GNU bug report logs - #23861
25.1.50; fast-but-imprecise-scrolling: What does "somewhat inaccurate" mean?

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

From: Phil Sainty <psainty <at> orcon.net.nz>
To: bug-gnu-emacs <at> gnu.org
Subject: 25.1.50; fast-but-imprecise-scrolling: What does "somewhat
 inaccurate" mean?
Date: Wed, 29 Jun 2016 01:03:00 +1200

It's unclear to me what the following excerpt from the docstring
for the `fast-but-imprecise-scrolling' variable actually means:

> Note that this optimization can cause the portion of the buffer
> displayed after a scrolling operation to be somewhat inaccurate.

"somewhat inaccurate" is incredibly vague if you don't already
know what it means.

Does it mean that the position scrolled to might be further (or
less far) than it would have been otherwise?

Does it mean that the font-locking may be incomplete or incorrect?

Does it mean that the buffer text may appear corrupted?!

I certainly can't tell what it means. It would be good if that
text was clarified.

Message #8 received at 23861 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Phil Sainty <psainty <at> orcon.net.nz>
Cc: 23861 <at> debbugs.gnu.org
Subject: Re: bug#23861: 25.1.50;
 fast-but-imprecise-scrolling: What does "somewhat inaccurate" mean?
Date: Tue, 28 Jun 2016 19:14:58 +0300

> From: Phil Sainty <psainty <at> orcon.net.nz>
> Date: Wed, 29 Jun 2016 01:03:00 +1200
> 
> It's unclear to me what the following excerpt from the docstring
> for the `fast-but-imprecise-scrolling' variable actually means:
> 
>  > Note that this optimization can cause the portion of the buffer
>  > displayed after a scrolling operation to be somewhat inaccurate.
> 
> "somewhat inaccurate" is incredibly vague if you don't already
> know what it means.

It means that what's on the screen might not reflect what's in the
buffer.

It's hard to tell anything more specific, since which redisplay
optimizations will be taken in each case depends on many factors on
which the user has no control.

> Does it mean that the position scrolled to might be further (or
> less far) than it would have been otherwise?

It could.

> Does it mean that the font-locking may be incomplete or incorrect?

It could.

> Does it mean that the buffer text may appear corrupted?!

It could, if faces change the font size.

Message #13 received at 23861-done <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefan <at> marxist.se>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: Phil Sainty <psainty <at> orcon.net.nz>, 23861-done <at> debbugs.gnu.org
Subject: Re: bug#23861: 25.1.50; fast-but-imprecise-scrolling: What does
 "somewhat inaccurate" mean?
Date: Mon, 14 Oct 2019 14:35:25 +0200

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

>> From: Phil Sainty <psainty <at> orcon.net.nz>
>> Date: Wed, 29 Jun 2016 01:03:00 +1200
>>
>> It's unclear to me what the following excerpt from the docstring
>> for the `fast-but-imprecise-scrolling' variable actually means:
>>
>>  > Note that this optimization can cause the portion of the buffer
>>  > displayed after a scrolling operation to be somewhat inaccurate.
>>
>> "somewhat inaccurate" is incredibly vague if you don't already
>> know what it means.
>
> It means that what's on the screen might not reflect what's in the
> buffer.
>
> It's hard to tell anything more specific, since which redisplay
> optimizations will be taken in each case depends on many factors on
> which the user has no control.
>
>> Does it mean that the position scrolled to might be further (or
>> less far) than it would have been otherwise?
>
> It could.
>
>> Does it mean that the font-locking may be incomplete or incorrect?
>
> It could.
>
>> Does it mean that the buffer text may appear corrupted?!
>
> It could, if faces change the font size.

That was 3 years ago.  It doesn't look like there is anything more to do
here, so I'm closing this bug report.

Please reopen the bug if that's incorrect.

Best regards,
Stefan Kangas

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