Minimal Processing app with Clojure

core.clj

(ns processing-with-clojure.core
  (:gen-class
    :extends processing.core.PApplet)                       ;; we need a class extending processing.core.PApplet
  (:import (processing.core PConstants PApplet)))

(defn -main
  [& args]
  (PApplet/main "processing_with_clojure.core"))            ;; generated class name has underscores(_)
                                                            ;; instead of hyphens(-)

(defn -settings [this]                                      ;; override settings() method
  (.size this 640 480 PConstants/P3D))                      ;; equivalent of size(640, 480, P3D)

(defn -setup [this]                                         ;; override setup() method
  (.background this 255 255 255))                           ;; equivalent of background(255, 255, 255)

(defn -draw [this]                                          ;; override draw() method
  (if (.-mousePressed this)
    (.fill this 0)
    (.fill this 255))
  (let [x (.-mouseX this)
        y (.-mouseY this)
        width 80
        height 80]
    (.ellipse this x y width height)))