bug#44826: 27.1; Display artifacts which stay on the screen when scrolling

bug#44826: 27.1; Display artifacts which stay on the screen when scrolling

[novim via Bug reports for GNU Emacs, the Swiss army knife of text editors]

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Here's a screenshot, check out the top right corner:

https://i.imgur.com/pgx46We.png

How to reproduce:

1. save this package which makes org tables pretty by putting unicode characters onto regular org table characters

https://raw.githubusercontent.com/Fuco1/org-pretty-table/master/org-pretty-table.el

2. eval it, so you get org-pretty-table-mode
3. download the attached org file
4. open it and go to the first character of table
5. turn on org-pretty-table-mode, the table should be switched to pretty mode
6. before the first character of the table type a space, so the header row is shifted by one character to the right
7. the display artifacts should appear at the top of the window
8. if you press cursor up until the window starts scrolling then you can see parts of the artifact staying on the screen during scrolling

Pretty table mode uses jit for highlight, it might be an issue with jit. I assume it's some kind of emacs problem, because of the artifact staying in place while scrolling.

I tested it on Windows: GNU Emacs 27.1 (build 1, x86_64-w64-mingw32) of 2020-08-12

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bug#44826: 27.1; Display artifacts which stay on the screen when scrolling

[Eli Zaretskii]

> Date: Mon, 23 Nov 2020 19:47:33 +0000
> From: novim via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> 1. save this package which makes org tables pretty by putting unicode characters onto regular org table
> characters
> 
> https://raw.githubusercontent.com/Fuco1/org-pretty-table/master/org-pretty-table.el
> 
> 2. eval it, so you get org-pretty-table-mode
> 3. download the attached org file
> 4. open it and go to the first character of table
> 5. turn on org-pretty-table-mode, the table should be switched to pretty mode
> 6. before the first character of the table type a space, so the header row is shifted by one character to the
> right
> 7. the display artifacts should appear at the top of the window
> 8. if you press cursor up until the window starts scrolling then you can see parts of the artifact staying on the
> screen during scrolling

The problem doesn't happen here, neither 7 nor 8.

Could it be some problem with your video driver?  If it has some
"optimization" features, disable them and try again.

> Pretty table mode uses jit for highlight, it might be an issue with jit. I assume it's some kind of emacs
> problem, because of the artifact staying in place while scrolling.

Artifacts that stay put while scrolling are a sign that Emacs's
display engine doesn't know they are there.  Which usually means some
problem outside of Emacs control.

bug#44826: 27.1; Display artifacts which stay on the screen when scrolling

[novim via Bug reports for GNU Emacs, the Swiss army knife of text editors]

>
> The problem doesn't happen here, neither 7 nor 8.
>

Interesting. I tried it with -q which I should have done in the first place and then it didn't occur for me either when typing only one space before the header line, but it did occur when I shifted the whole table to the right by one space in the first character column.

Could you try again, but in step 6 shifting the whole table to the right by one space, e.g using C-x r o or C-x r t in column zero of the table?

So with spaces where the "x"s are:

x| Country name | Area | Population | Region        |
x|--------------+------+------------+---------------|
x| USSR         | 8649 |        275 | Asia          |
x| Canada       | 3852 |         25 | North America |
x| China        | 3705 |       1032 | Asia          |
x| USA          | 3615 |        237 | North America |
x| Brazil       | 3286 |        134 | South America |
x| India        | 1267 |        746 | Asia          |
x| Mexico       |  762 |         78 | North America |
x| France       |  211 |         55 | Europe        |
x| Japan        |  144 |        120 | Asia          |
x| Germany      |   96 |         61 | Europe        |
x| England      |   94 |         56 | Europe        |


Please maximize your window first, because for me the artifacts are more likely to appear then.

bug#44826: 27.1; Display artifacts which stay on the screen when scrolling

[Eli Zaretskii]

> Date: Mon, 23 Nov 2020 20:22:39 +0000
> From: novim <laszlomail@protonmail.com>
> Cc: "44826@debbugs.gnu.org" <44826@debbugs.gnu.org>
> 
> Could you try again, but in step 6 shifting the whole table to the right by one space, e.g using C-x r o or C-x r t in column zero of the table?

Yes, I see it now.  Thanks, will investigate.

bug#44826: 27.1; Display artifacts which stay on the screen when scrolling

[Eli Zaretskii]

> Date: Mon, 23 Nov 2020 22:35:24 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 44826@debbugs.gnu.org
> 
> > Date: Mon, 23 Nov 2020 20:22:39 +0000
> > From: novim <laszlomail@protonmail.com>
> > Cc: "44826@debbugs.gnu.org" <44826@debbugs.gnu.org>
> > 
> > Could you try again, but in step 6 shifting the whole table to the right by one space, e.g using C-x r o or C-x r t in column zero of the table?
> 
> Yes, I see it now.  Thanks, will investigate.

This bug was introduced in Emacs 24.4.  Now fixed on the emacs-27
branch for Emacs 27.2.

Thanks.