`pdf-view-next-page-command` and `pdf-view-previous-page-command` scroll the wrong window

[YueRen]

Describe the bug
When having one pdf open in two windows in a single frame, pdf-view-next-page-command and pdf-view-previous-page-command scroll the wrong window.

Steps to Reproduce the behaviour

1. Open any pdf with two or more pages.
2. Split your frame (e.g. C-x 3 to split your window vertically), you should now have the pdf open in two windows.
3. Press PageUp and PageDown, and notice the pdf in the other window scrolling

(Note: The bug does not occur when opening the same pdf in two windows, i.e., first splitting my frame then opening the same pdf in each window via find-file. It also does not occur when scrolling up and down on a single page, it is only triggered on page switching.)

Your pdf-tools install
I have Emacs installed via snap:

GNU Emacs 30.2
Development version ff7d3f02b943 on master branch; build date 2025-12-17.
Copyright (C) 2025 Free Software Foundation, Inc.
GNU Emacs comes with ABSOLUTELY NO WARRANTY.
You may redistribute copies of GNU Emacs
under the terms of the GNU General Public License.
For more information about these matters, see the file named COPYING.

This is my pdf-tools version:

     Status: Installed in ‘pdf-tools-20260102.1101/’ (unsigned).
    Version: 20260102.1101
     Commit: e4b7f1f37cf59ddf025d609ffcdabe732a6e99ba
    Summary: Support library for PDF documents.
   Requires: emacs-26.3, tablist-1.0, let-alist-1.0.4
Required by: org-pdftools-20250714.1631
    Website: http://github.com/vedang/pdf-tools/
   Keywords: files multimedia 
     Author: Andreas Politz <mail@andreas-politz.de>
Other versions: 20260102.1101 (melpa).

And the bug can be reproduced with the following init.el:

(require 'package)
(setq package-archives '(("elpa" . "https://elpa.gnu.org/packages/")
                         ("melpa" . "https://melpa.org/packages/")
                         ("org" . "https://orgmode.org/elpa/")))
(package-initialize)
(unless package-archive-contents (package-refresh-contents))

(require 'use-package-ensure)
(setopt use-package-always-ensure t)

(use-package pdf-tools
  :mode "\\.pdf\\'"
  :init
  (pdf-loader-install))

[YueRen]

One quick note: the behaviour is fixed when pdf-view-roll-minor-mode is enabled, i.e., it will not arise with the following init.el:

(require 'package)
(setq package-archives '(("elpa" . "https://elpa.gnu.org/packages/")
                         ("melpa" . "https://melpa.org/packages/")
                         ("org" . "https://orgmode.org/elpa/")))
(package-initialize)
(unless package-archive-contents (package-refresh-contents))
(require 'use-package-ensure)
(setopt use-package-always-ensure t)

(use-package pdf-tools
  :mode "\\.pdf\\'"
  :hook
  (pdf-view-mode . pdf-view-roll-minor-mode)
  :init
  (pdf-loader-install))

[aikrahguzar]

Do you know if this bug appeared recently or was it present before the landing of pdf-roll?

[YueRen]

I started noticing the behaviour on my machine two or three weeks ago, which could very well have been the pdf-roll changes.

[YueRen]

The issue seems to persists in your fork. Here the init that I have tried (after deleting the existing pdf-tools folder):

(require 'package)
(setq package-archives '(("elpa" . "https://elpa.gnu.org/packages/")
                         ("melpa" . "https://melpa.org/packages/")))
(package-initialize)
(unless package-archive-contents (package-refresh-contents))
(require 'use-package-ensure)
(setopt use-package-always-ensure t)

(use-package pdf-tools
  :mode "\\.pdf\\'"
  :vc ( :url "https://codeberg.org/rahguzar/pdf-tools.git"
        :lisp-dir "lisp"
        :rev :newest)
  :init
  (pdf-loader-install))

[aikrahguzar]

Can you please evaluate,

(defun pdf-view-next-page-command (&optional n)
  "View the next page in the PDF.

Optional parameter N moves N pages forward.

This command is a wrapper for `pdf-view-next-page' that will
indicate to the user if they are on the last page and more."
  (declare (interactive-only pdf-view-next-page))
  (interactive "p")
  (unless n (setq n 1))
  (let ((window (selected-window)))
    (when (> (+ (pdf-view-current-page window) n)
             (pdf-cache-number-of-pages))
      (user-error "Last page"))
    (when (< (+ (pdf-view-current-page window) n) 1)
      (user-error "First page"))
    (let ((pdf-view-inhibit-redisplay t))
      (pdf-view-goto-page
       (+ (pdf-view-current-page window) n) window))
    (force-mode-line-update)
    (sit-for 0)
    (when pdf-view--next-page-timer
      (cancel-timer pdf-view--next-page-timer)
      (setq pdf-view--next-page-timer nil))
    (if (or (not (input-pending-p))
            (and (> n 0)
                 (= (pdf-view-current-page window)
                    (pdf-cache-number-of-pages)))
            (and (< n 0)
                 (= (pdf-view-current-page window) 1)))
        (pdf-view-redisplay)
      (setq pdf-view--next-page-timer
            (run-with-idle-timer 0.001 nil 'pdf-view-redisplay window)))))

and see if this fixes the problem?

I actually have no idea why pdf-view-next-page-command is doing a lot of the stuff it is doing and don't understand what there is causing this problem, so this is a shot in the dark.

[YueRen]

Sorry, that didn't fix it unfortunately. :-/

[zhixiao-zhang]

This bug seems to affect not only these two commands, but also operations such as mouse selection :-|

[aikrahguzar]

Can one of you try going back to 9d948a0? Does that fix this problem?

[aikrahguzar]

I added a commit to my fork that I think should fix this issue.

[YueRen]

Just pulled, can confirm that it fixed the scrolling issue for me, thanks!

There is still a minor problem that the page number shown in my modeline is the same across both windows (I believe it is always showing the number of the page that was scrolled onto last), i.e.:

1. Have the same pdf open in two windows
2. Scroll onto the next page in one of the windows
3. Note that the page number in the other window changes

[aikrahguzar]

I think the mode-line issue is related to the way you are constructing mode-line. I don't see the issue with the default construct pdf-tools uses i.e.

(setq-local mode-line-position
              '(" P" (:eval (number-to-string (pdf-view-current-page)))
                ;; Avoid errors during redisplay.
                "/" (:eval (or (ignore-errors
                                 (number-to-string (pdf-cache-number-of-pages)))
                               "???"))))

[YueRen]

You are right, can confirm that the default modeline works. This seems to be a bug in doom-modeline.

Since the problem is resolved, I'll be closing this issue. Many thanks!