eLOGO.el

;;;; Name: eLOGO
;;;; Author: Ryan Burnside
;;;; Date: 2014-03-06
;;;; Released under GPL v4

;;; This is the beginning of a LOGO like module to draw vector shapes
;;; Historically the cursor is called a "turtle"
;;; It has a small set of commands to draw primative line graphics

;;; Global variables for turtle maintenance

(defvar *x-pos* 0)
(defvar *y-pos* 0)
(defvar *previous-x-pos* 0)
(defvar *previous-y-pos* 0)

(defvar *direction* 0)
(defvar *step* 0)
(defvar *is-drawing* t)
(defvar *color* '(0 0 0))
(defvar *line-list* '()) ; Elements are (x y x2 y2 '(R G B))

;;; Turtle manipulation commands
(defun move ()
  "Move at the current angle and step size, save line to list if *is-drawing*"
  (if *is-drawing*
   (setf *line-list*
     (cons (list *previous-x-pos* *previous-y-pos* *x-pos* *y-pos* *color*)
           *line-list*)))
  (setf *previous-x-pos* *x-pos*)
  (setf *previous-y-pos* *y-pos*))

(defun rt (dir)
  "Turn the turtle right in degrees"
  (incf *direction* dir))

(defun lt (dir)
  "Turn the turtle left in degrees"
  (decf *direction* dir))

(defun fd (length)
  "Move forward in pixels at current heading"
  (setf *step* length)
  (setf *x-pos* (+ *x-pos* (* (cos (degrees-to-radians *direction*)) *step*)))
  (setf *y-pos* (+ *y-pos* (* (sin (degrees-to-radians *direction*)) *step*)))
  (move))

(defun set-pen-color (red green blue)
  "Set the RGB triplet for the turtle's line color"
  (setf *color* (list red green blue)))

(defun tail-up ()
  "Don't draw following step commands"
  (setf *is-drawing* nil))

(defun tail-down ()
  "Start drawing following step commands"
  (setf *is-drawing* t))

(defun clear-drawing ()
  "Reset the global line list"
  (setf *line-list* '()))


;;; We'll need to impliment a very small subset of XML file writing below
;;; We can easily do this with the *line-list* the turtle makes