When I use Gnome's window scaling, the virtual display's image is scaled up too. This results in a blurry image on spice-based renderers. Starting a client (virt-manager or virt-viewer) with the GDK_SCALE=1 environment variable fixes the size of the rendered image, but will result in smaller size for GUI elements, compared to other applications. See https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=868687 for further details.
I'd like to add that I can get a correct resolution and sharp picture in virt-viewer if I set the zoom to 50% to compensate a scaling factor of 2, with the downside that it makes the mouse cursor huge in guests.
The issue is related to the widget changing its dimensions which would then change guest's resolution to fit that widget. See: https://bugzilla.gnome.org/show_bug.cgi?id=782997 You would test it will fullscreen in some virtual workspace and see that it should not change.. because of the above bug.
> You would test it will fullscreen in some virtual workspace and see that it > should not change.. because of the above bug. That bug seems to be about changing scaling factor while the program's running is not firing events about size change due to it. This one happens while the scaling factor has been set before startup, and is not changed while it is running.
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