anchor.diff:           for stroke = (aref (line-strokes line) stroke-index)
            for stroke-dimensions = (stroke-dimensions stroke)
            do (draw-stroke pane view stroke (x1 stroke-dimensions) baseline)
  -         finally (progn (end-line-cleaning-up view pane line orig-x-offset cursor-y
  +         finally (progn (end-line-cleaning-up view line orig-x-offset cursor-y
                                                 line-width line-height)
                           (incf (displayed-lines-count view))
                           (return (values pump-state line-height)))))))
  
positive.code:                                          0
                                           (round x1))
                                  0)))
            (when (> y2 (+ y-position viewport-height))
              (full-redisplay pane)
              ;; We start all over!
              (display-drei-pane (pane-frame pane) pane)))))))
  
negative.code: anything. Will use the function specified in the drawing-options
  of `stroke' to carry out the actual calculations."
    (unless (and (= cursor-x (x1 (stroke-dimensions stroke)))
                 (= cursor-y (y1 (stroke-dimensions stroke)))
                 (not (stroke-dirty stroke))
                 (mark<= (stroke-end-offset stroke) (bot view)))
      (invalidate-stroke stroke :modified t))
    (when (stroke-dirty stroke)
      (funcall (drawing-options-function (stroke-drawing-options stroke)) stream view stroke
  