GNU bug report logs - #36633
Scrolling by pixels: visible stretch glyphs overwrite header-line.

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Package: emacs; Reported by: Keith David Bershatsky <esq@HIDDEN>; dated Sat, 13 Jul 2019 02:11:02 UTC; Maintainer for emacs is bug-gnu-emacs@HIDDEN.

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From: Tak Kunihiro <homeros.misasa@HIDDEN>
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To: 36633 <at> debbugs.gnu.org
Subject: Re: bug#36633: Scrolling by pixels: visible stretch glyphs overwrite
 header-line.
In-Reply-To: <m2pnmcd0ma.wl%esq@HIDDEN> (Keith David Bershatsky's message
 of "Sun, 14 Jul 2019 09:47:25 -0700")
References: <m2v9w6bs63.wl%esq@HIDDEN> <m2pnmcd0ma.wl%esq@HIDDEN>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.2 (darwin)
Date: Mon, 15 Jul 2019 21:26:32 +0900
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I confirmed the existence of ghost (of the first line with green blocks)
shown on the headline significantly with 26.2 on macOS 10.6.8 and less
significantly with 26.2 on macOS 10.14.5.

The essence of related code is `set-window-vscroll'.

 (let ((n (frame-char-height)))
  (when (> n 0)
    (let ((vs0 (window-vscroll nil t)))
      (dolist (vs (number-sequence (1+ vs0) (+ vs0 n)))
        (set-window-vscroll nil vs t) (sit-for pixel-wait)))))

I do not know how to fix it.


Keith David Bershatsky <esq@HIDDEN> writes:

> Here are links to two (2) youtube videos showing the issue on Emacs
> 26.1 (built by https://emacsformacosx.com/ a few months ago) and
> also
> the master branch that I built using a commit from 07/10/2019
> (40cd6278ba965f3a9fcdddc568eb9ee7c69cf899).  I don't have a 26.2
> build
> at the moment.  The issue is less noticeable on the master branch,
> but
> can still be seen nevertheless.  I have not studied the code as to
> what makes this feature work, but offhand would think that the
> header-line should not be overwritten by the row moving upwards
> (rather than updated after it has been overwritten).
>
> Emacs 26.1:  https://youtu.be/Y8cZfURSwZc
>
> Emacs Master Branch:  https://youtu.be/BO3r9_6OvYo




Information forwarded to bug-gnu-emacs@HIDDEN:
bug#36633; Package emacs. Full text available.

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I forgot to cc Stefan K. and Eli Z. with the attached post ....

;;;;;;;;;;;;;;;;;;;;;; FORWARDED MESSAGE ;;;;;;;;;;;;;;;;;;;;;;

Date:  Sun, 14 Jul 2019 09:47:25 -0700
From:  Keith David Bershatsky <esq@HIDDEN>
To:  Alan Third <alan@HIDDEN>
Cc:  36633 <at> debbugs.gnu.org
Subject:  Re: bug#36633: Scrolling by pixels: visible stretch glyphs overwrite header-line.

Here are links to two (2) youtube videos showing the issue on Emacs 26.1 (built by https://emacsformacosx.com/ a few months ago) and also the master branch that I built using a commit from 07/10/2019 (40cd6278ba965f3a9fcdddc568eb9ee7c69cf899).  I don't have a 26.2 build at the moment.  The issue is less noticeable on the master branch, but can still be seen nevertheless.  I have not studied the code as to what makes this feature work, but offhand would think that the header-line should not be overwritten by the row moving upwards (rather than updated after it has been overwritten).

Emacs 26.1:  https://youtu.be/Y8cZfURSwZc

Emacs Master Branch:  https://youtu.be/BO3r9_6OvYo

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

> Date: [07-14-2019 03:39:35] <14 Jul 2019 11:39:35 +0100>
> From: Alan Third <alan@HIDDEN>
> 
> * * *
> 
> Hi Keith, I can't replicate this behaviour. The worst I see is some
> flickering of the header line, which is unfortunately to be expected
> from the current implementation.
> 
> When you do it is the header line being overwritten and not immediately updated?
> --
> Alan Third




Information forwarded to bug-gnu-emacs@HIDDEN:
bug#36633; Package emacs. Full text available.

Message received at 36633 <at> debbugs.gnu.org:


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Here are links to two (2) youtube videos showing the issue on Emacs 26.1 (built by https://emacsformacosx.com/ a few months ago) and also the master branch that I built using a commit from 07/10/2019 (40cd6278ba965f3a9fcdddc568eb9ee7c69cf899).  I don't have a 26.2 build at the moment.  The issue is less noticeable on the master branch, but can still be seen nevertheless.  I have not studied the code as to what makes this feature work, but offhand would think that the header-line should not be overwritten by the row moving upwards (rather than updated after it has been overwritten).

Emacs 26.1:  https://youtu.be/Y8cZfURSwZc

Emacs Master Branch:  https://youtu.be/BO3r9_6OvYo

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

> Date: [07-14-2019 03:39:35] <14 Jul 2019 11:39:35 +0100>
> From: Alan Third <alan@HIDDEN>
> 
> * * *
> 
> Hi Keith, I can't replicate this behaviour. The worst I see is some
> flickering of the header line, which is unfortunately to be expected
> from the current implementation.
> 
> When you do it is the header line being overwritten and not immediately updated?
> --
> Alan Third




Information forwarded to bug-gnu-emacs@HIDDEN:
bug#36633; Package emacs. Full text available.

Message received at 36633 <at> debbugs.gnu.org:


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Date: Sun, 14 Jul 2019 11:39:35 +0100
From: Alan Third <alan@HIDDEN>
To: Keith David Bershatsky <esq@HIDDEN>
Subject: Re: bug#36633: Scrolling by pixels: visible stretch glyphs overwrite
 header-line.
Message-ID: <20190714103935.GB11787@HIDDEN>
References: <m2v9w6bs63.wl%esq@HIDDEN>
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On Fri, Jul 12, 2019 at 07:10:44PM -0700, Keith David Bershatsky wrote:
> Step 1:  Launch Emacs 26.
> 
> Step 2:  Evaluate the following code.
> 
> (progn
>   (find-library "simple")
>   (pixel-scroll-mode 1)
>   (re-search-forward "\t\t\t\t\t" nil t)
>   (set-window-start (selected-window) (match-beginning 0))
>   (setq header-line-format "hello-world")
>   (setq buffer-display-table (make-display-table))
>   (aset buffer-display-table
>         ?\t
>         (vector (make-glyph-code ?\u00BB 'font-lock-warning-face)
>                 (make-glyph-code ?\t 'highlight)))
>   (setq tab-width 8))
> 
> Step 3:  Move the mousewheel downward one time; i.e., one ratchet.
> 
> Step 4:  Observe the visible stretch glyphs overwriting the header-line.

Hi Keith, I can’t replicate this behaviour. The worst I see is some
flickering of the header line, which is unfortunately to be expected
from the current implementation.

When you do it is the header line being overwritten and not
immediately updated?
-- 
Alan Third




Information forwarded to bug-gnu-emacs@HIDDEN:
bug#36633; Package emacs. Full text available.

Message received at 36633 <at> debbugs.gnu.org:


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From: Eli Zaretskii <eliz@HIDDEN>
To: Stefan Kangas <stefan@HIDDEN>
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 (message from Stefan Kangas on Sat, 13 Jul 2019 10:32:16 +0200)
Subject: Re: bug#36633: Scrolling by pixels: visible stretch glyphs overwrite
 header-line.
References: <m2v9w6bs63.wl%esq@HIDDEN> <83zhli1mof.fsf@HIDDEN>
 <CADwFkmkROCUZJRXPWUDASHBZaCZ+9VGs6hyb1+aMyGid2KJOGg@HIDDEN>
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> From: Stefan Kangas <stefan@HIDDEN>
> Date: Sat, 13 Jul 2019 10:32:16 +0200
> Cc: Keith David Bershatsky <esq@HIDDEN>, 36633 <at> debbugs.gnu.org
> 
> > > (progn
> > >   (find-library "simple")
> > >   (pixel-scroll-mode 1)
> > >   (re-search-forward "\t\t\t\t\t" nil t)
> > >   (set-window-start (selected-window) (match-beginning 0))
> > >   (setq header-line-format "hello-world")
> > >   (setq buffer-display-table (make-display-table))
> > >   (aset buffer-display-table
> > >         ?\t
> > >         (vector (make-glyph-code ?\u00BB 'font-lock-warning-face)
> > >                 (make-glyph-code ?\t 'highlight)))
> > >   (setq tab-width 8))
> > >
> > > Step 3:  Move the mousewheel downward one time; i.e., one ratchet.
> > >
> > > Step 4:  Observe the visible stretch glyphs overwriting the header-line.
> >
> > This doesn't happen to me on MS-Windows, so I think this is
> > Darwin-specific.
> >
> > Can someone try reproducing this on GNU/Linux and report?
> 
> I can't reproduce this here.

Thanks.  I guess this confirms that the problem is specific to macOS.




Information forwarded to bug-gnu-emacs@HIDDEN:
bug#36633; Package emacs. Full text available.

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From: Stefan Kangas <stefan@HIDDEN>
Date: Sat, 13 Jul 2019 10:32:16 +0200
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Subject: Re: bug#36633: Scrolling by pixels: visible stretch glyphs overwrite
 header-line.
To: Eli Zaretskii <eliz@HIDDEN>
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Eli Zaretskii <eliz@HIDDEN> writes:

> > Date: Fri, 12 Jul 2019 19:10:44 -0700
> > From: Keith David Bershatsky <esq@HIDDEN>
> >
> > Step 1:  Launch Emacs 26.
> >
> > Step 2:  Evaluate the following code.
> >
> > (progn
> >   (find-library "simple")
> >   (pixel-scroll-mode 1)
> >   (re-search-forward "\t\t\t\t\t" nil t)
> >   (set-window-start (selected-window) (match-beginning 0))
> >   (setq header-line-format "hello-world")
> >   (setq buffer-display-table (make-display-table))
> >   (aset buffer-display-table
> >         ?\t
> >         (vector (make-glyph-code ?\u00BB 'font-lock-warning-face)
> >                 (make-glyph-code ?\t 'highlight)))
> >   (setq tab-width 8))
> >
> > Step 3:  Move the mousewheel downward one time; i.e., one ratchet.
> >
> > Step 4:  Observe the visible stretch glyphs overwriting the header-line.
>
> This doesn't happen to me on MS-Windows, so I think this is
> Darwin-specific.
>
> Can someone try reproducing this on GNU/Linux and report?

I can't reproduce this here.

In GNU Emacs 26.2 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.22.11)
 of 2019-04-13 built on joffe
Windowing system distributor 'The X.Org Foundation', version 11.0.11902000
System Description:    Debian GNU/Linux 9.9 (stretch)

Thanks,
Stefan Kangas




Information forwarded to bug-gnu-emacs@HIDDEN:
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To: Keith David Bershatsky <esq@HIDDEN>
In-reply-to: <m2v9w6bs63.wl%esq@HIDDEN> (message from Keith David
 Bershatsky on Fri, 12 Jul 2019 19:10:44 -0700)
Subject: Re: bug#36633: Scrolling by pixels: visible stretch glyphs overwrite
 header-line.
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> Date: Fri, 12 Jul 2019 19:10:44 -0700
> From: Keith David Bershatsky <esq@HIDDEN>
> 
> Step 1:  Launch Emacs 26.
> 
> Step 2:  Evaluate the following code.
> 
> (progn
>   (find-library "simple")
>   (pixel-scroll-mode 1)
>   (re-search-forward "\t\t\t\t\t" nil t)
>   (set-window-start (selected-window) (match-beginning 0))
>   (setq header-line-format "hello-world")
>   (setq buffer-display-table (make-display-table))
>   (aset buffer-display-table
>         ?\t
>         (vector (make-glyph-code ?\u00BB 'font-lock-warning-face)
>                 (make-glyph-code ?\t 'highlight)))
>   (setq tab-width 8))
> 
> Step 3:  Move the mousewheel downward one time; i.e., one ratchet.
> 
> Step 4:  Observe the visible stretch glyphs overwriting the header-line.

This doesn't happen to me on MS-Windows, so I think this is
Darwin-specific.

Can someone try reproducing this on GNU/Linux and report?




Information forwarded to bug-gnu-emacs@HIDDEN:
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Date: Fri, 12 Jul 2019 19:10:44 -0700
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From: Keith David Bershatsky <esq@HIDDEN>
To: Emacs Bug Reports <bug-gnu-emacs@HIDDEN>
Subject: Scrolling by pixels:  visible stretch glyphs overwrite header-line.
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Step 1:  Launch Emacs 26.

Step 2:  Evaluate the following code.

(progn
  (find-library "simple")
  (pixel-scroll-mode 1)
  (re-search-forward "\t\t\t\t\t" nil t)
  (set-window-start (selected-window) (match-beginning 0))
  (setq header-line-format "hello-world")
  (setq buffer-display-table (make-display-table))
  (aset buffer-display-table
        ?\t
        (vector (make-glyph-code ?\u00BB 'font-lock-warning-face)
                (make-glyph-code ?\t 'highlight)))
  (setq tab-width 8))

Step 3:  Move the mousewheel downward one time; i.e., one ratchet.

Step 4:  Observe the visible stretch glyphs overwriting the header-line.

BEHAVIOR EXPECTED:  The header-line should not be overwritten by the visible stretch glyphs that are being scrolled upwards from the row beneath the header-line.

I am on OSX 10.6.8 and performed this minimal working example with:

GNU Emacs 26.1 (build 1, x86_64-apple-darwin10.8.0, NS appkit-1038.36 Version 10.6.8 (Build 10K549)) of 2018-05-30




Acknowledgement sent to Keith David Bershatsky <esq@HIDDEN>:
New bug report received and forwarded. Copy sent to bug-gnu-emacs@HIDDEN. Full text available.
Report forwarded to bug-gnu-emacs@HIDDEN:
bug#36633; Package emacs. Full text available.
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