

[JackG]

I've been running a Windows 10 guest on an Ubuntu 18.04 64-bit (fully updated as of today), KDE Spin (kubuntu) host for a while. All of a sudden after a reboot of my host my guest came up looking very pixelated. I saw that 3d accell wasn't on, so I enabled it. With 3d acceleration enabled the guest comes up looking clean, but only taking up a portion of the window. The mouse behaves as though the guest filled the window. Resizing works, but with the same symptoms. I updated to the latest .deb from VirtualBox org (5.2.18-1234319_Ubuntu_bionic_amd64) and the latest guest additions (downloaded through the VM GUI), and nothing has changed. All works well but looks ugly without 3d accelleration enabled, 3d accell only takes up part of the window with the mouse using all of the window.

I've seen similar symptoms reported on Mac hosts, and the solution was to check a "no scaling" option on the display configuration, but no such box exists on Linux, or at least when I run it. I have disabled the font scaling option in KDE, and nothing changed.

What changed? Any way out of this mess? I've attached the "showvminfo" and VirtualBox log to this post.

[JackG]

VBox is definitely doing some scaling. The underlying display is 3840x2160, but in full screen mode the Windows 10 guest sees it as 2954x1662. Not that both dimentions are scaled the same amount. How do I get this to stop?

[JackG]

I found that I had KDE's display scaling set to exactly the mismatch between what Windows was seeing and what it should have seen in the display size. So turning the KDE display scaling back to 100% fixed my issue.

I still have no idea what changed between my last reboot and today, and now I have the fun of making my Kubuntu host look right now that VBox doesn't play well with KDE display scaling anymore. Argh.

[socratis]

So turning the KDE display scaling back to 100% fixed my issue.

Glad you got it going and thanks for the feedback. Marking as [Resolved].