[Linux] [KDE5] Windows Guest scales incorrectly on High DPI host with Guest Additions

[JonasDeMoor]

Hello,

I have a Dell XPS 15 9530 with a high DPI (3200x1800) screen. I'm running Arch Linux with KDE Plasma 5, which has support for high resolution displays.

With the migration of VirtualBox to QT 5, the GUI scales very well and is a pleasure to use on my high DPI screen. Except for one problem: when I install the VirtualBox Guest Additions on a Windows 8.1 or 10 host, the VM only fills up a quarter of the screen; the rest is black. The strange thing is that this only happens when the Guest Additions are installed on the Windows Guest. Without them, it runs fine.

Input is also registered wrong: I have to move in the "black area" in order to be able to click on something on the Windows desktop.

Another strange thing is that when pausing the VM, VirtualBox scales the VM perfectly fine, but when resuming, it's gone.

I attached screenshots to make things a little bit more clear, together with the VBox.log file from a Windows 8.1 guest.

[JonasDeMoor]

Windows 8.1 start screen with Guest Additions installed

[JonasDeMoor]

Windows 8.1 Desktop when VM is paused

[JonasDeMoor]

Log file of Windows 8.1 VM

[Frank Mehnert]

Could you test the most recent 5.1 Guest Additions image from here?

[JonasDeMoor]

Replying to frank:

Could you test the most recent 5.1 Guest Additions image from here?

Thank you for your reply. I'll test out the Guest Additions from the link you provided and report back.

[JonasDeMoor]

Replying to JonasDeMoor:

Replying to frank:

Could you test the most recent 5.1 Guest Additions image from here?

Thank you for your reply. I'll test out the Guest Additions from the link you provided and report back.

Latest Guest Additions didn't do the trick: still the same issue as described in the bug report.

[grueni75]

I have the same problem. KDE sets the env variable QT_DEVICE_PIXEL_RATIO to 2. So all QT applications scale their GUI for the high density screen. It seems that VirtualBox is some how using this also for the guest display in a wrong way. If you set the variable to 1, the guest resolution works as expected. But the GUI does not scale anymore...

[matthew-nm]

I would like to report experiencing the same issue.

• PC: Dell XPS 13 9350
• OS: Ubuntu running KDE package
• VM: Windows 10 Home

I used the Guest Additions to allow scaling to resolutions that match my machine's resolution, and while the active area of the VM window is the correct size (including mouse interactions), the actual graphics of the Windows 10 VM are scaled down to the ratio provided by KDE. My KDE is setup with a scale factor of 1.5, and for some reason, the Windows 10 VM is scaling down by as much, just like the original poster's Screen1.png image.

[antonp-im]

I hit a possibly related issue under KDE, though it looked more like the dpi was wrong. I found a workaround if launching via shell of

export QT_AUTO_SCREEN_SCALE_FACTOR= QT_SCREEN_SCALE_FACTORS= QT_SCALE_FACTOR=

before launching my vm window from command line. Hope it helps someone else out

[Aetf]

I'm still getting the same issue using the latest 5.2.12 version of VirtualBox.