In fact it's just using the Axoloti's midi out, but fun to add a visual part. Or to use Processing as XY-controller, etc.
Processing uses the MidiBus library (install from Sketch -> Import Library... -> Add Library... -> 'The MidiBus')
A simple etch-a-sketch type implementation using 2 pots on the Axoloti, sent over midi cc, and receiving midi thru from Processing.
... but now having this problem