(def side 500)
(def cols side)
(def rows side)
(def dampling 0.99)

(def current (volatile! (clj->js (mapv (fn [_] (mapv (constantly 0) (range side))) (range side)))))
(def previous (volatile! (clj->js (mapv (fn [_] (mapv (constantly 0) (range side))) (range side)))))
(def temp (volatile! (clj->js (mapv (fn [_] (mapv (constantly 0) (range side))) (range side)))))

(defn mouse-dragged []
  (let [x (Math/floor js/mouseX)
        y (Math/floor js/mouseY)]
    (aset @previous x y 2550)))

(defn setup []
  (js/pixelDensity 1)
  (let [canvas (js/createCanvas cols rows)]
    (.parent canvas "p5jsparent")
    (js/loadPixels)))

(defn draw []
  (js/background 0)
  (js/loadPixels)

  (doseq [i (range 1 (dec cols))
          j (range 1 (dec rows))]
    (let [index (* 4 (+ i (* j cols)))
          n-value (* dampling
                     (-
                      (/
                       (+
                        (aget @previous (inc i) j)
                        (aget @previous (dec i) j)
                        (aget @previous i (inc j))
                        (aget @previous i (dec j)))
                       2)
                      (aget @current i j)))]
      (aset @current i j n-value)
      (aset js/pixels index       n-value)
      (aset js/pixels (+ index 1) n-value)
      (aset js/pixels (+ index 2) n-value)))
  (js/updatePixels)
  (vreset! temp @previous)
  (vreset! previous @current)
  (vreset! current @temp))