;
; Turtle Graphics
; from Lisp in Small Parts, http://lisp.plasticki.com/
; Licensed under CC0 1.0: http://creativecommons.org/publicdomain/zero/1.0/
; 30/6/2012
;

(defparameter turtle-pane nil)
(defparameter turtle-x 320)
(defparameter turtle-y 240)
(defparameter turtle-theta 0)
(defparameter turtle-draw t)

(defun reset ()
  (setf turtle-x 240)
  (setf turtle-y 180)
  (setf turtle-theta 0)
  (setf turtle-draw t))

(defun forward (length)
  (let ((new-x (+ turtle-x (* length (cos turtle-theta))))
        (new-y (- turtle-y (* length (sin turtle-theta)))))
    (if turtle-draw
        (gp:draw-line turtle-pane turtle-x turtle-y new-x new-y))
    (setf turtle-x new-x)
    (setf turtle-y new-y)))

(defun radians (angle)
  (* pi (/ angle 180)))

(defun right (angle)
  (setf turtle-theta (- turtle-theta (radians angle))))

(defun back (length)
  (forward (- length)))

(defun left (angle)
  (right (- angle)))

(defun penup ()
  (setf turtle-draw nil))

(defun pendown ()
  (setf turtle-draw t))

(defun plot ()
  (capi:contain 
   (make-instance 'capi:output-pane :display-callback 'draw) 
   :best-width 480 :best-height 360))

(defun inspi (side angle inc count)
  (forward side)
  (right angle)
  (if (> count 0)
      (inspi side (+ angle inc) inc (- count 1))))

(defun ldragon (size level)
  (if (= level 0)
      (forward size)
    (progn
      (ldragon size (- level 1))
      (left 90)
      (rdragon size (- level 1)))))

(defun rdragon (size level)
  (if (= level 0)
      (forward size)
    (progn
      (ldragon size (- level 1))
      (right 90)
      (rdragon size (- level 1)))))

(defun draw (pane &optional x y width height)
  (declare (ignore x y width height))
  (setf turtle-pane pane)
  (reset)
  (ldragon 4 11))