From: JD Smith <jdtsmith@gmail.com>
To: Eli Zaretskii <eliz@gnu.org>
Cc: emacs-devel@gnu.org
Subject: Re: Temporarily select-window, without updating mode-line face and cursor fill?
Date: Sun, 2 May 2021 22:08:49 -0400 [thread overview]
Message-ID: <81F181EB-D3C1-4619-B42A-1F49321EC544@gmail.com> (raw)
In-Reply-To: <83eeep8w0m.fsf@gnu.org>
For very large file, line-number-at-pos, which uses count-lines, if far too slow to be used in a modeline :eval. I suspect this is why the “%l” mode line formatter does not itself use count-lines. Here’s my analysis of that (on top of some 7yr old complaints about the speed of line-number-at-pos): https://emacs.stackexchange.com/questions/3821/a-faster-method-to-obtain-line-number-at-pos-in-large-buffers/64656#64656
Summary: format-mode-line is >10x faster on “random” lines, and thousands of times faster for “nearby lines” (presumably due to caching). The latter is particular important for rapid scrolling updates.
I managed to get this working quite well on large files (like /usr/dict/words); see https://github.com/jdtsmith/mlscroll. I indeed use count-lines for incrementing line count from window-start to window-end, since they are “close”, and have simplified the fast line count to:
(defun mlscroll-fast-line-number-at-pos (pos &optional win)
(let ((old (window-point win)))
(set-window-point win pos)
(prog1
(string-to-number (format-mode-line "%l" 0 win))
(set-window-point win old))))
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.
> On May 2, 2021, at 2:55 AM, Eli Zaretskii <eliz@gnu.org> wrote:
>
>> From: JD Smith <jdtsmith@gmail.com>
>> Date: Sat, 1 May 2021 18:17:46 -0400
>> Cc: emacs-devel@gnu.org
>>
>> (defun mlscroll-fast-line-number-at-pos (pos &optional win)
>> "Line number at position.
>> Compute line number at position POS. Uses fast mode-line
>> formatting. If WIN is non-nil, find line number at position within
>> that window."
>> (string-to-number
>> (if win
>> (let ((old (window-point win)))
>> (set-window-point win pos)
>> (prog1
>> (format-mode-line "%l" 0 win)
>> (set-window-point win old)))
>> (save-excursion
>> (goto-char pos)
>> (format-mode-line "%l" 0)))))
>
> I don't recommend using format-mode-line for counting lines. Why not
> use count-lines instead?
next prev parent reply other threads:[~2021-05-03 2:08 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-01 18:46 Temporarily select-window, without updating mode-line face and cursor fill? JD Smith
2021-05-01 19:31 ` Eli Zaretskii
2021-05-01 20:32 ` JD Smith
2021-05-02 6:49 ` Eli Zaretskii
2021-05-03 2:15 ` JD Smith
2021-05-03 7:50 ` martin rudalics
2021-05-03 16:16 ` JD Smith
2021-05-03 17:32 ` martin rudalics
2021-05-02 7:40 ` martin rudalics
2021-05-03 2:23 ` JD Smith
2021-05-01 22:17 ` JD Smith
2021-05-02 6:55 ` Eli Zaretskii
2021-05-03 2:08 ` JD Smith [this message]
2021-05-03 2:25 ` Stefan Monnier
2021-05-03 2:49 ` JD Smith
2021-05-04 19:28 ` JD Smith
2021-05-04 19:40 ` Stefan Monnier
2021-05-05 0:49 ` Stefan Kangas
2021-05-05 11:54 ` Eli Zaretskii
2021-05-05 19:32 ` Stefan Kangas
2021-05-05 19:47 ` Stefan Monnier
2021-05-06 0:16 ` JD Smith
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