From bc12fdabb402a5573f156134e51548a20855ed79 Mon Sep 17 00:00:00 2001
From: Bruno Cichon <ebrasca.ebrasca@openmailbox.org>
Date: Fri, 26 May 2017 17:56:46 +0200
Subject: Add new function.

---
 package.lisp |  3 ++-
 turtle.lisp  | 31 ++++++++++++++++++++++++-------
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/package.lisp b/package.lisp
index 133e8df..ff513c9 100644
--- a/package.lisp
+++ b/package.lisp
@@ -16,4 +16,5 @@
            #:make-geometry
            #:circle
            #:push-turtle
-           #:pop-turtle))
+           #:pop-turtle
+           #:set-radius))
diff --git a/turtle.lisp b/turtle.lisp
index 3869477..9aa9fbc 100644
--- a/turtle.lisp
+++ b/turtle.lisp
@@ -17,6 +17,8 @@
                 :initform (v! 0.0 0.0 0.0 0.0))
    (rotation :accessor rot
              :initform (m4:identity))
+   (radius :accessor r
+           :initform 0.0)
    (pile :accessor pile
          :initform '())))
 
@@ -30,9 +32,13 @@
   (mapcar #'(lambda (vertex)
               (add-point
                (m4:get-column
-                (m4:* (m4:translation (v4:+ (tra turtle) (v4:*S (m4:get-column (rot turtle) 1) n)))
-                      (rot turtle)
-                      (m4:translation (v4:- (aref *vertices* vertex) (tra turtle))))
+                (let* ((x (v4:- (aref *vertices* vertex) (tra turtle)))
+                       (y (v4:*S x (* (r turtle)
+                                      (sqrt (v:dot x x))))))
+                  (m4:* (m4:translation (v4:+ (tra turtle)
+                                              (v4:*S (m4:get-column (rot turtle) 1) n)))
+                        (rot turtle)
+                        (m4:translation (v4:- x y))))
                 3)))
           (points turtle)))
 
@@ -43,7 +49,9 @@
       (push item
             *index*))
     (setf (points turtle)
-          new-points)
+          new-points
+          (r turtle)
+          0.0)
     (translation turtle n)))
 
 (defun jump (turtle n)
@@ -53,7 +61,9 @@
       (push item
             *index*))
     (setf (points turtle)
-          new-points)
+          new-points
+          (r turtle)
+          0.0)
     (translation turtle n)))
 
 ;;; Rotation
@@ -92,7 +102,8 @@
   "Remember the current state of turtle"
   (push (list (copy-list (points turtle))
               (copy-seq (rot turtle))
-              (copy-seq (tra turtle)))
+              (copy-seq (tra turtle))
+              (r turtle))
         (pile turtle)))
 
 (defun pop-turtle (turtle)
@@ -100,7 +111,13 @@
   (let ((pile (pop (pile turtle))))
     (setf (points turtle) (first pile)
           (rot turtle) (second pile)
-          (tra turtle) (third pile))))
+          (tra turtle) (third pile)
+          (r turtle) (fourth pile))))
+
+(defun set-radius (turtle r)
+  "Set how radius need to change."
+  (setf (r turtle)
+        (- 1 r)))
 
 ;;; Geometry
 (defun add-point (point)
-- 
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