Plasma 5 screen scaling on 4K monitor causes Windows guest to be 1/4 size of window.

[Raydude]

This is a very specific bug to KDE / Plasma 5.

I have a laptop with a 4K display. KDE / Plasma 5 are not yet suited to the resolution. To help with icon size I selected System Settings => Display and Monitor => Scaled Display (button) and set the scale to 2.0.

This doubled all my icons nicely, but within the Windows 10 VM, the graphics were scaled to half resolution on both axes, but were not scaled back up to fill the screen. Mouse clicking was difficult because they were based on the full size of the window but the graphics were 1/2 size.

This is a small issue as I just turned of the Plasma feature to fix VirtualBox. And since it limits display resolution, it's probably not a good fix for the small icons.

[mhlavac]

As workaround use this:

1. Compute reverse ratio as 1 / SCALE_IN_PLASMA (in your case 1 / 2 = 0.5)
2. Run vbox as export QT_SCALE_FACTOR=0.5; VirtualBox --startvm vm-name

No it uses native resolution and you can use scaling feature in vbox to resize. It looks much better