Re: master 5b5608c614: Fix glyph skipping optimization when a tab line is enabled

[Eli Zaretskii]

> Author:     Po Lu <luangruo@yahoo.com>
> AuthorDate: Mon Apr 18 13:23:23 2022 +0800
> Commit:     Po Lu <luangruo@yahoo.com>
> CommitDate: Mon Apr 18 13:23:23 2022 +0800
> 
>     Fix glyph skipping optimization when a tab line is enabled
> 
>     * src/dispnew.c (update_text_area): Compute vpos of header line
>     correctly when window has tab line.
> 
> diff --git a/src/dispnew.c b/src/dispnew.c
> index 0d95904..3cfe1b8 100644
> --- a/src/dispnew.c
> +++ b/src/dispnew.c
> @@ -3928,9 +3928,12 @@ update_text_area (struct window *w, struct glyph_row 
> *upd
>          However, it causes excessive flickering when mouse is moved
>          across the mode line.  Luckily, turning it off for the mode
>          line doesn't seem to hurt anything. -- cyd.
> -         But it is still needed for the header line. -- kfs.  */
> +         But it is still needed for the header line. -- kfs.
> +         The header line vpos is 1 if a tab line is enabled.  (18th
> +         Apr 2022) */
>        || (current_row->mouse_face_p
> -         && !(current_row->mode_line_p && vpos > 0))
> +         && !(current_row->mode_line_p
> +              && (vpos > w->current_matrix->tab_line_p)))
>        || current_row->x != desired_row->x)
>      {
>        output_cursor_to (w, vpos, 0, desired_row->y, desired_row->x);

I'm not sure I understand this change.  What exactly is the problem,
and how to reproduce it?  What if there's no header-line, but there is
a tab-line, or vice versa, or both are displayed?  And why mentioning
the date of the change in the comment?

Thanks.