Adaption of tween function to use requestAnimationFrame

tween.cljc

(ns tween
  "Simple tweening of values inside a map atom.")

(defn easeOutQuad
  [elapsed-t duration]
  (let [dt (/ elapsed-t duration)]
    (* dt (- 2 dt))))

(defn easeLinear
  [elapsed-t duration]
  (let [dt (/ elapsed-t duration)]
    dt))

#?(:cljs
   (defn tween-to! [state easing key new-value duration]
     (let [anim-key (keyword (str (name key) "-anim"))
           initial-value (key @state)]
       (letfn [(tick [_]
                 (let [a-map (anim-key @state)
                       t (- (.now js/Date) (::t0 a-map))]
                   (if (< t duration)
                     (let [progress (easing t duration)
                           new-val (+ (::initial-value a-map)
                                      (* progress (::delta a-map)))]
                       (swap! state assoc key new-val
                              ::ticker (js/requestAnimationFrame tick)))
                     (do
                       (js/cancelAnimationFrame (::ticker a-map))
                       (swap! state dissoc anim-key)
                       (swap! state assoc key new-value)))))]

         (swap! state assoc anim-key
                {::t0            (.now js/Date.)
                 ::ticker        (js/requestAnimationFrame tick)
                 ::delta         (- new-value initial-value)
                 ::initial-value initial-value}))))
   :clj
   (defn tween-to! [state easing key new-value duration]
     (swap! state assoc key new-value)))