anchor.diff:    "AA state. Hold all the cells generated when drawing lines."
     (current-cell (make-cell) :type cell)
     (cells nil)
  +  (scanlines nil)
  +  ;; these slots for reusing cells with state-reset
  +  (end-of-lines nil)
  +  (dropped-cells nil)
     (recycling-cells (cons nil nil)))
   
   (defun state-reset (state)
  
positive.code:            #:state-reset
             #:line
             #:line-f
             #:cells-sweep))
  
  (in-package #:net.tuxee.aa)
  
  
negative.code: faster or less memory consuming to reset a state and reuse it,
  rather than creating a new state."
    (cell-reset (state-current-cell state))
    (when (state-end-of-lines state)
      ;; join back the scanlines to form a single list
      (loop for line in (rest (state-scanlines state))
         for eol in (state-end-of-lines state)
         do (setf (cdr eol) line)))
    (let ((cells (nconc (state-dropped-cells state)
                        (state-cells state))))
      (setf (state-recycling-cells state) (cons nil cells)
            (state-scanlines state) nil
            (state-end-of-lines state) nil
            (state-dropped-cells state) nil
            (state-cells state) cells)))
  
  (declaim (inline state-push-current-cell))
  (defun state-push-cell (state cell)
  