Update: went ahead and forked QuakeSpasm, rewriting most of the rendering code. Some before/after shots:
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Replying to @andrei_drexler
Longer term, I've developed a really bad itch to fork QuakeSpasm (which vkQuake is based on) and to try moving as much code as possible to the GPU, but that seems like a pretty big chunk of time and not just some weekend coding. One more thing on the infinity pile, I guess...