Meanwhile, working on https://fifoci.dolphin-emu.org/ . Automated system to generate PNGs from FIFO logs for every new version of Dolphin, and provide a nice UI to see what revisions changed the rendering output + compare with the output from a real Gamecube rendering the FIFO log.
So far only the basics are there: starting a headless Xorg server with DRI support (was a lot harder than expected - using Xorg with the dummy output module seems to work well), running Dolphin in there with the OpenGL backend and "Dump Frames" enabled, running DolphinNoGui on a FIFO log, then using ffmpeg to dump frames from the AVI. Still missing a lot of things: running several instances in parallel on more than one FIFO log, detecting old versions of Dolphin that don't support disabling FIFO replay looping, adding timeouts and crashes detection, working on the visualization UI, ...
So far only the basics are there: starting a headless Xorg server with DRI support (was a lot harder than expected - using Xorg with the dummy output module seems to work well), running Dolphin in there with the OpenGL backend and "Dump Frames" enabled, running DolphinNoGui on a FIFO log, then using ffmpeg to dump frames from the AVI. Still missing a lot of things: running several instances in parallel on more than one FIFO log, detecting old versions of Dolphin that don't support disabling FIFO replay looping, adding timeouts and crashes detection, working on the visualization UI, ...