bug#57343: hscroll current-line scrolls short lines too far to the left

bug#57343: hscroll current-line scrolls short lines too far to the left

[Erik van Zwol]

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starting from 'emacs -Q':
Toggle-truncate-lines (so that long lines are truncated)
Evaluate the following:
(setq auto-hscroll-mode 'current-line)
(setq hscroll-margin 5)
(setq hscroll-step 1)
Insert enough text such that the line starts to hscroll
On the line directly below, insert enough text to fill about half the
width of the frame
Move point to the long line near the end (must be hscrolling the single
line)
Move point down to the next line, it should hscroll even though it does
not need to
See the animated gifs on this post:
https://www.reddit.com/r/emacs/comments/wgef0b/looking_for_better_alternative_to_autohscrollmode/

I have attached a patch that I think fixes the issue.  Please tell me
how to proceed, and what other information you need.


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 of 2021-11-22 built on erik-lair
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From 4936db1abb4137046cdd02d9be568c3e16d241cb Mon Sep 17 00:00:00 2001
From: Erik van Zwol <pa2ees42@gmail.com>
Date: Sun, 21 Aug 2022 21:36:11 -0600
Subject: [PATCH] ; * src/xdisp.c (hscroll_window_tree): hscroll current-line
 fix

---
 src/xdisp.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/xdisp.c b/src/xdisp.c
index 0248e8e53f..6719a858f7 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -15888,7 +15888,11 @@ hscroll_window_tree (Lisp_Object window)
 				      : (text_area_width / 2))))
 		    	  / FRAME_COLUMN_WIDTH (it.f);
 	      else if ((!row_r2l_p
-			&& w->cursor.x >= text_area_width - h_margin)
+			&& (w->cursor.x >= text_area_width - h_margin
+			    /* When hscrolling only the current line and the current line
+			       is less than (text_area_width - h_margin), it might be hscrolled
+			       almost completely off the left side unless we catch it here.  */
+			    || hscl))
 		       || (row_r2l_p && w->cursor.x <= h_margin))
 		{
 		  if (hscroll_relative_p)
-- 
2.25.1

bug#57343: hscroll current-line scrolls short lines too far to the left

[Eli Zaretskii]

> From: Erik van Zwol <thejofat@gmail.com>
> Date: Sun, 21 Aug 2022 22:03:29 -0600
> 
> starting from 'emacs -Q':
> Toggle-truncate-lines (so that long lines are truncated)
> Evaluate the following:
> (setq auto-hscroll-mode 'current-line)
> (setq hscroll-margin 5)
> (setq hscroll-step 1)
> Insert enough text such that the line starts to hscroll
> On the line directly below, insert enough text to fill about half the
> width of the frame
> Move point to the long line near the end (must be hscrolling the single
> line)
> Move point down to the next line, it should hscroll even though it does
> not need to
> See the animated gifs on this post:
> https://www.reddit.com/r/emacs/comments/wgef0b/looking_for_better_alternative_to_autohscrollmode/
> 
> I have attached a patch that I think fixes the issue.  Please tell me
> how to proceed, and what other information you need.

Thanks.

I feel there's something else at work here, because if you move the
cursor up instead of down (i.e., to the previous instead of the next
line), the problem doesn't happen.

So I need to look closer at what is going on and why.  Stay tuned.

bug#57343: hscroll current-line scrolls short lines too far to the left

[Stephen Berman]

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On Tue, 23 Aug 2022 16:13:27 +0300 Eli Zaretskii <eliz@gnu.org> wrote:

>
>> From: Erik van Zwol <thejofat@gmail.com>
>> Date: Sun, 21 Aug 2022 22:03:29 -0600
>>
>> starting from 'emacs -Q':
>> Toggle-truncate-lines (so that long lines are truncated)
>> Evaluate the following:
>> (setq auto-hscroll-mode 'current-line)
>> (setq hscroll-margin 5)
>> (setq hscroll-step 1)
>> Insert enough text such that the line starts to hscroll
>> On the line directly below, insert enough text to fill about half the
>> width of the frame
>> Move point to the long line near the end (must be hscrolling the single
>> line)
>> Move point down to the next line, it should hscroll even though it does
>> not need to
>> See the animated gifs on this post:
>> https://www.reddit.com/r/emacs/comments/wgef0b/looking_for_better_alternative_to_autohscrollmode/
>>
>> I have attached a patch that I think fixes the issue.  Please tell me
>> how to proceed, and what other information you need.
>
> Thanks.
>
> I feel there's something else at work here, because if you move the
> cursor up instead of down (i.e., to the previous instead of the next
> line), the problem doesn't happen.

I see the same hscrolling when moving to the next and to the previous
line, both the same length (too short for hscrolling), see the attached
screenshots.

Steve Berman


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bug#57343: hscroll current-line scrolls short lines too far to the left

[Eli Zaretskii]

> From: Stephen Berman <stephen.berman@gmx.net>
> Cc: Erik van Zwol <thejofat@gmail.com>,  57343@debbugs.gnu.org
> Date: Tue, 23 Aug 2022 18:56:34 +0200
> 
> > I feel there's something else at work here, because if you move the
> > cursor up instead of down (i.e., to the previous instead of the next
> > line), the problem doesn't happen.
> 
> I see the same hscrolling when moving to the next and to the previous
> line, both the same length (too short for hscrolling), see the attached
> screenshots.

You are saying that what you see on your system invalidates my
observations on my system?

All I'm saying is that what I see here tells me there's more here than
meets the eye.  AFAIU, your evidence actually affirms my feeling.

bug#57343: hscroll current-line scrolls short lines too far to the left

[Erik van Zwol]

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I believe the issue happens when the line you are moving the cursor from a
line that is hscrolled to a line that is shorter than (frame_width -
hscroll_margin), the issue occurs.  However, if the line you are moving the
cursor to is greater than or equal to (frame_width - hscroll_margin), the
problem does not occur.  This is more evident when you set the
hscroll-margin to something smaller, like 1 or 2.

The patch I attached has modified the if statement that has this condition
in it (point >= frame_width - hscroll_margin) or something like that, I
don't have the code in front of me.



On Tue, Aug 23, 2022 at 11:07 AM Eli Zaretskii <eliz@gnu.org> wrote:

> > From: Stephen Berman <stephen.berman@gmx.net>
> > Cc: Erik van Zwol <thejofat@gmail.com>,  57343@debbugs.gnu.org
> > Date: Tue, 23 Aug 2022 18:56:34 +0200
> >
> > > I feel there's something else at work here, because if you move the
> > > cursor up instead of down (i.e., to the previous instead of the next
> > > line), the problem doesn't happen.
> >
> > I see the same hscrolling when moving to the next and to the previous
> > line, both the same length (too short for hscrolling), see the attached
> > screenshots.
>
> You are saying that what you see on your system invalidates my
> observations on my system?
>
> All I'm saying is that what I see here tells me there's more here than
> meets the eye.  AFAIU, your evidence actually affirms my feeling.
>

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bug#57343: hscroll current-line scrolls short lines too far to the left

[Erik van Zwol]

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Looking at your screenshots, I believe if you make the bottom line almost
as long as the width of the frame, then the problem would not occur on that
line.

On Tue, Aug 23, 2022 at 9:48 PM Erik van Zwol <thejofat@gmail.com> wrote:

> I believe the issue happens when the line you are moving the cursor from a
> line that is hscrolled to a line that is shorter than (frame_width -
> hscroll_margin), the issue occurs.  However, if the line you are moving the
> cursor to is greater than or equal to (frame_width - hscroll_margin), the
> problem does not occur.  This is more evident when you set the
> hscroll-margin to something smaller, like 1 or 2.
>
> The patch I attached has modified the if statement that has this condition
> in it (point >= frame_width - hscroll_margin) or something like that, I
> don't have the code in front of me.
>
>
>
> On Tue, Aug 23, 2022 at 11:07 AM Eli Zaretskii <eliz@gnu.org> wrote:
>
>> > From: Stephen Berman <stephen.berman@gmx.net>
>> > Cc: Erik van Zwol <thejofat@gmail.com>,  57343@debbugs.gnu.org
>> > Date: Tue, 23 Aug 2022 18:56:34 +0200
>> >
>> > > I feel there's something else at work here, because if you move the
>> > > cursor up instead of down (i.e., to the previous instead of the next
>> > > line), the problem doesn't happen.
>> >
>> > I see the same hscrolling when moving to the next and to the previous
>> > line, both the same length (too short for hscrolling), see the attached
>> > screenshots.
>>
>> You are saying that what you see on your system invalidates my
>> observations on my system?
>>
>> All I'm saying is that what I see here tells me there's more here than
>> meets the eye.  AFAIU, your evidence actually affirms my feeling.
>>
>

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