GNU bug report logs - #28342
26.0.50; (OSX) Jumpy Scrolling using Trackpad

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: James Nguyen <james <at> jojojames.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 26.0.50; (OSX) Jumpy Scrolling using Trackpad
Date: Sun, 03 Sep 2017 17:22:29 -0700

Recipe:

emacs -Q

(setq scroll-margin 5
      scroll-step 1
      scroll-conservatively 10000
      scroll-preserve-screen-position 1
	  mouse-wheel-scroll-amount '(1)
	  mouse-wheel-progressive-speed nil
	  mouse-wheel-follow-mouse 't)

Open another buffer (init.el for example). Use only one window.
Scroll with trackpad up and down.
Use trackpad mouse to click past the scroll margin.
Try scrolling up and down with trackpad. It will jump wildly.

Video:
https://www.dropbox.com/s/2jwb3p2sul9q36d/JumpyScrolling.m4v?dl=0

Notes: Only seems to happen when there's one window. I could not
reproduce it if I opened a second window (as shown in the video.)

Happens on both Emacs 25 and Emacs 26 (master branch).

Message #8 received at 28342 <at> debbugs.gnu.org (full text, mbox):

From: charles <at> aurox.ch (Charles A. Roelli)
To: James Nguyen <james <at> jojojames.com>
Cc: 28342 <at> debbugs.gnu.org
Subject: Re: bug#28342: 26.0.50; (OSX) Jumpy Scrolling using Trackpad
Date: Tue, 05 Sep 2017 22:14:08 +0200

> Resent-From: James Nguyen <james <at> jojojames.com>
> Original-Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org>
> Resent-CC: bug-gnu-emacs <at> gnu.org
> Resent-Sender: help-debbugs <at> gnu.org
> From: James Nguyen <james <at> jojojames.com>
> Date: Sun, 03 Sep 2017 17:22:29 -0700
> Content-Type: text/plain
> 
> 
> Recipe:
> 
> emacs -Q
> 
> (setq scroll-margin 5
>       scroll-step 1
>       scroll-conservatively 10000
>       scroll-preserve-screen-position 1
> 	  mouse-wheel-scroll-amount '(1)
> 	  mouse-wheel-progressive-speed nil
> 	  mouse-wheel-follow-mouse 't)
> 
> Open another buffer (init.el for example). Use only one window.
> Scroll with trackpad up and down.
> Use trackpad mouse to click past the scroll margin.
> Try scrolling up and down with trackpad. It will jump wildly.

What jumps wildly?  Does removing any of these settings stop the issue
from occurring?

Message #11 received at 28342 <at> debbugs.gnu.org (full text, mbox):

From: James Nguyen <jamesn <at> fastmail.com>
To: "Charles A. Roelli" <charles <at> aurox.ch>
Cc: 28342 <at> debbugs.gnu.org, James Nguyen <james <at> jojojames.com>
Subject: Re: bug#28342: 26.0.50; (OSX) Jumpy Scrolling using Trackpad
Date: Tue, 5 Sep 2017 18:14:11 -0700

The cursor jumps from within the scroll-margins to end of file and back and forth.

Some of those settings can probably be removed but scroll-margin is probably important.

> On Sep 5, 2017, at 1:14 PM, Charles A. Roelli <charles <at> aurox.ch> wrote:
> 
>> Resent-From: James Nguyen <james <at> jojojames.com>
>> Original-Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org>
>> Resent-CC: bug-gnu-emacs <at> gnu.org
>> Resent-Sender: help-debbugs <at> gnu.org
>> From: James Nguyen <james <at> jojojames.com>
>> Date: Sun, 03 Sep 2017 17:22:29 -0700
>> Content-Type: text/plain
>> 
>> 
>> Recipe:
>> 
>> emacs -Q
>> 
>> (setq scroll-margin 5
>>      scroll-step 1
>>      scroll-conservatively 10000
>>      scroll-preserve-screen-position 1
>> 	  mouse-wheel-scroll-amount '(1)
>> 	  mouse-wheel-progressive-speed nil
>> 	  mouse-wheel-follow-mouse 't)
>> 
>> Open another buffer (init.el for example). Use only one window.
>> Scroll with trackpad up and down.
>> Use trackpad mouse to click past the scroll margin.
>> Try scrolling up and down with trackpad. It will jump wildly.
> 
> What jumps wildly?  Does removing any of these settings stop the issue
> from occurring?

Message #14 received at 28342 <at> debbugs.gnu.org (full text, mbox):

From: Alan Third <athird <at> googlemail.com>
To: James Nguyen <jamesn <at> fastmail.com>
Cc: 28342 <at> debbugs.gnu.org, "Charles A. Roelli" <charles <at> aurox.ch>,
 James Nguyen <james <at> jojojames.com>
Subject: Re: bug#28342: 26.0.50; (OSX) Jumpy Scrolling using Trackpad
Date: Wed, 6 Sep 2017 09:53:54 +0100

[Message part 1 (text/plain, inline)]

I can replicate on ms windows using just:

(setq scroll-margin 5)
(setq scroll-preserve-screen-position 1)
(setq mouse-wheel-scroll-amount '(1))

Open a large file. Make sure you're at the start of the file

M-<

Scroll down with the mouse wheel and within a few clicks point jumps to the
middle of the screen. A few more and it jumps to the end of the file.

On 6 Sep 2017 2:15 a.m., "James Nguyen" <jamesn <at> fastmail.com> wrote:

The cursor jumps from within the scroll-margins to end of file and back and
forth.

Some of those settings can probably be removed but scroll-margin is
probably important.

> On Sep 5, 2017, at 1:14 PM, Charles A. Roelli <charles <at> aurox.ch> wrote:
>
>> Resent-From: James Nguyen <james <at> jojojames.com>
>> Original-Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org
>
>> Resent-CC: bug-gnu-emacs <at> gnu.org
>> Resent-Sender: help-debbugs <at> gnu.org
>> From: James Nguyen <james <at> jojojames.com>
>> Date: Sun, 03 Sep 2017 17:22:29 -0700
>> Content-Type: text/plain
>>
>>
>> Recipe:
>>
>> emacs -Q
>>
>> (setq scroll-margin 5
>>      scroll-step 1
>>      scroll-conservatively 10000
>>      scroll-preserve-screen-position 1
>>        mouse-wheel-scroll-amount '(1)
>>        mouse-wheel-progressive-speed nil
>>        mouse-wheel-follow-mouse 't)
>>
>> Open another buffer (init.el for example). Use only one window.
>> Scroll with trackpad up and down.
>> Use trackpad mouse to click past the scroll margin.
>> Try scrolling up and down with trackpad. It will jump wildly.
>
> What jumps wildly?  Does removing any of these settings stop the issue
> from occurring?

[Message part 2 (text/html, inline)]

Message #17 received at 28342 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Alan Third <athird <at> googlemail.com>
Cc: 28342 <at> debbugs.gnu.org, jamesn <at> fastmail.com, charles <at> aurox.ch,
 james <at> jojojames.com
Subject: Re: bug#28342: 26.0.50; (OSX) Jumpy Scrolling using Trackpad
Date: Wed, 06 Sep 2017 19:55:41 +0300

> From: Alan Third <athird <at> googlemail.com>
> Date: Wed, 6 Sep 2017 09:53:54 +0100
> Cc: 28342 <at> debbugs.gnu.org, "Charles A. Roelli" <charles <at> aurox.ch>,
> 	James Nguyen <james <at> jojojames.com>
> 
> I can replicate on ms windows using just:
> 
> (setq scroll-margin 5)
> (setq scroll-preserve-screen-position 1)
> (setq mouse-wheel-scroll-amount '(1))
> 
> Open a large file. Make sure you're at the start of the file
> 
> M-<
> 
> Scroll down with the mouse wheel and within a few clicks point jumps to the middle of the screen. A few more
> and it jumps to the end of the file.

Even simpler: after evaluating the first 2 of the above 3 settings,
visit xdisp.c, then type this twice:

  C-u 1 C-v

After you type this the second time, Emacs will infloop.

This bug is already present in Emacs 25.1.

I will look into this when I have time.  Thanks for the recipe.

Message #20 received at 28342 <at> debbugs.gnu.org (full text, mbox):

From: Nick Helm <nick <at> tenpoint.co.nz>
To: 28342 <at> debbugs.gnu.org
Cc: Eli Zaretskii <eliz <at> gnu.org>
Subject: Re: bug#28342: 26.0.50; (OSX) Jumpy Scrolling using Trackpad
Date: Thu, 07 Sep 2017 13:58:45 +1200

Eli Zaretskii <eliz <at> gnu.org> writes:

> Even simpler: after evaluating the first 2 of the above 3 settings,
> visit xdisp.c, then type this twice:
>
>   C-u 1 C-v
>
> After you type this the second time, Emacs will infloop.
>
> This bug is already present in Emacs 25.1.
>
> I will look into this when I have time.  Thanks for the recipe.

I see this here as well.

The problem might lie in window_scroll_pixel_based in window.c. A small
tweak seems to help:

--- src/window.c	2017-09-07 13:16:29.000000000 +1200
+++ src/window.c	2017-09-07 13:10:04.000000000 +1200
@@ -4835,7 +4835,7 @@
 	 have the `scroll-command' property.  This avoids the
 	 possibility of point becoming "stuck" on a tall line when
 	 scrolling by one line.  */
-      if (window_scroll_pixel_based_preserve_y < 0
+      if (window_scroll_pixel_based_preserve_y <= 0
 	  || !SYMBOLP (KVAR (current_kboard, Vlast_command))
 	  || NILP (Fget (KVAR (current_kboard, Vlast_command), Qscroll_command)))
 	{

Message #23 received at 28342 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: athird <at> googlemail.com
Cc: 28342 <at> debbugs.gnu.org, jamesn <at> fastmail.com, charles <at> aurox.ch,
 james <at> jojojames.com
Subject: Re: bug#28342: 26.0.50; (OSX) Jumpy Scrolling using Trackpad
Date: Sat, 09 Sep 2017 17:22:47 +0300

> Date: Wed, 06 Sep 2017 19:55:41 +0300
> From: Eli Zaretskii <eliz <at> gnu.org>
> Cc: 28342 <at> debbugs.gnu.org, jamesn <at> fastmail.com, charles <at> aurox.ch,
> 	james <at> jojojames.com
> 
> > (setq scroll-margin 5)
> > (setq scroll-preserve-screen-position 1)
> > (setq mouse-wheel-scroll-amount '(1))
> > 
> > Open a large file. Make sure you're at the start of the file
> > 
> > M-<
> > 
> > Scroll down with the mouse wheel and within a few clicks point jumps to the middle of the screen. A few more
> > and it jumps to the end of the file.
> 
> Even simpler: after evaluating the first 2 of the above 3 settings,
> visit xdisp.c, then type this twice:
> 
>   C-u 1 C-v
> 
> After you type this the second time, Emacs will infloop.
> 
> This bug is already present in Emacs 25.1.
> 
> I will look into this when I have time.  Thanks for the recipe.

Should be fixed now on the master branch.

Message #26 received at 28342 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Nick Helm <nick <at> tenpoint.co.nz>
Cc: 28342 <at> debbugs.gnu.org
Subject: Re: bug#28342: 26.0.50; (OSX) Jumpy Scrolling using Trackpad
Date: Sat, 09 Sep 2017 17:25:45 +0300

> From: Nick Helm <nick <at> tenpoint.co.nz>
> Cc: Eli Zaretskii <eliz <at> gnu.org>
> Date: Thu, 07 Sep 2017 13:58:45 +1200
> 
> The problem might lie in window_scroll_pixel_based in window.c. A small
> tweak seems to help:
> 
> --- src/window.c	2017-09-07 13:16:29.000000000 +1200
> +++ src/window.c	2017-09-07 13:10:04.000000000 +1200
> @@ -4835,7 +4835,7 @@
>  	 have the `scroll-command' property.  This avoids the
>  	 possibility of point becoming "stuck" on a tall line when
>  	 scrolling by one line.  */
> -      if (window_scroll_pixel_based_preserve_y < 0
> +      if (window_scroll_pixel_based_preserve_y <= 0
>  	  || !SYMBOLP (KVAR (current_kboard, Vlast_command))
>  	  || NILP (Fget (KVAR (current_kboard, Vlast_command), Qscroll_command)))
>  	{

Thanks, but this change only fixes the problem when you start
scrolling with point on the first line in the window.  If point is on
2nd, 3rd, or 4th line (more generally, any line inside the
scroll-margin), the bug will still be there.

I installed on master a more general fix, which I hope solves this
problem.

Message #29 received at 28342 <at> debbugs.gnu.org (full text, mbox):

From: James Nguyen <james <at> jojojames.com>
To: Eli Zaretskii <eliz <at> gnu.org>, athird <at> googlemail.com
Cc: 28342 <at> debbugs.gnu.org, , jamesn <at> fastmail.com, charles <at> aurox.ch
Subject: Re: bug#28342: 26.0.50; (OSX) Jumpy Scrolling using Trackpad
Date: Sat, 09 Sep 2017 18:14:56 -0700

Eli Zaretskii <eliz <at> gnu.org> writes:

Working for me, will report back if it comes up again.

>> Date: Wed, 06 Sep 2017 19:55:41 +0300
>> From: Eli Zaretskii <eliz <at> gnu.org>
>> Cc: 28342 <at> debbugs.gnu.org, jamesn <at> fastmail.com, charles <at> aurox.ch,
>> 	james <at> jojojames.com
>> 
>> > (setq scroll-margin 5)
>> > (setq scroll-preserve-screen-position 1)
>> > (setq mouse-wheel-scroll-amount '(1))
>> > 
>> > Open a large file. Make sure you're at the start of the file
>> > 
>> > M-<
>> > 
>> > Scroll down with the mouse wheel and within a few clicks point jumps to the middle of the screen. A few more
>> > and it jumps to the end of the file.
>> 
>> Even simpler: after evaluating the first 2 of the above 3 settings,
>> visit xdisp.c, then type this twice:
>> 
>>   C-u 1 C-v
>> 
>> After you type this the second time, Emacs will infloop.
>> 
>> This bug is already present in Emacs 25.1.
>> 
>> I will look into this when I have time.  Thanks for the recipe.
>
> Should be fixed now on the master branch.

Message #34 received at 28342-done <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: James Nguyen <james <at> jojojames.com>
Cc: athird <at> googlemail.com, 28342-done <at> debbugs.gnu.org, jamesn <at> fastmail.com,
 charles <at> aurox.ch
Subject: Re: bug#28342: 26.0.50; (OSX) Jumpy Scrolling using Trackpad
Date: Sun, 10 Sep 2017 05:40:56 +0300

> From: James Nguyen <james <at> jojojames.com>
> Cc: 28342 <at> debbugs.gnu.org, jamesn <at> fastmail.com, charles <at> aurox.ch
> Date: Sat, 09 Sep 2017 18:14:56 -0700
> 
> Eli Zaretskii <eliz <at> gnu.org> writes:
> 
> Working for me, will report back if it comes up again.

Thanks, closing.

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