move_particles   xtlang

(bind-func move_particles
  "move the particles_verts according to their velocities"
  (lambda (np:i64 step:float)
    (let ((p:float* null))
      (doloop (i np)
        (set! p (pref-ptr particles_verts (* i 4)))
        ;; update x pos
        (pset! p 0 (% (+ (pref p 0)
                         (* (pref p 2) step))
                      1.0))
        ;; update y pos
        (pset! p 1 (% (+ (pref p 1)
                         (* (pref p 3) step))
                      1.0))))))