anchor.diff:                    (window-buffer-point window)
                     (lambda (string lastp)
                       (declare (ignore lastp))
  -                    (map-wrapping-line string
  -                                       (window-%width window)
  +                    (map-wrapping-line window
  +                                       string
                                          #'inc)))
         offset)))
   
  
positive.code:   (when (and (variable-value 'truncate-lines :default (window-buffer window))
               (not (first-line-p (window-view-point window))))
      (let ((charpos-list))
        (map-wrapping-line (line-string (if (start-line-p (window-view-point window))
                                            (line-offset (copy-point (window-view-point window)
                                                                     :temporary)
                                                         -1)
                                            (window-view-point window)))
                           (window-%width window)
                           (lambda (c)
                             (push c charpos-list)))
        (cond ((and charpos-list (start-line-p (window-view-point window)))
  
negative.code:                (window-buffer-point window)))
    (window-scroll window (- (floor (window-%height window) 2))))
  
  (defun map-wrapping-line (window string fn)
    (loop :with start := 0
          :and width := (1- (window-width window))
          :for i := (wide-index string width :start start)
          :while i
          :do
          (funcall fn i)
          (setq start i)))
  
  (defun %scroll-down-if-wrapping (window)
    (when (variable-value 'truncate-lines :default (window-buffer window))
      (let ((view-charpos (point-charpos (window-view-point window))))
        (line-start (window-view-point window))
        (map-wrapping-line window
                           (line-string (window-view-point window))
                           (lambda (c)
                             (when (< view-charpos c)
                               (line-offset (window-view-point window) 0 c)
  