Moxi paper: http://visgraph.cse.ust.hk/MoXi/moxi.pdf
Demo video: https://www.youtube.com/watch?v=Weq3VG_Hqic&ab_channel=CachaH
To paint a stroke, hold space while moving your brush.
A: decrease brush size
D: increase brush size
↓: decrease pigment concentration in brush
↑: increase pigment concentration in brush
←: decrease water (rho) concentration in brush
→: increase water (rho) concentration in brush