fluid-cube-add-velocity   xtlang

(bind-func fluid-cube-add-velocity
  (lambda (cube:fluidcube* x y z amount-x:double amount-y:double amount-z:double)
    (let ((N (tref cube 0))
    (idx (fluid-ix x y z N))
    (_Vx (tref cube 6))
    (_Vy (tref cube 7))
    (_Vz (tref cube 8)))
      (pset! _Vx idx (+ amount-x (pref _Vx idx)))
      (pset! _Vy idx (+ amount-y (pref _Vy idx)))
      (pset! _Vz idx (+ amount-z (pref _Vz idx)))
      cube)))