Duck Hunt Experiment

Last week, I came across this post via Hacker News, which explains how the gun for the original duck hunt game worked. The idea behind the gun seemed simple and elegant that I had to give it a shot.

It works like this, everytime you pull the trigger the screen goes black for a while in which time the light sensor on the gun take a reading which is used as a reference point, then it paints each target on the frame white and takes another reading the difference between the two is used to determine if the gun is pointing to the target or not.

(ns duck-hunt
  (:use :reload-all [clodiuno core firmata])
  (:import (java.awt Toolkit Color)
	   (java.awt.image BufferedImage)
	   (java.awt.event KeyAdapter)
	   (javax.swing JFrame JPanel)))

(defn screen-size []
  (let [screen (.getScreenSize (. java.awt.Toolkit getDefaultToolkit))]
    [(.getWidth screen) (.getHeight screen)]))

(def photo-pin 0)
(def button-pin 5)

(defn init-arduino []
  (doto (arduino :firmata "/dev/tty.usbserial-A6008nhh")
    (pin-mode button-pin INPUT)
    (enable-pin :analog photo-pin)
    (enable-pin :digital button-pin)))

On the Arduino side we don't need much, we only need a photoresistor / photodiode and a button.

(defn place-duck []
  (let [[width height] (screen-size)
	dir-x (if (= (rand-int 2) 0) -1 1)]
    [(/ width 2) height 50 [dir-x -1]]))

(defn move-duck [duck]
  (let [step 10
	[x y size [dir-x dir-y]] duck
	nx (cond (= 1 dir-x) (+ x step)
		 (= -1 dir-x) (- x step)
		 :default x)
	ny (cond (= 1 dir-y) (+ y step)
		 (= -1 dir-y) (- y step)
		 :default y)]
    [nx ny size [dir-x dir-y]]))

(defn step-ducks [state]
  (let [[width height] (screen-size)]
    (->> (map move-duck (:ducks @state))
       (reduce (fn[h v]
		 (let [[x y size [dir-x dir-y]] v]
		   (if (or (< y 0)
			   (> y height))
		     (conj h (place-duck))
		     (conj h v)))) []))))

At first the idea was to use a duck sprite but I couldn't find a sprite sheet of a flying duck so I used boxes instead. A duck consists of its coordinates (x/y), size and direction. Everytime we repaint the scene we move the ducks on the screen 10 pixels in their direction.

(defn state []
  (let [[width height] (screen-size)]
    (ref {:loop true
	  :scene (BufferedImage. width height BufferedImage/TYPE_INT_RGB)
	  :ducks [(place-duck)]})))

Game state consists of an image which we will draw the scenes on and a list of boxes on the screen.

(defn draw-background [g c]
  (let [[width height] (screen-size)]
    (.setColor g c)
    (.fillRect g 0 0 width height)))

(defn draw-duck [g c [x y size _]]
  (.setColor g c)
  (.fillRect g x y size size))

(defn draw-ducks [g c s]
  (doseq [duck (:ducks @s)] 
    (draw-duck g c duck)))

(defn draw-scene [g p s]
  (draw-background g Color/blue)
  (draw-ducks g Color/red s)
  (.repaint p))

There is not much to draw on the scene just some boxes.

(defn read-base [board g panel]
  (draw-background g Color/black)
  (.repaint panel)
  (Thread/sleep 100)
  (analog-read board photo-pin))

(defn read-duck [board g panel duck]
  (draw-background g Color/black)
  (draw-duck g Color/white duck)
  (.repaint panel)
  (Thread/sleep 100)
  (analog-read board photo-pin))

(defn triggered? [board]
  (if (= 1 (digital-read board button-pin))
    true false))

(defn handle-trigger [board state g panel]
  (let [base (read-base board g panel)]
    (map #(let [[x y size _] %
		diff (- base (read-duck board g panel %))]
	    (println "Diff:" diff)
	    (if (> diff -100)
	      [x y size [0 1]] %))
	 (:ducks @state))))

(defn game-loop [board state panel]
  (while (:loop @state)
    (let [g (.getGraphics (:scene @state))]
      (dosync
       (alter state assoc :ducks (step-ducks state))
       (when (triggered? board)
	 (alter state assoc :ducks (handle-trigger board state g panel))))
      (draw-scene g panel state)
      (Thread/sleep 50)))
  (close board))

In game-loop we periodically move the boxes around and check if the button is triggered, as soon as the button is pressed we paint the screen black and get a reading which we use as a reference point, then we replace each box on the screen with a white box and get another reading, if the difference is above a certain threshold we assume gun is pointing at the target.

(defn key-listener [state frame]
  (proxy [KeyAdapter] [] 
    (keyReleased 
     [e]
     (dosync (alter state assoc :loop false))
     (.setVisible frame false))))

We need to make sure, Arduino connection is closed when we are done or bad things will happen, any key event will cause the game-loop to exit and hide the frame.

(defn sketch []
  (let [board  (init-arduino)
	state (state)
	[width height] (screen-size)
	panel  (proxy [JPanel] []
		 (paintComponent [g] (.drawImage g (:scene @state) 0 0 this)))
	frame (JFrame.)]
    (doto frame
      (.add panel)
      (.addKeyListener (key-listener state frame))
      (.setBackground (java.awt.Color. 0 0 0 0))
      (.setUndecorated true)
      (.setAlwaysOnTop true)
      (.setSize (java.awt.Dimension. width height))
      (.setVisible true))
    (future (game-loop board state panel))))