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Comment by littlecranky67 | Hacker News Reader

I remember back in the day of AGP cards around 2002, you could use a 3d card on linux to render the grafix but use a different GPU for the actual output. I used XFree86 on linux with a voodoo banshee (or maybe was a riva tnt2) and a matrox mga200 for its sync-on-green support with my monitor to play games.

I know modern card architecture doesn't support this out of the box, but what is the actuall problem of forwarding a once-rendered frame to another card for output? Sureley DMA transfers PCIe->RAM->PCIe nowaday are fast enough to saturate 60fps at 4K?

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Trivial to do this on Linux. I run my desktop on the on-chip Ryzen 9950X iGPU and I offload games to my nVidia dGPU.

I had a crazier setup in the past with the Intel i7-8809G APU: it had an AMD iGPU for desktop connected to the display, nVidia eGPU for games and the Intel iGPU for video encoding.

Of course there is additional latency due to frame copying, but I can’t notice it in practice.

I had that setup working back in the day with a Voodoo1 which had the pass-trough construction to take over full screen: only on Linux you could read the completed frames and render them in an X window. It was dog slow though.

While transfers have improved a lot the amount data needed for 4K60 with HDR is about 18Gbps. There's no way that doesn't have an impact.

We cooked up a setup where we had a PCI video card for X, and a separate Voodoo 1 or 2 and monitor for 3D (Mesa) rendering. I don't remember the details any more, but it was nice to not take out the desktop when someone borked up their OGL homework.

the voodoo1 worked differently as you looped through the video input. The voodoo banshee i mentioned was a separate 2d/3d card (it actually was 3DFx first true, combined 2d/3d card - not an accelerator).

I know. Voodoo 1 and 2 had the ugly VGA passthrough hack. But the principle of reading VRAM from one card and copying it to another would remain the same I think.

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