A tiny CAD-like program in Clojure. Uses SeeSaw for the GUI.

nanocad.clj

; a tiny, simple CAD program prototype in Clojure.
; Carl Smotricz, 2015-07-22

(ns nanocad.core
  (:use [seesaw core graphics])
  (:require [seesaw.mouse :refer [location]])
  (:import [javax.swing AbstractAction]))

(def CANVAS-WIDTH 400)

(def CANVAS-HEIGHT 300)

(def CLICK-TEXT "Click here to draw!")

(def line-style (style :foreground "#FF0000" :stroke 2 :cap :round)


(defn -main [& args]
  (declare on-kanvas-click)   ; forward declaration, resolves circular dependencies
  
  (let
    [
     ; ---define a bunch of variables needed later.
     ;    some of those vars refer to functions.

     ; our only data structure.
     ; a list of points for drawing as lines.
     points (atom [])
     
     draw-lines (fn [c g]   ; function to draw lines from 'points' on canvas
                  (loop [segments (partition 2 @points)]
                      (when (not-empty segments)
                        (let [s1 (first segments)
                              p1 (first s1)
                              p2 (second s1)]
                          (invoke-later (prn "segments:" segments "; p1:" p1 "; p2:" p2))
                          (draw g (line (first p1) (second p1) (first p2) (second p2)) line-style))
                        (recur (next segments)))))
        
     ; creates a label we use as our canvas.
     ; the name "canvas" is already taken by seesaw.
     kanvas (label 
                   :text CLICK-TEXT 
                   :size [CANVAS-WIDTH :by CANVAS-HEIGHT]
                   :halign :center
                   :tip "Click here to draw"
                   :paint draw-lines)
     
     on-kanvas-click (fn [evt]   ; function to be called on canvas click
                       ; a new line will be drawn for every 2 clicks (= points).
                       (let [new-pt (location evt)]
                         (swap! points conj new-pt)
                         (invoke-later (prn "new-pt:" new-pt "; points:" points)))
                       (config! kanvas :text "Clicked. Again!")
                       (repaint! kanvas))   
        
     on-clear-click (fn [evt]   ; function to be called on clear click  
                      (invoke-later (prn "Cleared. points: " points))
                      (reset! points [])
                      (config! kanvas :text CLICK-TEXT)
                      (repaint! kanvas))

     ; creates a button with the given action
     clear-action (action
                    :name "Clear"
                    :tip "Clear the drawing pane"
                    :handler on-clear-click)

     ; --- end of variables. the following code executes in the context of those vars.
     ]

    (prn "nanoCAD starting")
    
    ; causes on-kanvas-click to be executed if canvas clicked
    (listen kanvas :mouse-clicked on-kanvas-click)

    ; assembles and displays the little GUI.    
    (invoke-later
      (-> (frame :title "nanoCAD",
                 :content (vertical-panel
                            :items [kanvas
                                    clear-action])
                 :on-close :exit)
        pack!
        show!))))

(-main)