Scaling filter preference

I'm viewing a low-DPI guest on a high-DPI screen. The guest has 1920x1080 resolution, the host has 3840x2160. When I go fullscreen with virt-viewer (or virt-manager's viewer, I guess they both use spice-gtk), the guest is all blurry.

What I'd like, if the guest screen is resized by an integer factor, is an absence of any antialiasing whatsoever. Just larger pixels.

Can we have it, please? Or, where should I look to make a local patch for myself to enable this? I could live with this too.

For an example, have a look at how VirtualBox does it. At 200% scale, the image is sharp.