@dc42:
This is something for the generation 3 Duets, because it needs more RAM than the current generation has and an RTOS. I already have plans for the next-generation firmware to read multiple streams of GCode from SD files at once.
Could it be done atm by assigning all the heads to a color mix mode, and instead of changing the tool, pushing a % ratio of the second, third or fourth color/material? Since for the e3d setup there’s no motion attached to the head but is a parking system if the wipe is fixed a-la bcn3dsigma as long as you can send a gcode to push 2/3/4 purge it would be already be purging (that’s the slowest part along heat/cooling). But for heat/cooling Cura already has a nice code to preheat before use, so mostly the remaining thing is just the purge.
Ofc multi gcode streams could be really nice, specially if the machine doesn’t ise a park system, but maybe (atm) is a bit overkill.
The only issue I see on my % theory is that the gcode will force the purge speed. But maybe that could be separated somehow, like just sending a G0 Purge&DontwaitToolX ?