GNU bug report logs - #78766
100-4000x redisplay slowdown with vscroll>0 and make-cursor-line-fully-visible=t

Previous Next

Full log

View this message in rfc822 format

From: Eli Zaretskii <eliz <at> gnu.org>
To: JD Smith <jdtsmith <at> gmail.com>
Cc: 78766 <at> debbugs.gnu.org
Subject: bug#78766: 100-4000x redisplay slowdown with vscroll>0 and make-cursor-line-fully-visible=t
Date: Sun, 15 Jun 2025 20:00:23 +0300

> From: JD Smith <jdtsmith <at> gmail.com>
> Date: Sun, 15 Jun 2025 12:37:03 -0400
> Cc: 78766 <at> debbugs.gnu.org
> 
> 
> 
> > On Jun 14, 2025, at 9:14 AM, Eli Zaretskii <eliz <at> gnu.org> wrote:
> > 
> > I've now looked at this.  It's like I guessed: this case of having the
> > cursor in the first visible line that is only partially visible is not
> > supported, and the code just loops until we forcibly stop that:
> 
> Good find, thanks for looking at this.  I tested the patch.  While it eliminated the slowdown, it led to other redisplay artifacts when point is on a partially visible top line, such as duplicated half overlapping mode-lines when invoking M-x.
> 
> But perhaps you did not intend to always return SCROLLING_SUCCESS here?
> 
> +   if (MATRIX_ROW_PARTIALLY_VISIBLE_AT_TOP_P
> + (w, MATRIX_ROW (w->desired_matrix, w->cursor.vpos)))
> +     rc = SCROLLING_FAILED;
> +   else
> +     goto too_near_end;
> }
>  rc = SCROLLING_SUCCESS;
> 
> If I modify that to return FAILED immediately, ala:
> 
>  if (MATRIX_ROW_PARTIALLY_VISIBLE_AT_TOP_P
> (w, MATRIX_ROW (w->desired_matrix, w->cursor.vpos)))
>    return SCROLLING_FAILED;
>  else
>    goto too_near_end;
> }
>       rc = SCROLLING_SUCCESS;
> 
> I get no artifacts, and it seems to do what I'd expect — if you try to move point onto a partially visible top row, the window is recentered according to scroll-conservatively.
> 
> Seems to work normally with line-move and tall images.  I will run with it for a while to see if anything else appears.

If that works for you, it's fine by me.  I thought that recentering
will effectively disable the effect of vscroll, and so assumed it will
be unacceptable for your package.

Will wait for your further feedback.

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.