improper behavior of (scroll-down 0)

improper behavior of (scroll-down 0)

[Shiyao Ma]

Hi,

To reproduce the problem,
for example,

1. go to the info node (elisp)Top > Positions > Excursions
2. go to the beginning of the window: (goto-char (point-min))
3. scroll the window, (scroll-down 0)

Oops, the window scrolls down by 1.

What's happening here and how to rectify this ?


Regards.

-- 

吾輩は猫である。ホームーページはhttps://introo.me <http://introo.me>。

Re: improper behavior of (scroll-down 0)

[Eli Zaretskii]

> Date: Thu, 11 Feb 2016 19:08:27 +0800
> From: Shiyao Ma <i@introo.me>
> 
> 1. go to the info node (elisp)Top > Positions > Excursions
> 2. go to the beginning of the window: (goto-char (point-min))
> 3. scroll the window, (scroll-down 0)
> 
> Oops, the window scrolls down by 1.
> 
> What's happening here and how to rectify this ?

What is the problem, exactly?  What do you want (scroll-down 0) to do,
and why?

Re: improper behavior of (scroll-down 0)

[Shiyao Ma]

On 12 February 2016 at 05:01, Eli Zaretskii <eliz@gnu.org> wrote:

> > Date: Thu, 11 Feb 2016 19:08:27 +0800
> > From: Shiyao Ma <i@introo.me>
> >
> > 1. go to the info node (elisp)Top > Positions > Excursions
> > 2. go to the beginning of the window: (goto-char (point-min))
> > 3. scroll the window, (scroll-down 0)
> >
> > Oops, the window scrolls down by 1.
> >
> > What's happening here and how to rectify this ?
>
> What is the problem, exactly?  What do you want (scroll-down 0) to do,
> and why?
>
>
The observed behavior is "the window scrolls down by 1.

The desired behavior is "the window doesn't scroll down at all"


Regards.

Re: improper behavior of (scroll-down 0)

[Eli Zaretskii]

> Date: Fri, 12 Feb 2016 08:56:51 +0800
> From: Shiyao Ma <i@introo.me>
> Cc: help-gnu-emacs@gnu.org
> 
>  > 1. go to the info node (elisp)Top > Positions > Excursions
>  > 2. go to the beginning of the window: (goto-char (point-min))
>  > 3. scroll the window, (scroll-down 0)
>  >
>  > Oops, the window scrolls down by 1.
>  >
>  > What's happening here and how to rectify this ?
> 
>  What is the problem, exactly? What do you want (scroll-down 0) to do,
>  and why?
> 
> The observed behavior is "the window scrolls down by 1.
> 
> The desired behavior is "the window doesn't scroll down at all"

Sorry, I should have been more clear.  The question I wanted to ask
is: if you don't want the window to scroll, why do you invoke
scroll-down at all?  I assumed you did that because you wanted some
effect other than scrolling, so I asked what was that effect.

Re: improper behavior of (scroll-down 0)

[Shiyao Ma]

Hi, Eli

On 12 February 2016 at 14:59, Eli Zaretskii <eliz@gnu.org> wrote:

> Sorry, I should have been more clear.  The question I wanted to ask
> is: if you don't want the window to scroll, why do you invoke
> scroll-down at all?  I assumed you did that because you wanted some
> effect other than scrolling, so I asked what was that effect.
>
> yup, I'd admit the plain (scroll-down 0) is meaningless.

Actually the scrolling down part is of the form (scroll-down scrollable),
the origin is here:
https://github.com/emacsmirror/evil/blob/master/evil-commands.el#L870

When `scrollable' becomes 0, the undesired behavior happens.

Another observation is, the undesired behavior doesn't happen under
*scratch* buffer or others alike.

The info mode has sort of a navigation bar, "(elisp)Top > Positions >
Excursions",  maybe (scroll-down) doesn't handle that well.



Regards.

-- 

吾輩は猫である。ホームーページはhttps://introo.me <http://introo.me>。

Re: improper behavior of (scroll-down 0)

[Eli Zaretskii]

> Date: Fri, 12 Feb 2016 17:41:11 +0800
> From: Shiyao Ma <i@introo.me>
> Cc: help-gnu-emacs@gnu.org
> 
> yup, I'd admit the plain (scroll-down 0) is meaningless.
> 
> Actually the scrolling down part is of the form (scroll-down scrollable), the origin is here: 
> https://github.com/emacsmirror/evil/blob/master/evil-commands.el#L870
> 
> When `scrollable' becomes 0, the undesired behavior happens.
> 
> Another observation is, the undesired behavior doesn't happen under *scratch* buffer or others alike.
> 
> The info mode has sort of a navigation bar, "(elisp)Top > Positions > Excursions", maybe (scroll-down)
> doesn't handle that well.

The first line you see in an Info buffer is not normal text, it is a
specially displayed string.  That is the reason for the somewhat
strange behavior.

Re: improper behavior of (scroll-down 0)

[Shiyao Ma]

Do you know the canonical name of the `specially displayed string', so that
I can find some reference on it.

btw, do you happen to know if there exists some setting that can rectify
the behavior of scroll-down ?


Thanks.

Re: improper behavior of (scroll-down 0)

[Eli Zaretskii]

> Date: Fri, 12 Feb 2016 20:20:02 +0800
> From: Shiyao Ma <i@introo.me>
> Cc: help-gnu-emacs@gnu.org
> 
> Do you know the canonical name of the `specially displayed string', so that I can find some reference on it.

'display' text property

> btw, do you happen to know if there exists some setting that can rectify the behavior of scroll-down ?

I suggest to submit a bug report, it might be a bug.