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bug#56008: 29.0.50; image-mode buffer scrolled down automatically
From: |
Eli Zaretskii |
Subject: |
bug#56008: 29.0.50; image-mode buffer scrolled down automatically |
Date: |
Thu, 16 Jun 2022 20:11:09 +0300 |
> From: Visuwesh <visuweshm@gmail.com>
> Cc: larsi@gnus.org, 56008@debbugs.gnu.org
> Date: Thu, 16 Jun 2022 22:25:05 +0530
>
> [வியாழன் ஜூன் 16, 2022 18:49] Eli Zaretskii wrote:
>
> > What do you mean by "it was `save-window-excursion'"? what is "it" in
> > this case?
>
> I thought the source of the random, unwarranted scrolling could be
> `save-window-excursion' since it did come with the following warning,
>
> BEWARE: Most uses of this macro introduce bugs.
> E.g. it should not be used to try and prevent some code from opening
> a new window, since that window may sometimes appear in another frame,
> in which case ‘save-window-excursion’ cannot help.
We don't create new windows in this case, so that warning is not
relevant.
But save-window-excursion is indeed part of the puzzle, see below.
> > And how did you see that this is not the case?
>
> Sorry, but it is close to a year since I looked at the source code. All
> I remember is being annoyed by the bug despite removing the
> `save-window-excursion' bit willy-nilly.
>
> [ This was all in ement.el's source code if I wasn't clear, BTW. ]
I don't know what ement.el does and whether this is related, but
here's what was happening in this case:
. we invoke eww to fetch some URL
. before it finishes to fetch the URL, we switch to another window
. eww finishes fetching the URL and calls shr.el to render it
. shr.el uses the selected window for rendering, and as part of
that, it calls set-window-buffer to temporarily make the buffer in
which it renders be the buffer of the selected window
. set-window-buffer resets the window's hscroll and vscroll values
. shr.el calls set-window-buffer inside save-window-excursion, but
save-window-excursion didn't preserve the value of vscroll, and in
addition shr.el called set-window-hscroll in one place that wasn't
inside save-window-excursion
. so both vscroll and hscroll of the window showing the image ended
up with zero hscroll and vscroll
. since image-mode overrides the usual definition of M-> with a
command that works by setting the window's hscroll and vscroll,
resetting these two makes the (mistaken) impression that the
window was scrolled
. the reason M-x and M-: appeared to "fix" the problem is that
image-mode defines a window-configuration-change-hook that forces
the display back to what it was -- this looked to us as if the
problem was caused by some redisplay bug, something that took me
some time to realize its being completely wrong
- bug#56008: 29.0.50; image-mode buffer scrolled down automatically, Visuwesh, 2022/06/16
- bug#56008: 29.0.50; image-mode buffer scrolled down automatically, Lars Ingebrigtsen, 2022/06/16
- bug#56008: 29.0.50; image-mode buffer scrolled down automatically, Lars Ingebrigtsen, 2022/06/16
- bug#56008: 29.0.50; image-mode buffer scrolled down automatically, Visuwesh, 2022/06/16
- bug#56008: 29.0.50; image-mode buffer scrolled down automatically, Eli Zaretskii, 2022/06/16
- bug#56008: 29.0.50; image-mode buffer scrolled down automatically, Lars Ingebrigtsen, 2022/06/16
- bug#56008: 29.0.50; image-mode buffer scrolled down automatically, Visuwesh, 2022/06/16
- bug#56008: 29.0.50; image-mode buffer scrolled down automatically, Eli Zaretskii, 2022/06/16
- bug#56008: 29.0.50; image-mode buffer scrolled down automatically, Visuwesh, 2022/06/16
- bug#56008: 29.0.50; image-mode buffer scrolled down automatically,
Eli Zaretskii <=
- bug#56008: 29.0.50; image-mode buffer scrolled down automatically, Visuwesh, 2022/06/16
- bug#56008: 29.0.50; image-mode buffer scrolled down automatically, Eli Zaretskii, 2022/06/16
- bug#56008: 29.0.50; image-mode buffer scrolled down automatically, Eli Zaretskii, 2022/06/16
- bug#56008: 29.0.50; image-mode buffer scrolled down automatically, Visuwesh, 2022/06/16
- bug#56008: 29.0.50; image-mode buffer scrolled down automatically, Eli Zaretskii, 2022/06/16
bug#56008: 29.0.50; image-mode buffer scrolled down automatically, Eli Zaretskii, 2022/06/16