gistfile1.txt

(defparameter *theta* 0)

(defsketch recursive-tree (:width 640 :height 360) ()
  (background +black+)
  (with-pen (make-pen :stroke +white+)
    (let ((*theta* (* 90 (/ (in :mouse-x) width))))
      (with-identity-matrix
	(translate (/ width 2) height)
	(line 0 0 0 -120)
	(translate 0 -120)
	(branch 120)))))

(defun branch (h)
  (let ((h (* h 0.66)))
    (when (> h 2)
      (dotimes (i 2)
	(with-current-matrix
	  (rotate (if (zerop i) (- *theta*) *theta*))
	  (line 0 0 0 (- h))
	  (translate 0 (- h))
	  (branch h))))))