空前のシダ描画ブーム到来！？(^^;)
あなたも得意なプログラミング言語でシダを描画してみよう！

Clojure版は既出ですが、マルチスレッドでリアルタイムに描画するコードを書いてみました。
(バグとかご意見ありましたら https://twitter.com/akmiyoshi までお願いします)

project.clj

(defproject sida "1.0.0"
  :main sida.core
  :dependencies [[org.clojure/clojure "1.6.0"]
                 [quil "2.2.2"]])

src/sida/core.clj

(ns sida.core
  (:gen-class)
  (:require [quil.core :as quil]))

(def QUIL-WIDTH 500)
(def QUIL-HEIGHT 500)
(def PLOT-STEP 500)

(def quil-count (atom 0))
(def plot-count (atom 0))
(def plot-queue (new java.util.concurrent.ConcurrentLinkedQueue))

(defn setup []
  (quil/frame-rate 200) ;; 200 FPS
  (quil/no-smooth) ;; アンチエイリアスなし
  (quil/background 0 0 0) ;; 黒 ⇒ RGB(0,0,0)
  (quil/stroke 0 255 0) ;; 緑 ⇒ RGB(0,255,0)
  (quil/stroke-weight 1))

(defn draw []
  (let [$size (.size plot-queue)]
    (dotimes [_ $size]
      (let [[$x $y] (.poll plot-queue)]
        (quil/point
          (+ (* $x (quil/width) 0.98) (* (quil/width) 0.5))
          (- (quil/height) (* $y (quil/height) 0.98)))
        (swap! quil-count inc)))
    (when (> $size 0)
      (println "Draw-Thread: $size=" $size "(quil-count=" @quil-count ")"))))

(defn W1x [$x $y] (+ (* 0.836 $x) (* 0.044 $y)))
(defn W1y [$x $y] (+ (* -0.044 $x) (* 0.836 $y) 0.169))
(defn W2x [$x $y] (+ (* -0.141 $x) (* 0.302 $y)))
(defn W2y [$x $y] (+ (* 0.302 $x) (* 0.141 $y) 0.127))
(defn W3x [$x $y] (- (* 0.141 $x) (* 0.302 $y)))
(defn W3y [$x $y] (+ (* 0.302 $x) (* 0.141 $y) 0.169))
(defn W4x [$x $y] 0)
(defn W4y [$x $y] (* 0.175337 $y))

(defn plot [$x $y]
  (.add plot-queue (vector $x $y))
  (swap! plot-count inc)
  (cond
    (< @plot-count PLOT-STEP) (Thread/sleep 5)
    (= 0 (rem @plot-count PLOT-STEP)) (Thread/sleep 5)))

(defn f [$k $x $y]
  (cond
    (< 0 $k)
    (do
      (f (- $k 1) (W1x $x $y) (W1y $x $y))
      (when (< (rand) 0.3)
        (f (- $k 1) (W2x $x $y) (W2y $x $y)))
      (when (< (rand) 0.3)
        (f (- $k 1) (W3x $x $y) (W3y $x $y)))
      (when (< (rand) 0.3)
        (f (- $k 1) (W4x $x $y) (W4y $x $y)))
      )
    :else
    (plot $x $y)))

(defn -main [& args]
  ;; Start quil (draw) thread
  (quil/defsketch draw-thread
    :title "Sida in Clojure"
    :draw draw
    :setup setup
    :size [QUIL-WIDTH QUIL-HEIGHT]
    :features [:exit-on-close])
  (println "Main-Thread Start")
  (f 20 0 0)
  (println "Main-Thread End: plot-count=" @plot-count))