Stumbled upon this page while searching for Clojure examples to try out with Griffon's brand new Clojure plugin. The provided example demonstrates how Clojure can be used in conjunction with Java2D to generate a Tree-like fractal, naturally I thought "hey, I bet it can be translated into a simple Griffon/Clojure app!". The following picture shows the result of this experiment



Now allow me to show you how it is done.

1. First, grab a copy of Griffon 0.1.2 if you haven't done so already.
2. Let's create the app, type griffon create-app fractal on your command prompt.
3. Go into the app's directory and type griffon install-plugin clojure, this will install the latest version of the Clojure plugin, along with the LangBridge plugin.
4. Alright, in order for the view to be able to call the drawing code written in Clojure we need an interface, let's call it FractalPainter. Go into src/interfaces and create a file named fractal/FractalPainter.groovy with the following content
   package fractal import java.awt.Graphics2D interface FractalPainter { void paint(Graphics2D g) }
5. Good, now for the actual Clojure code. Go into src/clojure and create a file named fractal/ClojureFractalPainter.clj with the following code
   (ns fractal.ClojureFractalPainter (:gen-class :implements [fractal.FractalPainter])) ; -- API START -- (defn radians [degrees] (. java.lang.Math toRadians degrees)) (defmacro rot [g2d angle & body] `(do (. ~g2d rotate (radians ~angle)) (do ~@body) (. ~g2d rotate (radians (- 0 ~angle))))) (defmacro trans [g2d dx dy & body] `(do (. ~g2d translate ~dx ~dy) (do ~@body) (. ~g2d translate (- 0 ~dx) (- 0 ~dy)))) ; -- API END -- ; -- CLIENT CODE START -- (defn draw_tree [g2d length depth] (if (> depth 0) (do (. g2d drawLine 0 0 length 0) (trans g2d (int length) 0 (rot g2d -30 (draw_tree g2d (* length 0.75) (- depth 1))) (rot g2d 30 (draw_tree g2d (* length 0.75) (- depth 1))) ) ))) (defn -paint [_ g2d] (draw_tree g2d 50 10)) ; -- CLIENT CODE END --The code is pretty much the same as the original, apart from changing the name of the main entry point from draw to paint.
6. Last piece of the puzzle is the view script itself, here we will call the ClojureFractalPainter.
   import fractal.* import java.awt.Graphics import javax.swing.JComponent class Canvas extends JComponent { Closure paint public void paintComponent(Graphics g) { if(paint) paint(this, g) } } fractalPainter = new ClojureFractalPainter() application(title:'fractal', size:[300,320], locationByPlatform:true, iconImage: imageIcon('/griffon-icon-48x48.png').image, iconImages: [imageIcon('/griffon-icon-48x48.png').image, imageIcon('/griffon-icon-32x32.png').image, imageIcon('/griffon-icon-16x16.png').image]) { widget(new Canvas(), paint: {c, g -> g.translate c.width/2, c.height*3/4 g.rotate Math.toRadians(-90) fractalPainter.paint(g) }) }
7. Run the application by typing griffon run-app.

As you can see, the view script is able to call an instance of ClojureFractalPainter implementation as if it were a regular Java class. Well, because it actually is. That is what the :gen-class macro does.

Keep on Groovying!