27 Nov 2015

Logo-ish drawing environment

Some months ago I bought a copy of "Turtle Geometry". I am looking for a LOGO environment to follow along and do the exsercises, but I could not find anything good enough for Mac OS X (which is quite surprising, if you ask me). So I decided to write my own version. The first usable thing I produced is not quite LOGO, but enough to do fancy drawings and (I'm guessing) translate most of the exercises without efforts. Code is on github.

screenshot.png

Update <2015-11-29 Sun 09:39>

One thing I'm not sure how I could do is the interactive environment, but I discovered I have something acceptable at no cost, thanks to how Lisp and the lispbuilder-sdl package work.

Here a piece of code from my project: 

;; [...]
    (with-events ()
      (:quit-event () t)
      (:key-down-event (:key key)
                       (when (sdl:key= key :sdl-key-escape))
                       (sdl:push-quit-event))
      (:idle (reset-turtle)
             (fancy 20)
             (draw-turtle *position-x* *position-y* *direction*)
             (update-display)))))

Since we're implicitly using the :poll event mechanism, the :idle event is triggered at each "game loop" iteration. Thus, if I redefine the functions used in the body associated to the :idle event while the program is running, I obtain a different drawing. What I do, at the end, is:

  • evaluate (main) (the SDL window appear)
  • focus in the Emacs window
  • edit some relevant functions (for example the body of fancy)
  • C-x C-e to re-evaluate the definition
  • voilà, new picture is drawn
Tags: dev lisp