Re: Temporarily select-window, without updating mode-line face and cursor fill?

[Stefan Monnier]

> If you had any concrete suggestions for calculating window positions
> (like window-start and window-end, not just buffer positions) in
> a non-active window without selecting it, which is superior to my
> approach, I’d be happy to hear. 

We really should simply speed up `line-number-at-pos`.
It shouldn't be hard.  See below what I do in nlinum.el.


        Stefan



(defvar nlinum--line-number-cache nil)
(make-variable-buffer-local 'nlinum--line-number-cache)

;; We could try and avoid flushing the cache at every change, e.g. with:
;;   (defun nlinum--before-change (start _end)
;;     (if (and nlinum--line-number-cache
;;              (< start (car nlinum--line-number-cache)))
;;         (save-excursion (goto-char start) (nlinum--line-number-at-pos))))
;; But it's far from clear that it's worth the trouble.  The current simplistic
;; approach seems to be good enough in practice.

(defun nlinum--after-change (&rest _args)
  (setq nlinum--line-number-cache nil))

(defun nlinum--line-number-at-pos ()
  "Like `line-number-at-pos' but sped up with a cache.
Only works right if point is at BOL."
  ;; (cl-assert (bolp))
  (if nlinum-widen
      (save-excursion
        (save-restriction
          (widen)
          (forward-line 0)              ;In case (point-min) was not at BOL.
          (let ((nlinum-widen nil))
            (nlinum--line-number-at-pos))))
    (let ((pos
           (if (and nlinum--line-number-cache
                    (> (- (point) (point-min))
                       (abs (- (point) (car nlinum--line-number-cache)))))
               (funcall (if (> (point) (car nlinum--line-number-cache))
                            #'+ #'-)
                        (cdr nlinum--line-number-cache)
                        (count-lines (point) (car nlinum--line-number-cache)))
             (line-number-at-pos))))
      ;;(assert (= pos (line-number-at-pos)))
      (add-hook 'after-change-functions #'nlinum--after-change nil :local)
      (setq nlinum--line-number-cache (cons (point) pos))
      pos)))