(bind-func fluid-step-cube
(lambda (cube:fluidcube*)
(let ((N (tref cube 0))
(dt (tref cube 1))
(diff (tref cube 2))
(visc (tref cube 3))
(s (tref cube 4))
(k 0)
(kk 0)
(density (tref cube 5))
(Vx (tref cube 6))
(Vy (tref cube 7))
(Vz (tref cube 8))
(Vx0 (tref cube 9))
(Vy0 (tref cube 10))
(Vz0 (tref cube 11)))