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Comment by yjftsjthsd-h | Hacker News Reader

I can't quite figure out what this is. Is it a way to run KVM VMs but make their windows show up on the host without a virtual "screen" that you have in a window?

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My understanding, though I've not played with it, is that Looking Glass is a way to have hardware GPU accelerated guests "render in a window on the host." Normally, GPU passthrough for gaming has involved "You pass an entire GPU through to the guest, and use a separate monitor connection from that GPU for the output." So it's a VM, but not in the "interacts with the rest of the system as a first class window" sort of way.

I believe Looking Glass is a collection of techniques to pass a framebuffer from the GPU accelerated guest "monitor" back to the host, so you can have full hardware GPU acceleration in a guest, and still treat it like a window. I've not messed with it, though. Hm. Though I've got enough hardware to, right now...

What it does is uses a PCIe pass-through GPU to render the output, but instead of sending the actual video result to the actual GPU output (and thus, needing to switch input on your monitor), it renders from the GPU into a shared memory buffer which the host can display (in a window, or full screen). So it sortof works like remote desktop, but lower latency and full resolution due to using a shared memory buffer instead of TCP.

Yes. It's a way to have a "viewer" of the VMs screen that has as little latency as possible. My understanding is that this is achieved by configuring shared memory between host and guest. It uses some nvidia capture api/sdk to capture the screen of the guest and write it to that shared memory.

It has a server component running on the guest and a client component running on the host. I've been using it for a while with a windows 11 guest. It works but I wouldn't say it's production ready as I often get crashes. Though it's usually the server/windows component that crashes and not the client.

If going for a passthrough setup I'd generally recommend setting up evdev. It allows you to switch keayboard and mouse input to the vm by e.g. pressing both Ctrl keys. I then just have to change the video input on my display.

> change the video input on my display

Many monitors support input switching via DDC, using CLI software that can be mapped to a hotkey with keyboard macro automation, https://joostrijneveld.nl/posts/2024-06-04-ddc-input-switchi...

It's a good addition. The reason why I personally don't have this setup is ironically because of Looking Glass. Sometimes I want to switch my mouse and keyboard over but still want to just see the video output of my vm in a Looking Glass client window.

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