virtualbox.org

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[ModEdit; related ticket: #17627: Unconditional upscaling of display on HIDPI systems]

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Hi,

I am using Virtualbox on a linux system equipped with a 4k display running KDE (with a scaling-factor of 1.4).
Everything works well, except for VirtualBox - which somehow tries to scale the emulated display and even reports wrong resolution to the guest OS (despite scaling is set to 100% in the VM's preferences).
Please see the attached screenshot - this was a maximized VirtualBox window on the 3840x2160 display, yet the guest OS reports only a fraction of that.

Any hints about how to solve this issue are highly appreciated.

best regards, Clemens

MrOSE wrote:with a scaling-factor of 1.4 ... 3840x2160 display

With a scaling factor of 1.4, your display becomes:

• 3840 / 1.4 = 2743
  2160 / 1.4 = 1542

And if you take out ~100 px for taskbar/menubar/window decorations, that should be ~ 1442.

With a scaling factor of 1.4, your display becomes

Sure, but the question is - how can I avoid image upscaling by VirtualBox, as the OS I run is already high-dpi capable.
The "scale factor" setting in VM settings is already at 100% - the lowest possible value the GUI allows.

Furthermore I don't understand why VirtualBox is upscaling the display using simple image upscaling - this way it is almost guaranteed to destroy text in a way to be almost unreadable (just take a look at the screenshot).

Best regards, Clemens

I am rather sure this is a bug in VirtualBox. It unconditionally applies bitmap-scaling to the virtual display (and limiting the slider in the VM preferences to 100% artificially removes the possibility to counteract that behaviour): https://www.virtualbox.org/ticket/17627

As this one is really bothersome I wonder - do VirtualBox devs accept pull requests?

Br, Clemens

Had the same issue on Arch with Plasma; but included some other Qt application artefacts.
Update and reboot later and everything is back to normal. I suspect a Qt libs and VirtualBox version mismatch.

HansComps wrote:Had the same issue on Arch with Plasma; but included some other Qt application artefacts.
Update and reboot later and everything is back to normal. I suspect a Qt libs and VirtualBox version mismatch.

Thanks for the hint! On my Fedora-27 system the issue is not fixed - but indeed after updating less worse.
Now the pixel-based scaleup of the display seems to be performed with at least billinear scaling - so fonts stay at least readable (but blurry).