Window size with DPI scaling

[Dadou]

Hello everyone,

I am having some trouble with DPI settings with VirtualBox:
My host OS is Windows 8.1 Professional x64 and I am running a Debian x64 Virtual Machine with the latest version of VirtualBox (5.0.8 ). The machine runs fine, I installed the guest additions and resizing works but something is bothering me: On my main monitor (a 28" 4K monitor),the virtualBox window has a normal size (rather small but it is normal since it has a high DPI) .
But when I drag the window on my secondary monitor, it is downsized in order to look the same size on the two monitors. It means it has more than 1 "virtual pixel" per actual pixel on the screen and it looks blurry. In simple words, I can have a 2560x1440 guest display on a 1920x1080 monitor.... I would like it to be the same size as the screen.

I ticked "disable dispaly scaling on high DPI settings" on compatibility tab of virtualbox.exe properties and this setting properly applies to VirtualBox main windows: it is not resied anymore when I move it to another display, but the window of the VM itself is still affected...
I don't understand how comes this window is not affected by the setting...

I can make the window look like its normal size on the secondary display by using a 150% scale factor in VB settings but the guest OS is still blurry, I guess because it is downsized by Windows and its stupid scaling functionnality and then resized by VirtualBox...
I can also make it work properly by completely disabling Windows DPI scaling but then my 4k monitor becomes unusable because everything is ridiculously small so sadly this is not an option...