window-bottom.el

(defun window-bottom--is-past-buffer/lines ()
  "Return a true value iff we scrolled past the buffer end."
  (save-excursion
    (goto-char (window-start))
    (let ((lines 0)
          (max-lines (window-height)))
      (while (and (< lines max-lines)
                  (re-search-forward "[\n\C-m]" nil t))
        (setq lines (+ 1 lines)))
      (goto-char (point-max))
      (when (bolp)
        (setq lines (+ lines 1)))
      (< lines max-lines))))